Underwater 'wing' ?

[MrBlueSkies]

Underwater \'wing\' ?

If a boat's centre-board (or keel, or daggerboard) were to be pivoted in the vertical plane so that it presented an angle (5 degrees?) to the windward of the direction of travel, rather than being fixed, wouldn't leeway be replaced by 'making up to windward' ?

Is there any literature on such an approach?
Steve

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[Talbot]

Re: Underwater \'wing\' ?

This was the concept of the winged keel, and certainly on a Sigma 365 it appeared to work - but it was the wing that caused the lift to windward. IRC there was a special keel a few years ago that in addition to the wing had a space between the front dection of the keel down to the wing, and then basically a second keel also attached to the wing. That was also supposed to be very good when going to windward.

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[aod]

Re: Underwater \'wing\' ?

I cannot remember the name of it but there was a small boat made with exactly this kind of dagger board. (I think it was called Red something) Yes, it does work at a certain speed. I am not sure why it didn't take off but it didn't.

Keels already generate lift but it had nothing to do with being wing in design which merely stopped the boat pitching while offering low weight. The scheel keel (I think that's how you spell it) which had a slot in it kinda had a brief life before dying a death.

I guess if you had a daggerboard that as you say rotated and controled by computer or something which calculated lift v's drag it could work. Certainly the old Americas Cup boats like Victory had a trim tab attached to the rear of the keel to generate lift but it also seems to have died a death now.

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[MainlySteam]

Re: Underwater \'wing\' ?

Is there a difference between that and just sheeting your boom well up to windward of the centreline of the boat (in a cat rigged boat with no foresail to worry about)?

A rudder is a foil that contributes to lift, do we regard it as helping us get to windward if we have heavy weather helm (ie the foil is angled to windward)?

John



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[peterb]

Re: Underwater \'wing\' ?

There were some racing dinghies using a dagger board in which the trailing edge of the board was fixed while the leading edge could move an inch or so in its slot. The result was that the keel always took up a position at a slight angle to the centre line of the boat, acting as a wing and giving decreased leeway.

Surprisingly, though, a boat sails more efficiently if the hull is making some leeway. A hull travelling through the water in the direction of its centr line generates no sideways force (lift), but does generate drag. As the angle at which the hull meets the water increases, lift is generated roughly in proportion to the angle; drag increases too, but initially only slightly. Since it's the ratio of lift to drag which is important, it's better for the hull to make a small amount of leeway.

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[charles_reed]

Are you referring to

canting keels?

Because they've been around for the past 10 years on high performance offshore boats.

Look at the Schott website.

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[chippie]

Re: Are you referring to

Charles, i dont think a canting keel has its axis in a vertical plane. The keel that is being dicussed has an axis in the same plane as the rudder. (Or at least that is how I read it.)

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[Jacket]

Re: Underwater \'wing\' ?

A yacht did this in the '80's- instead of a keel it had two assymetric daggerboards. You sailed with the leeward one down, which provided lift to windward. It was very suucessful - so much so that the rulemakers banned it.

The red fox 20 and red fox vision use the same system, and are very fast when you think that all the balast is internal.

Thats the problem with the system- as you need lifting daggerboards you can't have a ballasted keel providing stability. having said that, many of the swing keel open 60's use assymetric daggerboards.

Some yachts did try using a trim tab on the back edge of the keel to provide the same effect, but weren't very successful. I heard it suggested that this was because the keels are two thick a section, and the trim tab to small to produce a suitable section to provide lift.

I'm surprised that no-ones tried it on modern bulbed keels, which are much thinner in width, so would probably work much better with trim tabs.

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[MainlySteam]

Re: Underwater \'wing\' ?

If I read the original post correctly, what is meant is a daggerboard, keel, etc that can be rotated on its vertical axis in a similar way as a balanced rudder to present an angle to the flow of water and thus climb to windward.

Asymmetric daggerboards do not do that, they climb by using opposite foils such that the leeward one in use presents an aerofoil that climbs to windward. Asymmetric daggerboards are very common on race boats now as any look at Open 60's, multihulls, etc will show.

Maybe the original poster needs to clarify what he meant.

John

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[Jacket]

Re: Underwater \'wing\' ?

But they are just different ways of acheiving the same lift.

Doing it with a rotating keel has the advatage of still allowing you to have a keel, but would be an engineering nightmare to do safely at a sensible price, given the loads involved.

Daggerboards generally mean you don't have a keel, so you loose stability, but have the advantage that you can raise both when running, cutting down on drag.

The nearest to a rotating keel that I know of is the Schock 40, which has two rudders, one front and one aft, and rotates the front one upwind to provide lift to windward.

