What would you do with 40 sqm/430 sq' of sail?

[rob denney]

Have you ever wondered what the fastest rig and hull would be if there
was a limit on sail area, but everything else was open? cat, tri, foiler,
planing mono, canting keel, sloop, cat rig, kite, etc, etc. As far as I know
there has never been a class with the only rule being sail area, apart from the very specialized Speed Week boats.

I would like to propose one.

Sail area, (including spars) is 40 sqm/430 sq'. Everything else is open.
The sail area is low to keep costs down and encourage efficiency
and innovation.

The purpose of the rule is to find the fastest, most efficient boat and
rig type with this sail area both around the buoys and offshore.

I would like to propose 2 courses, although there is no reason why there
could not be others before or after, or at different locations.

First course: A race 3 times around an approx one mile diameter circle on
San Francisco Bay using government buoys and a gate or rabbit start. This
format requires no yacht clubs, committees or outside assistance. Although a yacht club or similar for pre and post race discussions would be welcomed. There could also be more than one race to vary the weather conditions and increase the fun.

The race will be organised by email. Everyone on the mailing list will be
told the buoys, what the rabbit boat looks like and where and when it will
be starting. Email your finishing times and excuses at the end of the
day.

No entry fee, no prize, no protests, no measurement or handicap nonsense.
Just a bunch of boat owners sailing round the bay as fast as they can and
talking about it afterwards.

Of course, if a sponsor or yacht club wants to come along and
organise/complicate it, so much the better.

Race day is a fortnight before the solo Transpac in June 2008.

Second Course: The solo Transpac 2008. Boats will need to comply with
the SSS NOR and Sailing Instructions.
http://www.sfbaysss.org/TransPac/transpac2006/index.html

Two such totally different race formats would be a great test of what is
fast and what is not in a variety of conditions. Boats could be optimised
for and enter either, and this is to be encouraged as the more data
points, the more we find out. However, for most people, the real interest will be in the boat that can do both well.

Please feel free to discuss what sort of craft you would design, but more importantly, start building it to see if you are correct.

regards,

Rob Denney

[waikikin]

Rob, so, what craft are you bringing to the start line? Just need to know what we'll be up against before puttin the $ where our mouths are & trash talkin' our undoubted speed potential on the course & developing a great range of post race xcuses for not bringing home the glory, I reckon you've gotta have a TROPHY & propose that some piece of bashed up boat be burnt & put in a jar (Vegemite) so the victorious can hold it aloft after shooting champers all over the other competitors from the podium.Seriously though its a nice pure concept that could have all manner of craft competing especially on the inshore course. Regards from Jeff.:)

[Doug Lord]

Rob, I think it would be exciting to consider the design of a boat with the only limitation being 430 sq.ft. of sail. That's right in the range of many sportboats around 24'.
But SA is not the only restriction in your proposal: you've introduced the requirement, if I'm reading it right, that the boat has to be solo sailed; is that right?
It could get real interesting if the limit was really just 430sq.ft. SA and ,in my opinion, might produce boats with wider appeal.
I couldn't possibly afford to build one in either case but it sure is interesting to contemplate...

[roeslerjd]

To me... small boat + big sail = lost of speed. Basical like early race cars... most powerful engine, and a small light car and make it pointy on both ends.

So I would use the full sail area.. as little boat as possible, make it thin and long... and a long heavy keel to keep it up right.

[gggGuest]

There's been planty of such classes in the past. The 30 Square metre for one... http://www.30sk.com/fotos/index.html Long thin and light with tall rigs would be the way to go. Of course for ultimate speed a catamaran would be quicker.

[rob denney]

G'day,

Jeff,
Would love the opportunity and excuse to burn dsome of the bits out the back, but there is no need for a trophy, this is just for fun and interests sake. Glad you like the idea.
My boat will be a 15m/50' proa which should weigh 500 kgs/half a ton on the start line, considerably less for the round the buoys stuff. Cost about $AUS18,000/$US13,000 and be very simple to build. Windward hull is nearly complete, weighs 27 kgs with the bunk and a shelf to add. Waiting for some carbon to finish the rest of the boat.

Doug,
The sail area is the only rule for the boat. Each course will add it's own constraints, whether it be crew sizes, bouys to round or whatever. The round the buoys race is for as many crew as you want.

Personally, I think the more the merrier. If boats with slightly more or less sail want to race, they are welcome. Equally, if someone wants to "race" in company with the solo Transpac in a crewed boat, they are welcome. There is also nothing to stop other courses and formats being used. I chose these two formats to start with as they are as different as they could possibly be, so will give more data points about which is the fastest set up. And because I am doing the solo transpac so will be in SF at the time.

gggGuest
The sqm rules were an attempt to do this, but it failed to do so. http://www.sitecenter.dk/hbh/brugerdefinerethtml/ Didn't fail as a class, they are hugely popular and lovely boats to sail. They were also restricted to monohulls, I am more interested in ultimate performance, which includes monos, cats, tris, foilers, different rig configurations etc.

regards,

Rob

[CT 249]

Didn't the square metre boats, like the Suicides, Frei Renjollen and (I think) D CLass cats also suffer from the fact that unrestricted length classes tend to hit an area of diminishing returns?

