DSS for "Foil Assist" on Multihulls?

Its ocurred to me that the DSS(Dynamic Stability System) horizontal sliding or pivoting foil might work for foil assist on an ama and be shallow draft as well. Could open up foil assist benefits for multihull cruisers concerned about the draft of other systems. And for speed freaks as well...

http://dynamicstabilitysystems.com/#/profile

Interview with Hugh Welbourn with good questions and answers about the system on monohulls;

http://www.harken.com/Interviews/DynamicStability.php

 

An intriguing concept, for sure. Gain a bit of righting moment, increasing with speed and heel, without any extra ballast.

It looks to me like it could be worthwhile for racers, esp. midsize to large monos. For a cruising mono, it may work, but I'm not sure you'd see the same benefit with a cruising rig as you would on an overcanvassed racer, apart from maybe being able to push a bit harder before reefing. You'd have to take the ability to use this foil into account right from the conceptual design stage, when deciding how the boat is expected to be sailed. I'm not clear on what the benefit to a cruising cat or tri would be, though.... since neither can heel significantly without flying a hull. But using it as a swim platform when at anchor would be kind of cool.

 

A cruising multi might heel enough to have this foil contribute to RM(it might not need to heel?). But what a simple, shallow draft way to power up a small tri or cat! But I agree the boat would probably have to be designed for it from the get go.
Something to think about....

 

DSS for multihulls

I'm looking at this again because of my "sudden" realization that curved foils
can reduce the righting arm and therefore the righting moment on racing multihulls that use them. Curved foils were originally intended as rule beaters but on a cat like Alinghi they would have reduced righting moment(on a boat already narrow compared to USA) while using a properly implemented pivoting(like a centerboard) horizontal foil would have increased RM as well as reduced wetted surface-without violating any rule.The tri is so wide that the slight reduction in RM is meaningless. Whether the trade off in overall L/D would have worked or not is not easy to say but I'd bet on it.
There would be a slight weight gain and each hull would still need a vertical foil(lee daggerboard designed to be vertical when the windward hull just clears the water*). The lifting foils are 100% retractable and easily adjustable for angle of incidence. The biggest problem I see is keeping the horizontal foil immersed enough to avoid surface proximity drag....

*Alinghi's daggerboards were canted toward the cl of the boat at the bottom about 10 degrees-this would be counterproductive in combination with DSS-they would need to be angled outboard at the bottom so that they were vertical when the windward hull just cleared the water-allowing for minimum wetted surface.

 

DSS tri application

The DSS does seem to have some credibility. The problem for a tri though is that you would like a relatively long foil for efficiency and it won't fit inside the hull.

I think I have a solution that is an improvement for all DSS systems and also lets it work on a tri. The foils they show are essentially a horizontal asymmetric DB. Instead, you want a CB. On a tri the foil will easily pivot into the hull for light air and docking. A shaft from the pivot can go up through the hull to a lever on top of the hull. Simple, clean, efficient.

If you can find the right sized tri you could ese the boards out of an M17 scow.

In a class like the NZ 8.5M you have a beam limit. There I think I would accept that you want maximum beam for the amas, so I'd put the foils on the insides of the two amas. I'd probably set up angles so that with two hulls flying the leeward hull is vertical and the foil provides lift and lateral force, like the curved foils on USA-17.

And because it's disclosed here, only I can patent it, I have a year to do that and I'm not going to, so it's open to anyone. I of course will modestly call it a Raymond Foil.

Fortunately, I'm going to finish writing this and immediately send it. If I let is sit for a little while I'm sure I'd take out the egotistical paragraph above, which would certainly reduce my potential embarrassment and the readers potential amusement.

 

Raymond foil--pardon me but I like Lord foil....or just DSS for Multies!

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Did you read my post? Besides my post(for multihulls), the "horizontal centerboard" idea was already conceived of by Hugh Wellbourn and is illustrated on a Wally on his site. Edit: "centerboard" type DSS foil: Go to the website, post#1; click on designs-superyachts-DSS100,then the thumbnail image on the right(of the two on the left of the screen and(whew!) you should see it).

