Are we making any real design improvements??

[Wardi]

A short quote from an interesting article in a local sailing magazine - Afloat:
http://www.afloat.com.au/external%20files/0504_Yesteryear.pdf

W (Billy) Hughes asks:
Are today’s lightweight ‘sea skiffs’ really better than the yachts of half a century ago?

His yardstick for measuring yacht performance is the Rhodes designed yawl Margaret Rintoul. She broke the record from Sydney to Hobart in 1951.
Her elapsed time of 4 days, 2 hours, 29 minutes, 1 second,(98.483 hours) gave her an average speed of 6.37 knots.

For a waterline length of 32ft she achieved a speed/length ratio of 1.126.
The front runners in this year’s Hobart race were :-
Yacht - Length - Time - Average speed - S/L speed Ratio
Skandia - 98ft - 63.235hrs - 9.915 knots - 1.002
Zana - 98ft - 63.475hrs - 9.878 knots - 0.998
Grundig - 66ft - 68.20hrs - 9.194 knots - 1.132
Skandia, the fastest and, over twice the length of Margaret
Rintoul, did not equal Rintoul’s S/L ratio!!

Are we really making any real progress??
The boats are going faster in absolute terms but is this accompanied by real advances in efficiency?? :?:

[astevo]

aside from just stiring the pot maybe look at similar size boats. things like mumm 30's would have speed/length rates far above this.

look at this the other way. is a old thing like 'condor' 'kialoa' or 'windward passage' even going to compete with a similar sized modern maxi? and these aer much more recent than the 1950's vintage margaret ringtoul 1975/6 for kialoa.

its the other side to the same coin.
and im thinking about that self leveling idea...

[SailDesign]

Since Open60s are regularly going round the world in less than 100 days - the answer is Yes!
Assume 27000 miles (probably an understate=ment in real distance travelled, but about the diameter of the earth), and 100 days for the passage. That's 27000 miles in 2400 hours, or 11.25 knots. Assuming LWL is 60' (again, an exaggeration), then sqrt(LWL) is 7.75, so the speed/length ratio is 11.25/7.75 = 1.452. Allowing for mph/knots conversion, that comes to 1.452/1.151 = 1.262 for a V/L.

Definately better than 1.126, and singlehanded t boot.
Of course, the boats do it in less than 100 days routinely now, and sail considerably further than the actual diameter of the planet, so this is all an underestimate.
Round-the-buoys boats getting better? Who knows - it doesn't really matter if they are racing level :p

Steve

[Wardi]

Given the difference in age, style, design and construction, the improvement of the open 60 does not look so big does it! ;)

How about doing the same comparison comparing speed to displacement/length ratio! :D

It is very easy to make a new design faster, just make it lighter and put on more sail. That does not make it more efficient or a better design though!!

I am rather disappoined to hear you have no interest to improve the real performance of boats vs D/L ratio. I guess you are happy then to just sail a Star or Finn. Why bother design anything better as they are good level racing one designs already! :p

[DaveB]

Wardi,

I'm havin' a hard time following your point... you're asking if we've made any improvements independent of "style, design and construction" and keep referring to parameters... Those parameters are used to describe boats and relate them to natural laws... As far as natural laws go I don't think that we'll ever improve...

As far as boats go I think we have improved a great deal... Whether it's due to the new tools that we have or the designers is another question...

Cheers,

Dave B

[SailDesign]

Wardy,
Yes, given the radically different D/l ratios and SA/D ratios in use today, it looks like we haven't come that far. But you're leaving out the singlehanded round the world aspect there. A fully crewed O60 will do very much better than a single-handed one can do over 2700 miles. :)
Don't be disappointed that I don't want to improve things - I do. But look at what the OC did, put the Star back in because, regardless of speed, it provided interesting racing. Personally, I dislike racing, preferring to just go out and go fast without having to compare to anyone else. I just don't "get" the whole tactical BS. Prolly scared by a tactician when just a baby :)
As far as improving performance per D/L, well, let's just say I want to improve performance, but I really couldn't care less about where the D/L falls. Would a 200 D/l boat be any more exciting at 25 knots than a 50 D/L boat? Would it be as safe and controllable (given a shi-ite-load more mass)
Steve "thoughts for the morning - now my brain hurts"

[astevo]

wardy it seems you are looking at design improvments that do not involve any of the following.
reduction in weight. or reduced disp/length ratio
better construction.
better or bigger rigs.
etc
to quote.
"Given the difference in age, style, design and construction, the improvement of the open 60 does not look so big does it! "

what factors do you consider to be 'design' improvements.
given that you have already effectively said that disp/lengh, and improvements in sail area, weight, beam, handling etc,are not real design improvements.

the only thing i have come up with which doesnt fail this criteria is reduction of drag.

i take it what you are really getting at is efficiency.
How fast a boat goes compared to another of exactly the same general parameters?
if the parameters of this boat include things like d/l and the things i listed above, the only thing that can make such a boat go faster is reducing drag by other means.

this sort of problem is what boat designers are trying to solve on a daily basis. the most intense protagonists of this are the development classes. but even here real improvements are coming from weight reduction and all the other stuff.

basically i get the feeling that you see efficiency as stemming from hull drag alone. not from increaing righting moment, reducing weight, or doing any of the other stuff which we know make boats more efficient in a real sense.

personally i see efficiency as relating speed to length and sail area. so really who could argue that the most efficient craft of any (in its ideal conditions) is a sailboard.

[Alvaro M]

This might be very off, but to be relevant, shouldn't comparisons between the races' mean speeds be somehow standarnized by the average wind speed/direction during the two events?
Alvaro

[Wardi]

I though it was simple, but here is another attempt!

The fundamental relation controlling the speed of a displacement boat is its Displacement/Length ratio.
For boats of a given D/L ratio, a canoe will generally go faster than a punt because it is a better design.
ie: it has less resistance at all speeds and angles of heel.

Thus if we are really making "real" improvements in hull design, then current boats should perform better than those of 50 years ago, based on their D/L ratio.

The article by Billy Hughes simply argues that little improvement has been made in fundamental design, even when based on Speed to Length ratio, let alone speed to D/L ratio.

Modern design advances are mainly in the area of improved materials allowing lighter weight and more stability. They can carry more sail area, so the boats go faster in absolute terms. But so they should!! We all knew that from the beginning!....

But are there any real improvements in the fundamental design when you compare them on the basis of their D/L ratio?.

[Jeff H]

I think that there have been huge improvements in design over the past 40 years, even given boats of the similar displacement to length ratios. Just compare a 40 foot CCA/RORC era boat to a 40 foot IOR era boat, to a 40 foot IMS era boat. Oddly enough they are not all that far apart in weight, but if we look at the differences, better engineering has allowed the IMS style boats to have lighter and stronger hulls, and as a result can carry greater ballast ratios carried further the from the center of buoyancy resulting in greater stability. This greater stability is what permits IMS derived designs to stand up to their larger sail plans.

But beyond that, the finer entries, and more powerful stern sections, careful hull modelling and better sail shaping on the fly allow modern boats to have way less drag as they pretty much stay in trim as they heel (at least compared to IOR ear boats), develop less weather helm, and lose less speed with each wave (as compared to CCA/RORC or IOR era boats). The highly efficient keel and rudder foils further contribute a reduced drag so these boats can actually be sailed with less sail area for their displacement in heavy going, which in turn is easier on the crew.

I get to sail on a wide range of boats from a lot of different eras throughout any given year, and it is not hard to percieve the massive improvements in speed and ease of handling in boats over the past 50 years.

I suppose that you could prove that older boats have equal performance by setting up a some kind of fanciful non-dimensional ratio, but in any kind of realistic comparison, either by length, sail area, or displacement, modern boats are much faster at either end of the spectrum (light or heavy going)and certainly a lot easier to handle at speed or in heavier going.

Respectfully,
Jeff

[SuperPiper]

Wardy, you are trying to tell these guys that there ain't no Santa Claus. They just do not want to believe you.

We know from this forum that most of the design work from the past 50 years has been spent on finding the corners of the various handicapping rules. If Herrschoff had had carbon fiber and canting keels, he would have built a VOR70. Modern boats are more stable, easier to crew, have large mainsails that are easier to reef, but, still only go as fast as Christopher Columbus.

You won't read that in the brochure for a new boat.

[PAR]

By the rather limited scope of the discussion that Wardi has placed in this comparison, I'd have to agree to some of what he suggests. Good design is always good design, but you must compare apples to apples.

Boats like LFH's big, seemly under canvassed ketch have a racing record to be envied by all, but is no match against a modern, similarly displaced vessel. They aren't even close in the numbers that mater. How can a boat that had a 30% ballast to displacement ratio compare with a 50% ratio'd craft? They could displace the same, but wouldn't have similar SA/D, drag coefficient, stability, acceleration potential, maneuverability and a host of other factors.

A first class racing yacht of 50 years would have a full working interior, complete with raised panel bulkheads and curtains. It would likely have a full keel, though well cut back by the standards of the day, undivided appendages, cotton sails, built down sections, and a pretty low ballast to displacement ratio by today's norms. The same "displacement" craft used currently will have sails a fraction of the "in use" weight of the old duck, rigging hard points and hardware that shave many pounds of weight aloft, fast acting winches, pipe berths and plastic down below, divided appendages of far better design and efficiency, much decreased wetted surface in her sections. This doesn't even touch the "numbers" but does show the advances made.

On the other hand, I'd much rather be at sea, racing or not in that big ketch of LFH. It's a much more comfortable, predictable and behaved yacht. I used to do a lot of deliveries and have had the pleasure of the helm on many fine sailing craft. None, without exception has compared with the joy of driving a "Bounty" or "big Ti" in whatever going there may have been up mother nature's butt that day. High ballast ratios make jerky boats, but quick in stays and can cling on to a wisp, but not a good time if you're on the fore deck and the skipper releases the helm while he swats a bee (time to practice the MOB drill)

I use to love the races and still do, but to a much less extent. I get much more joy from a well balanced boat, where a big gust, a trip away from the helm or not paying attention isn't going to toss my stuff all over the cabin sole. I'm finding it hard to pay attention to the race from my hammock hung between the sticks, maybe they'll design a course that is a long broad reach, followed by another and another, with maybe a brisk close reach back to the dock at around say happy hour.

[SailDesign]

Part of the problem is that physics is physics. I know, "duh!" But... for a given slenderness ratio, D/L ratio, etc, the "hull speed" is going to limit how fast a given boat is. If you want more speed, you simply go for a different point on the curve, or jump into a planing hull.
Advances in materials and structure have definitely introduced a faster boat, but not if you impose Wardi's restrictions that it have the same base numbers. As JeffH says, improved ballast ratios have upped the speed capabilities, but in the heavy stuff, a displacement hull is a displacement hull is a displace.... you get the picture.
THe only real improvement in recent times has been the ability to design boats that can plane/surf on a regular basis without the help of a large following sea. CAll it a "loophole in the laws of physics" if you will, but it IS faster :)

Steve

[astevo]

i just got around to reading the entire article from billy hughes( imguessing not the ex-AUS. PM). once again it really is worth reading. infuriating reading at its best. the kind of stuff that makes you want to plough down the old salts in their slow heavy vintage shitboxes

his description of racing talked about the benefit of being able to bake scones and roast dinners whilst managing to win an early syd to hobart. and how real yacht shouldnt need rail meat.

the article makes reference to the length of scandia zana Xena etc. these boats are all much bigger that margaret ringtoul, but if we actually look at waterline lengths not LOA it pulls up the s/l ratio by maybee 5 to 10%. if we look at similar sized boats in to 30-40 ft loa range you get s/l ratios far and above that of margaret ringtoul.

ask the question what would a mumm 30 do to margaret ringtoul. or a thompson 920 or even an old adams ten.

we dont go racing to bake scones. we race to get from a to b as fast a possible. thats what it takes to win a race of any kind. how much comfort or the number of scones you eat on the way has no reflection on the race.

[SailDesign]

we dont go racing to bake scones. we race to get from a to b as fast a possible. thats what it takes to win a race of any kind. how much comfort or the number of scones you eat on the way has no reflection on the race.

You go racoing to get from A to B "faster than anyone else", THAT is what wins races :)
Being able to cook scones while doing so, rather than sitting on the rail for hours getting soaked, must necessarily make for a more enjoyable time. PLEASE tell me you prefer eating scones and being warm to being hungry and cold...
Steve

[Jeff H]

I too just got around to reading the whole article and I also find it to be quite disingenuous and intellectually dishonest. Mr. Hughes seems to have a very sellective memory. Lets start with his prime criteria, waterline length to speed. Mr. Hughes is choosing to use the static waterline lengths for comparason. These older boats, designed to the RORC and CCA rules had incredibly short waterlines as a way to beat the rules. If I recall correctly, Margaret Ringtoul was a 46 footer sailing on a 32 '-6" static waterline length. Boats of this erea were designed to have extremely short static waterline lengths but to sail on much longer waterlines when heeled. If you were to compare speed to length of these boats using the sailing waterline lengths or the LOA's, or to compare speed to displacement for that matter, his whole contention would seem silly.

He choses to compare the upwind times of modern boats with the reaching times of the older vessels, choosing to ignore that when beating, a boat sails roughly 1.4 times the distance through the water of a boat going up wind. Comparing speeds based on distance through the water vs rhumb line distances and comparing reaching to reaching, alone would change his ratios to the point of invalidating his claims of no progress.

I raced on these older boats back in the 1960's. There was nothing easy or comfortable about sailing these old girls. They were sailed at heel angles that would be totally unacceptable today. They pitched and rolled through huge angles compared to modern IMS based designs, with roll and pitch rates that were not all that much slower than modern designs. When pushed hard they were miserably wet in any kind of heavy going, with their lee rails burried and solid water rolling across their foredecks and into their cockpits.

When pressed these older boats developed the kinds of huge weather helms that were hell on shoulder joints and steering gear. There is a myth that these short waterline boats like the 'Margaret Ringtoul' had better tracking than modern boats. That's just plan bunk. The race boats of 50 years ago did not track any better than modern designs. With their full ends, comparatvely short keels, and thier attached rudders, the race boats of the 50's and 60's developed very small longitudinal directional moments of intertia. Modern boats with their the longer waterlines, finer entries and the increased moment between their separated keels and rudders actually seem to track better. Beyond that, the best directional stability in a sailing yacht is achieved with dynamic balance of rig and sailplan and there these old boats really did very poorly when it came to dynamic balance.

Mr. Hughes cites 'Spray' as an example of why a multi-mast rig is better than a sloop, but if you do actually read 'Alone around the World' Slocum describes a boat that was grossly imbalanced under her original sloop rig, and so he was forced to cut down the rig pretty dramatically and then add the mizzen as a balancing sail. Yes, he made 'Spray' easier to sail by making her a yawl but I would categorize this rig change as solely overcoming what I would call a 'design flaw' in the original rig proportions, rather than a demonstration of the inherent advantages of a multi-mast rig. Right out of the box, modern racing sloops come with better balanced rigs, and with modern rigs whose balance can be quickly and easily fine tuned on the fly.

Anyone who has ever raced a gaff schooner, would tell you that there is nothing easy about racing one of these old birds. Twist is controlled by playing both the peak and throat halyards on both sails gaff, and that was a constant battle going upwind. Those were not 'good old days' for anyone with a decent memory.

I don't what boats Mr. Hughes raced on back in the 60's, but we sat on the rail back then just as we do today, only it was less comfortable (the high toe rails digging into your thighs and the solid water hosing you with each wave) and a whole lot less effective.

Anyone who has ever raced in a mixed fleet of boats that contains modern and older race craft, will tell you if compared by LOA, or sailing LWL, or displacement, modern IMS based craft are much faster under all points of sail. With their lighter loadings, balanced helms, smaller heel angles, and smaller roll and pitch angles, they are easier to handle and less tiring on the crew. I race on both modern and tradition boats. While there is a different set of challenges and aesthetics to old boats, performance wise, and ease of handling, these newer IMS derived designs really beat the older designs hands down.

I too want to return to the Mr. Hughes mention of the LFH quote (to paraphrase) 'When rating rules produce unwholesome yachts the rule is wrong." I don't disagree with that statement. I would say that boats like the 'Margaret Ringtoul', with their rule beating extremely short waterline length, deep canoe bodies and low ballast ratios, and dependence on huge headsails in order to beat the rule, would be a prime example of the case of a rule that produced an unwholesome design typeform. The IMS derived designs are less rule driven and seem to produce boats with better motions, more speed, and more seaworthiness. In that regard, I would say that LFH would approve of our current crop of race boats.

Respectfully,
Jeff

[tspeer]

...Are we really making any real progress??
The boats are going faster in absolute terms but is this accompanied by real advances in efficiency?? :?:

Ahem... Aren't you ignoring the elephant in the room?

There have been enormous strides in sailing comfort, speed, and efficiency in, say the last 40 years. Whether you look at passage-making speeds or race line honours, the winners are...

MULTIHULLS

The only way you can say there hasn't been progress is to exclude the category of boats in which the progress has been made. When you do that, it's not surprising the results are disappointing.

Compare the Margaret Rintoul with a modern cruising catamaran. For example, take the Gunboat 62, designed for Peter Johnstone by Morelli & Melvin. She can easily do 16 kt to windward in about the same wind speed, a S/L of 2.0, and reach maximum speeds in the high 20's - say S/L of 3 or better. Average speeds I'm guessing are are probably around 10 - 12 kt, for a S/L of 1.25 - 1.5, and equal to the speeds of the 98 footers and double the Margret Rintoul.

Take a look at this video (http://www.gunboat.info/video/safari.html) of a Gunboat 62 smoking a Reichel-Pugh 80 (doing 18.5 kt - S/L=2) and then say there's been no progress in sailing yacht design! Also notice the difference in heel angle. Not shown is the difference in interior appointments between the two boats. The catamaran is also unsinkable.

Here's another data point: Francis Joyon, around the world in 72 days 22 hours and 54 minutes single-handed. First non-stop single-handed circumnavigation, 1969, Robin Knox-Johnston, 312 days. That's a 427% improvement in average speed in 35 years.

I count advances in comfort, performance, safety. Cost, too, depending what you hold equal for comparison.

[SuperPiper]

A monohull is TYPICALLY limited to a S/L of 1.34 (+/-). Two monohulls racing side by side are each sailing at S/L = 1.34. But if the 2 hulls are attached they can sail at S/L = 2.0?

Explain that one to a stupid guy.

Is it the NARROW HULL rule?
Is it the fantastic reduction in weight?
Is it the increased sail-carrying capacity?

If the answers are YES, then what is the expected S/L for a light, narrow (DISPLACEMENT) hull with unlimited sail?

[redcoopers]

A monohull is TYPICALLY limited to a S/L of 1.34 (+/-). Two monohulls racing side by side are each sailing at S/L = 1.34. But if the 2 hulls are attached they can sail at S/L = 2.0?

An S/L ratio of 1.34 is not set in stone. To understand why most 'typical' monohulls do not exceed this speed in normal conditions, we need to know what causes the resistance in the first place.

If we divide all of the drag on the hull into two categories: viscous and residuary, two things can be shown. First, the viscous resistance is proportional to velocity^2 - it will always increase as speed increases. Residuary resistance, or wavemaking resistance, is a much more difficult monster. In fact, we are required to perform tank tests, CFD calculations, or other methods to find what the wave resistance will be.

Now, the wavemaking resistance is not a smooth curve such as simply ~V^2. Instead, it has many "humps and hollows". Most monohulls experience a large hump right after S/L=1.34. Simply, it's difficult to get the required power to exceed the drag.


Is it the NARROW HULL rule?
Is it the fantastic reduction in weight?
Is it the increased sail-carrying capacity?


The humps and hollws also explain why racing sleds are built so light today. These boats have enough sail-area that in certain winds, they produce enough power to get over this hump, and then start planing. Now, catermarans are different beasts than monohulls. When sailing upright, wake from one hull may interefere with the wake from another, causing cancellation and actually decreasing the wave-making resistance.

But, cancellation is a tricky area. Not quite yet are designers actively using this effect (however, there is a tool just being published which can help). Simply, catermerans can utilize a lot more sail power because of the increase in righting moment. This lets them get over the humps and hollows of the wavemaking curve a lot more easily.

So
1) Yes, cats are narrow - they don't need beam to increase righting moment. Wavemaking resistance can be shown to be loosly proportional to Beam^2.
2) Yes, a fantastic weight reduction helps a cat to accelerate off a wave. Remember, however, that weight will not directly affect the steady speed of a boat. (F=ma, not F=mV).
3) Yes, cats can carry a whole lot of sail-area. This is most responsible for letting them be able to exceed S/L=1.34.

So, what is the excpected S/L for a light, narrow hull with unlimited sail? For most monohulls upwind, it's 1.34. It's all because of the available righting moment which the hull and the keel can produce. If you have a 30 foot boat with a deep lead keel 13 feet down, you'd probably be able to exceed this because you have a massive righting moment.

If we're talking about downwind, however, you'd want to scrape the entire keel off of the boat to reduce the viscous drag. You don't need a righting moment when sailing downwind (well, practically, you do), so if you put on enough sailarea, a monohull could almost start to fly...

Hope this helps,
Jon

[tspeer]

Very few cats depend on wave cancellation - in fact the interference is generally adverse. But sailing multihulls also have such wide separation between the hulls that the interference effects are minimal.