As far as I can see, the best boat for a fixed sail area tends to be very, very long - which means you can often end up with a boat with a massive hull and a comparatively tiny rig. It will beat the boats in its sail-area class, but it can be slow for its length, bulk and expense. That is, after all, why the classes listed above all ended up putting dimensional limits. The 22 square metres ended up at something like 42 feet long, and as far as I can find out while they look beautiful they are pretty damn slow for a 42 foot long racing machine, or any boat of their price. That's why the 22s and (I think) 30s ended up with restrictions, and in fact ended up with two classes; a long expensive boat and a shorter, cheaper but only slightly slower boat.

This is not meant to be throwing cold water on a very interesting idea, it's just that there have been problems when this has been tried before.

I'd love to see what comes out of the concept, Rob. Sounds like a VERY interesting boat.

[rob denney]

Didn't the square metre boats, like the Suicides, Frei Renjollen and (I think) D CLass cats also suffer from the fact that unrestricted length classes tend to hit an area of diminishing returns?

As far as I can see, the best boat for a fixed sail area tends to be very, very long - which means you can often end up with a boat with a massive hull and a comparatively tiny rig. It will beat the boats in its sail-area class, but it can be slow for its length, bulk and expense. That is, after all, why the classes listed above all ended up putting dimensional limits. The 22 square metres ended up at something like 42 feet long, and as far as I can find out while they look beautiful they are pretty damn slow for a 42 foot long racing machine, or any boat of their price. That's why the 22s and (I think) 30s ended up with restrictions, and in fact ended up with two classes; a long expensive boat and a shorter, cheaper but only slightly slower boat.

This is not meant to be throwing cold water on a very interesting idea, it's just that there have been problems when this has been tried before.

I'd love to see what comes out of the concept, Rob. Sounds like a VERY interesting boat.

G'day,

Answering these questions is the reason for the rule. My take on it at present is:

Those are all long keeled boats where the point of diminishing returns occurs relatively early. It has not been tried on fast boats, apart from speed week designs, which are pretty specialized. We have huge experience with what works on boats which are overcanvassed for their length. We have no idea of where the limits are for fixed sail area boats. We cannot even agree on what hull type would be fastest, much less how long it should be.

A fixed sail area boat will be slow for it's length compared to the same length boat with unrestricted sail, but why should length be more important (apart from marina fees) than sail area or weight? The long boat will have a nicer motion, be more seaworthy and easier to sail, all else being equal. It will also be much cheaper.

A long hull does not need to be massive. There are structural arguments (related to shell buckling) for smaller cross section hulls and if we get away from the need to have high bows to keep the foredeck dry, then a long hull can have a very low bow. This is more pertinent to multis, but also applies to monos.

Chris, I don't suppose you find it interesting enough to sell some of your fleet and have a go? Base it on your knowledge of boat history and what has worked and what has not and it would be a fascinating boat.
-
regards,

Rob

[Doug Lord]

Sure would be interesting to see what a two person bi-foil mono or multifoiler would do...
It's completely feasible to do such a boat using this sail area between 22-24' with upwind foiling capability in a wide range of conditions.Hmmmm...

[PI Design]

CT249 - Rating a boat's speed as a function of its length is only one way to skin the cat. If two boats , A and B, are the same speed and boat A is 10m long with 20sqm of sail, and boat B is 5m long with 30sqm of sail, I would consider boat B to be slow for its sail area, not boat A to be slow for its length.

Anyway, for the race round the cans, I think I'd go for a supersized C class cat.

[sharpii2]

Hi All:

I would add another stipulation: A cost limit of 10,000 Euros per square meter.

BTW, does this sail area limit apply to 'all sail set' or merely to 'all working sail'.
Extra points should be awarded for creative cheating.

I would expect a fair fight between multihulls and canting keelers. I understand that San Francisco bay can get quite rough at times and I don't know how well foilers like rough weather.

Has a foiler ever crossed an ocean?

Bob

[sharpii2]

Didn't the square metre boats, like the Suicides, Frei Renjollen and (I think) D CLass cats also suffer from the fact that unrestricted length classes tend to hit an area of diminishing returns?

As far as I can see, the best boat for a fixed sail area tends to be very, very long - which means you can often end up with a boat with a massive hull and a comparatively tiny rig. It will beat the boats in its sail-area class, but it can be slow for its length, bulk and expense. That is, after all, why the classes listed above all ended up putting dimensional limits. The 22 square metres ended up at something like 42 feet long, and as far as I can find out while they look beautiful they are pretty damn slow for a 42 foot long racing machine, or any boat of their price. That's why the 22s and (I think) 30s ended up with restrictions, and in fact ended up with two classes; a long expensive boat and a shorter, cheaper but only slightly slower boat...

Up to about the 1930's, '40's, or maybe even '50's, I would agree. But since then we have gotten down wind planing, light fast multihulls, canting keel monos (that , I understand, can plane upwind), and now foilers. None of which really long length is going to help that much.

I would almost expect a trend toward the other end of the length spectrum (20 to 30 footers).

Bob

[gggGuest]

Up to about the 1930's, '40's, or maybe even '50's, I would agree. But since then we have gotten down wind planing, light fast multihulls, canting keel monos (that , I understand, can plane upwind), and now foilers. None of which really long length is going to help that much.

Length seems to be paying mightily with the big round the world catamarans which are the fastest distance boats on the planet. And even on the speed 500m it did awfully well with the likes of Crossbow up to the 70s.

If you add to the rules that a boat must finish both events to qualify then I'd be very suprised if a long light catamaran wasn't the winning craft.

