Proa with canting (flying) keel why not

Carrying lead around on a multi is just nuts. 180 degrees from the right direction. As Herreshoff noted in the previous to the last century, "multihulls are nothing if not light". A little water ballast to adjust for varying range of pressure or fore and aft trim is one thing . It can be jettisoned.

 

Movable(or unmovable) Ballast on Multihulls

So where is the cutoff, Mr. Greenwood: multies from 14- 30+ feet use movable ballast as an integral part of their ability to go fast-and it can't be jettisoned! So when does movable ballast cease to be a speed producer on multihulls?

PS-for years people have told me that the idea of a foiling keelboat was "just nuts"-and now, of course, there is one- done by a major naval architect and sailing innovator.

 

And an example would be?

 

Movable(or unmovable) Ballast on Multihulls

Hobie 14, 16, S9,F16, F18, A Class, Tornado etc,etc. The movable ballast on these boats is equivalent in some cases to the weight of the whole boat-and, even if it could be controlled, the boat would not perform if this movable ballast was removed.
Ballast is ballast-alive or dead- and it seems to me that saying that a particular form of ballast is "nuts" ignores the potential proven beyond a shadow of a doubt in many multihulls where the ballast is critical for performance and ,again, can't (legally) be jettisoned.
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It just seems to me with the progress that's been made in design and materials that maybe it is time for a more enlightened look at the use of ballast on multihulls up to and including using ballast to achieve self-righting(and or crew righting) in addition to greater speed.


Quant 23 -foiling keelboat: http://www.boatdesign.net/forums/sailboats/quant-23-foiler-scow-53468.html

 

So Doug--you don't see a fundamental difference between weight that must be carried on the boat to meet rules, or for safety and maintenance of the crew and placing that optimally, compared to adding unnecessary weight ?

Where do you come up with this maxim "ballast is ballast" ? Nothing could be further from the truth. The point of a multi is seeking righting moment with use of the least amount of weight possible. So now we are going to start adding weight?

 

Ballast

Weight(ballast) is already added on some of the fastest multies around-large and small as I pointed out earlier. Thanks to modern design, engineering and materials I think there is room to consider ballast as a speed producer on some types of multihulls. The movable ballast(crew) on smaller multies is proof positive that it works-thats why I asked you earlier : what is the cutoff in your thinking of the size multi where it doesn't work??
I know that a 19.5' oversquare, singlehanded tri, designed specifically for it, can foil as well as being self-righting. And I think the concept would work on other trimarans-specifically designed for it. I don't know enough about proas to know for sure whether or not it would be viable but the likelyhood is-maybe.

 

Doug,

From a design standpoint it will always be better to just make a boat wider than to add more weight to the same hull. On small catamarans crew weight is generally a necessary evil, not ideal. Which is why there isn't an A-Cat made that is intentionally overweight.

For a large cat water ballast may work in some situations because they can also get rid of it when conditions don't favor it, and generally they are constriained by maximum beam not maximum RM. So when beam is the constraint you add weight because in heavy air it's the last option, but no one would add lead because the penalty when the breeze is light is far too high.

Getting back to the original question, adding beam to a proa would be a far better option than adding a canting keel. Which is why no one ever has tried adding a ballasted keel to a proa in the past. It's a silly idea.


And no foiling monohulls have nothing to do with this conversation, they are fun in their own way, but a complete non-sequitur.

 

Ballast for multihulls

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Depends on what you're trying to achieve. Adding beam and ballast may be the best solution.

Not when you understand the attitude many had toward the foiling keelboat for years and years. Similar attitude that many have toward the value of ballast in some types of multihull.

 

Ballast at the multihulls.

Everything depends on the arm ballast. I think that for the proa flying keel is the best from all the multihulls.

 

Yes adding lead to a proa is a better option than adding lead to a catamaran, but thats just because proa's always need the weight on the same side (when they need weight at all that is).

 

It is not as if one day it came to designers that foils on monohulls could contribute to righting moment. It was in their minds long before the uptip foil came into the picture. Also the current foils being TESTED on the open 60s have not been proven. (relax a second Doug and let me finish). They have shown to be fast, but fast is no good of they are too vulnerable. That has yet to be tested thoroughly. If there is a high percentage chance that foil damage will put an IMOCA out of the Vendee then they will be gone. That is a calculation each team will have to make and decide, but a 20% chance of not finishing the race because of foil problems is something to think hard about. These shorter races are an opportunity to check this out.

 

Multihull Ballast

Mr. Greenwood, I used the example of the Quant 23 because it actually is a foiling keelboat-not "foil assist" like this years IMOCA's. And I didn't use it as an example of extra RM-though I could have. Just as an example of a keelboat with foils that lift the entire hull clear of the water- something many , many people told me was completely impossible over the last 10 years! The point was to illustrate the fallacy of the old wives tales(for lack of a better description) about using ballast on multihulls.
This is not an age where the old rules that say something is impossible or "silly" can be relied upon.........

PS- I'm watching the IMOCA boats closely-and they will probably be foiling after the next rule change but they aren't yet. They're at the stage the big tri's were 15 years ago with ama "C" foils that partially lifted the boat. Exciting but not "foiling" in the true sense.

Quant 23-foiler keelboat scow

 

Hinestly I am not sure that this is a real consideration for the IMOCA fleet. While there is no doubt that in order to win you have to finish, in order to win in this class you not only have to finish but also have a huge helping of luck. Increasing speed at the tradeoff for less durability is so bred in the bones of the IMOCA's...



Right now I think the biggest issue the boats are dealing with is the limited RM the masts can absorb. Due to the OD nature of the masts the boats wi foils are quickly closing in on the max RM they can absorb. I think there is a fair chance that under the current rules a full foiling boat would just snap the masts off.

This is the reason some programs have chosen to use old boats (no mast restrictions) just to allow them to build stronger sticks.

 

Going from canting keel proas to foiling IMOCAs is quite a bit of thread drift.

The design in the OP seems to be a jumble of ideas without any clear thought to what the boat might be used for. If the intention is to design a "planing and foiling proa with flying (canting) keel and reefing soft wingsail" then that goal has been achieved.

But if the intention was to design a foiling proa that anyone other than an eccentric loner would want to build, it seems to fall short.

As for the "why not" in the title, likely because:

1. It's very complex, both in construction and operation
2. It's unlikely to foil with any stability given the line–astern configuration of the foils on the main hull
3. Has very limited application for someone wanting to use a sailing boat for the things they are most often used for, i.e. it's impractical