The real answer to their speed is the drag hump at hull speed is so much flatter for the narrow hulls than it is for the wide heavy displacement monohull that the same drive results in a much higher speed. Their drag increases monotonically with speed, albeit steeper in some areas and flatter in others, but overall the curve is much more shallow than for a monohull.

So they're not exempt from the same influences that lock in the ballasted monohull, it's just that the consequences are far less severe.

The issue of righting moment is the other reason for their speed. A multihull can shift its center of buoyancy all the way out to the leeward hull, making the separation between center of gravity and center of buoyancy almost half the total beam. A monohull can only move its ballast, say, half the keel depth to windward (30 deg heel) and the center of buoyancy maybe 1/3 the beam to leeward. That's a difference of maybe, a beam's width? So the sail-carrying capacity of the multihull is far higher.

Then there's the lighter weight, which means less wetted area and less wave drag.

So the end result is far higher sail area/displacment, far lower displacement/length, and much more easily driven hull shape. These all contribute to the speed.

[Wardi]

Measure of performance
Billy Hughes has chosen to use Speed/Length ratio as a basic parameter for comparing performance. Many of the responses so far have also chosen to refer to this measure, but in fact it is not a good parameter to use at all. Boats of the same length can vary greatly in displacement and sail area. In practice there is around 25% difference in speed/length possible between heavy displacement and light displacement boats of the same length. This has been completely overlooked in the arguments put.

So when Margaret Rintoul achieves S/L= 1.126, it would equally be expected that an open 60 should be able to manage at least S/L of 1.3 under the same conditions to be considered of equal performance. And yet the figures quoted show a S/L ratio of only 1.26. So it is not so clear on this basis that an open 60 is in fact a design improvement!
Faster.... absolutely, faster for its length.... well yes, as would be expected, ...........but not necessarily faster when you consider its displacement, length and sail area! :-)

Configuration vs fundamental design improvements
I am actually quite intrigued at the very mixed response to this discussion. ;)
Perhaps most surprising to me is how difficult it seems for most people to separate fundamental improvements in performance from basic configuration changes. To be very clear I think I need to explain what I mean:

a) Fundamental design improvements
Let us assume we have two boats of the same displacement, waterline length and sail area and of similar configuration. Then any improvements to the rig, hull shape etc resulting in one being consistently faster than the other could be termed a "fundamental improvement" in performance. Typically you could find such improvements within restricted design classes. For example the clear superiority of higher aspect flexible rigs vs fixed, low aspect stiff rigs would be one such improvement.

b) Configuration changes
It is very well known that longer, lighter craft with more sail area go faster. So it is quite obvious that if you make a boat with a longer waterline, lighter displacement and sit lots of people on the gunwhale to hold up an even larger sail area, of course it will go faster than its predecessor!!

I do not consider this a fundamental design improvement at all, simply a configuration change. The only reason it was not done 100 years ago was limitations of materials and in some cases racing rules prohibiting the use of moveable ballast, including crew!

Hence comparisons given so far with Open 60's, Mount Gay 30's, Catamarans etc are not really valid, as they obviously go faster in absolute terms, simply because they have a different configuration, not necessarily because of any fundamental design improvement!.

It is only when you can prove improved performance based on their Displacement, Length and Sail area, that we can say a fundamental design improvement has been made. So far, this has not been proven for the examples given! :)

[Jeff H]

Wardi, I think that I understand why you are not getting the kinds of responses that you are expecting. The way that I am reading your last post, you are saying that you are looking for changes that bring speed improvements but which don't change the 'configuration of the boat'. In my mind you seem to be defining this term so narrowly that almost any alteration in the design of the boat becomes a change in the 'configuration of the boat'. That does not meant that improvement in performance is not happening, it just means that any change large enough to improve performance would also imply a change to 'configuration of the boat' as you are defining it.

Getting away from Mr. Hughes S/L numbers which do not appear to be a fair comparason of the speeds of the boats that he is comparing (as I explained in my easlier post) I would like to suggest that we look at particular models over a 45 year period:

I think that I can start to demonstrate my point by looking at three boats from the same boat builder over a 16 year period. If you look at the PHRF ratings on the Beneteau First Series, you will see that over an 16 year span they have produced three boats in the same general size range: Beneteau First 42, Beneteau First 42s7, and Beneteau First 40.7. They have similar waterline lengths and similar displacements. In most ways, they represent the norm for pretty advanced, high production quantity, performance oriented, club level racer-cruiser boats of their era. (Although I was the mainsail trimmer aboard the box stock, 4 year old 40.7, that won the IMS North Americans so argueably the 40.7 is more than a club racer) The 42 rates 78, the 42s7 rates 63, and the 40.7 rates 54, a jump of 24 seconds a mile.

If we went back and looked at these rated speeds vs older high production performance cruisers, the trend continues. For example, if we look at the S&S designed Tartan 41, which was a very fast performance cruiser for its day in the early 1970's, the Tartan 41 rates 111-114. Again if we compare that to a Cal 40 which was a very fast boat for its mid-1960's era, a tall rig Cal rates 126. And if we compare that to the Rhodes 41 (a late 1950's design) that was considered quite fast for its day, the Rhodes rates 174 which is roughly a 25% increase in performance over a roughly 44 year period. Oddly enough, in its normal sailing configuration (155 % genoa) the Rhodes carries the most sail area of the bunch and has close to the same SA/D as the other boats. That said, the Rhodes sails on a much shorter static waterline length. Argueably, its dynamic waterline is not all that different from the other boats on this list but its displacement is roughly 15%-20% higher.

So what were the changes that caused these very real increases in speed? If we look at the Beneteaus, in absolute terms, comparing these boats with the genoas and kites that these boats typically fly (and not with 100% fore triangles typically used for calculating the rated sail area of the boats) the 42 carries the most sail area of the three in its typical sailing configuration, the 42s7 carries the next and the 40.7 the least sail area, and they have very close SA/D's (roughly 25 using the sail area of a 150% genoa) and fairly close D/L (178, 174, 161). The big differences in these boats are hull shapes, vertical center of gravity relative to their vertical centers of gravity, and rig proportions. The 42 had its center of buoyancy much further forward, a deeper canoe body, pinched ends, and a comparatively blunt bow, the 42s7 begins to move the C of B aft and the 40.7 has a very fine bow, carefully modeled lower drag sectional properties, the C of B further aft still, and substantially smaller and more efficiently shaped foils. The 40.7 with its deeper bulb keel has a tremendous stability advantage over the earlier 42s7 or 42. The 42s5 and the 40.7 have fractional rigs which are generally thought to offer greater efficiency than masthead rigs. Combining the 40.7's greater stability with its fractional rig, which allows it to be depowered more easily, the 40.7 can carry more of its sail area through a wider wind range than its earlier cousins.

In my life I have raced on a Pearson Rhodes 41, Cal 40's, Tartan 41's, Beneteau the 42's and Beneteau 40.7's. With each generation, it has gotten easier for the skippers and crew to achieve more consistent speed. The boats have gotten much easier to handle with smaller crews. In any kind of absolute terms, the newer boat are better cruisers as well. In absolute terms they have offer a more comfortable motion in hard conditions and frankly the interiors are more voluminous and the accomodations have gotten nicer and more comfortable, albeit lighter. At either end of the wind ranges there are enormous increases in speed on all points of sail with the newer designs (less so at the moderate wind ranges that the PHRF uses for its ratings)

All of that said, it would be very easy to dismiss the performance improvements as changes that represent changes in the configuration of the boat and so I am not sure that the above really addresses Mr. Hughes or your original point.

Respectfully
Jeff

[Wardi]

Hello Jeff,
In fact you have in fact now understood very well what I am proposing and have provided some very good information and comparisons.
Please do not get me wrong, I am not saying that there have been no design advances at all over the past 100 years, I am sure that there have, but perhaps not as many and as big advances as we might first think, especially when looking at the responses presented in this forum!

While I agree with you that my interpretation could be considered a narrow definition, I do not see any other way of evaluating real performance improvements.

As I see it, anyone can change basic configuration to make a boat go faster, if their pockets are deep enough (make it twice as big), or if you are prepared to bend the rules (sit all of the crew on the gunwhale, or better still put them on trapeze!). This is not necessarily reflecting fundamental advances in boat design. I think we have generally been conned into thinking it is, perhaps because it is not easy to visually "see" changes to displacement or stability, only that the boat is faster.

I believe it is important to maintain a consistent basis for true comparisons. Hence the requirement for comparing craft of a similar configuration. I do not mean to be highly restrictive with this and all of the examples you have given are pretty valid comparisons. It should be entirely up to the designer to decide rig configuration, areas and centres of lateral plane, bouyancy, stability, ballast ratio, distribution of displacement, hull and appendage shapes etc etc, in order to come up with the fastest possible design. True advances should be properly recognised, not just improvements at beating the current rating rule!

By using the term "same configuration", I not only mean monohull vs catamaran, but also apply it to the means of providing stability within monohulls. There are several quite distinct categories including Keel Ballasted, Crew Ballasted, Trapeze, Water Ballasted, Canting Keel and even within these there are Cruising and Racing versions. Unfortunately the distinction is somewhat blurred between these categories, especially Keel ballast and Crew ballasted configurations, which has been used as a way of cheating the rules and does not seem a fair comparison.

It is mostly only meaningful to compare performances within each configuration type, but we can compare across all of these types if we use just three fundamental parameters, Displacement, Length and Sail area. It would be really good if you could supply values for Displacement, LWL, Sail Area and rating for each of the boats you have mentioned. I am not familiar with the rating system mentioned. Can I use this to calculate a realistic speed of the boat? Does this rating reflect true performance of these designs or is it a handicap rating only.

regds, Ian

[Jeff H]

Hello Ian,

I think that I can supply LOA, LWL, Disp, and SA for these boats but it will take me a little while as I was writing these numbers on an old evelope as I was working on the prior post last night. PHRF is not a measurement rule like the CCA, IOR or IMS but handicapping rule based on past performance. In that regard it is a pretty good indicator of the boat's relative speed at a single moderate wind range. Argueably the numbers my be off by 6 or so seconds a mile but they are generally are pretty close to a boat's performance, especially on the older models for which there is a long history from which to derive the rating. That said, it is hard for an older boat to race competitively against newer faster boats under PHRF because the greater speeds give the newer boats a tactical advantage.

Jeff

[henrikb]

The wheel was designed some 1000 years back, it still looks the same... Better materials, but no major improvment in design *s*

[SailDesign]

So when Margaret Rintoul achieves S/L= 1.126, it would equally be expected that an open 60 should be able to manage at least S/L of 1.3 under the same conditions to be considered of equal performance. And yet the figures quoted show a S/L ratio of only 1.26. So it is not so clear on this basis that an open 60 is in fact a design improvement!

Not fair, really, since the Open60 speeds were based on a 27000 mile single-handed voyage, and were based on a minimum speed (100 days) rather than the winning speeds (90 days or so)

Using cats as a "yes, we have improved" is not fair either, since we're talking apples and cats are definitely oranges in this case. :) That's like saying that the internal combustion engine was a "design improvement" compared to the horse.

Steve

[SeaDrive]

My opinion is that the actual advance in yacht design is mostly controlled by the advance in materials. The designers learn to use new materials pretty quickly. The better D/L ratios are due to stronger building systems, for the most part. The larger rigs are due to better masts, better rigging, and better sailcloth. Designers are now very greedy about draft. They seem to think that 6ft of draft is appropriate for a 30' cruiser.

I admire the skill that goes into design and construction of a modern racing boat, but I don't admire the boats that much. As fast and seaworthy as they are, they don't look very comfortable to be on. Most are very low inside, and the storage space complements the thinking of the captain who makes sure the crew cuts half the bristles out of their toothbrushes to save weight.

Racing rules have muddied the waters all along, and invalidate most of the comparisons that one would like to make. Still, a 40' Island Packet is probably a better boat all around than Finisterre.

[Wardi]

I think that I can supply LOA, LWL, Disp, and SA for these boats...... PHRF is not a measurement rule like the CCA, IOR or IMS but handicapping rule based on past performance. In that regard it is a pretty good indicator of the boat's relative speed at a single moderate wind range.

This PHRF sounds ideal for our discussion! It is quite straight forward to predict a boats potential speed from the D,L & SA data, but I do not have much quantative info on their actual performance, from which we can conclude whether real advances have been made and by how much.

It is also much more realistic to make comparisons of the performance of craft of similar configuration based on reliable data, rather than trying to deal with the extremes of one-off performances of an Open 60 vs Margaret Rintoul that began this discussion.

[SeaDrive]

PHRF stats can be helpful, but they don't tell you if you need 5 guys on the rail to go upwind, or if the boat is suitable for a weekend cruise.

Multihull development was very rapid from the time of Piver until it became more or less mature about 10 years ago.

[Stephen Ditmore]

Hi, all. A few quick points, having just skimmed through this thread.

- The most recent Sydney Hobart was not sailed in particularly favorable conditions. For this reason no record was set, but other records have been falling right and left, and the new IRC 30 meters might well have established new marks given the right circumstances. Sailing is still sailing.

- Many new IRC 30 meters and MaxZ86's are different from the Open 60s that Steve Baker advocates (bless your enthusiasm, Steve!) in that they are relatively narrow. A lengthened Open 60 (Grundig?) sailed the last Sydney-Hobart, but I don't think it's performance was anything particularly outstanding. Steve - do you think Reichel/Pugh, John Swarbrick, and other designers of recent relatively narrow performance monohulls are headed off in the wrong direction?


Then what is the expected S/L for a light, narrow (DISPLACEMENT) hull with unlimited sail?
Glad you asked, Super. In the end, speed is a product of horsepower over resistance. In order to have horsepower, you not only need sail area, but the stability to carry it. Wave drag at high speed is dependent upon, among other things, frontal (midsection) area. If the assumption can be made that each boat has the stability to utilize its sail area effectively then an unusual but interesting ratio to look at might be sail area to midsection area, which is to say sail area / displacement ratio with length and Cp factored out of the denominator. Monohull and multihull performance might be compared meaningfully using such a ratio if one were to consider the PROJECTED sail area of each, thus taking into account heel angle.

Waterline beam may be a bigger contributor to hull resistance than the other frontal area factors: fairbody draft and midship coefficient. Waterline beam helps monohull stability, and therefor sail carrying ability (a plus) but also increases both wave drag (at some speeds more than at others) and wetted surface.

Multihulls detach the issue of stability from the factor of (each hull's) waterline beam.

[SailDesign]

bless your enthusiasm, Steve!)

I'm not sure whether the reply with a "ppppfffttttt...." or not, so I won't :)

The Open 60 example was really just a stab at a "modern" boat for comparison. Yes, they are usuallyfat little beasts, which gives them sail-carrying power at a cost. THe coat being that they are bitches to sail in a good sea, especially into it. "Noise" doesn't even begin to descibe the sound.
As far as the narrower boats being built and designed (or vice versa), I think they are going in the right direction. Dave Adams in True Blue showed that skinny(-er) is not a race-loser, even RTW. Certainly their behaviour in waves improves, and they are much more gentle on the skipper, resulting in higher personal efficiency (not to be discounted as a tactic in long races).
Steve

[Wardi]

PHRF stats can be helpful, but they don't tell you if you need 5 guys on the rail to go upwind, or if the boat is suitable for a weekend cruise.
You are correct, but we need to start somewhare and perhaps it is easy enough to categorise each type based on experience. Another point is that if Crew ballast is used, then presumably they can handle more sail area, which would be taken into account in their D-L-SA ratio.

Multihull development was very rapid from the time of Piver until it became more or less mature about 10 years ago.

A couple of weeks ago I had the privelege to sail a currrent top German Olympic Tornado cat..very impressive!!. They were originally designed in 1952.

They perform very well and as far as I know there is almost nothing that is as fast for their size. Have there been any real advances since 1952?

[yipster]

wake from one hull may interefere with the wake from another, causing cancellation and actually decreasing the wave-making resistance.
and
Very few cats depend on wave cancellation - in fact the interference is generally adverse.
than why do 2 (mono) hulls sailing paralel get atracted, i'm having trouble understanding that.
would think there is a pressure buildup or is that conserved energy giving a faster sucking flow like in bernoulli's equation?

[SailDesign]

Yipster, the simple explanation would be that the water has speeded up between the hulls (being "squished" through the gap) abnd thus there is a lower pressure there, so the hulls are sttracted. In cats, this is present as well, leading to extra drag as the hulls get closer. While the hulls cannot be physically moved together, it does add compression in the cross-beams, and the energy has to come from somewhere.
That particular problem made for a fun tank test exerfcise at college - complete with strain guages on the beams.

Steve

[SuperPiper]

Real development:

Whatever happened to the "Bubbler" attempts? Were there not some ocean yachts that bubbled air through the hull to do something to the boundary layer? Obviously this did not work or there would be more of them about.

The new Parlier catamaran has hulls shaped like airplane floats. This could be a new idea with applications.

What is the name for the technology that keeps the hull fully submerged? Are these boats capable of S/L greater than 1.34?

Three bow types: raked, spoon & plumb. Are these just 3 ways to redefine water-line length or does each have a hyro-dynamic advantage?

Wardi's own foiling developments are truly the next generation of sailing technology.

[Wardi]

I think that I can supply LOA, LWL, Disp, and SA for these boats but it will take me a little while as I was writing these numbers on an old evelope as I was working on the prior post last night. PHRF is not a measurement rule like the CCA, IOR or IMS but handicapping rule based on past performance. In that regard it is a pretty good indicator of the boat's relative speed at a single moderate wind range.

I have found a nice resource of data at http://www.yralis.org/
under "Handicap Racing Information with Rating Froms" , "Base Ratings".

I now have data on over 2000 boats with their basic dimensions and actual performance rating. The results of initial comparisons is very surprising!!

Most of the boats covered by this data are standard yachts 20-60ft from a wide variety of manufacturers. Unfortunately there is not so much information on the very latest racing craft such as Open 60's, V60, V70, Maxis etc or one designs like Mumm36, Farr40, Sydney38 etc.

Does any anyone know where I can get data for these types of craft?
Ideally I am after: Displacement, LWL, Sail Area, Beam, Draft, Ballast, Age, rating and most importantly a measure of their actual speed, not just their IMS or IRC. In a spreadsheet would be ideal!!

[Jeff H]

A lot of the kind of information that you are looking for can be found in listings for these boats on www.yachtworld.com. Boats like the Open 60's and Volvo Boats will vary quite widely in terms of their dimesions actual as they are not a one design class. There are a lot of sources for PHRF ratings although the ratings for individual boats will vary considerably with region. Also IMS certificates are a pretty good predictor of boat speed. The IMS rule is VPP based as a such predicts better predictions than earlier measurement rules.

Some of the key factors in the improved speed of new boat designs are the location of the longitudinal center of buoyancy, buoyancy and weight distributions, cross sectional modeling, more efficient foils, heeled hull form modeling, a move to more efficient and controllable fractional rig sailplans coupled with masthead assymetrical chutes, and the fineness of the bow entry angles. These kinds of subtle factors do not show up on any table.

Respectfully,
Jeff

[SeaDrive]

A couple of weeks ago I had the privelege to sail a currrent top German Olympic Tornado cat..very impressive!!. They were originally designed in 1952. They perform very well and as far as I know there is almost nothing that is as fast for their size. Have there been any real advances since 1952?

I think there is little doubt that if you were to compare, say, an Iroquois from 25 years ago to a current boat of similar size and purpose, you find find the new boat to be better in every way. Speed, capacity, safety, etc. Probably even cheaper (inflation adjusted price).

[crispilo]

A couple of weeks ago I had the privelege to sail a currrent top German Olympic Tornado cat..very impressive!!. They were originally designed in 1952.

They perform very well and as far as I know there is almost nothing that is as fast for their size. Have there been any real advances since 1952?

I had the chance to take a deep look on a Tornado wich was trying to reach Athens 2004 this spring, so a very up-to-date model; if you compare this boat with a "vintage" Tornado, you will see that is a whole different boat; sails are different both in material and in design/concept, rig is different, foils and rudders are deeply different, deck gear is absolutely more sophisticated, lighter e stronger; just the hull shape is quite the same, but in a easy-planing multihull like tornado mere hull shape is one the latest parameters you have to consider to evaluate global performances.

Crispilo

[yipster]

on transverse wave cancelation and their effect at various speeds on a variety of multi hull design there is a good read at http://www.cyberiad.net/library/pdf/tl98.pdf

[Stephen Ditmore]

in a easy-planing multihull like tornado mere hull shape is one the latest parameters you have to consider to evaluate global performances.
I would dispute that the Tornado planes often. I've seen it written that a boat is planing when more than half its displacement is being supported by dynamic force (as opposed to static pressure). This means a boat that is barely planing is only "displacing" half the volume of water (at any given instant) as when it is stationary. I consider the Tornado to be a displacement catamaran because it does not lift half or more of it's static displacement out of the water at speed.

[SuperPiper]

I think there is little doubt that if you were to compare, say, an Iroquois from 25 years ago to a current boat of similar size and purpose, you find find the new boat to be better in every way. Speed, capacity, safety, etc. Probably even cheaper (inflation adjusted price).

Perhaps the skipper of 1979 preferred the ride of a deep, pointy hull over the performance of a flat-bottomed, wide-transom sled. Shifts in personal preference may be mis-construed as "advancement".

[Jeff H]

First of all the 'Iroquois from 25 years ago' mentioned in the quote was a catamaran and so I am not sure what you point is about the sleds relative to an Iroguois.

