# Roll Control using foils

Discussion in 'Sailboats' started by Wingz, Oct 19, 2010.

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### WingzJunior Member

In the world of sailboats, It seems that advances are being made in the areas of sails, and hulls. However the limiting factor in the speed of sailboats is the ability to control roll, or heel. Too much wind, or too much sail, and the boats will roll in a spectacular fashion, often times to show their bottom side in a most undignified manner.

The problem has been worked on in two ways. The most often used is ballast. Attach a lead weight that may be 30 to 50% of the total displacement of the boat, to the bottom of the boat in what ever form you think is most advantageous, so that gravity can keep the bottom down, just like a fishing bobber. The other way is to make the boat very wide, like a catamaran or trimaran so that as the boat heels, the weight of the lifted hull combined with the lever of the width of the boat acts against the heeling force. Both of these methods have there limitations.

But water is a fluid, like air. And fluids follow the rules of fluid dynamics. If you are a little rusty on fluid dynamics, may I suggest the MIT course on this, available here: http://videolectures.net/mit801f99_lewin_lec28/ . Don't shy away as this man is very interesting and easy to listen to. It is highly recommended for any boat nut.

But to shorten the story, when a fluid moves over a curved surface, it increases speed, which causes a low pressure area. That is why airplanes fly. That is why hydrofoils work. The question is 'Can we apply this principle to the problem of controlling roll on boats?'

I offer the following proposition: a pair of opposing, independently operable, hydrodynamic wings extending downward from the bottom of the boat, of sufficient size and foil shape such that the low pressure lift created by the movement of the wing through the water will balance the roll, or heeling motion of the vessel. One wing provides the force to balance the roll to one side of the vessel. The other wing provides the force to balance the roll to the other side of the vessel. The wings are independently operable from 0 to 90 degrees to provide a means of adjusting the necessary control force to the conditions.

or in a pdf file here: http://tampicoventures.com/Boats/Using Water to Fly.pdf

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and this: http://dynamicstabilitysystems.com/
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This system(DSS) not only adds to the righting moment but it provides vertical lift that can reduce wetted surface and wave making resistance. Wellbourn's foils are also retractable.

From the illustrations I saw of one version of your system using vertical foils you have the hydrofoil lift acting to leeward-seems like that would seriously impact the windward performance of the boat. Explore Albert Calderon's second CBTF patent where the canting keel strut is turned into a hydrofoil when it is fully canted. The "lift" acts down as if the keel strut had more weight on it with lateral resistance taken care of by twin vertical foils that also steer the boat.

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The SECOND CBTF patent illustrates the concept of the strut as a hydrofoil. The number is: 5622130 and an overview with images is here: http://www.wikipatents.com/US-Paten...tem-for-sailing-yachts-and-sailing-yacht-hull
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Pictures: DSS illustrated--click on image-

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### WingzJunior Member

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### WingzJunior Member

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### daiquiriEngineering and Design

Wingz,
Judging by what I've read in your site, I'd say that you have focused so much on a single tree that you've forgotten about the surrounding wood.
So please let me ask you just one question: do you know what is the purpose of a keel in a sailboat? Think of it...

7. ### CutOncePrevious Member

Short answer is no. Your concept of two asymmetrical boards configured to counteract heeling will result in underwater foils designed to make the boat go sideways and lose VMG to windward. Foils provide lift to windward by design - and using the foils designed for this purpose to generate righting moment will defeat the more important purpose of creating lift to windward.

Like most "get-rich-quick schemes" this one fails to consider all the forces in play.

Mr. Lord's Dynamic Stability Systems horizontal foil is a more sophisticated and attractive scheme to get rich quick, but adds wetted surface area and surface piercing drag and only works when the boat heels - far less effective than keeping a boat upright via crew movement to windward.

Go back to Newton's Third Law - for every action there is an equal and opposite reaction. Physics rules apply to sailing no matter how hard we wish they didn't.