[CT 249]

Rob, I'm afraid selling the full fleet wouldn't pay for the mast! :-)

I have to admit that I regard development design as a fascinating spectator sport these days. In some very small ways I've done one recent "design conception" (putting a small rig on the WIndsurfer One Design to make a junior class) and while it was hardly original or complex, it means I'm now busy running a class and training sessions! It's also been interesting to see how a big "hull" and small rig copes. Even in boards the same rules often seem to apply; big hulls with little rigs make for plenty of speed proportionate to rig size.

I do reckon your idea could be a great class, and probably way better than just limiting LOA which is a pretty ancient idea.

PI, I fully agree that speed-for-length is only one way to measure a boat's performance, and that short boats with big rigs as often pretty innefficient in many ways.

All I was saying is that historically, classes with only sail area restrictions have tended to end up creating boats that were quite slow for their length and cost, compared to more moderate boats.

What's the best boat?

Boat A at 10m and 20sq m?
Boat B at 5m and 30sq m?
Boat C, at 7 m and 25 sq m? (Perhaps cheaper AND faster than A or B)
Boat D, 20m long and 20 sq m? Perhaps it would beat Boat A and win the 20 sq m class, but be so large and overcanvassed for its length that it would be dull to sail and expensive to own.
Boat E at 5m and 50sq m? It would beat boat B but cost waaaay more and be harder to sail.

I ran some figures once that indicated (from memory) that on a straight proportion of speed-for-sail basis, the most efficient (non foiling) dinghy of them all was the Laser 4.7. The standard Laser, on that basis, is arguably more efficient than the non-foiling Moth, I think. I bet a Laser 4.7 is faster on a speed-for-sail basis than a foiler Moth in many conditions and possibly overall; but which is more exciting? If you were to design a new boat to achieve maximum speed-for-sail, would you end up with something with a giant hull for its rig which may not be cheap or really exciting?

So I'm basically just wondering - does the totally unrestricted route (whether it's sail area or LOA) end up with the fastest possible design for those specifications, but at the cost of ending up in the area of diminishing returns? I'm not saying Rob's boat will end up being a boring or expensive boat, merely wondering about where the class could end up. We often see the faults in the boats we have, and then look at possible alternatives with rose-coloured glasses.

I don't mean to be attacking Rob's concept (which is a good one) merely to be trying to foresee problems that could perhaps be avoided. Since every rule or class gets pushed in unexpected areas, wouldn't it be a good idea to seek possible flaws and weaknesses so that they could be plugged as soon as possible?

Sharpii, maybe length is still vital these days, depending on what conditions and fleet you sail in. The 18 Foot Skiff designers reckon an 18 "should" be about 22 feet long, and the optimum length would only get longer as technology (read expense) increases. The foiler Moths use stern gantries to maximise effective LOA to spread their footprint. Nigel Irens reckons the 60' tris are too short for their rigs.

Even in windsurfers, the Formula boards (about 8kg, 12.5sq m of sail, about 7' long) are often much slower than the old IMCO Raceboards (16kg, 7.4 sq m of sail, 12'6" long) or even an original Windsurfer. On a speed-for-sail basis, a 5m rig on one of the old 15' "Dart" U-bottom displacement windsurfers would normally probably win; but with no restrictions it would be an incredibly expensive board and rig and very difficult to sail in any conditions.

Please note again, this is not meant to be attacking the proposed class. Any class has some areas where it's less than perfect; the one I launched a while ago has many and varied flaws, but it still seems to be working.

[Doug Lord]

Hi All:

I would add another stipulation: A cost limit of 10,000 Euros per square meter.

BTW, does this sail area limit apply to 'all sail set' or merely to 'all working sail'.
Extra points should be awarded for creative cheating.

I would expect a fair fight between multihulls and canting keelers. I understand that San Francisco bay can get quite rough at times and I don't know how well foilers like rough weather.

Has a foiler ever crossed an ocean?

Bob
-------------------
Bob, Williwaw did a lot of ocean cruising but I don't have time right now to research it further; more info may be on Tom Speer's site.
DAK HYDROFOILS - Williwaw
Address:http://wingo.com/dakh/williwaw.html Changed:6:10 PM on Sunday, May 8, 2005
----------------
I'm convinced that a well designed "sportboat" foiler would win this contest hands down at least in inshore racing. Because of the SA the foiler would have to be fairly small which would probably impinge on it's ability in a transpac type race.
But a canting keel foiler could be built-not too much larger- to do the job in a configuration that would make the boat rightable in the event of a capsize or pitchpole...
Under Robs' rules I think his boat is the most likely to succeed in a transpac type event.

[rob denney]

[QUOTE=sharpii2;113399]Hi All:

I would add another stipulation: A cost limit of 10,000 Euros per square meter.

BTW, does this sail area limit apply to 'all sail set' or merely to 'all working sail'.
Extra points should be awarded for creative cheating.

G'day,

Cost limits are impossible to enforce and can seriously impinge on the results. If someone can build a solid wing sail boat capable of crossing an ocean, I would like to know about it, regardless of cost. However, it would be nice if builders kept records of their costs as it gives everyone more data points. 10,000 euros per sq m would be nice. My budget, including shipping it and flying me to San Fran is $AUS40,000/24,000 Euros, or 600 Euros per sq m

Sail area is actual sail area used to propel the boat, including spars plan view area, as per the IYRU rules. If you can cheat on this, go ahead.

CT249: "I don't mean to be attacking Rob's concept (which is a good one) merely to be trying to foresee problems that could perhaps be avoided. Since every rule or class gets pushed in unexpected areas, wouldn't it be a good idea to seek possible flaws and weaknesses so that they could be plugged as soon as possible?