As to the rest of your statement, I think most of us would prefer the motion comfort of the modern IMS type form derived boats over the ride of a 'flat-bottomed, wide-transom sled' by which I am guessing that you mean Open Class type boats. But most of us also would prefer the motion comfort of the modern IMS type form derived boats over the miserable rolling, pitching motion, crash into every wave ride of more traditional designs. You are right that in 1979 the canoe bodies were deeper, but they were also far less pointy. In those days you had a choice between traditional hull forms with comparatively blunt ends and IOR style hull forms with their center flats and thier pinched ends. Neither offered very comfortable motions.

Jeff

[Wardi]

The rating rules do tend to favour boats of a particular configuration or seek to handicap out any real advances in design in the interests of "fair" competition.

I would like your thoughts therefore on:
"What should be considered a suitable basis upon which we can evaluate fundamental performance improvements?"

It is quite clear that Speed/Length ratio is the norm used by most casual observers, but we all know that displacement and sail area contribute significantly. So shouldn't a proper comparison be based on all of these parameters?

Could we perhaps establish a simple measure as a reference, based on the fundamental data established by Taylor in his Resistance vs speed/length ratio for hulls of various D/L ratios?

What do you think?

[a_stevo]

re:'Could we perhaps establish a simple measure as a reference, based on the fundamental data established by Taylor in his Resistance vs speed/length ratio for hulls of various D/L ratios?'

.i dont really see it being very simple a process. we have pretty much already shown that all ims irc irm ior etc rules have lead to weird boats with a bias toward slow or ugly designs.

this leaves the boats we can compare with being only
...........boats designed within the same rule for a long period of time
..........or boats designed to no rule at all.

which brings us to development classes really. development dinghys is where real design improvements have come. consider ns14 of 30yrs ago or moth of 75yrs ago. these rules and classes have been around for long periods and clearly the improvements in speed with the same boats are huge.

no rule boats
unlimited boats probably fail some of the other criteia which have prevented us analysing different boats. they have become lighter, got bigger sails and narrower hulls almost exclusivley, so are not really grounds for comparing. right?
the only other type of un measured boats which have not changed in fundamental terms are cruisers.

only cruisers and development classes are designed without the weird rating rules or extreeme dimensions which have been shown to be the domain of unlimited and rule rated boats.

in terms of development in yachts as we have been refering too mostly, the only way to see is real development is in which boats win the ims irc or whatever races. these rated boats are not developed to be fast exclusivley but are designed to be faster than the rule thinks they are. thats the objective and as you will find in general the newer boats are winning in the rated classes too this indicates real improvement in design.

we are getting better at design simply because new designs keep winning races. thats the measure of how well they are designed, how well they perform their task and how well they meet their design objectives.

andrew stevenson

[redcoopers]

Hi everyone,

Well, this doesn't exactly answer the question of speed, but over the course of a year or two, I've assembled something which could help.

I have a parametric analysis of over some 200 recent yachts. They vary from custom built to mainstream yachts. From these boats and the calculation of disp/L and SA/disp, I conducted a regression.

Personally, I use this spreadsheet for design purposes. The regression I calculated specifies a scale from 0-10, with zero being slowest and 10 being a speedster. A '10' has a disp/L of about 80 and a SA/disp of about 30.

Anyway, this data doesn't solve the issue from this thread, but it's useful for me for design purposes. Maybe this parametric regression can be useful for other people in measuring relative boat performance.

-Jon

[redcoopers]

Oh, by the way:

Some ballast ratios are approximate. If a ballast ratio is = 0.42, then it is an assumption I put in myself.

Also, I apologize for the sloppy spreadshet. I forgot to unlink it from one of my design spreadsheets.

Anyway, I hope this is still useful.

-Jon

[Wardi]

we have pretty much already shown that all ims irc irm ior etc rules have lead to weird boats with a bias toward slow or ugly designs.

The issue I am raising here is:
"How do you know if they are slow designs or not?"

There must be fundamental basis on which we can make a sound judgement. I suspect you are only looking at speed for the length of the boat in many instances.

I am proposing a sound basis, which is rather easy to use, but not getting any feedback on whether this would be an acceptable measure.

I am rather sceptical of using IMS and VPP for predictions, firstly for the reasons explained in the recent IMS thread, and secondly because I want to compare actual performances, not just theoretical ones.

[SeaDrive]

I skeptical of using ratings or racing results to determine design progress. The technical changes are too confounded with rule changes, fashion, and other "social" factors.

There are some changes over the last several decades that are accepted as progress: rod rigging instead of wire, fin keels instead of long keels, light foam core construction instead of carvel wood construction, modern sailcloth, etc. Would your analysis method detect them?

Many other changes are far more subtle, such as anti-pitch hull shapes.

[Wardi]

There are some changes over the last several decades that are accepted as progress: rod rigging instead of wire, fin keels instead of long keels, light foam core construction instead of carvel wood construction, modern sailcloth, etc. Would your analysis method detect them?

As I see it, the answer is definitely "Yes", a basic reference using Displacement, Length and Sail area would quite clearly identify the most efficient designs.

It would also be completely independent of rules, ratings and handicaps. It is quite simple to calculate and apply to all boats, even those 80 years old, from existing data. That is why I am seeking reference data.

It would not identify which of these individual factors makes the difference. That would be up to the individual designer.

What it can highlight though, is whether these material developments are being applied to fundamentally poor designs, which I suspect may be the case.

[a_stevo]

we know that they are slow designs simply because the unlimited boats and development boats dont wouldnt touch the concepts with a fifty foot pole.

if there were a basis where performance could be compared it would be an excellent design tool for certain. but what rules have shown is that they dont work.

every rating rule has the same objective of what you are trying to acheive. that is to measure boats in a way which can be used to predict speed. the people making these rules are not idiots. they have found such a basis impossible to find and so imperfect rating rules are introduced. it would be naieve to say that design could be compared to some sort of relative speed of some simple form. i hapen to like this concept=length*squareroot(sailarea)/cubed (root mass). butit is nlyapproxiame as it will always be.

The issue I am raising here is:
"How do you know if they are slow designs or not?"

There must be fundamental basis on which we can make a sound judgement. I suspect you are only looking at speed for the length of the boat in many instances.

I am proposing a sound basis, which is rather easy to use, but not getting any feedback on whether this would be an acceptable measure.

I am rather sceptical of using IMS and VPP for predictions, firstly for the reasons explained in the recent IMS thread, and secondly because I want to compare actual performances, not just theoretical ones.

[Wardi]

If there were a basis where performance could be compared it would be an excellent design tool for certain. but what rules have shown is that they dont work. Every rating rule has the same objective of what you are trying to acheive. That is, to measure boats in a way which can be used to predict speed. They have found such a basis impossible to find and so imperfect rating rules are introduced. It would be naieve to say that design could be compared to some sort of relative speed of some simple form.

I am not trying to create a rating rule, or even a design tool, but simply to find a basic reference measure from which true performance can be evaluated.

I disagree with your assumption about rating rules as they have quite different philosophical requirements. In general they try to handicap the actual performance of a boat so they can all be raced "equally", effectively removing the design element from the equation and allowing skippers and crew to be judged "fairly" on their sailing ability. This means in effect that real new design advances are actively discouraged.

IMS goes to incredible lengths in an attempt to predict the actual boat speed, effectively penalising any advancements, but it also seems to favour certain hull types and configurations. refer to the IMS discussion forum.

What I have proposed is not based on a simple proportional relationship between displacement length and sail area, but is based on well established actual test data of hulls in water, which shows non linear behaviour and is applicable to all displacement and planing craft.
When I calculate the values I can quite simply and reasonably accurately predict IMS ratings. The point is that these do not necessarily reflect the actual performance of the boat, otherwise they would have the new and much older designs all finishing closely on handicap, with no need for age allowances etc.

You are in fact correct in saying that rating rules are imperfect, but they are not trying to encourage better designs, just predict speed so they can produce close racing on handicap. The basic measure I am proposing is only a reference point. If a boat performs better than this, it is an improvement. The boats which exceed this measure by the greatest margin may be considered the most efficient designs. Because of the handicap rules, in many cases these "efficient" designs are heavily handicapped and so do not easily win races, hence they can go unrecognised. Conversely inefficient designs, well sailed can win on handicap quite easily.

What I am seeking is if this proposal to use fundamental data as a reference could be considered useful, or if people have other ideas.
Has such a proposal been made before?

[ErikG]

Just an idea... if it's dumb, youl'll tell me :)
Long rambling ahead, consider yourself warned! ;) :!: :D

After a big number of reference boats have been collected, it might be a good idea to simplify the mission a bit. Ok what's "generally" different between a 70's IOR Racer a 90's IMS and the latest version of IMS and how does that compare to boats built whithin the same timespan that are ULDB's or sportboats (or any other type we can think of).
Then selecting a number of existing boats as model references and then finally trying, to as best as we as a collective can, gather as detailed info as possible about the specific boats (without trying to splash the designs. To show what advances, and evolutionary changes have been made through the years but excluding the dispacement, sailarea, CG, increase/decrease in wl from "the equation". How many boats to actually compare is another issue :)

But I don't think that an analysis like that can ever be totally analytic and numeric. It has to be evaluated and expressed in general language. Otherwise you will one way or another build yourself into the same kind of corner as the handicap rule writers do.

Is this along your line of thinking Wardi?

An open paper like this would be immensly useful for design students, and probably quite a few practicing designers as well.

This IS what any designer does in his/her own way, to figure out what and how, to change and improve stuff. But a designer does NOT disregard the stuff i mentioned earlier dspl etc. as they are very important in the design process. But having the knowledge of things that physically improve speed or handlig through the shape of the hull is still the part that remains partially untold in any designbook, good and bad.

Flow analysis is beyond the scope of most students and quite a lot of designers as well. So having evolutionary design differences like these could be a nice help.

As we say in sweden: "Am i totally out on my bike?" (yes swedes are crazy)

[Wardi]

Hello Erik,
Yes I think you are on the right track!.
I now have data on around 3,500 boats. I have the age for around 1000 or so of these and actual performance data for all of them, so I am able to plot performance improvement over the past 80 years.

Unfortunately I cannot readily identify which designs are to which rule, nor which ones have the crew sitting on the gunwhale. That is where you may be able to assist me. Also many of the designs are from the US and I am not so familiar with them.

I agree with your methodology. We already have PHRF actual performance data available and dates it is not so difficult to compare boats.

There is not so much data on Sports boats or new rule IMS. This information would be very useful. I have tried ORC staff, offices etc and been told they will not let me have even the basic IMS measurement info and do not have race result data available. I am now trying individual sailing clubs instead.

I have been able to graph several relationships already which are very interesting. It certainly confirms many current observations, such as the dramatic reduction in Displacement/Length and clear improvement in Speed/Length over the past 80 years.......but it also brings up some rather controversial results when you look at which designs are in fact the most efficient. I hope to show this shortly.

The analysis is not deeply numeric, but does tell us a lot of basic things and is very interesting to see developments over time.

I am only measuring performance against Displacement, Length and Sail area.
As I see it, all the rest should be left up to the designers to come up with the most efficient possible design.

The only really contentious part is how to manage stability, but that is self limiting anyway until we get to trapeze and canting keels etc.
One way is to do as you suggest and separate Keel Ballasted boats from Crew and Water Ballasted boats, also Cruising from Racing etc. Within each category I see no need to divide any further. Unfortunately the data does not help me with such categorisation.

I am putting together a paper on this and will certainly share it. What I am most interested in at the moment is feedback on the basic principle of using Taylors resistance data as a fundamental reference point. Do you see any problem with this?

[ErikG]

Swedish ramblings... [[[ in english :) ]]]

Wardi then I might be misunderstanding what it is that you want to achieve...

I do agree that your camparisions ARE interesting and being able to se how much speed has increased over the years when it comes to comparing SA/D/V is certainly a good thing to be able to do. But...

In my opinion the most interesting things to look at from an evolutionary standpoint is not the general change in SA/D/V and how those factors have changed over time. It is interesting but what's left AFTER you have been able to deduct the main parameters out of the equation is the changes in hull shape and how that has changed over the years and what effect if any the changes have made on performance.


We all know the basics that a slim hull makes for improved displacement sailing and that most boats of light to medium displ that wants to be eble to surf or even get up and plane, needs to have quite a large area to generate lift.

But the rest...
How much rocker and why, overhangs or not and how it affects differnt kinds of vessels. Hard knuckle bows or not. How cp compares between different boats of the same general chracter and why hull differences generates the effects it does. Wake reduction, and on and on...

Personally I think that theese things currently seems to be an area where only experience or software like shipflow counts...

But as a student there's so many things that aren't very well explained in any design book, and there's hardly any online source that really discusses any of these issues at length. We all know how to improve speed and stability with weight reduction and techology. But finding the information on why one should/could choose a certain configuration over another weighing the pro's and con's against each other.

Yeah yeah I know nothing beats experience on the water with different kinds of boats, but on any two boats not only one thing will differ, so how to evaluate the small differences?

Jeez Now I'm rambling again... Well I warned ya! :cool: :D

[Wardi]

...what's left AFTER you have been able to deduct the main parameters out of the equation is the changes in hull shape and how that has changed over the years and what effect if any the changes have made on performance.

Hello Erik,
Yes I agree entirely to everything you wish to achieve, and I even think it is quite possible to get a lot of useful information about these detailed design issues, from the basic data, but let's not rush too far all at once!

As I see it, you cannot compare design improvements unless you have a sound basis for making the comparison. ie: how do you know which is the fastest boat in the beginning?

The simplest way of course is to have identical boats and make changes to one. The problem is that this is expensive, impractical and does not allow you to easily compare size effects etc.

What I am proposing simply allows you to compare the performance of any two boats, they don't have to be identical in the beginning.

As far as I am aware, there are no methods available for doing this today, except via rating/handicap rules, which have been consistently shown to be flawed.

So therefore I am concentrating on getting the reference point right in the beginning. I also want it to be simple, effective, readily available and simple to apply.

Step one is to agree that this is worthwhile and that the method proposed is valid.
(I have no concrete feedback on this yet, actually I am stunned by the silence, so I assume I am on the right track, or I would be shot down in flames already!)

Step two is to apply it and see what we find.
(I have been doing this over the past couple of weeks. It looks to work very well and raises many questions which I am trying to solve before publishing.)

Step three is to compare results and see which boats are actually efficient.
(This is the step you want to jump to in order to identify which detailed design features are beneficial. I have not got this far yet, but am getting some insights as I go...I am sure you will be able to find out what you want.. but as this is an entirely new exercise perhaps the results will not be what you expect!)

So back to step one...do you think the fundamental basis for this proposal is sound?
ie: Is it valid to use Taylors resistance data to determine a Speed Potential based on the Displacement, Length and Sail Area of the boat.

[ErikG]

Unfortunately I can't recall what the Taylor resistance data stated. I'm sure there's a link somewhere in this thread that I have missed, if you could post a link I would be most grateful.

Well now I have to prep myself and the little boat for a racing weekend. I'll be back late sunday and try to search for the taylor resistance paper and have a look. Although I'm not altogether sure that my math and comparative knowledge is enough to really say wether his data/method is the best way forward, but I can/will have an opinion :)

Have a great weekend all :) [I will] :D

[Jeff H]

As I am reading the direction that this thread seems to be following, it looks like you are almost trying to develop and validate a VPP system. Many of the improvements that have occured over the past 25 or so years involve the kinds of subtle changes that do not show up on any data sheet. For example, if you compare a year 2000 IMS boat to the last of the IOR boats, you would find that the vertical center of gravity is much lower relative to the vertical center of buoyancy, that the IMS boats had the longitudinal centers of buoyancy and gravity further aft in the boats, That they had comparatively longer waterline lengths for their lengths on deck, giving them finer bows and lower D/L ratios. That they were modeled to produce less assymetry and therefore less heel induced weather helm through their normal range of heel angles. That they had higher lift, lower drag foils. That they had more easily powered up and down rigs. That they were opitimized to minimize pitch and roll angles and minimize rapid accellerations (mostly because large or jerky motions make sail and keel flows harder to maintain rather than crew comfort but the crews benefited just the same.) And so on.

These are not the kinds of things that are easy to quantify and yet cumulatively they produce significant speed gains. And even if you had a VPP program that could precisely predict the actual speed of the boat, there are very big tactical advantages that comes with small speed gains. A faster boat has the ability to sail slightly farther in order to place itself in a position where wind or current offers some advantage.

In talking to designers of early IMS boats, the goal was to simply produce boats that were optimized for speed. There was no real effort to 'beat the rule' since the rule was pretty equitable with regards to real boat speed from one boat to another so that a wide variety of boats were able to race pretty equitably under the IMS during the early days of the IMS. The IMS typeform boat's real advantage came from their very real speed advantage on a boat for boat basis and that allowed them a lot of tactical advantages which is how they won races.

(Just to give an example of this, while this happened pretty routinely in those days, one of the first times that one of these early IMS type form boats showed up on the starting line in a race that I was in, the boat set up to leeward of the rest of the hot boats, which were fighting for position at the committee boat. All of us in the first row got off the line with moderately clear air, but the IMS boats ability to point higher and make less leeway allowed them to come up from below each of us and pinch us off one by one until he was out front sailing in completely clear air. That mean less clearing tacks, and a higher and faster pointing ability.

Another example might be something that came up in a conversation with Bruce Farr about the second generation Volvo 60's nee Whitbread 60's. The second generation boats were more optimized for light air performance rather than for heavy air performance. Mr. Farr explained that days could be gained in the light air venues as a light air optimized boat could continue to jump from puff to puff and keep moving. Those kinds of time gains could not be made up from the minor speed gains of a heavy air oriented boat. In otherwords the advantage of the light air oriented boat was not in quantifiable boat speed but in the tactical advantage of being able to keep moving and find more wind in the nearly no wind conditions.)

It was the ability of these fast boats to break away from the pack and sail thier own race that gave these boats their unrated speed advantage rather than the fact that the boats were actually faster than the rule thought they were, which in both cases I don't think that they actually were. As a result, the rule promoted boats that were simply fast and easily handled, and that is how a properly written VPP based rating rule would work.

So back to your problem of figuring out where the advances were made and validating them, I am not sure that without detailed data on these boats such as sailplan, hull lines, weight distribution data, etc. that you really can tell accomplish what you are proposing. And even if you could accurately predict a boats straightline speeds when sailing a boat is sailing by itself, it is next to imposible to rate a boat for the tactical advantages that comes from that straight line speed.

Respectfully,
Jeff

[SuperPiper]

Wardy:

I am not qualified to comment on Taylor's Resistance.

But, I have been waiting anxiously to see what you may have uncovered; whether it is perfect or not! I think that you should publish the numbers and then let the critics analyze the results. I believe that all the discussion is by the folks that don't really want to find out that a '70s PHRF boat is still as fast as an IMS built racer.

Besides, you are the one DOING ALL THE WORK. Don't let the rest of us stand in your way.

Show me the numbers.

[Jeff H]

Do you really believe that "a '70s PHRF boat is still as fast as an IMS built racer." ?

It is not hard to show you the numbers. I think that I gave some numbers earlier, but comparing boats based on length you can compare a Tall rig deep keel version of a Tartan 41 (1972) which was a extremely competitive boat in its day to a shoal keel version of a Beneteau First 40.7 (2000). Both are designed by leading race boat designers at the moment that they were designed, both offer reasonable interiors and tankage, and both were dual purpose boats.

Under PHRF, the Tartan 41 rates 111 to 114 and has trouble sailing to that rating while the Beneteau 40.7 rates 54-63 and sails to that rating pretty easily. That is approximately a minute a mile which is an enormous speed difference in real life. On a 30 mile trip the 40.7 would be almost four miles ahead of the Tartan 41 at the end of the trip. The Tartan needs a bigger crew and more of its crew on the rail to achieve its rating than the Beneteau. If you look at more mundane performance boats of the 1970's like an Ericson 41 they have ratings that in the 130's another 20 seconds a mile slower still.

If you compare a purpose-built raceboat like a J-36 (1979 or even its faster modification the J-35 from 1983) to a contemporary purpose-built raceboat like the Farr 36 you find a similar spread with the J-35 at 72 and the Farr 36 at 0. And again the J-35 is much more dependent on a larger crew perched on the rail to achieve its speed. Comparing boats by displacement instead of length the numbers get even larger.

There is no problem finding the order of magnatude differences in speed that have resulted over time, they are very large. If I understand what this thread is about, I think what this thread seems to be asking is, 'what are the breakthroughs (both large and small) that have resulted in these speed gains?' and not whether a speed increase has occurred.

Jeff

[Wardi]

Hello Jeff & Superpiper,
Firstly I agree with Jeff about the benefits of tactical advantage, and that certainly is an issue when one boat has a small advantage over another.

What I am referring to here is not anything to do with VPP. As I see it, VPP is a tool which may assist to refine a design. What I am creating is a simple basic reference point of how fast a boat of that size should be able to go and then compare with how it actually goes. This reference point has nothing to do with the individual attributes of the shape of the boat. It should be up to the designer to come up with the best shape possible.

Yes, I intend to make what I have found available for your scrutiny and would really appreciate your feedback. It should be nicely summarised within a couple of days.

