Foil / Wings - Aftermarket fitment ?

[Dave_S]

Just dreaming, looking for some interesting reading. Won't do any of it but fun to plan for it.

If I were to fit wings on my rudders and dagger boards I imagine it could conservatively create 400kgs lift @ 10kn....., 800kgs @ 15kn...., and 1,600 @ 20kn.

Must be worth having ?

Anyone know of it being done to existing boats.

Interested in your thoughts.

[NevilleCat]

Ask Jeff what he thinks?
Some pretty interesting forces involved, might need some re-engineering?

[Dave_S]

Your right, I will talk to Jeff before doing anything. My next liftout will include some extra buoyancy in the outboard wells and I don't want to make 2 changes with similar intended outcomes at once so I have lots more time to consider this.

When I started asking around I was just looking for some reading to keep my mind on something of interest. Work is killingly boring at the moment.

However I now find myself actually considering fitting wings on my rudders. Not for lift but to reduce pitch, from what I understand so far is if you fit the wings with 0 Angle Of Attack (AOA) it can have a similar effect on speed, pointing and comfort to increasing the length of the boat.

It partly makes sense but also I can't help thinking there must be a negative side effect that I haven't seen yet other than a small increase in drag in calm water.

The idea is simple. When the boat pitches bow down the AOA of the rudder wing is pulling the stern down providing lift to the bow and vice versa.

This reduces the effort sliding through the swell.

[NevilleCat]

Have seen pics of a Jensen (Colin Ayres?) cat with end plates on the rudder and end plates on the keels too.
There's a big old Crowther cat down here which had low buoyancy hull ends and they fitted the whole sterns with an under-wing. It is apparently still a very fast cat.

[Dave_S]

That's an interesting idea, I was thinking of fitting the wing lower on the rudder. Maybe 100mm from the bottom to reduce the chances of it comming out of the water. I should be able to make it stronger by not attaching it right on the bottom.

[a64pilot]

Most would consider that a “Trim tab” look at power boats and like a power boat, you may want to consider making it adjustable?
An end plate is usually at the end of an airfoil, and it’s purpose is to reduce the wing tip vortice and thereby reduce drag, it does have a similar effect that increasing the aspect ratio does (making the wing longer). If not at the end of the wing, they are called flow fences, you can of course Google flow fence and learn something on them. Both end plates and flow fences can cause “Issues” if the airfoil section isn’t stiff enough
End plates on aircraft well predate the now popular “Winglet” but perform a similar function

[thinwater]

I've thought of this, but I'm not convinced a cruising cat is a good fit.


Rudder. Unless the rudder is fully supporting the boat, there will be a considerable amount of up-and-down motion. I would bet dinner that the wings will be stalled much of the time and the net effect is an increase in drag and reduction in lift. A few inches more length would be more efficient. Stretching the transom is well proven to add lift and reduce pitching. It also lifts the bows, if you move some of your storage aft, which is the obvious thing to do.



Dagger Board. Same problem, but less severe because the pitching is less (near center of gyration). Is lift generated by a foil more efficient that lift generated by buoyancy, when the hull is not going to be lifted much at all? I doubt it because you still have most of the wetted surface drag. What about stability issues? Are you more likely to pitch massively into a wave? Though AC cats ride on foils, they don't do it in the big waves that 20-30 knot winds generate on open water or in swell. Again, longer foils are a safer way to gain windward lift.


There are boats that benefit from foil stabilization, but I'm not sure a cruising cat--even a fast one--fits the mold. But it is an interesting exercise.

[psk125]

Unless you can get the boat going fast enough to begin with, the "wings" will not develop enough lift to overcome the extra drag they create. Twelve meter designs have "wings". Ever see one foiling? Also to consider: wings on the keel and/or rudder that might develop lift (if you DO get going fast enough) could act to oppose righting moment - making the boat heel more. Dinghies that foil are sailed pretty much absolutely flat. Look at the Figaro foils for a wing that might be more attuned to a keelboat application. It's not attached to the keel or rudder.

[psk125]

Re-reading thread makes it apparent that the OP is thinking more catamaran than keelboat, but many of the same issues, as others have pointed out, apply.

[longjonsilver]

Check out this thread:
http://www.cruisersforum.com/forums/...ri-183906.html

[hellosailor]

Well it worked for the America's Cup hydrofoil cats, right?

Simple matter of taking some college-level courses in hydrodynamics, engineering, materials, some math, then just fab up the parts.

That shouldn't cost more than lunch money, right?

[Dave_S]

It's purpose is not so much as an end plate but a self leveling system by creating negative lift at the stern when the boats attitude is nose down and positive lift when the nose is up. This will reduce pitching and create drag. But will it create less drag than punching through the swell, I think it might.