Of course, but I don't necessarily expect this to be a long lived class, just looking for some answers to what is quickest when only sail area is measured. Looking at the suggestions so far, it is pretty obvious that there is a pretty wide spread of ideas (and we have not got into sail plans or actual lengths yet), so building and sailing some options could be beneficial.

regards,

Rob

[SuperPiper]

Somewhere on this forum was a statement that the most efficient sailboat would be a submarine with a parasail.

So, you could foil above the water with Doug or slide under the water with Neptune. Or maybe a submarine for displacement sailing and retractable foils for when the wind got up would be the optimum combination.

Is the TransPac a downwind run?

[Doug Lord]

This concept won't leave me alone-it is fascinating! I've just done a bunch of research showing that a 24' 2 or three person sportboat foiler is possible using weights from existing boats as a reference point. Since a monohull "sportboat" is a keelboat the two boats I came up with used a 490 lb. canting keel with close to 600sq.ft. of sail.
But after re-reading what Rob is achieving weight wise with a 50 footer it has occured to me to look at the foiler as a multihull instead of a ballasted monohull(which I'm convinced will work).
I was thinking of something like Kotoro Horiuchis "Winged Trimaran":
ImageShack - Hosting :: img0289fy2.jpg
Address:http://img64.imageshack.us/my.php?image=img0289fy2.jpg
But then, in taking a cue from Rob-sort of- I thought that maybe one of the two trimaran hulls could be removed so ,in essence, off the foils the boat would be a proa but different from Rob's in that the rig would still be in the mainhull and the mainhull would have racks extending outward around 9'(wrong ,see below) on one side; the other side the same but with a small ama(actually the rack on the side opposite the ama would have to be slightly longer to compensate for the weight of the ama when the crew is at max beam-I think). This would allow a multifoiler sailing on just two foils- like Koriuchi's boat- only scaled up to maybe 25-28' or so. Using the same techniques Rob is using to build a 1000lb"at the starting line" 50 footer and getting rid of the "sportboat" ballast this thing could be built light enough for minimal accomodation-probably-while still having the numbers for upwind foiling. Of course, the ability of the sportboat foiler to be righted might be lost but that's not for sure: it might be possible to design a righting system.
The downside may be requiring two crew but the more I get into this the more I think that some form of sliding waterballast tank could be used to singlehand this proafoiler*.
So, basically you have a singlehanded(with some form of movable ballast) or doublehanded boat with an unstayed 430sq.ft. camber induced square top main only rig. You have a main hull with minimal accomodation and racks on each side. For stability off the foils you have a small ama on one side only. And if brilliance prevails in the final design a fairly lightweight righting system is included.... Yes!
==================================
I couldn't resist doing some numbers for the "sorta proa foiler"*:
--LOA 28'
--LWL 28' (off foils)
--Beam 27'(I guessed wrong above)
--SA 430 sq.ft.; unstayed camber induced square top rig.
--Displacement 1028 lb./467.27 kg. incl. 320lb./145.45 kg crew or 160lb/72.7kg. crew + 160 lb movable water ballast or any combination thereof not to exceed 320lb./145.45
================================================
1) all up sailing weight of boat minus crew:
708lb./ 321.8kg. "on the start line"
================================================
--Foils
1) area 5.2 sq.ft/.48sq.m main foil ; 2.6 sq.ft./ .24sq.m rudder foil
2) Loading: 158 lb per sq.ft./ 772kg. per sq.m main foil
3) Sq. ft. SA per sq.ft. mainfoil area: 82.6
166sq.m Sa per sq.m foil area.
NOTE: these targets,if achieved, would produce a foiler with exceptional upwind and downwind speed.These power and load figures are almost identical to the Foiler Moth.

---------------
Rob,do you think a 28' "sorta proa"* could be built at 708 lb/321 kg. ? UPDATE: I e-mailed Rob with this question. His response was a rough estimate of 440lb/200kg. My own rough estimate for the boat is 395lb./179.5kg.
This boat would be somewhat slow off the foils or in conditions where the thing bottomed out.
---------------------------------
* This boat is probably more a trimaran minus one ama than it is a proa since it would tack normally-not shunt. The one ama is removed just to save weight but it might be easier to sail off the foils with two small amas and the extra- very small ama- would not add too much weight.

[sharpii2]

Length seems to be paying mightily with the big round the world catamarans which are the fastest distance boats on the planet. And even on the speed 500m it did awfully well with the likes of Crossbow up to the 70s...

I would agree. But aren't they allowed unlimited sail area?

It's when you are limited in sail area, the tough choices start adding up.

Once the boat is long enough not to trip over its own bow (longer for multis than monos, I might say), the cost of extra length will start to add up fast. For any given matterial choice, a shorter boat of the same Beam will be lighter than a longer one of the same Beam and matterial.

Once you get a boat to plane properly, short length is no where near the handicap that it was in the days of non planing boats.

If you are free to add sail along with length, even if the additional sail area is small in proportion to the added length, the longer length will again start to pay off.

I will say this, though. The canting keel mono will probably be shorter than the multi. This is because the multi doesn't need to plane to go fast and, to a point, is rewarded for extra length by extra finess of the hulls. But, even then, diminishing returns will start to come in fast. The longer hulls will soon start adding unwanted wetted surface, making light weather sailing, one might say, a real drag.

Meanwhile, the canting keel mono would be planing most of the time and sailing at or near hull speed when she is not.

Bob

[CT 249]

"Once you get a boat to plane properly, short length is no where near the handicap that it was in the days of non planing boats."