[SeaDrive]

Looking into the numbers, we see the Beneteau has a little more waterline, a little more keel depth, and about 2000lbs (11%) less displacement. Interestingly, the weight is mostly from the ballast keel. The rigs are also very different. The Beneteau has a much shorter J and longer boom than the Tartan. I can't really speak about the underbody and ballast, but certainly the Tartan rig was designed to suit the rating rules of the times. If the Beneteau is faster because it was designed to a better rule, or to no rule at all, does the difference count as "real design improvements", or just rule improvements. I'm not quite sure the boats are equivalent in carrying capacity or blue water capacity, but that is out of my sphere anyway.

There has been a lot of progress in keel shapes, and in rig development.

Another comment: the observed speed difference will be different on various points of sail. The "4 miles behind after 40 miles" is a reasonable interpretation of the difference in rating. However, boats (except the very light ones) tend to sail at closer to the same speed off the wind, with speed differences exaggerated upwind. Reaching along on a cruise, they might arrive nearly together, while on a upwind day, the Tartan might be more than the 4 miles behind.

[Wardi]

Hello Jeff,
I have data on all except the Farr 36. I will make some comparisons shortly based on this data and my analysis.

I have found that even the Farr 40 ODR is rated at "9", so I doubt the "0" figure for the Farr 36, could you please check this one and reconfirm if it is correct. If you also have Disp, Length, Sail Area, draft and beam and age for the Farr 36 I could include it in my comparison.

One thing I note is that you are generally comparing performances based on Length alone. Surely displacement and sail area also affect performance. This is what I have taken into account...more to follow.

kind regards, Ian

[Jeff H]

A couple quick replies because I need to get out of here to cruising, but to answer the replies,

SeaDrive: I purposely chose the Tartan 41 because it really was one of the first of the IOR I boats and as such was not terribly optimized to beat a rule. In its day, these were considered outrageously fast boats so much so that when I was racing on one in the mid-1970's the conversation on board was about how none of us could imagine that boats could get any faster than that generation of boats. I think that you are mistaken about the fact that the big gains are up and down wind. I think that the big gains are on all points of sail and infact the Beneteau 40.7's real gains are when reaching lighter winds or in moderate to higher winds. Argueably there is a narrow wind range somewhere around 10 knots where the 40.7's advantage would be smaller than its rating, but as the wind falls or drops the 40.7 really would leg out.

Using my boat, a Farr 11.6 (because I know it quiet well) which is somewhat antiquated compared to the 40.7 but a 9 year newer design than the Tartan 41 and which also has the same waterline length. Reaching in winds over 15 knots it is unsual to sustain speeds near and sometimes over 9 knots. The highest speed that we saw in the Tartan 41 (surfing in very steep 7 to 8 foot waves in high winds) was just below 9 knots.

Wardi: 0 is the correct rating for the Farr 36. This is a none rule derived 36 foot one design that was designed in 2002. They are faster on a boat for boat basis than the Farr 40 which has adequate accomodations to qualify for an IMS certificate. I chose the Farr 36 and J-35 because both represented the best thinking of their times ignoring all of the rules of their eras.

Jeff

[yipster]

just saw on tv an old planked ventilating flat bottomed surfing vikingship race against a modern mono hull that -only barely- won.
dont hate me for interfering and mentioning it ;-)

[Wardi]

Wardi: 0 is the correct rating for the Farr 36. This is a none rule derived 36 foot one design that was designed in 2002. They are faster on a boat for boat basis than the Farr 40 which has adequate accomodations to qualify for an IMS certificate.

OK, sound like the Farr 36 is pretty qick for its length. Are these the correct details of displacement, sail area etc for me to include in my study?

Dimensions
LOA 11.00m 36.1 ft
LWL 10.00m 32.8 ft
Beam 3.582m 11.72 ft
Draft - keel down 2.6m 8.5 ft
Draft - Keel up 1.83m 6.0 ft (in water)
Displacement 3,059 kg 6,744 lbs (empty)
Ballast 1,396 kg 3,078 lbs
Fin 105 kg 230 lbs
Bulb 1,300 kg 2,866 lbs
RMC 106 kg/m 764 lbs/ft
LPS 137°
Stability Index 130°

Rig Dimensions
IM 14.26m 46.78 ft
J 4.02m 13.19 ft
P 15.22m 49.93 ft
E 5.68m 18.64 ft
ISP 16.71m 54.82 ft
TPS 6.42m 21.06 ft
Mast Height WL 17.9 m 58.73 ft
Mainsail Area 56.2 sq m 604.85 sq ft
Jib Area 32.9 sq m 354 sq ft
Spinnaker Area 163.9 sq m 1,763.7 sq ft

[Wardi]

Observations

1) The following observations are based on PHRF data for some 3600 boats.
Age data exists for 1000 of these boats, designed over the past 80 years.

a) Speed based on Speed/Length ratio has been steadily increasing over the years.
http://boatdesign.net/forums/attachment.php?attachmentid=1374&stc=1

b) This has primarily resulted from boats getting lighter for their length.
http://boatdesign.net/forums/attachment.php?attachmentid=1375&stc=1

c) As boats get lighter, they can go even faster for their length. The fastest boat will generally be the longest with lowest displacement for its length.
http://boatdesign.net/forums/attachment.php?attachmentid=1376&stc=1



Links:

Speed Potential
http://boatdesign.net/forums/showpost.php?p=22338&postcount=68

Performance Improvement
http://boatdesign.net/forums/showpost.php?p=22338&postcount=69

[Wardi]

Speed Potential
The proposed "Speed Potential" is a measure of efficiency, calculated on the following basis:

The force produced by the sail area is balanced by the resistance of the hull. For a given sail area we can calculate the force and hence resistance of the hull. With reference to Taylors data we can find the potential speed of a boat based on its D/L ratio.

In order to make this calculation easy, I developed a formula using basic curve fitting techniques to match Taylors original data. This formula is used in a simple spreadsheet from which the analysis in this study was conducted.

The calculated "Speed Potential" has proven quite reliable in predicting potential performance and in fact reflects quite closely the IMS rating speeds for all D/L ratios. Here is a comparison for the entire Sydney Hobart race fleet. The error bars represent +/- 2% of the value. This is used to confirm the validity of this tool as a standard basis for performance comparison.

http://boatdesign.net/forums/attachment.php?attachmentid=1377&stc=1

Links
Observations
http://boatdesign.net/forums/showpost.php?p=22338&postcount=67

Performance Improvement
http://boatdesign.net/forums/showpost.php?p=22338&postcount=69

[Wardi]

Performance Improvement

The Performance Improvement is the % difference between how fast a boat should be able to go based on its displacement, length and sail area and how fast it actually goes, in this case determined from PHRF base rating. This can be taken as an indicator of the efficiency of the design. Those boats which exceed their Speed Potential by the biggest margin may be considered the most efficient.

a) The best performers do not necessarily have the lowest D/L ratio
http://boatdesign.net/forums/attachment.php?attachmentid=1378&stc=1

Despite this, the D/L ratio has been reducing over the years.
http://boatdesign.net/forums/attachment.php?attachmentid=1375&stc=1

b) In general the Performance of boats increased until about 30 years ago and since then there has been a small decline in efficiency. The efficiency of the best performers has not improved significantly during the years.
http://boatdesign.net/forums/attachment.php?attachmentid=1379&stc=1

Your thoughts and comments appreciated!


Links
Observations
http://boatdesign.net/forums/showpost.php?p=22338&postcount=67

Speed Potential
http://boatdesign.net/forums/showpost.php?p=22338&postcount=68

[Wardi]

Jeff,
I have analysed the efficiency of each design you have mentioned, based on the displacement, length and sail area. here is a short summary of the results:
http://boatdesign.net/forums/attachment.php?attachmentid=1382&stc=1

I would appreciate if you could confirm the parameters I have used are correct. From this evaluation it would appear that the J35 is the most efficent design and surprisingly the Farr 36, which is obviously fastest for its length by a long way, is in fact the least efficient.!

There are several basic reasons for this, but it would appear the Farr 36 has insufficient stability to match its sail area and therefore does not sail as fast as it should.

The Farr 36 is around 30% of the weight of the Ericson 41, with around 230 square feet extra sail area, so it is an entirely different configuration and you should expect it to go very much faster!.

[CT 249]

Hi Wardi.

Interesting stuff here. I’m familiar with the general description (approx age etc) of many of the US PHRF fleet, d’yawanna drop them to me and I’ll see if I can sort any missing details out for you?

Secondly, when (a long while ago) I went over to your place and we discussed dinghy design (for my rather large project I’m still working on) you were wondering whether anyone had a similar efficiency measurement for dinghies. I found two; one that US Yachting mag used for their one of a kinds, and a modified version of same used in Victoria. Shall I drag one out for you?

Thirdly, I don’t know that the Farr 36 is (according to gossip) actually sailing to that rating, but the Thompson 35 (which is actually 37) is sailing to something similar if you have those dimensions.

I can see if I can dig out the numbers for John Spencer’s 1960s lightweights (28’, 33’, 40’ and 73’ boats with half an eye on the rule, 35’, 45’ and 62’ go-fast boats), which could form an interesting addition to the plot. You’ll find a well-uprated Van De Stadt Black Soo in the San Francisco PHRF listings which will also give you an illustration of old ULDB speeds – she’s called “Starbuck”. Other Black Soos (in Victoria and observed performance in NSW) would be about 180 PHRF.

Finally, it’s interesting that the J/35 comes up so well. I spoke to the designer about the boat a few years back. It’s definitely the J/36 modified (as Jeff mentioned, g’day Jeff) with less interior, a bit off the stern, and a masthead rig. I can’t recall whether the foils were changed. Rod Johnstone said the main problems with the 36 were the cost and (to a lesser extent) weight of the interior and the fact that they couldn’t get a light enough fractional spar in those day. He says it would be a lovely boat with a modern carbon spar.

I just found in interesting, as it underlined (once again) how technology and social factors impact on “efficiency”.

Something that’s interesting about “progress”. It’s often said that classes that don’t progress die – yet the oldest International dinghy class of all, the 1912 International 12 (a little cat-rigged clinker lugsail yacht tender) is still bloody popular in Italy and doing OK in Holland and Japan. The class association for the 1935 O-Jolle, built for the 1936 Olympics and similar to an older heavier Finn, claim more active boats than the Finn, Moth, Canoe, all of the singlehanded skiffs put together – and like the International 12, the new boat market is healthy.

Hey, while talking boats – do you have any info (out of interest) to confirm the almost simultaneous dual creation of wide alloy Moth wings from Chris Edward (former UK, now BYRA) in 1971, and a kiwi whose name escapes me but who turned up for the ’70(?) worlds in Black Rock? Chris doesn’t recall the Kiwi wings and I don’t think many northern guys did that regatta, so it seems that both arrived at the same area by independent routes – not for the first time (flares and 18’ skiff wings were also appearing independently).

By the way, having raced some of the great boats of the ‘60s (the 12 metre Weatherly, the 38’ Sunstone which has taken her class in Fastnets 4 times (in the ‘80s and ‘90s) and been top of the year 4 times in the UK (under IOR, IMS and IRC) AND won her class in the Hobart – I can only say that there has been huge advances and I can’t see how boats are now going slower – or is it just slower for their ratios and dimensions? Do your measurements allow for the fact that boats built recently normally have 105% overlap instead of 150% genoas that were almost universal in earlier times? The J/105 data provides a clue to the importance of overlaps, the genoa boats are much faster IIRC. Finally, moderate-speed boats like J/105s are slower (but easier and more fun0 with assys.

PPS d'want me to try to find my IRC/Portsmouth/IMS/NZ PHRf conversion ratios?

[Jeff H]

g’day Mates,

Wardi, I want to commend you on your analysis. As I read it everything made sense until I came to your final conclusions that older boats were somehow faster. I did not want to respond until I had a chance to think about what you have written and I think that your conclusions may result from the way you set up the study.

More to the point, I think that CT249 touched on some very good points that explain your study's seemingly contrary to real life conclusion. As suggested in CT's post, it is somewhat difficult to really compare older and newer boats on a D/L basis or SA/D basis. To beat the earlier rules, older boats were often designed to have a very short static waterline that increased pretty dramatically as the boat heeled. While that does not result in the speed of a boat that has a static water equal to the rule beater's heeled waterline, it would skew the numbers a little if speed is compared to the a D/L using the static waterline length of the rule beater.

Similarly, your SA/D probably uses the total SA that is typical based on 100% fore triangle area. Again the trend has been towards smaller overlaps on jibs. 170-180% genoas were quite common in the 1960's and were needed for light air performance. Modern boats often eschew the use of larger overlapping genoas getting by on 105-110% jibs, a wonderfully rig proportion when combined with a bendy fractional rig, but also one that looks huge if the comparison between an older boat's and a newer boat's SA/D uses the 100% foretriangle. If instead the comparason used the actual sail area upon which the PHRF rating is based, then I think your conclusions would fall in line with actual experience.

Respectfully,
Jeff

[Wardi]

I want to commend you on your analysis. As I read it everything made sense until I came to your final conclusions that older boats were somehow faster.

Hello Jeff,
Yes I understand the apparent confusing conclusion.

It is not saying that older boats are faster...for their length. In fact quite the opposite, as the newer boats are definitely faster for their length, but only because that are very much lighter....as would be expected.

What it is saying, is that the newer boats are not performing significantly better for their overall proportions, ie: Displacement, Length and Sail area than the old boats, ie they are not any more efficient.

One might wonder how this could be, but it seems related to the fact that the newer boats have relatively less stability and more sail area, and so they are not getting the best out of the boat. The reason for this may become apparent when reading the IMS thread which seems to confirm exactly this trend!

I am using PHRF base data including sail area data for all boats.

[SeaDrive]

I think you are in danger of circular reasoning. If boats are faster because they are lighter, perhaps the design improvment is that we know how to build a lighter boat. As I remember, when Lapworth drew the 'light displacement" Cal 40, etc. it was an open question whether a lighter boat could be competitive.

About a half-lifetime ago, there was an article in Yachting by Pierre de Saix about tanktesting a model of Americal. He drew the conclusion that with almost a century of additional experience, it would be hard to draw a hull if America's D/L ratio that had less resistance.

[Wardi]

I think you are in danger of circular reasoning. If boats are faster because they are lighter, perhaps the design improvment is that we know how to build a lighter boat.

I am not quite sure about the circular reasoning..., but you are absolutely correct that we can now build lighter boats and therefore make them faster for their length.

But we have known all along that this would be the case. This is simply a change in configuration of the boat. Equally we could simply increase the sail area or length and make it go faster also!.

What the results are telling us, is that for the decrease in weight, the boats should in fact be going a lot faster than they actually do. ie: They should be more efficient than they are!.

.....would be hard to draw a hull if America's D/L ratio that had less resistance.
This may in fact yet prove to be correct, however with modern materials you might expect that that he could achieve greater stability and go even faster for the same D/L ratio.

[SuperPiper]

Wardi:

Wow, great presentation!

Even using "Best Fit" algorithms, some of the lines/curves through the scatter of points are somewhat subjective (?). The one conclusion that is undisputed is the fact that boats are tending to get lighter. And, I would have thought that more of the boat weight may be making its way to the keel bulbs that are getting popular. So, I thought that modern boats must be getting MORE stable. However, you are suggesting the opposite.

A few thoughts:
If a skipper was to take his 70s PHRF racer, gut the interior, install a carbon rig and a bulb keel, would he expect a speed increase? Would the 70's hull shape (designed for X knots) still be efficient at the new speed (X+1 knots)? Is it possible that it has taken decades (or centuries) to optimize the wooden/glass boat hull shape but have not yet optimized the new lighter/faster hull shape?

Wardi, I need to examine and think more about all of your data. Great work!

[Wardi]

Even using "Best Fit" algorithms, some of the lines/curves through the scatter of points are somewhat subjective (?).

Yes I would agree, and I am quite sure it is possible to much better than with the standard Excel functions. However I have made several other comparisons which all support the basic trends indicated. The basic fact remains though, that the lighter displacement boats, in general are no more efficient than the older designs.

The one conclusion that is undisputed is the fact that boats are tending to get lighter. And, I would have thought that more of the boat weight may be making its way to the keel bulbs that are getting popular. So, I thought that modern boats must be getting MORE stable. However, you are suggesting the opposite.

Actually I originally thought that this was the case also, but can confirm from discussions with some top designers and builders, that only part of the ballast is in the bulb, the rest is in the hull! This is confirmed in the IMS discussion in this forum. Notwithstanding this, some boats do have lots of lead in the bulb and are still not that efficient.

If a skipper was to take his 70s PHRF racer, gut the interior, install a carbon rig and a bulb keel, would he expect a speed increase? Would the 70's hull shape (designed for X knots) still be efficient at the new speed (X+1 knots)? Is it possible that it has taken decades (or centuries) to optimize the wooden/glass boat hull shape but have not yet optimized the new lighter/faster hull shape?

This is a vexed question. Certainly to lower the C.G. with a bulb keel and carbon mast would make a big improvement, although I am not yet convinced that this hybrid design would necessarily give the best possible end result for efficiency. Certainly in Jeffs judgement based on Speed/Length, it would not go anywhere near the speed of the latest designs, but that is only because they are so much lighter. Personally I think you are correct in saying the that we have "not yet optimized the new lighter/faster hull shape".

For the designers right now it is really too easy, just go lighter, with more sail and of course it goes faster, not too much genius in that formula for success. It is the materials and construction techniques which are actually giving the speed improvement. When it comes to rating boats, the role of the designer is to beat the rule, not necessarily make a faster boat. It will not be until there is an incentive to have efficient boats that we will see real "design" advances to optimize the performance for light displacement boats.

[Wardi]

Interesting stuff here. I’m familiar with the general description (approx age etc) of many of the US PHRF fleet, d’yawanna drop them to me and I’ll see if I can sort any missing details out for you? PPS d'want me to try to find my IRC/Portsmouth/IMS/NZ PHRf conversion ratios?

G'day CT249,
The J35 comes up OK in the comparison for Jeff, but is by no means the most efficient design.

Yes it would be ideal if you have data available, also on dinghies.
Perhaps what would help most is to know what basic type of boat each one is, as I am unfamiliar with many US designs. I had in mind to put together a list of the top 10% most efficent designs and categorise them as Pure racing, Racing, Cruising, crew ballasted etc so that we can see which is the best design in each category. This would be most useful, as it does not seem fair to compare stripped out day sailors with cruising boats carrying engines, fuel water etc.

all the best

[Jeff H]

With all due respect, I very strongly disagree with your statement about IMS typeform boats being less stable than earlier typeforms and in particular the implication that you are drawing from this statemement:
"only part of the ballast is in the bulb, the rest is in the hull! ........ Notwithstanding this, some boats do have lots of lead in the bulb and are still not that efficient."

I have two main issues with your statement;

First of all the trend towards inside ballast in IMS style boats is extremely new. I would guess that this has been happening for something like a year now, but not much longer than that. And,

Second, having sailed a lot on these IMS typeform boats, as well as earlier CCA, RORC, and IOR race boats, these (pre- internal ballast) IMS typeform boats offer an enormous amount of stability in comparison to their drag. The very recent anecdotal change in design approach on IMS typeform boats, should not lead you to believe that the type in general is less stable as these internal ballast boats are still very rare in the IMS fleet.

Beyond that one of the strengths of the pre-internal ballast IMS typeform boats is their ability to carry the same sail plan through a wider range of windspeeds and to get by, and still remain at speed with a physically smaller sail plan in really high winds and big seas.

When I have looked at the numbers, the really big advance in these earlier IMS boats, (besides the more efficient hull shapes at least as reported in towing tank and in actual sailing conditions) has been the fact that they generally carry a larger percentage of their weight in ballast than earlier race boats (with the exception of a brief period under CCA when centerboard boats were popular) and carry that ballast much lower in the boat both by carrying deeper drafts and carrying the weight in a bulb. While there may be a new (and deplorable) trend in IMS boats to move weight out of the keel, even as recently a 2 years ago, grand prix level IMS boats were being built with cast iron or composite keel foils so that more weight could be placed in their bulbs. The slighter lighter weight of the typical IMS boat of a couple years ago meant that they had a higher center of buoyancy which when combined with their historically low centers of gravity resulted in amazingly stable boats for their length.

I still think that there is something really wrong with your data if you think that older IMS type boats are less efficient that previous design periods. It just is not being born out in tank testing or in every day experience. One of the simpliest anecdotal measures of efficiency that I experience with a fair regularity is the amount that these boats will forereach. Older designs would typically forereach something like 2 1/2 times their boat length. When ever I of the adjustments that I need to make is that the newer boats forereach jump back and forth between an older design and newer IMS type boat one more like 4 or more times thier lengths. Until I got used to that I was constantly overshooting. Even boatspeed under power is much greater in these IMS typeforms using the same 3gm30 Yanmars that are all over the fleets, so I really can't see any indication of less efficiency.

I also want to point out that displacement numbers are very hard to compare as methods of measurement have changed over time. In CCA days boats were measured 'in their normal equipage and state' which meant all sails aboard, all gear aboard, partial or completely full tanks and lockers. Under IOR, boats were measured with a prescribed loading, with 'gear stored in normal position'. That means sails and sailing gear on board, tanks were typically half full, etc. IMS boats are measured dead empty. What that means is that the displacements are much closer together than your numbers would indicate. In the case of my boat, the IMS certificate (and PHRF certificate for that matter) shows a tad over 11,000 pounds displacement. From actual measurement in an IOR measurement state of loading, my boat weighs closer to 14,000 lbs.



