Imperfections--63 Series Verses The 00 Series Compound Tapered Foil Keel

I have now built two prototype male keel molds based on the 63 series foil. After careful construction and fairing i can get overall frontal area tolerence within 1/8 of an inch. This would include say the entire 25% of the keel back from the nose. I can get the nose area faired within 1/16 in. tolerance. I am refering to the male mold itself when i list the above tolerances. I expect that these will be compounded somewhat after laying up and no matter how much fairing i do after I will be luckey to keep within the above tolerance levels. The Idea here is to come up with a fabrication system that the average home builder can work with. Question ? Am i better to stick with the 63 series and live with the above tolerances or go with the more forgiving 00 series. My Thinking, The 00 series mold could be built within the same tolerances by an experienced woodworker easily enough but would be more tolerant of imperfections of less talented workers. Keep in mind these are low aspect elongated foil shapes(parallel mid section) home built keels meant for use on cruisers and motorsailers. All input much appreciated---Geo.

A yacht is not defined by the vessel but by the care and love of her owner--

 

The oo series will be easy to build and more effective on moderate aspect appendages. I'll assume that you parallel sided foils are the straight or slab sided foils I often employ on cruisers and low budget builds.

If this is the case (can you post a drawing of the foils section?) just rounding over the leading edge, I use a slightly elongated shape, more of an ellipse, is all that's necessary here. Then an easy taper to a crisp trailing edge. The low aspect appendage can't generate enough lift to make much more shaping effort worth the bother. In fact, some will argue it does little if any good at all, but I disagree. I've run side by side tests on identical boats, one with a square faced and sided, low aspect appendage, while the other had slab sided foil sections of the exact dimensions. The shaped foil had much better "penetration" when the wind was forward of the beam. This was most obvious when in very light conditions, as the square faced appendage would act as a brake, while the shaped appendage manage to carry through and make way.

As to accuracy of the appendage shape, symmetric sides are probably going to be more important then the occasional surface imperfections. Naturally, if the count or size of these imperfection is large, you'll see a noticeable difference, but only in a testing tank. In most cases sail trim and skipper attentiveness can account for the majority of preformance differences, not imperfections in the foil surfaces.

In other words, don't get too anal about it, the average builder/skipper will not be able to tell the difference. If their skill level or willingness to fair the appendage, leaves substantial imperfections, I'll wager that they'll also lack the helm experience to notice any differences.

 

Thanks PAR I knew I should have posted a photo--In this case it's not straight sided that would have been simplier but because the existing keel is so wide I had to taper in the cross section to get down to a reasomable width at the bottom of the keel. (from 91/2 in. to 7 in.) In my first prototype I tried to taper in the first 6in. of keel dept then run flatsided cross sectionally from there but it was just getting too dam difficult to control the dimensions accurately plus the resultant glass shell would have been a nightmare to re fit.( left and right photos). I then disgarded that approach and am now building the keel and skeg molds tapered directly to fit the existing keel (middle photo) I will blend the existing wide keel into both the new keel and skeg foils using plastic deck lumber shaped to suit, glassed over and faired into the new appendages. I've used plastic deck lumber in boat projects before, it steams and shapes much easier than wood into complex forms. Particularly, as form shaping where high impact loads occur.( stronger than foam) --Geo.

 

To continue my post(company dropped in) You have answered my concerns. The imperfections I was worried about were not surface smoothness but small variations in the overall curivature of the front sections and the nose of the keel itself. In otherwords the results of failing eyesight and steadyness of hand cutting the foil shapes from 3/4 ply . I can now continue with my 63series build. On my posted build site I'll recommend to those with challenges of tool operation go with the 00 series foils. Thanks again ---Geo.