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[richardandtracy]

Re: Underwater \'wing\' ?

I'm sure one of the Jules Verne challenge yachts (or some such long distance/high performance race) had this idea a few years ago. The keel was pivoted at its aft edge, and a hydraulic ram shifted the forward edge a couple of inches to port or stbd (unless I got my directions wrong from the TV pictures and it was pivoted at the forward edge).

Always struck me as a 'fail-unsafe' idea, same as canted keels.

Regards

Richard.



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[Jacket]

Re: Underwater \'wing\' ?

The reason for having it pivoted at the aft edge was probably weight reduction. If its pivitode at the forward edge, it would need either a locking mechanism, or for the ram to be kept permanently powered up (as all hydraulic systems loose pressure over time), to hold the keel in place. With the keel pivoted at the aft face the water flow will keep the keel in place, and so the ram is only used in short bursts to move the keel during tacks.

I'd argue that the system is fail safe. If the jack fails the boat will still sail, even if it does make a lot of leeway. Unlike canting keels, which seem leathal to me as well (sorry QSIV) unless you can rig up a block and tackle canting mechanism easily and safely should the hydraulics fail.

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[wiggy]

Re: Underwater \'wing\' ?

I know of an MG Spring that fitted adjustable canard on either side. They were rotated by wheels on top and had the amazing effect of making the boat sail upwind like a church. A complete waste of time and money.


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[richardandtracy]

Re: Underwater \'wing\' ?

You're probably right about the weight saving.

What I meant by 'fail unsafe' in this case was that the failed system is worse than if you'd not had it in the first place. Loose wording on my behalf.
Canting keels are truly wildly unsafe when they fail and will cause a catastrophic failure of the vessel. Not for use by the fainthearted (like me!).

Regards

Richard.


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[Bergman]

Re: Underwater \'wing\' ?

Suspect that the main effect would be to increase drag to such a degree as to offset any gain to windward. Particularly so as angle of heel inceased when the additional lift generated by the keel would tend to increase the angle of heel thereby increasing leeway thereby increasing angle of incidence of keel thereby increasing drag - and so ad infinitum.



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[Avocet]

Re: Underwater \'wing\' ?

I agree with the last post. If you angled the keel to generate lift to take you upwind, the power to do this comes from...

...the wind!

So you'd be inventing a something-for-nothing machine. I'm not saying the idea won't work but I think the boat will sail slower as a result. Whether the decrease in speed is more than offset by the "velocity made good" is debatable- maybe on an over-canvassed racing boat with power to spare it would help?

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[MainlySteam]

Re: Underwater \'wing\' ?

Agree entirely.

John


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[peterb]

Leeway

To resist the side force due to the wind, a boat has to generate a sideways 'lift' from its hull and keel. It does this by presenting its keel at an angle to the water. On a conventional hull that means that the hull points a little closer to the wind than the boat is actually moving. The course indicated by the compass will be the direction that the hull is pointing; the difference between this and the direction the boat is moving in we call leeway.

If you had a keel which could be set at an angle to the hull, then it would be possible to have a boat in which the direction of travel is the same as that in which the boat is pointing. But it doesn't necessarily follow that the direction of travel will be closer to the wind than in a conventional boat. Remember that the critical direction is the one that the keel is pointing in; the keel has to be set at an angle to the water so the keel is still making leeway. You would find that although the boat is apparently not making leeway, you would not get it to point quite so close to the wind, and the two effects would almost balance out.

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[MADFISH]

Re: Underwater \'wing\' ?

This concept has been around for years in the Metre classes (ie 12 metres). Fitted to the rear of the keel is a trimtab. This can be moved through about 15 degress via a wheel within the sterring wheel. It works by creating lift, but if too much is applied it creates too much drag. (12 metres go upwind at 9knots+, this makes it work better!)

Wing keels in my experiance are only advantagous when the draft of the boat is restricted. The drag caused by the wings is that high. This was proven by all the racing Mustang 30's binning their wing keels and fitting deeper fins. This improved their upwind preformance significantly.

Why do 12 metres have wing keels? The metre rule restricts their draft to 9'.

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[MainlySteam]

Re: Underwater \'wing\' ?

If anyone is interested there is a very good and simple explanation of how mutliple keel foils and winglets COULD work, giving lift and reducing induced drag, on International America's Cup Class yachts here <A target="_blank" HREF=http://www.esotec.co.nz/condorkeel/Html/intro_F.html>http://www.esotec.co.nz/condorkeel/Html/intro_F.html</A>. Note that it is a theoretical proposal by an aircraft designer and not a description of how the concepts are actually being applied.

I do not think it mentions it there, but the maximum draft of an IACC boat is 4 metres before penalty.

John

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