In the end, however you measure it (displacement to speed, or length to speed) the pre-internal ballast IMS typeforms are wildly faster than ealier designs (as shown in their phrf ratings) and get by on physically smaller sail plans. To me that sounds like they are much more efficient so I am unclear how you have set up your model so that it somehow reflects the opposite.

Respectfully,
Jeff

[deseely]

Wardi

[des]

Wardi

This is some interseting information but I have a few questions. How did something like the J24 do in your comparison? My guess would be that it did fairly well, not because it is particularly efficient but because it has been raced so much that the people sailing them very efficiently. I also question if your measurment of efficiency accurately depicts the diminishing returns of increasing the sail area. Directly relating sail area to speed through the resistance of the hull completely ignores the losses created by the increase in hull drag and loss of sail efficiency due to the increase in heeling forces associated with the increase in sail area. Sorry for the blank post, I seem to hit the wrong key while typing.

[Wardi]

The J24 along with many pure racing boats such as Soling, Etchells 22, Dragon, 6m etc has done reasonably well. One reason for this is that they do not carry engines, fuel, water, provisions etc. and therefore should perform well. In fact it would be rather useful to categorise the boats as racing, cruising etc but I have no way to do this at present.

I have included a sample of these boats below. PI is the efficiency measure of actual performance vs speed potential. The higher the %value, the more efficient the design.
http://boatdesign.net/forums/attachment.php?attachmentid=1389&stc=1
It is interesting that the J24 does not perform as well as some of the others. This is confirmed by my own observations that a Dragon will easily beat a J24 upwind in a breeze. The Hobie 25 goes well because of the trapeze, not necessarily because of other design improvements.

While I would agree that some data may be considered potentially innacurate because they are "one off" designs etc, I would think that the PHRF rating for the other comparable classes, ie: Etchells, Dragons, IOD etc would also have been determined based on competitive fleets also. Therefore this comparison should be valid.

With regard to the efficiency calculation, the driving force from the sail is taken to be directly proportional to the sail area. Based on this force, I simply read off Taylors test data to see what speed the boat should have. There are in fact no "theoretical" calculations involved at all!

As I see it, it is completely up to the designer to balance the tradeoffs of sail area vs heeled resistance, efficiency losses etc in order to come up with the best possible design for those proportions of D,L & SA. The efficiency measure simply represents the outcome of this ie: is it an efficent design or not.

[Wardi]

I also want to point out that displacement numbers are very hard to compare as methods of measurement have changed over time.

Hello Jeff,
I agree with what you say about displacement measurement. That is why I have used all data from one source, ie: PHRF and assume that the displacement information is equally determined for each boat to overcome this potential error.

I have spoken to boat builders, who as long as 15 years ago were marvelling at the concept of using titanium fittings inside the boat at the base of the mast to take rig loads, with pigs of lead strapped down next to them!. It seems that internal ballast for correction to get boats to float on their lines has been used for many years.

I still think that there is something really wrong with your data if you think that older IMS type boats are less efficient than previous design periods. It just is not being born out in tank testing or in every day experience.

With respect, I am not trying to pull the wool over your eyes or use special tricks with my analysis. I do not even use any theoretical calculations of hull resistance to determine speed. I am simply referring to well established practical test results of Taylor.

I suspect that much of your evidence of increased "Speed" for newer boats is actually based on the speed/length of the boat and does not take into account the effects of displacement or sail area. As I have said before, speed/length has definitely increased, supporting your anecdotal observations, it is just a matter of "at what price"!

One of the reasons it is difficult to accept these results may be that such a simple and basic comparison does not seem to have been done before!

[redcoopers]

Wardi,

I'm curious about Taylor's data. The systematic Taylor series which I know of is for ships, not yachts. Furthermore, isn't this data apropriate for only upright resistance - not heeled?

Also, how do you estimate Cp, LCB, and LCF? I know that Taylor used Cp as an parameter, but I was under the impression that his family of hull forms did not vary by LCB or LCF. The Delft testing has shown that wave-making resistance can change significantly by differences in LCF and LCF.

Just curious about your velocity prediction,
Jon

[Jeff H]

Briefly,

"I agree with what you say about displacement measurement. That is why I have used all data from one source, ie: PHRF and assume that the displacement information is equally determined for each boat to overcome this potential error."
The displacements used in PHRF are provided by the owners. There is no measurement involved. The displacements numbers generally reflect the period in which the boat was constructed and the method of calculating displacement that was in vogue at the time that the boat was designed. So earlier boats would show higher displacements that reflect a displacement that includes 'their normal equipage and state', vs newer boats which are measured and advertised stripped of everything. In other words the actual displacements of older designs are much closer to those of newer designs than their PHRF slips would suggest.

"I have spoken to boat builders, who as long as 15 years ago were marvelling at the concept of using titanium fittings inside the boat at the base of the mast to take rig loads, with pigs of lead strapped down next to them!. It seems that internal ballast for correction to get boats to float on their lines has been used for many years."

I don't know what boat builders you have been talking to but trim ballast hasn't been used in production performance sailboats since the IOR era, at least not here in the States. While all kinds of stunts were pulled in the bad old day of the IOR, better computer modeling and quality control has pretty much eliminated it in newer boats (with the exception perhaps of the lastest European aberation of the IMS)


"I suspect that much of your evidence of increased "Speed" for newer boats is actually based on the speed/length of the boat and does not take into account the effects of displacement or sail area. As I have said before, speed/length has definitely increased, supporting your anecdotal observations, it is just a matter of "at what price"!

Again if you compare the performance of pre-internal ballast IMS type forms to earlier type forms on a speed to displacement basis, the IMS type forms do extremely well as they have a very high stability to displacment, and a very low wetted surface and residual drag. This becomes especially true when you compare these boats using their actual sailing displacements.

Using Taylor in this manner is a misapplication that creates a circular logic that cannot be reconciled with real life behaivor. You are correcting out of the equation the factors that lead to better performance such as higher stability and more efficient hull forms, weight distribution, foils, and rigs, then of course more efficient vessels will look slower, but when you actually get out on the water your results bare no resemblence to reality.

Respectfully,
Jeff
Respectfully,
Jeff

[Wardi]

Wardi,

I'm curious about Taylor's data. The systematic Taylor series which I know of is for ships, not yachts. Furthermore, isn't this data apropriate for only upright resistance - not heeled?

Also, how do you estimate Cp, LCB, and LCF? I know that Taylor used Cp as an parameter, but I was under the impression that his family of hull forms did not vary by LCB or LCF. The Delft testing has shown that wave-making resistance can change significantly by differences in LCF and LCF.

Just curious about your velocity prediction,
Jon

Jon,
Yes, you are quite correct, Taylors work is based on ships models, not yachts and it is upright data. This in fact makes it a very good basis as a reference, because it is not biased to one type of yacht hullform.

I think I need to make it quite clear that I am not actually trying to predict the speed of any individual boat.

I am leaving it entirely up to the designer to find the best possible solution for distibution of displacement, LCB, LCF etc. Also to find the best possible balance of sail area to stability, surface area, lowest heeled resistance etc to come up with the most efficient overall design.

[Wardi]

Again if you compare the performance of pre-internal ballast IMS type forms to earlier type forms on a speed to displacement basis, the IMS type forms do extremely well as they have a very high stability to displacment, and a very low wetted surface and residual drag. This becomes especially true when you compare these boats using their actual sailing displacements.


Using Taylor in this manner is a misapplication that creates a circular logic that cannot be reconciled with real life behaivor. You are correcting out of the equation the factors that lead to better performance such as higher stability and more efficient hull forms, weight distribution, foils, and rigs, then of course more efficient vessels will look slower, but when you actually get out on the water your results bare no resemblence to reality.


Jeff, You may well be right about comparisons with various versions of IMS and IOR. I do not have any way currently to split the data on this basis, but woul dbe happy to do so. Perhaps I caould ask for your assistance with some of specific designs. I will compile a list.

On the basic method I have employed....., with respect, I think you have the wrong end of the stick entirely!! I am not trying to predict the speed of any individual boat. I am actually leaving it entirely up to the designer to find the best possible solution for those factors that lead to better performance such as higher stability and more efficient hull forms, weight distribution, foils, and rigs etc, in order to come up with the most efficient overall design.

I do not take any of these things into account at all and I do not calculate anything related to these items. So I do not understand how I can be mysteriously discounting their effects. The only thing being discounted is length, weight and sail area, so that boats are compared on a fair and equal basis.

In practice it is the rating rules such as IMS and PHRF which do actively discount these improvements in the interests of fairness between racing crews and this is the reason I began this study in the firstplace!!

[CHRIS 249]

Wardie;

Do you want to post the list of designs so some us can have a shot at classifying them? We should also work out a similar classification system – something like

Full keel cruiser.

Fin keel cruiser.

CCA/RORC long keel type.

Late CCA fin and skeg boats and similar (these late ‘60s/early ‘70s US boats had much bigger rigs than the IOR types IIRC).

’68-’74 IOR/RORC/CCA boats (Swan 38, Ranger 37, East Coast 31, Scampi 30, Contessa 32).

’75-’80 IOR racers. (Farr 1104, Petersons, etc)
’75-’80 IOR cruiser-racers. (Farr Dickerson 37,

IOR racers post ‘80.
IOR cruiser-racers post ’80.

MORC/JOG Aust. Racers (J/24, Capri 25, S2 7.9, Capo 30)

Early IMS cruiser-racers; J/35, Lightwave 395, J/44, IMX 38,

“Club cruiser-racers” ie non IOR cruiser-racers from the very late ‘70s but mainly ‘80s on – Farr 11.6, Northshore 38, Farr 1020, J/36. It’s a murky line between this bunch and the early IMS boats. Also some that should be here are quicker – Young 88s and 11s etc.

Early ULDBs – a varied bunch, everything from Dash 34s, Ross 780s, Express 27s, Olson 40s, “Ragtime”, SC 70s and other maxi sleds

Old IMS Racers (ie Mumm 36, High 5 type Farr 40, maybe ILC boats - I think some called these “Phase III IMS” boats although the ILC boats are too new for this label really.)

Current IMS racers

Modern sportsboats/One Designs/PHRF racers/IRM boats/IRC lightweight racers – Mumm 30, ID 35, Farr 40 OD, Kerr 11.6, Thompsons.

Metre boat (square metre, Universal rule or International Rule would have to go together I assume).

Inshore racer (lightweight fin and skeg) – Soling, Etchells, Flying 15, Tempest.

It's all pretty rubbery.....some boats are easy but many around the esdges are hard.

I suppose one thing which could be interesting is to locate a couple of very popular boats with firmly-tested ratings from each category and see how they relate.

One thing about boats now being “inefficient”. Efficiency for racing isn’t a straight line, is it? I mean, it’s an S curve of input (whether dollars, sailing ability or sail area) versus performance, and therefore the last little “X” % is going to take more of everything. That doesn’t mean it’s not vital or significant that the improvement is made.

I mean, my old Effineffable scow cost about $25. It would go around the course at (judging from yardsticks etc) 90%+ of the speed of Thorpie, at about 2% of the cost. Does that mean it’s more efficient?

If I cut a Moth sail down to 50% of the area, I'd always finish last, but maybe by 25% on time. Does that mean it's more or less efficient?

If you have to hang on an extra 10% of rag, but it means you go .00025% faster and win instead of losing, is that less efficient? OK, it may cost yoou $100k more, but if you win a worlds with a $2.1 mill campaign is that more or less efficient than finishing 2nd out of 100 boats with a $1.5mill campaign? It is definitely not, to some. Sail area etc is similar, isn't it?

All activities hit the law of diminishing returns, do they not?? Particular those with a speed limit like displacement sailing. So a straight-line meaasurement may not be right.

Finally, your measurements use LWL which is a bit unfair since it’s easy to get a big boat with a short LWL. Because old boats were designed to have a short measured waterline for rating purposes (end girths) which are no longer counted, that biases the system. Boats now have a longer LWL compared to older boats, even when nothing else changes, ‘cause no rule rates LWL any more and no-one uses end girths so there’s no incentive to shorten waterline artificially. I think the Dragon was a 20 sq m skerry cruiser and that rule used girths so it’s got a short WL on a long hull. The J/24 was a MORC boat and they used something like the average of 60%WL and 40% LOA to assess rated length. The rule didn’t put such a limit on LWL, it did limit LOA (unlike the skeerry cruiser rule IIRC) so the J/24 has a longer waterline despite being a shorter boat.

Finally, that old dinghy One of a Kind rule-

Rating = L + 1.3 Sail Area
2

Where L = LOA + .7 LWL
2

Measured WL was obtained with fully-rigged boat carrying 168 lb for each crew, at normal C of G.

This was based on an old North American yacht racing union rule as modified for Aussie winds. One thing I’ve noticed is that it seems to give slower boats a really tough time. I’ve heard of Int 14s and Tasars winning major races, most seemed to go to 505s, FDs etc, and I don’t think ANY boat under 13’ ever did well in results I’ve seen.

It’s a great project, I hope this is constructive input.

[Wardi]

Hello Chris,
Many issues covered here!
Most outside the scope of my efforts i'm afraid... but at the end of the day its about enjoyment, not money...and I do not think there is an efficiency measure for that!! :)

I will put together that spreadsheet and let you guys classify the boats. I suspect that may make it much clearer, as it may distinguish designs of different eras and perhaps point to what general changes in efficiency have taken place.

[Chris 249]

[QUOTE=Wardi]Hello Chris,
Many issues covered here!
Most outside the scope of my efforts i'm afraid... but at the end of the day its about enjoyment, not money...and I do not think there is an efficiency measure for that!! :)

Yep, I know it's just about fun, not cash. I was just using $$$ as an example of the ol' law of diminishing returns, which may affect an analysis of whether we are getting more efficient.

[Wardi]

.....

[SailDesign]

Now, Wardi, if you are going to include appendages like foils under "design improvements", then I guess the use of carbon spars and better materials is fair game, right? ... :)

Steve

[Wardi]

Yes absolutely, I certainly have not ruled out any of these at all.

What I am saying though, is that it is the lowering of the Centre of Gravity of the rig and reduction in pitching moment which gives the efficiency improvement, not the weight saving.

[SailDesign]

Yah, but.... A hull is no more "efficient" with a lower CG and pitching moment than the same hull with higher values - it just is able to sail faster.

Sound familiar? :)

[Wardi]

.....

[des]

Here is the problem I see with using the perameters you list. Something like a Melges 24 will look to be very inefficient because of its light weight and large sail area. To make a boat look efficient, using the perameters in the way you are evaluating them, all you need is very little sail area, a lot of ballast and a narrow beam. The sail area need to be minimized since it is treated in a linear nature. Displacement is compenasted for so that there is no advantage to making a boat light so there is no reason not to have a deep heavy keel. Now that you have much more stability than needed you can narrow the beam to reduce wetted surface area and wave drag. Now this configuration will likely be reasonably fast up wind but it will be a stone on any other point of sail. Take a look at the boats that are very efficient in your data and see if they follow these trends. I bet most of the efficient boats tend to be heavy and have little sail area and the least efficient tend to be light with lots of sail area.

[SailDesign]

Wardi,
I'm getting confuddled here (not a new thing, to be sure :)) You have since the beginning of this thread been talking about hte efficiency of the hull, and yet you are willing to consider that foils are an allowable way to improve this. Why not just stick a honking big engine on the back? It would have as much bearing on hull efficiency.

Steve "not QUITE joking...."

[Wardi]

.....

[Wardi]

Wardi,
I'm getting confuddled here .....you are willing to consider that foils are an allowable way to improve this.

Sorry for the confusion, this was just an example of the fact that not everything in yacht design costs money. It is a reference to another thred here on foiler design...nothing to do with this thread on yacht design.

[ErikG]

I'm sorry to sound like a broken record, but I still feel that what could be interesting with any comparision like this is WHAT and WHY certain design differences causes a specific result. And to be able to get that info without having to resort to CFD.

The comparision is indeed interesting, but I do wonder about it's usefulness...
What, if anything, can actually be conluded from it, I wonder?
---That we all like different kinds of boats perhaps?--- :cool:

[Wardi]

.....

[Jeff H]

First of all, I still say that there is a problem with your analysis if you think that a the speed of a 1960. 1970's or 1980's boat would appear to be faster if compared to a more modern design filtered either by real sailing displacement or by actual sail area. To understand the reasons that modern boats are faster would require a more sophisticated analysis than you can do off of the limited data that is readily published since the speed gains have come from a few big advances plus a whole host of pretty subtle changes.

Erik,
It is also becoming clear to me that heeled resistance of the hull is also an important key to good performance, but is currently not in the spotlight as it is easier to stack crew on the gunwhale, trim the sheets or cant keels than address this difficult issue.


When I read a statement like that I really have to question how much you have really looked at the current performance yacht design process, at least as it is practiced by the better design offices. Heeled resistance has been an important area of design for at least a decade now. With computer modeling and better and fairly accurate VPP programs, one of the big performance gains is in the area of heeled performance. (Pre-internal ballast) IMS type forms from the better design offices tend to be remarkably balanced even at pretty high angles of heel and rudder angles tend to be smaller and with lighter loadings. The levels of sail trim required to keep them at speed and balanced is quite small compared to the magnatude of trimming that older designs required to stay at speed. Modern designs seem to hold their speed longer in a changing condition and gain back speed losses much quicker as well.

Beyond that, when you say things like "as it is easier to stack crew on the gunwhale.........than address this difficult issue.", all I can say is, 'you obviously have a very short memory'. I have been racing sailboats for roughly 40 years now. Over this period, crews have gotten smaller and lighter. From the beginning of my sailing carreer these crews have sat out on the rail (or hiked tooth and toenail on smaller keel boats). These days a 40 footer is sailed with a crew of the size and weight that we might have used on a 33 to 35 footer in the 1970's and 1980's. Except at the most extreme grand prix levels, crew weight is not the determinant that it once was.

When you look at the best of the (pre-internal ballast) IMS type forms, these are boats that benefit from all kinds of subtle messaging of their hull forms, buoyancy and weight distribution, foils, rig proportions, hardware and deck layouts, sail designs etc. While some of these may be slightly adjusted to accommodate percieved loopholes in the rule, at least until recently, these improvements have produced steadily faster boats that are much easier to handle no matter how they are measured.

Respectfully,
Jeff

[Wardi]

.....

[redcoopers]

Wardi,

I don't want to criticize your work because it is very extensive. However, in your last post, you said that no one yet thought the work was unsound.

I think that using Taylor's series as a reference for yachts is very misleading. First, have you seen what a Taylor series ship looks like? Compared to a yacht-type hull, this is like towing a brick through the water. I can tow a series of different disp/length Canines through the water (Chihuahua all the way to St. Bernard), but scientifically, I shouldn't be allowed to extrapolate this data to sailboats.

The big problem relates to wave-making resistance. First, a ship will have a radically different wave-making pattern than a yacht. Secondly, especially at high froude-numbers, a highly-efficient modern sailboat will rise-up on a plane.

A Taylor series ship could NEVER rise on a plane. In the same manner, a Melges 24 normally sails on a plane. This is due to difference in trimming moments, heave, LCB, and LCF, which are mostly combined in the distribution in the sectional area curve.

A ship has one function of wave-making resistance versus Froude number. A full keel, older, yacht will have something that looks a lot different. A modern dinghy-type yacht will be different than the older yacht.

This is why your prediction thinks that older style yachts fair better than newer yachts. Most simply explained, it can't predict the performance enhancements of things such as planing.

What I would say is: if you want a baseline comparison for a sailboat, the first order of business is to pick a model that looks something like a sailboat.

I'm sorry if I may have criticized your work too much. It still is a good starting points, but I don't think you can use Taylor's series to compare different types of sailboats.

-Jon

[Stephen Ditmore]

Anyone tried http://www.sailrater.com/? I would assume the formula is similar to Americap, which is probably based on both the IMS VPP and PHRF results.

(See also http://www.boatdesign.net/forums/showthread.php?t=3741)

[Wardi]

......

[Wardi]

.....

[astevo]

wardy.
i think much of this discussion is steming from people not understanding the purpose of you analysis. As you explained to me, the taylor data sets up a reference for an arbitary hull shape. At low froude numbers he measures test and calculated for all sorts of disp/length, and power/length ratios. this can be used as a reference point for all boats because of the general nature of this data.

I think that all of the points criticising this analysis are largley irrelevent when refer to you data or taylors data. What we have seen in this data is that increases in efficiency do not stem from the things people have been sugesting. An increase in performance due to lighter weight may not correspond to an increase in efficiency in terms of taylors data.
Such absolute performance increases are not really considered prior to this simply becuse we are in the habit of analysing performance on the basis of length alone. The bloke in the marina wants a faster 30 footer than the other bloke and he dosent are if it is lighter, heavier or shaped like a giant boot.


the point im tryng to make is that this sort of thing does not try to predict how fast a boat goes or how a boat should be designed. it is simply a reference point which can be used for all boats independent of their length or weight or what ever else you might like to measure. this was somethig that took your explanations whilst looking at the taylors data in order to fully understand.