Short length may not be as big a problem, but it's still a massive handicap, isn't it? Apart from everything else, it tends to ensure that a boat has a harder time getting up to planing speed (fatter entry angles for the same displacement, higher DLR= higher form drag, hits the "hump" before it gets planing, etc).

Look at skiffs. The 12 Foot Skiff has a 45kg hull, both crew on traps, 20sqm of upwind sail and a 50-55sq m assy. The 14 Footer has a 68kg hull, about 20 sq m of upwind sail, and a 30-35 sq m assy, and racks for two crew on trap. The 16 Foot Skiff has a 68kg hull; 22 sq m of upwind sail; and a 45 sq m assy. One of its three-man crew isn't allowed to trap.

So the 12 has by far the best ratios in many ways, yet it seems that it is no faster around a course than the 14 or 16; probably slower in fact. The 16 has by far the worst ratios in many ways, yet it's thought to be at least as fast as the two shorter skiffs. The skiffies recognise that length is speed.

All of the recent 18 Foot Skiff designers reckon they'd be faster at 20' or more, yet 18 Foot Skiffs are the ultimate planing dinghy. The 49er and 29er are very long boats for their roles, because Julian feels that's the best way to design a boat - yet the 49er planes pretty well. Julian actually feels that an ideal two-man boat is actually longer than the 49er - 5.3m (17ft6in).

The only really short and really fast planing machine I can find is the windsurfers, and even the Formula boards are very restricted in their performance band; they can be short because they don't race in light winds.

[sharpii2]

"Once you get a boat to plane properly, short length is no where near the handicap that it was in the days of non planing boats."

Short length may not be as big a problem, but it's still a massive handicap, isn't it? Apart from everything else, it tends to ensure that a boat has a harder time getting up to planing speed (fatter entry angles for the same displacement, higher DLR= higher form drag, hits the "hump" before it gets planing, etc).

Look at skiffs. The 12 Foot Skiff has a 45kg hull, both crew on traps, 20sqm of upwind sail and a 50-55sq m assy. The 14 Footer has a 68kg hull, about 20 sq m of upwind sail, and a 30-35 sq m assy, and racks for two crew on trap. The 16 Foot Skiff has a 68kg hull; 22 sq m of upwind sail; and a 45 sq m assy. One of its three-man crew isn't allowed to trap.

So the 12 has by far the best ratios in many ways, yet it seems that it is no faster around a course than the 14 or 16; probably slower in fact. The 16 has by far the worst ratios in many ways, yet it's thought to be at least as fast as the two shorter skiffs. The skiffies recognise that length is speed.

All of the recent 18 Foot Skiff designers reckon they'd be faster at 20' or more, yet 18 Foot Skiffs are the ultimate planing dinghy. The 49er and 29er are very long boats for their roles, because Julian feels that's the best way to design a boat - yet the 49er planes pretty well. Julian actually feels that an ideal two-man boat is actually longer than the 49er - 5.3m (17ft6in).

The only really short and really fast planing machine I can find is the windsurfers, and even the Formula boards are very restricted in their performance band; they can be short because they don't race in light winds.

I agree entirely.

What I meant by shorter length was moderately shorter. Going too short will have its own accumulation of negatives (which I think you have laid quite well), just as going too long will. I don't think this would go anywhere near the extremes that the old 'square meter' classes went, an extremely long, canoe like hull that was mostly ballast topped with a, relatively, tiny rig.

Anorexia is the main abuse I would predict under these proposed rules. Lighter is, after all, almost always faster.

I'll shoot from the hip here and predict that the canting keel monos will end up in the mid twenties length wise and the multis will end up in the low thirties.

Both types will be almost obscenely fast in moderate to strong winds. On a windy day, your typical planing cabin cruiser would have to work hard to keep up.

Bob

[gggGuest]

I don't think this would go anywhere near the extremes that the old 'square meter' classes went, an extremely long, canoe like hull that was mostly ballast topped with a, relatively, tiny rig.

Why not?

And why do you think anyone would try a canting keel monohull? Why drag your ballast to one side in high density water as a canting keel mono when you can drag the ballast to one side in low density air as a catamaran?

Obviously you can go too long: as well as structure weight wetted area also goes up, but all the evidence is that too long is very long indeed. Beam might
be quite an interesting variable though, with the desire to fly a hull contesting with the desire for extra righting moment, as the craft would certainly be running a very moderate sized rig for its size.

An interesting corrollory to the claim that a sail area limited craft would be large and most especially long for its size is the observation Chris (CT) has made elsewhere which is that adding sail area seems to be a remarkably ineffective way to make a boat go faster. Consider: if the craft is underpowered you need an awful lot more rag to make much difference, and if its overpowered the extra rag slows it down...

[sharpii2]

Why not?

And why do you think anyone would try a canting keel monohull? Why drag your ballast to one side in high density water as a canting keel mono when you can drag the ballast to one side in low density air as a catamaran?

Because the windward hull is not only going through the air. It is often plowing through head seas as well. Along with its bulky connecter beams and/or bridge deck. Also, a canting keeler can be made self righting without severely compromising its performance. A multihull can't. I see both approaches as equally viable, though. Hence the prase 'fair fight'.

Obviously you can go too long: as well as structure weight wetted area also goes up, but all the evidence is that too long is very long indeed. Beam might
be quite an interesting variable though, with the desire to fly a hull contesting with the desire for extra righting moment, as the craft would certainly be running a very moderate sized rig for its size.

