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

Above & Below

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?

 

430

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":
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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!
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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
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1) all up sailing weight of boat minus crew:
708lb./ 321.8kg. "on the start line"
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--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.

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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.
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* 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.

 

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

 

"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

 

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...

 

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

 

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.

 

50 footer

Rob, an absolutely brilliant design!

 

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

 

430

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.
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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.....

 

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.

 

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

Steve