I think that clearing this point up will help the discussion to move forward into where the real arguements will begin. that being why we see some of these trends.

and if you still dissagree on the validity of the series just have a look at the results wardy has already shown. Aside from the anecdotal evidence which we critics (myself included) claim makes the results invalid we have seen no good theories as to why the analysis is invalid. things like planing or not and lead here or there just dont matter at all in the analysis. we have to distinguish the difference b/w the analysis and the results. if we can agree on the validity of the method we can then go on to discuss the results.

so maybee we should just use the results and go from there. because with the line of logic in the last couple of pages we are going nowhere.

lets get on with the interesting stuff.
andrew stevenson

[Wardi]

Andrew,
I should like to say that your response is extremely well put and goes right to the essence of my proposal and analysis so far, I agree entirely!. :)

[Jeff H]

I would have to agree with you that we do not seem to be getting anywhere in this discussion but at some level I disagree with your conclusions for a number of reasons that various people have articulated which critisize the data in as follows:

-The Taylor regressions are based on PHRF ratings. For any given boat the PHRF rating is a single number that is based on its percieved performance at a single windspeed. In most U.S. regions the wind speed used is a comparatively moderate wind speed (8 to 10 knots) while really big differences in speed in newer designs occurs at the higher and lower wind speed range. (Boats like the Melges 24 really accell in very light air and in high winds where their ability to plane really comes into play.)

-Weights, waterline lengths, and sail area are being taken from the PHRF or IMS certificates and so do not reflect the actual weight, waterline length, and sail areas in sailing condition.

-That in any kind of objective measure that I can think of (speed per pound of real displacement, just plain drag, or drag to stability, drag to drive, stability to sail area, speed to length, whatever) these pre- internal ballast IMS type form boats greatly out perform older designs to a large degree.

It is on those criteria that the results come into question.
Jeff

[des]

Wardi

Again I want to make clear that I'm not criticizing the way you are comparing boat, I am just looking at the way you are comparing them and pointing out a few things that I notice. As you have said, your comparison is very much like a ratings rule. As I pointed out in my previous post we can design a boat to look very good by your measurment just as designers have designed boats around other rating rules. What is interesting is to look at a two boats that are both designed for the same purpose, lets say racing. One that would rate very poorly under your system and one that would rate very well. I mentioned the Melges 24 in my previous post because I knew it would rate very poorly. The Melges is at the very far end of the sail area/displacement spectrum and as I pointed out in my previous post, a very efficient design under your ratings would be at the other end of the sail area to displacement spectrum. Unfortunatly there isn't many very heavy under canvased racing boats since these are counter productive to speed. One racing boat that rates very well under your system that already exists is the Etchells 22 and I have sailed on one of these so I know a little bit about them. I don't have the specs in front of me but the two boats are very different. If the crew on both boats were not allowed to use crew weight to decrease heel, the differences in efficiency would be even larger. Sitting on the windward rail of the etchells had no noticable effect. The narrow beam and the heavy keel made crew weight on the rail ineffective. Its just the opposite on the Melges. Sitting on the rail makes a huge difference. The Etchells seems to go about the same speed up wind as down wind. The Melges is much faster down wind.
Obviously the Melges is a much faster boat around the course but it may not be as fast on all points of sail. Now lets look at making the Melges more efficient by your measurement system. The first thing we could do is reduce the sail area. This would make the boat slower but would it make is so much slower that the efficiency doesn't change? From looking at your date you can see a few examples of the same boat with different sail area and how it effects the PHRF and efficiency, it would make the boat slower but it would also make it more efficient. So making the Melges more efficient by your system would also make it slower which brings me back to an observation that I made in a previous post. If sail area is treated in a linear fashion as you have, adding sail area will make it faster but less efficient by your measurement. There is diminishing returns with anything that makes the boat faster. If that were not true, I could hang 2000sq feet of sail area on my 22 foot S2 and compete with the open 60's.

[Wardi]

.....

[Guest]

No this is not at all what I have found!. Certainly the very lightest displacement boats do not seem perform so well, but so too, very heavy boats and also underpowered boats do not perform well either. In fact there seems to be an optimum, sail area, not related so much to displacement, but much more closely aligned to stability. So it is definitely not true that if you keep decreasing sail area the boat would appear more efficient. There is in fact an optimum sail area to stability ratio...as might be logically expected since there is no point having extra sail area if you cannot extract the power from it. This observations is in fact one of the very useful outcomes of this study!.


...or conversely the Melges is much slower upwind....which is just the point. I think you are viewing the results with a bias towards speed/length and top downwind speed, not speed around the course!

The Etchell vs Melges is a rather good example. It would seem that the basic difference is that the Melges is around half the dsiplacement of an Etchell and they have very similar length and sail area. Obviously the Melges should be much faster. According to PHRF the difference is only 0.3 kts in 12 kts of wind, in spite of the Melges being half the weight, using moveable ballast with crew sitting on the gunwhale and planing downwind!.

Since these boats actually have very similar Length and Sail Area, perhaps we should look at this another way. Why not make a real life comparison. Simply double the weight of the Melges so that both boats then have the same D, L and SA. Race the two boats and see which is faster, you will then have a proper comparison of which is the more efficient design. An easy way to do this is put an extra 5 people or water ballast weighing 1500lbs on the centreline of a Melges and then race an Etchell.

In real terms the Etchells is not the same length as the Melges. The Melges is a 24 footer while the Etchells is a 30 footer. The 22 referred to in Etchells is the static waterline length. The Etchells sailing length is much more than a Melges.

Etchells also use live ballast very effectively, hence the class rule for max crew weight. Prior to this rule the crew weights for competitive crews were getting out of hand.

Your idea to double the weight of the Melges is rather silly. No boat is going to sail anywhere near the designed lines if the weight is doubled. Your race would be meaningless.

Fact is you seem to have constructed a meaningless case study based on linear measurements that manipulates the data to prove your point of view. You are welcome to it. In spite of your opinion keelers of similar length and displacement continue to go better than their predecessors on all points of sail.

Boats are still bound by physical restraints like wave trains and that may be what's got up your nose. You'll have to take that one up with whatever god you worship, certainly not with the naval architects.

[ErikG]

I do have to agree with our anonymous guest, but I try not to sound like an ass about it!

Doubling the weight makes it a totally meaningless comparision.
It was not designed to be that heavy and would therefore have ahorrible wet surface!
That is why the differences between design paticulars have to be compared on boats that are not as far apart as the meslges and the etchells.
If we compare the melges to a Thompsson 770. The Thompson is one foot longer and 250 kg heavier and they dont look very similar, but comparing these two boats ae more interesting, and also trying to figure out why the differences are what they are.

It IS interesting to try to figure out a general effectiveness between designs, bu personall I doubt that the basic measurments are enough...

[SailDesign]

I do have to agree with our anonymous guest, but I try not to sound like an ass about it!

Put me on the list, too. Wardi, I think you are trying to do something interesting here, but may have developed a little tunnel vision.

Steve

[Wardi]

Gentlemen, and others....
It is clear that there is nothing further to be gained in this discussion with those currently actively participating.

I therefore conclude this discussion, especially in light of recent, completely unwarranted scathing comments by those who write anonymously and offer nothing more than anecdotal commentary.

To those of you who have offered your own thoughts, positive contributions and constructive criticism, I should like to thank you for your input and wish you well in your endeavours to design better boats.

[sorenfdk]

To the anonymous guest: Of course you have a right to your own opinion, but if that is the way you prefer to share it with others, then please go somewhere else. That is no way to treat someone, who like Wardi has put a lot of work into something that should be of interest to us all! I'll try to be polite, so I won't use words like idiot, jerk or *****!

To Wardi: Please come back! I'm not sure whether you'll succeed in your endeavours (I'm not even sure that what you're trying to do is possible at all!), but as long as we all learn a little bit, then it's worth every effort.

Best regards,
Søren

[redcoopers]

Seriously,

This is just a boat design forum... Myself, I may be skeptical of some calculations, but I am still very interested in the results. There shouldn't be the opportunity to belittle someone's hard work here.

There's no reason to have an attitude on this web page (remember guest, we only use this forum for recreation, not to gain political influence). Does anyone know if we can have a moderator cut out abusive posts when they appear?

-Jon

[ErikG]

redcoopers wrote: Does anyone know if we can have a moderator cut out abusive posts when they appear?

Sure Jeff can do anything :-)

Stuff like this makes me think that forcing posters to register is a good thing.
It's not as cool being an ass if people can find you...

[SailDesign]

It's not as cool being an ass if people can find you...

It's not cool being an ass at all, whether you are "you" or a guest.

That being said - Wardi, please don't take my post as a personal slight. I think you are trying to do something useful, but I'm not sure if it can be done at all. How do you differentiate between advances in hull design (the original point of all this, IIRC) with advances in rigs/materials/techniques? Well, I can't answer that question, but if it can be answered, this is the place and these are the people to help you figure it out.
Steve "not in the diplomatic service for a reason :))

[Jeff H]

While I think that this discussion has run aground, or at least gotten becalmed after a brief thunderstorm, I do want to say that I hope my previous comments and crititques were not seen as being out of line here.

From my point of view, I think that the conceptual goal of this discussion is worthwhile. I applaud Wardi for raising the point and putting in his hard work in this exploration. The goal of all of my comments are to try to help provide input that will lead to an intellectually honest discussion of the topic. They were meant to plug loop holes in the process and not to really critisize any one individual personally. I think some of the comments above have been out of line. In these internet discussions, I believe that it is never appropriate to attack an individual, but that an exchange of honest critiques of the ideas being put forth helps us all learn and grow.

Respectfully,
Jeff

[SailDesign]

I believe that it is never appropriate to attack an individual, but that an exchange of honest critiques of the ideas being put forth helps us all learn and grow.

True, and laudable. I also feel that not enough "feeling" can be expressed on a keyboard, and there is a sense of escalation in some threads. If you say something borderline nasty, even if unintentional, it can be answered with something on the same lines, and pretty soon insults are flying all over the place. Not good - either for the forum or the individuals.
Wardi, let's not kill this one - yet. The original intent was to find out if modern hulls have less resistance than older ones - i.e. have we made any progress in reducing drag for a specific type of hull-form? Let's go back and re-visit that.
Why not start with a development class - non-planing if that's easier. Say 6-metres. Has the modern 6 metre become faster than the old ones? If so, why? If not, why not?
If you can factor out the materials "thang", that would be good - just focus on hullforms.
Steve

[sorenfdk]

I agree 100% - let's get this thing up and running again! It's much too interesting to let it die away because of one individual!

Unfortunately, I used some not-so-nice words about the guest in an earlier mail. I hereby excuse, but I was p..... off by his statements. BTW: I've been called a ***** myselft once in another thread. Maybe I am - I don't know...

Best regards,
Søren

[SailDesign]

BTW: I've been called a ***** myselft once in another thread.

Heehee... You're not alone, Soren. Some newsgroups seem to feel it's a rite of passage.

Steve

[SailDesign]

Forgot to add - it's WHO calls you a ***** that is important. A man should always be judged by his enemies :)

Steve

[des]

It looks like Wardi deleted his response before I got a chance to read it. Its unfortunate because I thought is was an interesting comparison. One was the older style narrow beam, heavy, deriving most of its stability from ballast and I believe this is the kind of hull shape he is trying to defend. The other very light, reletively wide beam and the beam carried very far aft leading to lots of form stability. I see from pieces of his reponse in the next post that he suggests adding 1500 lbs to a Melges. Obviously that would completely defeat the design of the boat and make extreamly slow. My question would be, would removing 1500 lbs from the Etchells make it much faster. Unfortunatly that brings us back to the same problem of floating on the designed waterline but from iudging from the hull shape I don't believe the Etchells would ever be able to plane or surf even if it weighed as little as the Melges.
I hope that wardi will come back and defend his position again. I really think I can convince him I am right, given enough time.

[dionysis]

Wardi, let's not kill this one - yet. The original intent was to find out if modern hulls have less resistance than older ones - i.e. have we made any progress in reducing drag for a specific type of hull-form? Let's go back and re-visit that.

I am mentioning the bleeding obvious here: no sailing boat is a hull alone - everything works in synergy together. It would not be hard to draw a set of lines for a minimum resistance hull, it would be long and skinny. That is just hydrodynamics. I think this is what Wardi is getting at; factor in form stability, resistance goes up, but so does speed.

In the old acc yachts you see - despite lots of art, science and technology, very small increases in speed are gained, if you factor out rig, keel and rudder efficiencies.

The canoebodies of these yachts, I would think were very similar; even going way back. When you get differences between yachts of a fraction of a knot, then I think you are right up against the physical limitations to minimizing resitance for a given hull configuration.

If it is a question of overall efficiency, I am sure there are many boats that have brought all the elements together is a beautifull way. Both old and modern. For a conventional yacht of medium displacement - you are close with an old 12 metre design.

I am not sure wheather this is what the issue is here.

[a-stevo]

i think this is not a discussion of heavy boats vs light boats as some of us are implying. I think it was more about how well we design boats for a given load. We all know that light is fast and we dont need to bother talking about that. The question is more about if a boat of similar length rig and mass and everything else were built today, how well would the old vs the new go? In truth there is no absolute data really applicable since the trend toward the lighter boats has begun. That's why the study wardy was doing was important.

[ErikG]

I totally agree with A-stevo.
The problem of comparing new vs old is that iw we "redraw" an old design and in theory "build" it lighter, it would not, have been drawn the same way as it was originally.
Wardy's comparisions are indeed very interesting, at least as general data to start from, and see if the Taylor resistance really is appliciable, by comparing several boats that we have more data from and try to compare them more closely.

But that is no small task, and neither was Wardis original work a small task or insignificant in any way. But this would perhaps best be worked on at a naval education somewhere as a thesis as this is hard work without any financial benefits in the short term.

This IS very interesting and validating Wardy's ideas or proving with data that his ideas are not quite accurate would be very beneficial for us all.

Unfortunately as a part time student, I don't even have enought time to study, so it's out of the question for me, but I hope that someone, somewhere want's to pick up the torch and run with it.

ErikG

[SailDesign]

Wardy's comparisions are indeed very interesting, at least as general data to start from, and see if the Taylor resistance really is appliciable, by comparing several boats that we have more data from and try to compare them more closely.

I'm probably dis-remembering again :), but... I had been assuming that we started talking about whether we were now able to design out resistance from a given hullform. In other words, if you took an old hull, and redrew essentially the same boat, all coefficients the same, same LOA, LWL, beam, BWLm draft, etc, can we now make it faster? i.e. have we developed the ability to draw section shapes that are lower drag than in previous generations.
As dionysis says, if you take advantage of modern materials and hullforms, of course you can maj=ke a faster boat. But can you "cheat" the Taylor series by drawing better sections (that being all that can really be changed) ?

As i say, I may be disremembering the genesis of this discussion.

Steve "or maybe not..."

[SuperPiper]

Wow! I was away for a few days and this thread really evolved. I think that after the initial shock and name-calling, there is finally going to be some worthwhile discussion.

Yeah, there probably have been some improvements over the last 30 years. If we believe that then we should be able to list them. We should be able to quote patent numbers and developers' names too. There should be the Smith transom and the Jones bow and the Korean half-something-or-other.

Let me start:
I believe that bow shapes have evolved. But I don't know if the new shapes are just ways to get more waterline length or if they are more efficient?

CBTF is the subject of multiple threads in this forum. I believe that this technology is a bonafide DEVELOPMENT.

Nobody has mentioned hull coatings. Are teflon and poly-urethane paints more efficient than gelcoats?

Do winged keels improve efficiency or are they just trying to get as much mass to the bottom of the boat without increasing draft?

I previously mentioned the "bubbler" technology that has not caught on.

I am intrigued by the airplane float shape of the Parlier catamaran hull. We are waiting to see how it performs (Parlier had to retire from the Transat).

Is there a sailboat equivalency of the stepped hulls of speed boats?

On our cottage lake, there is a Scandinavian-built power boat that has a hull just like a sailboat. But, it has ridges or grooves that run down under the hull at the quarter. This looks like an attempt to provide efficient low speed operation but also to allow quick planing.

That's enough for now. What do the rest of you think?

[sorenfdk]

I think we should try to differentiate between pure design developments and engineering developments. (I said "try"!)

The sharper bows are design developments, the CBTF is an engineering development (or at least a combination of design and engineering). The shapes of modern light-weight sailboats are design developments made possible by the use of lighter materials, and that is engineering development.

Best regards,
Søren

[ErikG]

I agree with Søren. I feel that the specific change from med displ to light weight is an engineering development. The hull design changes that have followed creating light weight planing boats are a design development.

Well I know you did say try! :)

BTW, Søren, is the CDE 850 in production anywhere? I read about it on your webpage ages ago, but I could never find any pic of completed boats...
I could live with owning a CDE 850 until I've built my own first design :D

[Jeff H]

I like the direction that this discussion seems to be going. Although the individual improvements are hard to quantify, they are comparatively easy to identify. I think that the change in bow shape is a good example. In the early 1980's I attended a presentation of a paper that looked at the effects of altering bow shapes. In that study, the sections aft of the midship station were kept fixed and only bow sections altered. The general shape of the bow sections were maintained but the waterline was stretched between the typical 'destroyer' bow of the era and essentially a plumb bow.

As Super piper queried, the increased waterline length showed a small reduction in drag in flat water as the boat approached the normative hullspeed allowing a higher ratio of speed to the square root of waterline length. In other words a small increase in overall efficiency. This increase over the expected linear coeficient in the hullspeed formula was attributed to a decrease in bow wave production associated with the finer bow.

The paper looked at other factors as well. As you may remember, light weight boats at the beginning of the 1980's had a tendancy to pound brutally in chop and to be greatly slowed by the impact with each wave. It was this phenomina that gave light boats the reputations for being slow in a chop. In this study one of the dramatic results of lengthing the bow waterline was the reduction in energy required to get through waves and a dramatic reduction in wave induced pitching. In other words this allowed a lighter weight boat to pass through waves more easily, and faster, and with a more comfortable motion that would also produce a reduction in the diturbance of the flow over the sails and underbody foils further adding to performance in waves.

He also noted that with heeling, the elongated bow waterline models tended to have less of a trim change tendancy to go 'bow down' with heeling.

By the late 1980's the early IMS typeform boats had also moved the longitudinal center of buoyancy (LCB) aft in the boat. This did two things, it allowed a further fining of the bow and provided greater buoyancy aft which allows the boat to begin to climb onto its own waves with a reduction in required energy. In other words the hull form had shifted to a semi-planning hullform. It should be noted that without this movement of the LCB aft, the prismatic coeficient would have dropped below an acceptable range in other words to a speed robbing number.

With the more sophisticated modeling permitted by computers careful hull form modeling allowed a minimization of the negatives that previously had been associated with moving the LCB aft.

All of that combined allowed IMS type form hulls to routinely have a hullspeed approaching 1.5 times the Sq.Rt. of the waterline vs the earlier 1.25 and 1.34 coeficients that are routinely quoted.

Lastly I want to touch on the various powerboat derived ideas being floated. Sailboats generally have so little power compared to their weight that the kinds of ideas (step baffles for example) that work well on a power boat, rarely work on sailboats other than very stripped down special purpose performance sailboats.

Respectfully,
Jeff

[SuperPiper]

Jeff:

It is your description of the bow modifications and the shift aft of LCB that we needed to hear about. You have successfully listed and quantified these advances.

So, what else?

Is it fair to just discuss hull advances? One of my favourite topics is wing masts and rotating masts. Do less rig drag and less heel also have an impact on hull efficiency?

With regards to transoms, whatever happened to double-enders? Whatever happened to reverse-angle transoms? Are truncated/open transoms more efficient or just in style?

[sorenfdk]

Double-enders are usually good-looking and very well-balanced boats, but they don't win races. There are a number of reasons for this - they tend to bury the stern when under spinnaker and they don't surf.
The reverse-angle transoms are good for cruisers because of the added deckarea, but for racing that deckarea is only added weight where you don't want it!

Best regards,
Søren

[SeaDrive]

As the LCB is moved back, it becomes more and more difficult to get the necessary volume behind it in a double-ender. It's an idea left over from boats of substantial displacement with the LCB in the middle of the boat.

In the US, the term "reverse transom" would mean the top edge forward of the bottom (i.e. less deck area).

[sorenfdk]

In the US, the term "reverse transom" would mean the top edge forward of the bottom (i.e. less deck area).

Ahh - I thought it was the other way round! Then the answer to SuperPipers Question should be: Nothing happened to the reverse-angle transoms - they're still here, just a little more vertical.

Oddly, the angle of the transom has always been dictated by the rules. In the days of the IOR, the transoms were extremely flat - under IMS it's quite the opposite.

The old IOR-transoms were often very elegant, The IMS-transoms are very ugly. Have a look at Siemens Mobile, designed by Frers - probably the ugliest boat afloat!

Best regards,
Søren

[SuperPiper]

Another favourite topic of mine: Tumblehome.

The new breed of Open ocean racers seem to have very rounded topsides. This feature was illegal in the last Volvo Ocean Race. If a VOR60 looks like a canoe, the Open60 looks like a kayak. If tumblehome was illegal on a crewed boat but not illegal on a solo boat then the rule was probably not a safety item. What are the advantages of tumblehome? Has the tumblehome philosophy changed in the past 2 decades? Are the slab-sided IMS boats more or less efficient because of the apparent lack of rounded topsides?

[sorenfdk]

I've noticed that some of the slab-sided IMS boats are floating with the stem knuckle well above the water when upright. When they heel they "sink" to make the waterline longer. "Rule thinking" again, I believe.
I believe that is more or less the case with ACC boats too. I read somewhere that the waterline is increased about ½ meter this way.
I would also like to know if there are any advantages of tumblehome - in my eyes it is ugly and impractical.