I think the ultimate length trade off will be some factor of the square root of the sail area combined with some factor of the CA of the rig. Because the canting keel mono can now be reliably expected to plane, I just don't see a lot of extra length being much help. This is, of course, assuming all the boats will be made out of the lightest matterials possible.

An interesting corrollory to the claim that a sail area limited craft would be large and most especially long for its size is the observation Chris (CT) has made elsewhere which is that adding sail area seems to be a remarkably ineffective way to make a boat go faster. Consider: if the craft is underpowered you need an awful lot more rag to make much difference, and if its overpowered the extra rag slows it down...

This is a very interesting concept, but I think here it is being taken a bit out of context. That is unless you have been reading different yachting journals than I have. It seems to me that in just about every case, from Bahaman keel boats that wouldn't plane if you paid them to, to Open 60's, that do plane quite frequently, crowding on the canvass improves average speed if not peak speed. The only exception to this I have seen is when the amount of canvass routinely exceeds the initial stability of the boat in question. Then the extra sail area, along with the longer spars to carry it, become a real drag. My own off shore design has a relatively tiny rig for this reason.


As always, I appreciate a lively debate.

I think a 'sail area only' would be a wonderfull laboratory for boat design in this age of planing and super hull speed sailboats.

I'm afraid that only when the actual full sized boats are built and tested will our competing contentions be validated or debunked.

BTW, how long do you think the boats would be under this rule?

Bob

[PI Design]

I'd go for:

Monohull - 35-40'
Catamaran - 28-32'

So, I'm with you on the cat, but I'd have a much longer monohull. For me length is still king, until the point where the extra weight is counterproductive. I reckon the cat would win 9 out of 10 races between the two though.

[rob denney]

[QUOTE=PI Design;114004]I'd go for:

Monohull - 35-40'
Catamaran - 28-32'

G'day,

Add proa at 50' For details, see http://www.harryproa.com/SoloTranspac/SoloTranspac_1.htm

regards,

Rob

[Doug Lord]

Rob, an absolutely brilliant design!

[sharpii2]

I'd go for:

Monohull - 35-40'
Catamaran - 28-32'

So, I'm with you on the cat, but I'd have a much longer monohull. For me length is still king, until the point where the extra weight is counterproductive. I reckon the cat would win 9 out of 10 races between the two though.

I'm surprised that you would make the mono longer than the multi. It seems, from all I've read, that it is the multi that would most benifit from longer length.

First, they don't generally plane, so the added length increases the Length/ Beam ratio, making it easier to push them through the water, with absolutely no sacrifice in initial stability (because stability in multis comes from distance between hulls, not the beam of the individual hulls)

Second, multis tend to stuff the lee bow when driven hard, often causing them to flip over end to end. As the boat gets bigger, weighing in at thousands of pounds rather than hundreds of pounds, it becomes harder and harder to over come this problem wit crew placement. Moving the rig aft, or extending the bow (making the boat longer) is said to help out a great deal in this regard.

As for canting keel monos, consider the Mini Class, with it's mandated length at around 21 ft. Some I have read about carry as much as 500 sft of sail. They resemble high sided cat boats and, IIRC, have attained speeds at least in the high teens. Now, supposing I take one of those and extend the bow out about six or seven feet, but leave everything else unchanged. I will now have a hull that will split waves cleanly as well as plane readily.

Why go longer?

Bob

[Doug Lord]

I know that most people view the on- going monofoiler/bi-foiler revolution with some skepticism as to applications bigger than dinghies
despite the fact that the size of working monofoiler/bi-foiler's has grown each of the last 3-4 years. It is still a developing technology with a long way to go.
But I know for a fact that there is serious interest from at least one well known Australian sailor in developing a boat similar to the boats in the Sportboat thread.Whether he goes ahead or not is still up in the air, so to speak.
In this thread I proposed a "multihull" bi-foiler in a previous post-in essence an unballasted trimaran. In fact it is very similar to the boats in the Sportboat thread minus the canting keel and with lower sail area.
You can talk planing hulls or multihulls but as long as the hull is still in the water the very experimental bi-foiler has a tremendous potential advantage: over 20/1 sail area to wetted surface ratio on foils! And around 4.4/1 off foils. I don't think any existing boat can touch numbers like the foil borne number-not even close.
I would think a boat along these lines will be sailing sometime in the next couple of years or so. Of course, a lot of questions remain and a lot of development will have to be done to make something like this work at anywhere near it's potential-but watch out when it does.
---------------------------
From a solo transpac perspective I think Robs harryproa has the edge even on a well developed and designed bi-foiler particularly since it is the first self-righting multihull that I know about.....

[PI Design]

Sharpii,

My logic was as follows:

A cat with 40sqm of sail is not much more than a C Class, or even a Tornado. I basically scaled from these, figuring that they are proven to work well. These hulls already have a very high slenderness ratio and I don't see much advantage in going any slenderer. You do need a bit of length in front of the mast to help prevent pitching, but I reckon that 15ft should be enough for this. Any more is unneeded weight and design complexity.

The mono on the other hand needs to go one of two ways to improve performance. Either plane early, or have a high 'hull speed'. If going for the planing option, a shorter hull could be used, but performance will suffer in sub-planing winds. Going to extremes, an Int 14 probably has more than 40sqm of sail going downwind, but would not win this proposed event ( a standard beach cat would beat it). To my mind, this suggests that the short, light planing hull does not have the all round performance to win.
So the alternative is to go for a design with high 'hull speed'. As we all know, hull speed is primarily a function of length, but also of slenderness, DLR and a number of coefficients of form. I therefore believe that a relatively long hull can help significantly, up to the point where beam and/or draught have to be reduced (to maintain a constant displacement) to a level where stabilty and motion suffer.

