Surface piercing foils, why set at 45 degrees

[Doug Lord]

Proven benefits from windsurfers to Hydroptere-do it if it doesn't add too much complexity at your size. Cool thing about a monofoiler is that veal heel does that and a lot more including a big increase(20%) in RM for "free".
Look forward to more about your project!

[tspeer]

Originally Posted by waynemarlow

...What are the pitfalls of outer facing foils ?

The side force and the coupling with leeway goes the wrong way.

If you generate vertical lift on the leeward foil, the sideways component is directed to leeward. Some other foil will be needed to oppose the side force from the sails, and it will have to carry a higher load than normal.

When a gust hits and increases the leeway angle, the vertical lift will decrease due to the leeway reducing the angle of attack of the foil. This will cause the boat to roll to leeward - just what you don't want at that time.

[Gary Baigent]

Tom is correct about the to leeward shift - but I found, even in some savage gusts, with the boat sailing at speed, the lee float and foil never buried further than a few cms. below the float rocker - so outward slopers do work. One important advantage of outgoers is that the main beam/beams can be reduced in length - the foil creates a longer overall beam, therefore lighter platform because of less material. The opposite occurs with conventional in slopers, beam reduces with lift off, as does stability. That is why l'Hydroptere is 80 feet wide by 60 length. Having said all this, I've changed to inverted Y's.

[Doug Lord]

Originally Posted by Gary Baigent

Tom is correct about the to leeward shift - but I found, even in some savage gusts, with the boat sailing at speed, the lee float and foil never buried further than a few cms. below the float rocker - so outward slopers do work. One important advantage of outgoers is that the main beam/beams can be reduced in length - the foil creates a longer overall beam, therefore lighter platform because of less material. The opposite occurs with conventional in slopers, beam reduces with lift off, as does stability. That is why l'Hydroptere is 80 feet wide by 60 length. Having said all this, I've changed to inverted Y's.

==================
Gary, have you ever sailed your boat(w/"outgoers") upwind against another boat that was fast enough for you to judge the upwind ability of your boat?

[Gary Baigent]

Doug, was excellent to windward, couldn't see any difference in pointing ability - but then my wing mast rig is clean and efficient and that might help. In light airs, larger keelboats (where they're at their best) could outpoint me by a few degrees - but Groucho was always faster - pretty normal for multihulls. You could point as high as the keelers but your speed was down and they moved away, let the boat sail itself, pretty soon you were ahead of fleet. Remember Groucho has a main hull dagger, not relying on entirely on foils for countering leeway. Without dagger, not good windward performance, definitely went skidding. But then that was the same with inward slopers too.

[Doug Lord]

Thanks Gary. Did the dagger rotate(change angle of incidence from tack to tack) or was it fixed?

[Gary Baigent]

Bit more useless information - used to sail a Newick 36 Mokihi with angled in 40 degree foils. Winning Coastal Classic one year it was beat in 5 knot airs from Cape Brett to Russell - we pushed the main hull dagger down to its limit, leeward float foil down too, and just walked away from the closest competitors, multis and much larger keelers, no one could touch us and we could hardly see them astern at Tapeka - that main dagger is very important on a foiler.

[Gary Baigent]

Dagger fixed.

[waynemarlow]

Originally Posted by tspeer

The side force and the coupling with leeway goes the wrong way.

If you generate vertical lift on the leeward foil, the sideways component is directed to leeward. Some other foil will be needed to oppose the side force from the sails, and it will have to carry a higher load than normal.

When a gust hits and increases the leeway angle, the vertical lift will decrease due to the leeway reducing the angle of attack of the foil. This will cause the boat to roll to leeward - just what you don't want at that time.

Surely as both windward and leeward foils are creating lift in opposite directions, the windward foil must be generating lift toward the windward countering the leeward foil ?

I need to have a flat downward foil of some kind at each end of the foils to prevent " beaching " damage, I had thought perhaps like the winglets used on gliders and aircraft, perhaps these would have enough area to act as leeward stabilisers.