Planing sailboat theory question.

[ErikG]

According to Pierre Gutelle "Design of sailing yachts"

He writes that having a v shaped bottom will deflect spray not forward (wich creates the optimum lift) but sideways and therefore reducing lift.

But here are some thoughts from me...
Since a planing sailboat almost always have a slight heel (you never go dead downwind), couldn't a slight V shaped bottom actually create a "flatter bottom" in real life while heeling?

Have someone compared drag and lifting force between similar hulls where the only diiference is bottom shape rounded vs. slightly V'ed under real life conditions, with a slight heeling to the yacht?
-------------------------------
I know most fast sportboats have a semi-rounded shape with almost or completely flat aft sections. Is this the best compromise? (I guess it might be, but dont know why). Could it be because the V actually inreases resistance causing eddies?

Any ideas, thoughts or suggestions?

If I can find the time I'll try to make som models and measure the diffence in drag, but if someone already have done it... No need to reinvent the wheel...

ErikG

[tspeer]

One thing that's different between a sailboat and a powerboat hull is the sailboat is making leeway going to windward - when the drag is most critical. A V hull will promote separation and a draggy vortex along the centerline when the flow's not parallel to the ridge.

[Pointyendfwd]

I have thought about his a little.

The 18 foot skiffs have assymmetric spinnakers, which are used to broad reach at high speeds.

These spinnakers actually lift the bows of the boat out of the water, so the only the aft part of the hull touches the water.
The shape of the bows become unimportant in this mode of sailing. It is however important while the boat is moving from displacement to planing mode.

The skiffs have an almost completely flat aft section, and are sailed pretty upright, with a crew standing out theeeere on outriggers.
This is my take on the hullshape of the skiffs, but of course I can be completely wrong and would like to know from someone who has actually sailed them.

On the dinghies I have drawn, I looked at the wetted surface comparison between an upright hull and one which is heeled slightly.
With the vee bottom, the wetted surface decreases as the boat is heeled, up to a certain point. This obviously decreases viscous drag, but I do not know what happens to the from drag.

If you also pitch the boat slightly forward ( in addition to the roll,) the drag further decreases, and this is practically possible on dinghies and used in light air sailing.