Of course, I could well be wrong, but that's my thinking.

[lewisboats]

So the alternative is to go for a design with high 'hull speed'. As we all know, hull speed is primarily a function of length, but also of slenderness, DLR and a number of coefficients of form. I therefore believe that a relatively long hull can help significantly, up to the point where beam and/or draught have to be reduced (to maintain a constant displacement) to a level where stabilty and motion suffer.

Of course, I could well be wrong, but that's my thinking.

I think that's been done...witness the "Plank on edge" boats around the end of the 1800s

Steve

[PI Design]

So has short and fat. Designing sailboats is the second oldest profession, there's not much hasn't been tried before.

[Stephen Ditmore]

Sure would be interesting to see what a two person bi-foil mono or multifoiler would do...
It's completely feasible to do such a boat using this sail area between 22-24' with upwind foiling capability in a wide range of conditions.Hmmmm...

I know you've seen JPZ's 18' foiler, Doug. For anyone who hasn't, check out http://boatdesign.net/forums/showthread.php?t=13513&page=2

It seems to me the boats to beat, in the near-shore contest, will be sailboards & Ketterman hydrofoils (a.k.a. Hobie Trifoilers). But that shouldn't stop others from trying.... sounds fun!

I'd like to nominate Bob Esmer to create the trophy: www.bobemser.com

[Stephen Ditmore]

I therefore believe that a relatively long hull can help significantly, up to the point where beam and/or draught have to be reduced (to maintain a constant displacement) to a level where stabilty and motion suffer.

Metacentric height varies with Beam^2 / Fairbody Draft.
As long as that ratio remains constant, you should be able to make your boat as long as weight/structural considerations allow without having a big effect on stability.
Each time the beam is halved, the draft needs to be quartered, meaning you will only have 1/8 the midsection area. Therefore you only halve the beam if you are increasing length by a factor of 8 and maintaining the same displacement. I want to say beam would scale with 1 / the cube root of the length scale factor, while draft would scale with 1 / the square root -- but I'm not sure that's exactly right. Anyone want to take a shot at writing the function correctly?

[Doug Lord]

Good on the trophy if it didn't cost about the same as one of the boats.
The Ketterman or Bradfield three foil foiler would have a good chance inshore in winds over 15; the monofoiler or "bi-foil tri" in lighter and probably rougher conditions. The Ketterman and Bradfield boats don't come close to the pointing ability of already existing monofoilers but their top end speed may be higher. I've seen a Rave up close in 15 knots and video of a Moth in similar conditions-I think the Moth would beat a Rave in 5-20knots with a 9m² sail particularly around a course where the monofoiler's superior upwind ability would be a major player. I think a 24-28' super Moth(either bi-foil tri or canting keel foiler -see sportboat thread) that had been debugged and refined in a two boat test program would be the fastest boat with 430 sq.ft.in inshore conditions and quite possibly in a relatively peacefull transpac as well. If the conditions were less than 50% foiling conditions Robs boat wins hands down in the ocean.
I urge anyone- who hasn't already- to read Rob Denney's technical description of his 50' proa -link in his last post.

[SuperPiper]

Metacentric height varies with Beam^2 / Fairbody Draft.
As long as that ratio remains constant, you should be able to make your boat as long as weight/structural considerations allow without having a big effect on stability.
Each time the beam is halved, the draft needs to be quartered, meaning you will only have 1/8 the midsection area. Therefore you only halve the beam if you are increasing length by a factor of 8 and maintaining the same displacement. Beam, in other words, would scale with the cube root of the length scale factor, while draft would scale with the square root.

Stephen, could you please repeat that slowly for me? I am cranium-challenged.

[PI Design]

I agree with what you are saying, but the trouble is that maintaining a constant B^2/T whilst increasing length results in a lighter displacement (for a constant block coefficient). You therefore have to carry less lead, assuming the boat is being built as light as possible anyway - so there is no chance of using lighter hull materials. With only 40sqm of sail, you don't need that much ballast, but obviously there comes a point where you will have too little. Without having done any calcs, I guess this will be when L = 35-40ft.

[PI Design]

Sorry, SuperP, I didn't see yuor post when I put mine in. What Stephen is saying is that you don't halve the beam when you double the length, to maintain a constant displacement or initial stability. You only halve the beam when the boat is eight times longer. The problem (that's too strongh a word, but I can't think of a better one of the top of my head) is that stability and displacement don't scale the same, so you'll need to change the block coefficient (and hence hull form) to keep the two balanced.

Is that right Stephen?

[Stephen Ditmore]

I was assuming a constant block coefficient, a constant displacement, a constant VCG, and that we're talking about a monohull sailboat. The main point is the first, about maintaining a constant B^2 / T to maintain comparable form stability. The implication, as I see it, is that if you're thinking about increasing length and decreasing midsection area, fairbody draft (T) should diminish faster than beam (B).

When I say fairbody draft, I mean hull draft, not counting the keel. And what I'm really referring to when I speak of its diminishing is all vertical offsets (waterline to outer surface of hull) diminishing by some factor.

I've made an edit to my earlier post because I'm not sure I had the math exactly right. Not your fault you were confused :confused: :).

[Stephen Ditmore]

I urge anyone- who hasn't already- to read Rob Denney's technical description of his 50' proa -link in his last post.

