Variable pitch keel?

[Rumrace]

I agree OP fascinating topic. I vision a keel which could retract from 8’ to 5’ or deploy foils which could balance on way or the other as well as fore and aft.
Anodized aluminum with machined PEEK gears and hydraulics Twin rudders with fold down foils.
Let’s go steal the Mule from New York.
Kidding
The Wright Brothers sued Curtis for their twisty wing but Curtis used an aileron. Curtis also appears to have invented the step hull for the SA3 to show up on Donzi Marine 50 years later. Curtis also made a few Marine V8 and a couple V12.
If you think of a sailboat as a crashed sail plane the keel is lacking control.
While performance increases with a deeper keel maybe it’s just the wrong direction. I don’t think a civilian version of the Figaro 3 is going to be realistic. The Wazsp is quite the little machine living on the edge. I’ve sailed an Ice Sailer where outriggers have long skates. Wild ride on Lake Simcoe.
I think Ferrari was using sliding weights in F1 and Mercedes’ got busted for spying on them.
The computers now used on AC-75’s are nuts. Closer to a flight controller on an aircraft.
If you watch the profile of a Navy 44 on heel. It’s profile in the water changes from under 36’ tubby waterline to a 40’ ribbon. Which I believe is your point.
I can see it on the option list right below base price.

Finebobber 43 2 cabin base fake Oak 280€
Hydraulic anodized T6 aluminum keel with wing rudders 180€
…

[Rumrace]

Dihedral as in Corsair or Stuka gave them diving control.
The Avro Arrow had a dozen models made to experiment with various split dihedrals mid wing. They were shot off into Lake Ontario and filmed in the 50’s We’ve spent years recovering them and searching for them.
I’ve read some good arguments a sail should have a tip like jet liners have added to wing tips. Q

[AuChante]

Originally Posted by Muaddib1116

Heeling is not required for the keel to create windward lift. It in fact decreases it because it creates a downward lift vector. Keel lift is created by the boat slipping sideways as it moves forward, creating an angle of attack on a symmetrical foil.

The issue I would see with comparing it to an airplane is that an airplane has a thrust created by the engine. So you can balance the plane out by increasing lift on one wing or the other, and your loss of overall lift can be counteracts by increasing throttle or angle of attack. On a sailboat, if you balance the heeling force with the leeward keel lift, you go further to leeward. In a race, your loss of ground to leeward could easily outpace the gain you have in sail lift.

I think I'm way underestimating the force this would take. I'm basing a lot on this video.


https://youtu.be/WGAzt-8minI


Let's say that's two, 8 cf bags (997 lbs) at 30' to get to a decent heel angle. that's 30,000 ft-lbs. If the aileron thing is 6' down, it'd be the equivalent of 3300 lbs to accomplish the same thing. That'd be a tough accomplishment at 6 kt. It'd probably have to be a pretty large aileron down there. on top of that there'd need to be a ton of keel to get the boat to track at all.


Then again, hydrofoiling boats have tiny foils, but they're much faster too.

[wingssail]

Originally Posted by AuChante

This seems like a good section for this. I’ve wondered about the physics of this for a long time. The keel acts as a counterweight to keep the dry side up and resistance to to keep it from being blown sideways. The weight doesn’t kick in till it heels, but that reduces its effectiveness at keeping the boat straight.

Would it be possible to have an adjustable “aileron” on the very bottom of it to counter rotate the boat against the wind? That would tend to push the boat leeward, but it’d be a balancing act in the design phase to balance the two forces.

There are other solutions… canted dagger boards and laterally swinging keel weight… but I’ve always been curious about the aileron idea. It seems like you could get a ton more efficiency out of the sails if you can actively keep the mast vertical.

Yes, you can make the sails more effective by keeping the mast vertical. The keel will also be more effective at reducing leeway if it is vertical.

What you are suggesting is placing a movable foil at the bottom of the keel to create a force opposing the heeling force of the sails. Sort of to add to the righting force of the keel weight.

Trim tabs previously used on some keels worked in the opposite way as you suggest. They increased the "lift" of the keel, which actually tended to cause more heeling, it would seem, but it decreased leeway.

So using negative trim tab, cranked the opposite was as they were cranked previously, would create a righting force as you suggest. However, it seems like it would reduce the "lift" of the keel and increase leeway. Hmm? maybe not good.

Placing this moveable foil at the end of the keel as you suggest would apply more leverage but still, the overall effectiveness of the keel to create lift and reduce leeway would be reduced I think.

Think about aircraft wings: they have ailerons to create more lift on the wing, usually on one wing they create more lift, and on the other they create less and the aircraft rolls. Your idea would be equivalent to moving the ailerons upward, reducing the lift of wings. Plane loses overall lift.

