Teardrop End Plate On NACA Flat Bottomed Fin Keel ??

[webbwash]

Two additional thoughts come to mind --
1. If you are set on the additional "ground plate" follow JeHardiman's advise and make it come shy of the leading edge of the keel, you want to keep the kelp from becoming entangled.
2. If you don't want to improve your AR, Aspect Ratio, hence improve efficiency to windward, then the addition of "winglets" ala the twelve meters and some of the Hunter Boats, is viable. You have to do the displacement/wetted surface/performance design spiral a couple of times around to find out that the improvement is not $$$$$. Change the rig to a "modern" carbon fiber, get improved sails, and smooth bottom may add better performance than messing with the keel.

There is only so much you can do to increase the performance of cruising boat -- have you thought about adding a scoop which would add a nice swim platform and some waterline length.

Every change that you make - including taking out the interior and the extra bathtub and replacing them with lightweight joinery or nothing at all will "improve the performance" but at what cost to the comfort of cruising and the enjoyment of just being on the water.

[RDKinard]

Guys,

Part of our problem may be the 1-2" gap (along the tangent streamline) between the skeg and rudder, adding drag (see attached photo). Looks like the builder located the rudder pivot about 3/4" aft of what the architect wanted, leaving a large sucking gap between the two.

The marina suggested adding Teflon fins between the skeg and rudder which fill the gap and flex with rudder angle. The Navy 44's all have such fins added.

Does this make more sense to reduce drag than a foil on the bottom of the keel?

Captain Rich

[sorenfdk]

Originally Posted by RDKinard

The marina suggested adding Teflon fins between the skeg and rudder which fill the gap and flex with rudder angle ... Does this make more sense to reduce drag than a foil on the bottom of the keel?

Short answer: Yes.

[prancer]

So, did you ever try adding an end plate to the keel, and if so, how much quicker was the boat?

[tspeer]

Marco Trucchi had posted one of the few really decent papers on the fluid mechanics of keels.

This figure is particularly relevant to this thread:

It shows that if you want to improve the performance of your keel, you're far better off tacking the wing on as a straight extension of the keel than you are using it as a winglet.

Wings only make sense if there is some non-hydrodynamic constraint on the depth of the keel, such as class rules or the depth of the water.