Glad you think it will work for multihulls-how would you avoid surface proximity drag?

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From Ocean Navigator:

How would DSS foils be fitted to a voyaging boat? The 27-foot DSS test boat has an internal tunnel that runs from one side of the hull to the other. On a voyaging sailboat, the options would presumably be greater, depending on the size of the vessel and its configuration. Rather than a tunnel running across the beam of the boat, it would be possible to build foils into individual tunnels on either side of the boat. Welbourn comments via email: “The choice between individual P&S foils or the straight-through foil system can depend on several aspects of the overall design of the boat in question. On many typical medium displacement boats then the transverse foil system will disappear under the floorboards and so not impinge on any internal arrangements. This is the simplest and lightest solution, but sometimes there is a case to be made for separate foils — in this case typically they fit outboard of the bunk fronts so have no impact on the saloon area.”

http://www.oceannavigator.com/ME2/d...91&tier=4&id=DF2EAC7BF4204ADCBA2BE20418A962A7

 

Pivoting foil

It's amazing, how did you copy it from me before I wrote it?

 

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incredible talent

 

If you have watched the 45' America's Cup winged racers, you have seen the scary mark roundings as they bear away and bury the leeward forward hull. The very fine hulls are fast on all points of sail except these roundings as they do not have enough bounce forward to counteract the pitching moment forward exerted by the very efficient and powerful wing masts. If they were fitted with a DSS centerboard foil forward, that was deployed for the mark rounding or some heavy air runs, they could counteract these moments and greatly improve safety and probably gain speed overall around the courses (a pitchpole is really slow).

Imagine the 72' boats in the same conditions- a pitchpole in one of those could be very dangerous.

 

bounce should read buoyancy

 

DSS for multihulls

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Probably would work but at(maybe ) too much cost in drag compared to curved lifting foils as used on the NACRA 20 and A Class cats with proven anti-pitchpole results combined in a single foil that also provides lateral resistance. Good experiment, maybe...

 

Doug: My conception would be to leave retracted except when needed, especially at bear away marks, so there would be no increase in drag except from the additional weight in the bows, except the brief period they are deployed. When the AC45s bury the bows, the boat slows way down from the huge increase in drag, or stops and pitchpoles.

 

Any discussion with regard to an AC72 has to start with understanding what an AC72 is. From the AC72 Class Rule:

1.4 In interpreting this AC72 Class Rule the definitions in Article 1 of the Protocol shall apply, and:
(a) appendage means any component that is outside the hull, excluding wing and cross structure, daggerboard bearings and daggerboard fairings (providing
these bearings and fairings comply with 1.4(a)(ii) ) , but including integral components that extend from outside the hull into the hull, (e.g., daggerboard
head or rudder stock) that is:
i. wholly or partially submerged at any time during racing; and
ii. used to affect stability, leeway, steerage, directional stability, motion damping, trim, or displaced volume.
...

5.1 The AC72 Yacht shall be a vessel, generally known as a catamaran, with two hulls connected by cross structure that are arranged symmetrically about the yacht centerplane, and that has two rudders, two daggerboards, and no other appendages.
...

A catamaran with DSS foils would not be an AC72.

An AC45 has straight daggerboards for simplicity and to teach the crews how to handle a catamaran with a rigid wing sail. Curved boards would improve the performance of the boat, but weren't compatible with the mission of the boat and the time available for development. Curved boards are allowed on the AC72, and would provide vertical lift to improve their pitch-pole resistance. There's a beam restriction on the AC72, so horizontal foils will project inward, not outward to increase the righting moment, as with DSS.

So, other than providing vertical lift with the daggerfoils, ala A-class cats, NACRA 20, etc., there's nothing about DSS that is applicable to the AC72.

 

I'm reawakening this thread because since it was begun a designer that I don't know came up with a great solution. It could be modified to have the board pivot like a centerboard for retraction.