--
CutOnce

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Dss

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You don't know what you're talking about. DSS was conceived of by Hugh Welbourn and is currently being applied across a wide variety of sailboats. When the foil is used properly it is not a surface piercing foil. His DSS25 won its very first race in convincing style and the system has been extensively tested. The "get rich quick" comment is just plain nonsense as it applies to DSS.

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### WingzJunior Member

Suppose that we were building an airplane, and we built the body, and put a motor up front. Then to make it fly, we put a wing on just one side of the body. As we tried to fly our new airplane, we found that this arrangement didn't keep the top side of the airplane up very well. So, after long discussion, we decided that to keep the top side up, we should use a hot air balloon attached to the top of the body. That would keep us in level flight, even though it added a lot of drag.

Then we decided that we wanted to go faster, so we put on a more efficient wing. But to balance that we needed a bigger balloon to keep the top up. That added more drag, which meant that we needed a bigger engine, and to support the added weight of a bigger engine, we needed a bigger wing, which meant a bigger balloon. Round and round we go.....

The wing of a sailboat, is the sail. The sail works strictly by the rules of fluid dynamics. The wind either pushes or pulls it. In the past we have balanced those forces by the force of gravity - Lead weight often equal to the weight of the entire boat. That means more drag, more displacement, more power (sail) needed to do the same thing. Round and round we go.....

Air is a fluid, and water is a fluid. Compensating for density, we should be able to balance the forces available from these fluids precisely, just as airplanes did when they decided to put a wing on both sides of the body, and do away with the balloons all together

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What prevents a sailboat using your system from going sideways(to leeward) fast? How does it sail upwind?

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### WingzJunior Member

If the density of water is about 833 times the density of air, then given the same conditions, one sq. foot of wing would balance 833 sq feet of sail. However since real life just doesn't work that way, the wings are made considerably over-sized. On the boat I am testing the wing surface is 7 feet long and one foot wide with the ends tapered. The sail is about 180 sq feet.

This should give considerably more righting force than needed for all but the worst conditions. That means that the other wing can be lowered part way. This will cancel some of the righting force from the fully deployed wing, but then provides the effect of twin keels for directional stability, or side slip.

Up wind the boat would handle like any other boat, although faster since it is a planing hull with no ballast. The foil section is made for maximum efficiency in the 10 to 20 knot range. once this is exceeded, the foil will loose efficiency. At this point, the wing is retracted somewhat. This changes the effective chord length of the foil, ie: the distance from the front edge to the back edge of the wing, as the water sees it, elongating it due to the angle of retraction.

This ability to change the apparent foil shape, allows the wing to be used over a broad speed range.

12. ### CatBuilderPrevious Member

What happens at anchor or when you are going slowly though very rolly seas?

What keeps you upright then?

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### daiquiriEngineering and Design

Wingz, you don't get the point. You are considering only the heeling and righting moments. Note the word "moments".

The main purpose of the keel in a sailboat is to counter-balance the sideways force (note the word "force") which is generated by the sail. To do that task a keel must generate an equal, but mirrored to boat's centreline, force. Which is exactly contrary to what your keel is designed to do. Without that balancing force, the boat will accelerate to a sideways direction, without being able to keep a steady course.

You have designed a keel (which you call foil) which generates a force acting in the same direction of the force generated by sails. So who or what will provide the sideways balance of these two forces?

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### WingzJunior Member

At anchor, your sails are down and there is little or no heeling force to contend with. Depending on how slow and rolling you are talking about, the width of the boat provides basic stability at slow speeds. Too much rolling seas, and perhaps you should get some speed up, and call it a day.

The boat I am testing is a 5 meter skiff with a waterline beam of only about 1.2 meters. I built it somewhat narrow this way to push this point. Capsizing it meant grabbing the mast as high as possible and swinging way out. It took three tries.

Righting the boat again, meant extending one wing and standing on it.

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### WingzJunior Member

The mast of a sailboat is a lever, the force of the sail rotates that lever around a line form the bow to the stern of the boat at about the waterline (the centerline). These wings equally are levers, which rotate around that same line and are placed very close to the mast. These wings are designed to counter the heeling force of the sails. That is the point of them.

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