However there is a way this is done. Some boats have been developed with a foil which extends out the leeward side of the hull, parallel with the surface of the water (this is in addition to the keel, not part of the keel). This foil creates an upward force counteracting the downward heeling force of the sails. The keel remains efficient at resisting leeway and the foil helps keep the mast vertical. (it is actually like adding several crew members on the windward rail).

Finally there is a boat sailing in Europe called Flying Nikka with a foil out the leeward side AND a keel. On this boat the foil creates enough upward lift to raise the boat out of the water, while the keel keeps it upright and resists leeway. Quite a balancing act.

As far as I know nobody has combined those two effects into one foil, (the keel), as you suggest.

[TrentePieds]

Rumrace said: "Dihedral as in Corsair or Stuka gave them diving control."

No. Dihedral of an aircraft's wing has nothing to do with diving whatsoever! Dihedral is there so that when the aircraft "heels" (rotates around a horizontal, fore'n'aft axis through its centre of gravity), the "low" wing will have more projected horizontal area than the "high" wing. That, in effect shift the aircrafts CG to the "high" side, thereby causing that side to "sink" until the projected areas of the two wings become equal again, and the lift of each wing is again equal to the lift of the other, and the aircraft therefore will remain stable athwartships.

If AuChange wants to play with concepts from aerodynamics, the two he needs to get a grip on is "Angle of Incidence" and "Angle of Attack". Given the different viscosities of air and water, he will also need to get a rudimentary understanding of Reynold Numbers

The heeling of a sailboat has to be understood via the concept of "moment arms". To that extent there is a similarity twixt an aircraft's thwartships stability and a sailboats resistance to heeling, but the similarity is only comprehensible once you've got an intellectual grip on the physics of each of the cases. They are discrete!

Rumrace also said: "Think about aircraft wings: they have ailerons to create more lift on the wing..."

No, they do not! That is what FLAPS are for. AILERONS are used to induce a rolling moment around the aforementioned horizontal axis through the aircraft's CG.

TrentePieds

[wholybee]

Originally Posted by AuChante

I'm not getting this part... at all. That article completely separates heeling and all the sailing forces. Airplanes have dihedral (equivalent of heeling?) to make the plane more stable. when the plane tilts, the low wing becomes flater, increasing lift, and the high wing becomes more angled, decreasing lift. This gives the plane natural stability. A boat ought to be the same. The sail and keel ought to be most efficient when it is perpendicular to the lift and drag forces.



The sail lift and the keel lift both act to roll the boat (green). buoyancy and keel weight act to right the boat (blue). I want to add a control surface at the bottom of the keel (red) to supplement, or replace, the righting forces. The boat will be balanced between the sail and added control surface, and the keel.


Catamarans seem to do fine. As I understand, they tend to be quicker but cant point into the wind as well.


**Not trying to argue with anybody... I just don't get why the prevailing answer is that heeling is a good thing. Seems to me to be more of an inherent behavior of a monohull that is tolerated.


Edit: actually the red, control surface vector ought to be pointing perpendicular to the keel... a bit more efficient than as drawn.

As I said, that articel wasn't great.

Ok, so first, a keel does work better while vertical. But you need to keep it vertical with ballast, an outrigger, or second hull (multihull boats). If you use a trim tab, then you spoil all the lift. And if the trim is enough to counteract the heeling force of the sails, you are creating lift in the opposite direction of what you want.

A keel is needed to sail up wind. The sail is a wing, which creates lift. That lift is mostly at a right angle to the sail. So, while close hauled or on a close reach, almost all of the lift is sideways, and only a little bit is forward.

The keel does NOT work by drag, by stopping the boat from slipping sideways. If that were the case, you could never prevent leeway, only reduce it, and not by very much. The keel creates lift. So, both the keel, and the sail are working to heal the boat. The lift sideways created by the keel is exactly the same as the lift sideways created by the sail(ideally-if the boat is balanced).

I made a quick sketch, excuse my lack of artistic ability. On the left is how a keel works. Note the lift from the sail is at a right angle to the sail, and the lift from the keel at right angle to the keel. And note how those 2 vectors add to determine the direction the boat moves. (I am excluding drag for simplicity, but that is a 3rd vector) I also included the rudder in the drawing, as the water flows over the keel and the rudder, and they act as a single wing. This is why a boat must have weather helm, so you get a little bit of rudder to create the needed lift.

On the right is what you propose. To counter the heeling force of the sail, you are creating lift in the opposite direction. When those vectors add, the boat will move sideways, and not forward at all.