I did, on your advice Doug, and I approve. I'm liking those Harryproas quite a bit.

As the site itself notes in discussing the most radical of the proas <http://www.harryproa.com/Texel/texel.htm>, though, the achilles heel is lack of ability to move weight aft, resulting in the bow being pressed if pushed hard.

But perhaps this is an opportuinty for a design breakthrough, esp. where Rob is in Australia. Is there an active Moth fleet where you are, Rob? Sensor wands and T-foils on proas might be the answer! Another possibility might be a kite sail or a canted sail to leeward like http://www.boatdesign.net/forums/showpost.php?p=114875&postcount=406... the idea being that the sail pulls & lifts rather than pushing the bow down (of course).

Quite a group of innovators down under.... Lindsay Cunningham (Yellow Pages Endeavour), John Ilett (Fastacraft), Andrew McDougall (KA Sails), Rohan Veal and the other Moth sailors, Leo Lazauskas on theory, and Rob Denney with his proas. Get all those guys in a room and put a challenge like this in front of them...

Hey wait a minute, Rob, you're the guy who started this thread! Sometimes it takes me a while.

No relation to the proas, but the general direction of this caused me to think of the boats in these photos:

[rob denney]

[QUOTE=Stephen Ditmore;115352]I did, on your advice Doug, and I approve. I'm liking those Harryproas quite a bit.

As the site itself notes in discussing the most radical of the proas <http://www.harryproa.com/Texel/texel.htm>, though, the achilles heel is lack of ability to move weight aft, resulting in the bow being pressed if pushed hard.

But perhaps this is an opportuinty for a design breakthrough, esp. where Rob is in Australia. Is there an active Moth fleet where you are, Rob? Sensor wands and T-foils on proas might be the answer! Another possibility might be a kite sail or a canted sail to leeward like http://www.boatdesign.net/forums/showpost.php?p=114875&postcount=406... the idea being that the sail pulls & lifts rather than pushing the bow down (of course).

Quite a group of innovators down under.... Lindsay Cunningham (Yellow Pages Endeavour), John Ilett (Fastacraft), Andrew McDougall (KA Sails), Rohan Veal and the other Moth sailors, Leo Lazauskas on theory, and Rob Denney with his proas. Get all those guys in a room and put a challenge like this in front of them..

G'day,

I am in Perth, where the foiler moths originated, so yes there is some potential. However, I think I would be way out of my league with those guys. I'd be happy to just sit and listen.

We are part way through the design of a 16' proa foiler. Some novel problems which normal boats don't have, and some easy fixes for some of their problems. Should be fun when it finally sails.

Another solution to the lack of fore aft stability is extreme length, which is why my 40 sqm/430 sq' of sail is on a 15m/50' hull. If I can keep it light enough, light air performance should not be a problem, and once it starts to blow, we should be pretty quick. SA/wetted surface is 3.8 at rest, 4.3 with the hull flying.

regards,

Rob

[tspeer]

Limiting sail area drives the class to very high aspect ratios and does not allow for adding sail area for downwind legs. Basically you're talking about an A - D class catamaran without any constraints on the hull. The American open-class landyacht classes are of this type. The tall rig leads to a large chassis to counter the heeling moment, and you end up with a large, spindly, lightweight craft.

I think an even more interesting class would be one that only had a limit on the height of the mast. This would allow you to vary the sail area as appropriate. The limit on mast height also limits the height of the center of effort, and that naturally limits the beam because there's no point in making it too wide.

The interesting trade here would be efficiency vs area. There may be an optimum area to drive long, fine hulls. More sail area would add parasite drag and weight, cutting into the L/D and limiting speed. For example, my landyacht is faster with its small sail than with its big one in all but the lightest winds.

[rob denney]

Limiting sail area drives the class to very high aspect ratios and does not allow for adding sail area for downwind legs. Basically you're talking about an A - D class catamaran without any constraints on the hull. The American open-class landyacht classes are of this type. The tall rig leads to a large chassis to counter the heeling moment, and you end up with a large, spindly, lightweight craft.

I think an even more interesting class would be one that only had a limit on the height of the mast. This would allow you to vary the sail area as appropriate. The limit on mast height also limits the height of the center of effort, and that naturally limits the beam because there's no point in making it too wide.

The interesting trade here would be efficiency vs area. There may be an optimum area to drive long, fine hulls. More sail area would add parasite drag and weight, cutting into the L/D and limiting speed. For example, my landyacht is faster with its small sail than with its big one in all but the lightest winds.

G'day,

How large, spindly and lightweight the craft become is what I am interested in. Racing with crew mid summer on a short course in San Francisco and sailing solo across the Pacific will ensure that the boat has some robustness, and may penalize ultra high aspect ratio rigs.

However, thinking about what I would design for these two races with a mast height limitation, I don't think I could do much better than a very long, light proa with a single sail. My mast is 11m/37' off the deck. F 27 tri, Stilletto 27 cat, Thompson 770 sportsboat, Hobie 33 keel boat are all a little higher than this and I will be disappointed if I don't beat all of them on all points of sail in most, if not all, breeze strengths.

I have a lot of respect for your opinion and knowledge, I would be very interested to hear your thoughts on what would be fastest under both rules, for both or either, courses.

Curious about your land yacht. Is the smnall rig advantage due to a stability limit, or a sail shape control limitation? Is there anything you can change to make it faster with the big rig? If nothing, does it follow that small land yachts beat big ones? If so, what is the optimum smallness? These are genuine questions, I know next to nothing about land yachts.


regards,

Rob