Best regards,
Søren

[Jeff H]

Thank you for your kind words. Wing masts make sense on beamier boats where staying can be more simply accomplished. For a normal monohull, the added weight, windage and complexity does not seem to pay for itself. Obviously, reducing weight aloft and drag are good things performance wise as the allow a boat to carry more sail area longer and with a flatter incident angle.

Double enders offer some advantages in very slow speed vessels but as they approach hull speed there is a tendancy to squat in the stern which creates a lot of drag. The steeply reversed transoms were intended to cheat the IOR rule and was seen as lowering the center of gravity near the stern. The truncated transoms come from trying to move the center of bouyancy and gravity futher aft, and the open transoms lower the vertical center of gravity and provides a way to quickly drain the wide open cockpits popular on race boats (unless your race boat happens to be from New Zealand).

Regards,
Jeff

[Chris 249]

My question would be, would removing 1500 lbs from the Etchells make it much faster. Unfortunatly that brings us back to the same problem of floating on the designed waterline but from iudging from the hull shape I don't believe the Etchells would ever be able to plane or surf even if it weighed as little as the Melges.
.

Iain Murray's challenge for the first AC using IACC class boats had a couple of Etchells, radically lightened and re-keeled and re-foiled, as trial horses. From watching them and talking to the guys who sailed them, I don't think they were consistently on a Melges' pace. The problem was that the reduction in waterline stuffed the shape. The same problem was found when IOr boats were converted to IMS.

Re fine bows. This is a trend that has been going on for many decades - but like so many, I think it's technology driven. Older spars and sails weighed so much more that the resulting pitching moment had to be fought with extra buoyancy up forward. Stick a few bricks at the hounds of a modern dinghy to compensate for the heavy old rigs, and you'll find the boat nosedives and pitches excessivley pretty quickly.

An example of how old the trend is can be seen by looking at Uffa Fox's 14s from the '30s - they show a fining of the bow and a broadening of the stern.

One area I can see as an advance is the shift to U shaped sections, from Vee shapes. The advantages are, of course, lower wetted surface and more dynamic lift. But why did it take so long for designers to go to "U"s and "planing flats" along the keel? In hard-chine skiffs, the use of sheet ply restricted the amount of U, but not in other classes. When many designers tried to increase volume (to reduce beam or float more weight), they simply increased the deadrise and stuffed up the planing qualities. It went on for years, until boats like March Hare came along. Even then Mike Jackson wrote how scared he was to go against conventional wisdom and go from Vee to U.

Yachts stayed Vee for even longer, until Carter etc started flattening hulls and then (IIRC) Peterson and Farr brought in very U-shaped bows - more effective, but ironically Farr at least did it to increase the rated displacement 'cause the "shoulders" of his U were on the fwd depth points. Ironic that IOr cops abuse yet it was the reason that Farr moved to a faster shape!

Some dinghy designers see more immersion of the stem as an advance. Maybe topsides flare should also be seen as an advance, although sometimes (IMS and IACC) it's restricted by peculiarities in the rules or boats.

IOR sterns leaned forward, btw, because the aft girth measurement was taken from the forward meeting of sheerline and transom. Moving the transom forward shortened the rated length, which was taken from one girth to another. However, moving trhe transom forward also put the measurement on a fatter part of the boat, increasing the rated width aft and therefore pushing the rating back up. So placing the corner of the transom was a game depending on the exact shape of the hull underneath IIRC.

Have you guys seen Francis Herreshoff's designs for canters and inclined solid wingsail cats from the 1940s (IIRC)? Scary. Jim Young (famous NZ designer, who emplpyed a kid called Bruce) built one of Herreshoff's canters. I wonder where it is?

[SeaDrive]

One area I can see as an advance is the shift to U shaped sections, from Vee shapes. The advantages are, of course, lower wetted surface and more dynamic lift. But why did it take so long for designers to go to "U"s and "planing flats" along the keel?

When Olin Stephens' Columbia beat Septre, there was a huge fuss in the press about how Columbia's v-eed sections got through the waves better than Septre's U sections, complete with aerial photos showing differences in the splash. The theme of Stephens' genius with bow sections ran through several AC challenges. So, I suppose it took the lesser mortals a while to discover that different, i.e. much lighter, boats could use a different shape.

[YYY]

Fiery Cross (built in 1953ish) is still in NZ. Was banned from racing unless the keel was fixed. Jim Young used to cant the keel mailnly for reaching and leave it in the centre for the upwind stuff as it had no other foils apart from the rudder. It's a 45ft by 7ft double ender.

[stew fl]

In ten years of sailing and racing I have become somewhat confused!
I'm on this guy's catalina 22 and look at my GPS
and it reads 5.5 knots he said "this boat won't go that fast" (water line).OK my GPS is lying.
Im trimming another guy's catalina 22 on the inland waterway, 18 to 20 knots of wind, I hate
these boats but I got to admit, it is boring a hole thru the water, we catch up to and pass a benataue
36 and burn it up.
What I am getting at is, that even my stinky McGregor 25 has gone 12 K for extended periods W/ spinnaker, and commonly goes faster than hull speed even up wind.
Apparently there is some force at work that is not quite planing but close.
Thanx again!

[SailDesign]

Apparently there is some force at work that is not quite planing but close.


That either be your engine :) or what is loosely termed "semi-planing", which basically translates to "can't quite get itself up and over the hump, but has enough power to try"

Steve

[stew fl]

I'll call you steve now!
Perhaps I just don't know the actual water line length to do the calculation, therefore I and others just think we are going faster than the theroetical max when actually our WL's are longer than we think or the published data is wrong.
Is there an accepted procedure for measuring a boat to find this ever so elusive number or is it a closely guarded secret of designers much like magicians who don't give away their secrets either.
Thanx kindly,
STEW

[Jeff H]

First of all hullspeed is typically quoted as 1.34 times the square root of the waterline length and that formula is derived from the height and speed of waves. That formula described the theortical speed at which the bow wave moved aft combining with the quarter wave and altering longitudinal trim there by creating an inclined plane that requires a large increase in energy to climb. Planning is defined as the point at which the boat has climbed up on its own bow and stern wave.

There are a number of ways that a boat can exceed hull speed without actually planning. The most common in displacement monohulls is surfing where the slope of the wave face creates a downhill inclined plane and gravity imparts the necessary energy to exceed hull speed.

There is also a state called semi-planning in which a boat can exceed its theoretical hull speed by producing a smaller bow wave and by moving the center of buoyancy aft so that the stern does not squat. Semi-planning hulls are usually very narrow or will often have very fine bows to trick the water into thinking that the boat is very narrow. Few, if any, multihulls actually plane. They get their high speeds from thier narrow beam and minimal wave production. Boats like the Transpac sleds get their high speeds the same way. Modern IMS typeform racing sailboats pretty frequently exceed thier theoretical hull speeds by reducing the size of the bow wave with a very fine bow and a center of buoyancy that is located pretty far aft reducing the amount of squatting at speed.

With regards to your anecdotal evidence, a Catalina 22 has a waterline that is roughly 19.33' and so would have a theoretical hull speed of 5.89 knots. A Catalina 22 would have a bear of a time hitting that speed very often because of its hull form, minimal stability, and inefficient sail plan and foils. Often when a GPS shows a boat like a Catalina 22 or Macgregor 25 seeming to be moving upwind at speeds approaching or exceding hull speed, there is a favorable current adding to the speed over the ground. For a Magregor 25 to sustain 12 knots it would need to be in big enough waves to be surfing and to use the momentary energy of the wave to accellerate it up onto a plane. It is generally cited that a boat designed to plane with any regularity needs to have roughly 400 square feet of sail area per 1000 lbs of displacement. A Magregor is no where near that.

Respectfully,
Jeff

[O'Hurley]

undefinedI though it was simple, but here is another attempt!

The fundamental relation controlling the speed of a displacement boat is its Displacement/Length ratio.
For boats of a given D/L ratio, a canoe will generally go faster than a punt because it is a better design.
ie: it has less resistance at all speeds and angles of heel.

Thus if we are really making "real" improvements in hull design, then current boats should perform better than those of 50 years ago, based on their D/L ratio.

The article by Billy Hughes simply argues that little improvement has been made in fundamental design, even when based on Speed to Length ratio, let alone speed to D/L ratio.

Modern design advances are mainly in the area of improved materials allowing lighter weight and more stability. They can carry more sail area, so the boats go faster in absolute terms. But so they should!! We all knew that from the beginning!....

But are there any real improvements in the fundamental design when you compare them on the basis of their D/L ratio?.

[O'Hurley]

I agree the D/L ratio is always a good start to any design,and depending on witch ratio is used ,it will set the requirements as to both speed ,power requirements and performance.
I am currently working on building a Redwing 23',which is based on an old design of Howard Chappelle,brought up to date by Karl Stanbough.

[patrirck lane]

Hey Guys Can You Help Me With A Project For Power Tech
Thanks Guys
Patrick Lane

[FAST FRED]

"First of all hullspeed is typically quoted as 1.34 times the square root of the waterline length "

This "formula" is only for fat (LWL /BWL) 3-1 or 4-1 boats .

Skinny boats 8-1 or better do not observe this rule , as the bow wave IS small enough to power thru. Lightness helps but not that much.

FAST FRED

[Sean Herron]

Hello...

Like most things - the comparing of asthetics and engineering improvements based on ratios and percentages - seems more like one is hiding behind some rather simple math - or burying redundant statistics in useless percentages or comparisons against non similar boats - sort of like Presidential election 'percentages'...

I just design what I want - then go build it - then go sail it - then sell it - then build a boat that is more of what I want based on getting rid of the little things that bugged me about the last boat...

I personally think that some of the most stunning designs and innovations within this industry have been accomplished by people with an intuitive feel for just making things float and go fast...

The math is not the be all and end all - it is more of a means for comparison or projection...

But then I have been called simple...

SH.

[MikeJohns]

Trouble is Shaun that if you can put the numbers together you are getting close. Only then should the artist appear !

I have seen so many badly designed one-off boats designed and built by amatuers who thought that their design looked "right". Many of them sit on moorings unused and unsalable ( and unsailable too) waiting for the owner/builder to die so they can quietly sink.

One magnificent yacht I test sailed with a prospective owner had a sheet winch to operate a long tiller ! A quick inspection of the sail plan showed that a 12' bowsprit would need adding to balance the boat and the winch was there to fight the weather helm. Turned out the builder had simply shortened a 40 foot design to 30 feet by simply ommitting the stern an adding a brutal transom. The boat looked good, the nubers said it wouldn't work.. That boat is for sale again, it sells every year.

Remember
If it looks right ...it might be right.
If the number say its right and the system of producing the numbers is proven...it will be right.

Thats an engineering viewpoint ;-)

[Sean Herron]

Hello..

I agree and I do the math first - basic centers and such - I just hate getting caught up in finite discussions that seem to revolve around beer hall techno me speak more bits...

Anyway - off to work...

[Jeppe]

Erik! I got a CDE 850! Do U want to know more about it? Just send me a mail. :)

[OrionsSword]

I do think that we are making some design improvements but there is one problem...they are not showing up because all (or almost all) production boats now underconstuction are not sailing boats for sailors they are meant for the people that hardly go beond sight of a marina and as for the new "racing" boats under production the ones available finacially to real sailors are wimped up w nice interiors, roller furling and all kinds of unracelike trinkets. personnally i have given up on any production boat and have now at the drawings stage a new boat underway. If i were to purchase a boat it would have to be an older boat C&C or F3.

Dylan

958 days till allingy vs challanger americas cup 2007

[lucas adriaanse]

Theories about planing a hull are fine, but don't forget practise .... What I mean is: I have read the theoretical number given by Jeff H (400 sq feet per 1000lbs), but this would all depend on a.o. what windspeed you will be sailing in. In other words what kind of fuel you put in your tank.
As I am in the metric part of the world this would be about 36m² per 450 kg, if I am correct.
Even modern (race) yachts do not have that much canvass up on a broad reach/run, yet they plane. I've been planing my 24', 30', 35' footers for long stretches (sometimes for miles) simply because I keep up all the canvass in 30-40 kts of true wind. We have been planing with yachts even on relatively flat water (lakes) with only 1 or 2 mtr of water under the keel.

This is what all VPP's and ratingsystems have problems with.

If your foils are thin enough to not produce too much resistance, your hull is shallow enough to not produce too much resistance, the hull provides the right lift and you have enough wind (tornado's could even lift the boat right out of the water .....) and a rig that will stay up, planing a modern race yacht is quite possible.
I owned two IOR two tonners and they just went submarine in too much wind on a spinnaker run. But the newer boats just keep accelerating. Handling the boats gets lighter and lighter as they speed off (until .....).

From reshaping a keel on a 30-footer from a 80mm chord to a 120mm chord I know how important low resistance is: with the 80mm chord the 30' planed in 30kts of wind, after the reshaping she needed a 35% bigger spinnaker to plane at about the same windspeed.

Now, whether this is to be seen as an improvement in yachtdesign is up to the individual. Personally, I think it is. I like this kind of sailing (can't wait for the (too) few occassions every year) and it's never been hazardous for my yacht and crew. So, as long as you know when to quit, it's thrilling !

Lucas

Question: do we agree that planing is when the yacht constantly does speeds double her theoretical hull speed or more, her bow and slamming section being lifted from the water to about her keel, on flat water or on waves if she does so also going up waves (not just surfing down) ???

[K4s]

Hell yes! Progressing every year,better sails ,better boat construction for both cruising and racing options,better construction techniques,more fun to sail,easier to sail all adds up to improvements to my addiction(sailing).
I really couldnt care less about the equations that go into making my boat go fast and when I think about it I have never actually sailed an equation,could be kinda wet and slow me thinks.
Forget the math and go sail a reasonably new boat.See how much nicer it is to use and there is your improvement.Hopefully the industry can continue in the same vain.
K4s

[249]

Lucas, what sort of 35'er do you have which will plane for miles on lakes?

Re what we call planing. Naval architects say that it planing occurs when the dynamic lift raises the C of G above the height it is at when the boat is stopped (and supported only by dynamic lift) AFAIK. So it's not really easy to pick from on the boat, is it?

[lucas adriaanse]

249, I think establishing what sailors call planing is important, if we want to be able to talk about we experience on the water. Measuring the shift in centre of gravity is neither very practical nor what gives us a kick. It is the sustained high speeds that do.

That is why I described what I feel planing is. To mention some of the boats we did long stretches of 14-16 kts downwind on (with tops around 20) over the years are:
Sprint 95 (32'), VR30 (30'), Corby 34.7 (35'). The first one with a spinnaker that even was not that big (± 58m²), the other two with 122m² gennakers. If you do not need 'to fall down from a wave' to reach these speeds (surfing) I call it planing. May be incorrect theoretically, but practical for the sailor.

Anyhow, my comment was meant to counter the theory of needing 36m² of sail per every 450kg of boat, which I believe dates from the old days ...
Downwind we now carry 36m² main + 122m² gennaker = 158m² on a 3T yacht incl. gear ex crew. Nowhere near 36m²/450kg. Reaching at around 125-130° in 25kts of wind gets the boat to sustained speeds between 13 and 14,5 kts (GPS readings) .... yes on a lake.

Lucas

[249]

The Corby planes on flat water? Impressive.

Re "do we agree that planing is when the yacht constantly does speeds double her theoretical hull speed or more, her bow and slamming section being lifted from the water to about her keel, on flat water or on waves if she does so also going up waves (not just surfing down) ???"

Is the degree of bow lift important? Look at some boats that definitely plane - the skiffs. The 12's plane extremely bow-high, yet 49ers and other Bethwaite boats plane with the bow very low; Julian always designs them that way. The bow-high angle can actually be quite innefficient. I've sailed an Open 66 (modified Open 60) that definitely planes, but she doesn't lift out of the water all the way back to about her keel.

I know we can't really measure the C of G rise, but it does seem that strictly defining planing in a way that can be seen from aboard may be so hard as to be practically impossible, AFAIK.

[lucas adriaanse]

Hi 249, (why not become a member, you're here so often .... and it's nice to call someone by his (nick)name ...)

Indeed, bow up is not the way to go. Or better said: the transom down is bad. The 3 boats I mentioned all were/are quite flatbottomed, so out of the water to the keel does not mean bow up (at least not much). We usually keep crew weight at normal positions, unless waves are short and steep (on the Solent for instance). At sea we even sometimes try to get the bow down going off the wave (shifting crew positions) to get her surfing if there is just not enough wind to really get going.
In 1992 I switched from submarining IOR 2-tonners to smaller downwind flyers. That's where I get my kick. And upwind speed has not suffered. It's just a 'little less comfortable'. So to answer this threats topic: yes, to me we gained a lot from material development and research, allowing for design improvements.

Pic attached shows previous 30' one off in typical downwind spinnakerstyle. At 18-20kts of wind doing 11-13 through the water.
Hope we'll get some pics of the Corby on flat water for you next year ...
2nd pic: my 2-tonner had masses of sail, but did not plane !

Lucas

[249]

Lucas, the 30 looks sweet.

I still like the old IOR busses. That to me looks like maybe like one of the former Hong Kong Dubois 44s from 1979 - La Pantera or Uin Na Mara or something???

Yes, I agree we've gained. My boat (a 2000kg 28 foot/8.5m 1968 NZ lightweight offshore cruiser-racer) was about as quick as any offshore boat of its length in its day, but a new boat of the same dimensions would be faster. Not enormously, though; perhaps 5-7% or less???????????????

[lucas adriaanse]

Hi 249, homerun: Uin-na-mara ! The 1979 Dubois 44.

I also had the 1977 Holland 44 Mandrake. Excellent boats to sail, but not as much fun as the Corby 34.7 .... She would be thundering past them on any course off the wind. Upwind in a breeze the old 2-tonners were a delight, of course.

Lucas

[SuperPiper]

In the Vendee Globe, the new generation of Open 60s are beating the older generations of Open 60s. Although . . . the better skippers have the better boats and the better sponsored campaigns . . .

[DryWaves]

Speaking of ratios, do you know of any resource that would have the SA/DSPL and DSPL/L figures for the Olson 40 designed by George Olson? I've been running some comparisons with newer designs, but I don't have the numbers on the Olson 40.

Thanks :rolleyes:

[edward]

Just on this issue, i have just posted a new thread about clinker hull design which is an older hull design. I have heard it said that the clinker design on certain hulls is faster that a smooth hull of the same shape. If this is so then we may be going backwards.

[edward]

Wardy

I have got interested in hull design because of another problem I am looking at - the design of curving canals across rough terrain that maximise the flow of water. I think boat hull design might provide a few ideas on how canal shapes might be modified to increase the flow rate for a given canal cross section area. Have you discovered any trends in boat speed from you data base, particularly in relation to clinker designed boats? I have a hunch that the ridges play a role in stopping transverse flows around the hull and that this might reduce overall drag.

[D'ARTOIS]

Check the America Cupper's designs - it has be executed by a long time already; specifically designs under Dennis Connors or whatever his name is - in the period that the Van Oossaanen keel was introduced.

There are no new idea's in marine design, only variables.......

[Tim B]

edward,

It depends under what circumstances they reduce drag. Let me give a similar example...

A powerboat with a stepped hull is incredibly efficient at high-speeds, but pitifully in-efficient at anything below planing speeds.

Similarly, there is a time and a place for clinker. The "transverse flow" does not actually exist at any great amount I'm afraid, the flow may be a few degrees from the centre-line but SIN (4 degrees) = 0.069 ie. 7% of the flow, which is incident to the hull along the forward section. I believe it straightens out after that (have yet to do the sums). What I suspect the clinker-style is doing is effectively giving a vertical lift vector, thus reducing the wetted surface area (and hence drag).

Anyway, that's my thoughts on that (I'll go and run the CFD at 4 degrees sideslip now)

Oh, and before I forget... D'Artois, which planet are you living on, man? of course there's new ideas in marine design. It's just that nobody's talking about them because they want to get there first!

Cheers all,

Tim B.

[usa2]

one would think that there are design improvements happening because people keep building new boats that are getting faster. Granted, they might be getting faster by 0.000000001 of a knot, as the Americas Cup has proved, but designs are still getting better.

[yipster]

"0.000000001 of a knot" isnt much i agree. AC boats hardly make 10 knots becouse they are limited by rules.
the new 50 meter high supercats and tri's do 20 / 30 knots without foils, now isnt that called progress?

[CT 249]

Not all of that improvement in speed is "progress" in the original sense of the thread, because waaaay back then Wardi was trying to isolate improvements due to reduced displacement, technology etc. The existence and performance of the 50m high supercats etc may well be largely due to improvements in technology that have fed back into design improvements.

It's not just the obvious things, like creating a strong, light structure, it's what else feeds into it.

If you look at a good '70s cat or tri (say a Crowther Kraken or Spindrift) and know what the designers were trying to achieve, you'll see that they were burdened by sails that became too full in strong winds, so the area had to be reduced and the boats had to be driven by less power than a modern boat. Therefore they had fine ended hulls, which then further limited top-end speed.

Now, with modern sails, a boat of the same dimensions will move much faster, so it can have fuller ends, increasing top-end speed in turn. But the progress is not due to some breakthrough in thought by designers, they just have different tools.

Another long-term trend has been to finer bows in dinghies and skiffs. It's easy to think we've progressed in that way, and in some ways we have - but there is evidence that the old guys woould have created narrower bows IF they didn't have the problem of having to support really heavy rigs swinging back and forth in the chop, and to cut down spray 'cause bailers weren't that good.

Sail one of the replica 1930s 18' skiffs and you'll quickly realise how important improvements even in mainsheet block and cleat design are, in that superior mainsheets make boats much easier to sail, so you can then move towards narrower waterlines, more "dangerous" shapes etc.

Even Moth design shows the trend; old gear like a heavy old alloy mast, big soft mainsheet on crude ratchet non-roller blocks, heavy wooden battens and dacron sail would make a modern narrow skiff unsailable.

Earlier in the thread there was some comment that restricted dinghy classes were the only place to look for "real" design improvements (ie those not influenced by "other" parameters). I'd have to say that the influence of superior technology is so vast that even those boats are influenced in design by the enormous improvements in sailcloth, spar material, hull material, gear and even clothing and health; modern physio and medicine allows for many guys to sail champion 18' skiffs into their 50s, whereas most of them used to retire much earlier. Now there's a bunch of people in each class with enormous experience in boathandling, and that (with coaching as well) seems to be feeding back into improved techniques that allow people to handle much faster but more "difficult" boats.

[yokebutt]

Yes, we've been making headway the last half-century and longer, may I for example mention monocoque construction (wood veneer or the many assorted fiber products available) instead of a giant bloody parallelogram like most plank-on-frame wooden boats are. Then, of course, there is the modern sail-cloth that doesn't need to be wetted down to hold air, and, of course, modern cordage, that doesn't stretch to the moon......


Please, give me a call if you wish me to slap you on the head some more.

All in good jest, Yokebutt.

[dionysis]

Yes, it seems to me that one of the major advances in modern times is the recognition that lighter displacement boats can be made to be faster and more seaworthy than the traditional kind.

[FAST FRED]

" modern cordage, that doesn't stretch to the moon......"

Could be an advantage for racing , But I had the priveledge of sailing with LINEN line at one time and it was fantastic.

So soft a 5/8 line would lay on both sides of a verticle hand, easy to handle and not at all harsh on the hands.

Have never experienced cordage as user friendly , EVER.

Is Linens loss an advantage?

FAST FRED

[saeble]

heh... I fell asleep at about page six, with all the large words and nitpicky numbers... my apologies if this has already come up...

If you're looking for a 'large leap' type change in sailing vessel design then you'll find its a pretty fundamental one and its only recently occured.

In order to make a sailboat go faster, you need to delete the sail.

"Huh?" you say... "What is he smoking ?" is the next thing to form in your mind...

I'd be willing to bet the biggest single improvement in sailing vessel... or, more accurately... and to give the game away partially...'wind powered vessel', will be when we remove the mast and install a driving rail or post for something like this :

http://skysails.info/index.php?id=13

The fully automated system proposed on that site is perhaps beyond your average sailor... but... if you accept the principile in its broadest sense then a whole world of new thoughts will populate your head.

The airfoil used in this system is too large and ungainly and no doubt expensive, but it does, as I say open the door to some possibilities.

My thoughts are that if you were to utilise a largish cat and put a simple hydraulically (or cable winch in an emergency)operated, 'canting mast', in place of your existing one, perhaps give it two axes of movement, seeing as you've already commited yourself to hydraulic rams/winches for mast control. Then you could attach your four control lines and attendant fast action electric or hydromotor winches and utilise a foil to yank you along at an obscenely fast rate of knots.

I wonder how much foil area you could get away with before your boat becomes an aircraft ? :D

I wonder how much this sort of vessel would turn the sailing world on its head ? :D

If you want a personal appreciation for air foils and kite type experiences you cant go past a two or four line stunt kite or foil, it will soon illustrate to anyone who flies one that there is most certainly another excellent way of harnessing the energy of the wind. Try this site for kites :

http://www.intothewind.com/

For more information on how foils work and are controlled, this is a good place to start :

http://www.flexifoil.com/

There are a bazillion other sites out there that deal with non-rigid, semi-rigid and even rigid foils. The adaption of these sorts of technologies to intermediate to large vessels is, to me, only a matter of time.

Incidentally, I am NOT in any way associated with any of the sites listed in this post. Seek your own reference material if you wish, its only a google search away...:)

[CT 249]

You're right in many ways, but originally the thread was about improving efficiency WITHOUT such major alterations.

Such thoughtsare far from "beyond the average sailor", but having (like many others) discussed these things in depth with those who sell them, it's clear that they also bring major problems of their own. To get upwind or maximum speed, the kites are laid low to the water - can you imagine Sydney Harbour on a Saturday, with 200 kites laid low and each of them trailing 100m of high-tension 4mm (IIRC) line out to the side? I sail cats at a beach popularly used by kitesurfers and there have been problems. They also work only when they have enough windspeed to develop lift (about 8 knots in the case of some IIRC), and again in a typical crowded, fluky port (Solent, Sydney, LIS) the idea of the average club/cruiser crew trying to handle one of these when they hit a lull and 100m2 of kite hits the water 100m astern is not nice.

Then again, I go sailing for fun and the popularity of boats like Lasers, J/24s Hobies and Beneteaus prove that (like me) most people don't need ultimate speed for fun; in fact some of the most efficient boats are quite boring to many sailors.

[GAZZABO]

Iain Murray's challenge for the first AC using IACC class boats had a couple of Etchells, radically lightened and re-keeled and re-foiled, as trial horses. From watching them and talking to the guys who sailed them, I don't think they were consistently on a Melges' pace. The problem was that the reduction in waterline stuffed the shape. The same problem was found when IOr boats were converted to IMS.

Re fine bows. This is a trend that has been going on for many decades - but like so many, I think it's technology driven. Older spars and sails weighed so much more that the resulting pitching moment had to be fought with extra buoyancy up forward. Stick a few bricks at the hounds of a modern dinghy to compensate for the heavy old rigs, and you'll find the boat nosedives and pitches excessivley pretty quickly.

An example of how old the trend is can be seen by looking at Uffa Fox's 14s from the '30s - they show a fining of the bow and a broadening of the stern.

One area I can see as an advance is the shift to U shaped sections, from Vee shapes. The advantages are, of course, lower wetted surface and more dynamic lift. But why did it take so long for designers to go to "U"s and "planing flats" along the keel? In hard-chine skiffs, the use of sheet ply restricted the amount of U, but not in other classes. When many designers tried to increase volume (to reduce beam or float more weight), they simply increased the deadrise and stuffed up the planing qualities. It went on for years, until boats like March Hare came along. Even then Mike Jackson wrote how scared he was to go against conventional wisdom and go from Vee to U.

Yachts stayed Vee for even longer, until Carter etc started flattening hulls and then (IIRC) Peterson and Farr brought in very U-shaped bows - more effective, but ironically Farr at least did it to increase the rated displacement 'cause the "shoulders" of his U were on the fwd depth points. Ironic that IOr cops abuse yet it was the reason that Farr moved to a faster shape!

Some dinghy designers see more immersion of the stem as an advance. Maybe topsides flare should also be seen as an advance, although sometimes (IMS and IACC) it's restricted by peculiarities in the rules or boats.

IOR sterns leaned forward, btw, because the aft girth measurement was taken from the forward meeting of sheerline and transom. Moving the transom forward shortened the rated length, which was taken from one girth to another. However, moving trhe transom forward also put the measurement on a fatter part of the boat, increasing the rated width aft and therefore pushing the rating back up. So placing the corner of the transom was a game depending on the exact shape of the hull underneath IIRC.

Have you guys seen Francis Herreshoff's designs for canters and inclined solid wingsail cats from the 1940s (IIRC)? Scary. Jim Young (famous NZ designer, who emplpyed a kid called Bruce) built one of Herreshoff's canters. I wonder where it is?

Well well I am Gary Underwood and own Fiery Cross the Herreshoff/young Ultimate Sailing Machine featured in The Commonsense Of Yacht Design. Now 50 years old and in perfect condition. Jim Young kindly copied some photos of her building. Great little boat!

[Paul B]

Well well I am Gary Underwood and own Fiery Cross the Herreshoff/young Ultimate Sailing Machine featured in The Commonsense Of Yacht Design. Now 50 years old and in perfect condition. Jim Young kindly copied some photos of her building. Great little boat!

Does the canting mechanism work?

If so, how? In Common Sense it is described as a worm gear mechanism.

[Gary Baigent]

Here is a quick drawing Jim Young drew to show the mechanism of the Fiery Cross canting keel. Incidentally FC was not the same beam as drawn by L. Francis Herreshoff; Jim Young increased it by a foot or so, still a very narrow boat.

[Paul B]

Here is a quick drawing Jim Young drew to show the mechanism of the Fiery Cross canting keel. Incidentally FC was not the same beam as drawn by L. Francis Herreshoff; Jim Young increased it by a foot or so, still a very narrow boat.


That looks nearly identical to the drawing in Common Sense.

[GAZZABO]

The canting keel was later(4-5yrs) fixed by Jim Young. He was not allowed to race with it! He has said there were balance issues with it as the cetre of lat. res. changed alot. Hence the dagger boards in the Volvos etc. However in the light it was devastating-- set the keel to LEEWARD the boat heals to leeeward the sails go to sleep, the keel vertical, nobody could keep up, this all in less than 5knots of breeze.
As Gary B says now has 7 ft of beam by 45ft by 6ft by 10600lbs.
I recently singlehanded down from the Bay of Islands- Cape Brett to Bream Head 44 n miles in 5hrs 25 mins Easterly (just forward of the beam) 1 reef full working jib 20knts reducing to 15 in the last 10miles
She is now on the hard having been wooded back and new paint job. Hopefully launching labour day.

[Paul B]

The canting keel was later(4-5yrs) fixed by Jim Young. He was not allowed to race with it! He has said there were balance issues with it as the cetre of lat. res. changed alot. Hence the dagger boards in the Volvos etc. However in the light it was devastating-- set the keel to LEEWARD the boat heals to leeeward the sails go to sleep, the keel vertical, nobody could keep up, this all in less than 5knots of breeze.
As Gary B says now has 7 ft of beam by 45ft by 6ft by 10600lbs.
I recently singlehanded down from the Bay of Islands- Cape Brett to Bream Head 44 n miles in 5hrs 25 mins Easterly (just forward of the beam) 1 reef full working jib 20knts reducing to 15 in the last 10miles
She is now on the hard having been wooded back and new paint job. Hopefully launching labour day.


Any chance you can post photos of the boat? It must be a blast to own such a piece of design history.

The Herreshoff design was only 6 feet on the beam and about 7500 lbs (IIRC), a good bit smaller than the Young version.

Whenever I read internet bulletin boards where nutters disparage lightweight boats, and try to invoke Herreshoff in their tirades, I crack open Common Sense and read what L. Francis really thought about boats. If he was designing today he would be happy to see the TP52s, Maxi Cats, and Open Class racers.

I wonder if most of the "heavy is good" bunch has ever actually read what he thought about designs based on, or mimicking, pilot boats and the like?

[GAZZABO]

Will need help with getting image-stand by!

[Gary Baigent]

Here's one - with owner Grunda rowing in the foreground.

[Paul B]

Here's one - with owner Grunda rowing in the foreground.

I am surprised to see the Masthead rig. For some reason I assumed a fractional rig like the Herreshoff version.

The house does have a NZ37 family look to it. I prefer the more minimalist look of the Herreshoff, but that wouldn't be useful for most people's idea of cruising.

I would love to see more photos from different views. That 7 foot beam on 45 feet length must look crazy. My little 28 footer with just over 7.5 feet beam looks skinny.

[Gary Baigent]

Three more Fiery Cross jpegs.

[Gary Baigent]

Thin layers of glued wood in dinghies had been developed by Dave Marks but it was Jim Young who first used this building technique in a large yacht by constructing a very advanced light displacement yacht with a canting keel (over 30 years ahead of its time). This yacht Fiery Cross was based on theorist drawings from L. Francis Herreshoff and was built in two layers of diagonally laid kauri planks that were glued along with countless copper fastenings, on deep stringers. “I was going against the grain using glues and double diagonals, it wasn’t the done thing, not the way any self respecting builder would approach a job,” said Young.
Working part-time while he built commissioned yachts in his Little Shoal Bay yard it took him five years to complete the yacht and Fiery Cross was not launched until late 1958 – coinciding with the launching of another light displacement yacht Ariel, a Scandinavian 30 Square Metre design by Knud Reimers, commissioned by Jim Lidgard. Ariel however, had been altered from original Reimers plans and had been lengthened to 50 feet and was carrying more lead “to wet the long overhangs.” Contrary to Young’s thin double diagonals that were glued and fastened, Ariel was built in three layers but also epoxy glued with the addition of metal fastenings. No-one then, trusted all glue, no metal.
“When Des Townson and I first sailed Fiery Cross,” said Young, with the keel unpinned (I sailed her after launching with it fixed vertically as if she was a normal keeler) we were very tentative, thought the boat would flop over to leeward and we gingerly went about the process of unlocking the keel. You have to remember that no-one had done this before – it was completely new territory for us. But there was no problem because of course, there was plenty of ballast even with the keel to leeward; it was just higher internally in the boat. We would sail gently along, unpin, the keel would swing leeward, we’d lock it then tack and the keel would be set up properly for the new board.
Compared to yachts of today Fiery Cross was shallow draft – 45 long x 7 ft 6ins beam x 6 ft 3ins draft – we didn’t know about these things then, really Fiery Cross should have had 9 foot draft. My idea was that the canting keel (we called it a pendulum keel) would make our narrow overall beam act as if it was eleven feet wide. But I have changed my mind now, narrow boats with a swing keel are not as fast as wide beam, form stability boats because there is not as much leverage with the narrow hull compared to that of the wide hull with its flared, shallow and flat bottomed hull.
Interestingly I felt that Fiery Cross sailed better to windward in light airs with the keel in the supposedly wrong place, flopped to leeward – that is because the keel was really vertical to the water surface and therefore making best use of the boat’s shallow 6 foot draft, the boat heeled over above it and the sails nicely to sleep and at their best shape. But set up this way we found we had weather helm - in those days I was experimenting with early New Zealand spade rudders and they were, we know now, too small (I still broke quite a few stocks) – then Fiery Cross wanted to go into irons and if we ended up in this position, we’d sit there feeling foolish, not going anywhere. Conversely with the keel canted to windward in light air conditions, Fiery Cross had lee helm and wanted to bear away. All this is obvious and commonsense today from what we have learned on sailboards, but then it was a different story. However because Fiery Cross was very narrow for its long length and even though the rudder was small, we didn’t suffer the broaching problems of the wide beamed Stewart 34’s. Fiery Cross’s canting keel was looked at aghast in those days and because officials considered the boat had moving ballast (it did) was therefore considered illegal. I wasn’t allowed to race the boat with the keel unpinned and some years later, when I sold Fiery Cross, the new owner wouldn’t have a bar of the swinging keel and demanded it be locked up permanently before he took over the boat.”

[GAZZABO]

Baigentes---- Thanks for stepping in to help with the pics. When you come up on the 11th show me how eh! By the way FX was glued with Resoircinal Glue, which Im pleased about as I trust it more than Epoxy. This year Ive also replaced back to (smaller) the 4 forward windows. They are now rabbetted with lam. glass ( how I hate looking thru Plastic). She was originally launched with the fractional rig, but changed to masthead alloy 41 years ago, the chap from Aitchesons rowed over last year and said he buitit and it was the first keeler mast they built.

[GAZZABO]

Fiery Cross pics

[GAZZABO]

More Fiery Cross pics.

[Brent Swain]

My last two boats had sharp V foreward sections. Like clipper bows ,they would drop deeply into a headsea then stop the boat suddenly when the buoyancy built up suddenly near the deck. They pounded like hell beating from Vanuatu to Fiji. For my current boat I put an extra 3 inches of outside curve in the foreward sections, and she glides thru a head sea much more easly and smoothly, without the sudden buildup of buoyancy foreard, without slowing down much.
Leaner bows and wider sterns drastically reduce a boat's directional stabilty and the ability to self steer downwind.
My last boat was far too wide in the stern and lean in the bows. She had little directional stability. For my current boat , I added three inches in the bows, and reduced the stern lines by three inches. The difference was huge . This boat will self steer, without the vane , on a broad reach in 15 knots of wind on the quarter.On all points of sail I can leave the helm free for far longer than I ever would have dreamed of in my last boat.
Brent

[White Knight]

Pardon a new guy buttin' in, but Superpiper's post (#131) hit a note I've been waitin' ta' hear. Like - what's being done to reduce drag? I've tried teflon based wax but didn't quantitate the results. It did feel sexy to be trying to be slippery! Seriously though, I've heard the Navy is interested in Bio-engineered shapes like the grooves on whale bellies and the dental patterns on sharkskin (have you seen them under a microscope?). Maybe similar results can be achieved with nano materials. We've used sandpaper too, to scratch long longitudinal grooves (it's supposed to hold minute bubbles on the hull). What about drag reduction in the rigging. Flying wires went out of vogue in airplanes long ago! Maybe struts inside the hull would help, or prestressed X-rods inside the mast. Perhaps, fabric hulls that can be reconfigured on the fly. Look guys, Wardi's project is a good if not perfected starting point. I've been soppin' up the free education and ya' know, work such as his must be carried out to establish baselines from which to measure further advances -- or we might as well all save $ and just sail old boats.

[White Knight]

Saeble, For another option for kite sails see: http://www.kiteship.com/index.php. It seems that they had a more affordable and prettier product. I have no relationship with these guys either. Mark

[CT 249]

Pardon a new guy buttin' in, but Superpiper's post (#131) hit a note I've been waitin' ta' hear. Like - what's being done to reduce drag? I've tried teflon based wax but didn't quantitate the results. It did feel sexy to be trying to be slippery!

DONE IN THE '60S, IIRC - NO SIGNIFICANT ADVANTAGE

Seriously though, I've heard the Navy is interested in Bio-engineered shapes like the grooves on whale bellies and the dental patterns on sharkskin (have you seen them under a microscope?). Maybe similar results can be achieved with nano materials.

DONE IN THE '80S - NO SIGNIFICANT ADVANTAGE

We've used sandpaper too, to scratch long longitUdinal grooves (it's supposed to hold minute bubbles on the hull).

DONE IN THE '70S - LITTLE SIGNIFICANT ADVANTAGE

What about drag reduction in the rigging.

What about drag reduction? It's been a goal of designers for decades. There were fully aerofoil rigs and rigging in the '30s. Even some IMS boats had freestanding rigs.

It's not normally a huge advantage.



Flying wires went out of vogue in airplanes long ago!

A world-famous aerodynamacist, who is sometimes here, has posted on other forums about how airplane pilots would love to have the incredible adjustability of a conventional stayed IACC rig, with its amazing ability to adjust depth, twist, and angle easily.

He's set world flying records yet he seems to say that boat rigs work well and that lessons from planes cannot always be transferred to boats.

Maybe struts inside the hull would help,

DONE IN THE '70S

or prestressed X-rods inside the mast. Perhaps, fabric hulls that can be reconfigured on the fly.

FABRIC HULLS? 1920S. RECONFIGURABLE? 1980S, 2000S. FASTER? NO.

Look guys, Wardi's project is a good if not perfected starting point. I've been soppin' up the free education and ya' know, work such as his must be carried out to establish baselines from which to measure further advances -- or we might as well all save $ and just sail old boats.

People have been trying all sorts of stuff for many years. Some of them look at what is actually working and compare it to what some theories say should work, and assume that the theories are right and the practice is wrong.

Maybe it's the other way around? Maybe it's not that sailors and designers are closed-minded and ignorant. Maybe what actually works, out there on the water, is what actually works?

And even where rules are restrictive, maybe that's because most of the classes that succeed have restrictive rules. The rules may not be the enemy of progress, they may be the thing that actually keeps the sport alive so that progress can be made.

[PI Design]

I think the rules are often inconsistant, which is as much due to the history behind them as anything else. There are many ideas that could be explored with double skinned sails, masts, swing rigs etc that are penalised or outlawed, yet canting keels and exotic materials are allowed.
Applying aeroplane theories to boats is fraught with problems. For a cruising boat a wireless rig may be a good idea, but the wires do add a degree of control and adjustement that is impossible with a simple cantilevered mast. Horses for courses and all that...

[gggGuest]

double skinned sails, masts, swing rigs etc that are penalised or outlawed, yet canting keels and exotic materials are allowed.
No and no... All the things you list are allowed in some boats but not in others...
The big challenge with radical ideas is that the bar to success is so very high...
Lets say, perhaps conservatively, that current Skiff type dinghy rigs, which wave far too many wires about in the air for me to be truly content with, are developed to 90% of their potential speed.
Now, supposing I come up with an idea that has the potential to be 15% round the track, which is a pretty substantial jump... I have to get that idea operating to nearly 80% of its potential before it will break even with the current state of the art.
That really is a pretty big ask...

[PI Design]

I totally agree with you, and that is sort of the point i was trying to make. Swing rigs are obviously allowed in cruising boats, but ISAF rules require the jib tack to be nrear the centreline. Consequently, no one has seriously developed the concept and the Aerorig etc probably are only 60% of their potential. Sure there are some racing classes that ignore some ISAF rules, but they are the exception.
I think the fact that, fundamentally, all A Class cats look the same, all Moths look the same, all 18' skiffs look the same, all NS14s look the same etc, is not necessarily because they have evolved to the optimum configuration, but because it is much easier to tweak an existing idea than to create a competitive radical design. The single sailed DCs, for example, have potential but haven't yet proven themselves faster. Will they stick with the una rig and develop it, or switch back to the tried and trusted bermudan rig?