Apparently the mold from which this all-lead keel came wasn’t perfect. One side is definitely better shaped than the other. Someone at Hunter R&D back then was a little slack.
My dad had a book of NACA (National Advisory Committee for Aeronautics) aerofoil shapes which he used in developing keel sections. But do not be too literal or liberal when it comes to applying what we know of airplanes to explain the ‘black science’ of yacht design. The two are not directly analogous. For one thing, an airplane wing, though it must minimize drag, does not generate thrust, only lift. A sail generates thrust as well as lift. A keel generates lift; but the standard single-keeled sailboat must be symmetrical; thus even as one side generates upwind lift, the other side, being the same shape, tries to negate it. It’s kind of like the reason why a helicopter can’t go as fast as an airplane.
For the curious or just terminally nerdish there is some good information on Wikipedia about the NACA shapes. I don’t know where my dad’s book has got to but Wikipedia makes it easier to find. I suppose I am just too lazy to learn this stuff any more; but I promise you my dad was a genius at trigonometry and talked aerofoils like some people talk baseball stats, second-nature and effortlessly.
After I rebedded and faired the hull-keel joint I took a few power tools to smooth out the shape. I was frustrated that the right side would just not get as lean and flat as the left side-- until I observed that I was starting to grind lead. (No, Mom, I didn’t have a mask on. No, I don’t care. I’ve spent a lifetime doing this stuff.) So the task had to be to fill out the slacker left side, the side I’d thought was the better of the two.
Upon further inspection I realize that the right side really is better. Right now Diana has about 3/16” of putty on the left side, in attempts to flesh out the keel shape. At the root (where an aerofoil meets the hull or fuselage) a little too much chord is probably better than too little. It’s not where lift is created but where drag has to be reduced, including that of skin friction. But it’s also where strength can be had from surface area; so I am making the keel fatter here.
[2011.09 keel 1a.jpg]
Photo 1 shows the right side. You can see the obvious convex curve in the root of the keel; the small dark oval shape on the hull is just about right over the chord point. The keel is about 5 inches wide here. This is as it should be.
The two roundish patches are from the removal of the toilet through-hulls. I put duct tape over the hole on the outside, cut out ‘cookies’ of fibreglass mat and lay them up on the inside, roller out all the bubbles (using some pressure), and then go out and grind off the resulting bulge that pushed out against the duct tape. Imagine if you patched it on the inside first-- and then you would never, ever, be able to lay up ‘glass over your head without having bubbles. Doing it once the wrong way, I learned. Now you know-- so you have no excuse to repeat my mistake.
[2011.09 keel 3a.jpg]
Photo 2 shows the left side. This was so slack along the root that I had to carry the filler aft to the trailing edge. Someone had ‘glassed over the trailing edge with a cuff of glass that was, in alternate places, either barely hanging on or impossible to remove. I ripped the whole thing off, faired the lead where trapped water had helped the lead corrode into alarmingly-wide striations, and applied the olive putty. Wherever the putty is were low spots. It is faired and smooth in this photo, despite the color changes, but it is not out to where it should be yet.
Since this photo I came back after too long a hiatus and applied more putty and then woke in the middle of the night realizing I had stupidly used the fairing compound (the white) and not the structural one (the olive). I actually had forgotten what the stuff looked like uncured (the can labels are too messy to read now). So I will fair off the white and just apply more olive. My cousin Lee likes the WM structural putty, which is like the more expensive 3M variety. ‘Sticks to anything and won’t fall out,’ he says. Back in the CBC days we used to make it out of a variety of nasty things, including chopped fibers from the chopper-gun and even actual sand, calling it ‘mishmash’ or ‘Dark Vader’, and kicked it with (a lot of) plain MEKP. The prepackaged stuff contains plain fibers about 1-1/2” long and comes with cream hardener. It’s easy to work with and easy to sand fair. I will just have to have a sandwich of olive-white-olive on the left side; but so long as it’s all adhering it won’t be a problem. This keel joint has so much 5200 in there that even a slight horizontal crack someday won’t be anything to worry about.
What did I say once about most boat work being half mooyock? Guilty as charged.
The whitish places farther down are bare lead where the bottom paint parted. This bottom paint is very old, and it’s copper-based. The cupro-nickel content applied directly to the bare keel for use in salt water caused some chemical decomposition of the lead. NEVER apply bottom paint to bare metal. Even spraying the metal with Krylon before bottom-painting is better than leaving the metal unprotected. I will trowel Interprotect or maybe even just WEST epoxy all over this keel before painting the bottom again. I just do not know how much I will worry about existing bottom paint with good adhesion. You can see here I’ve puttied right on top of it. If it’s sticking that well, why rip it off? I can fair any imperfections before the paint stage.
The hull itself is actually in very good condition but for the sake of weight, ease of fairing and general anal-retentiveness I have been stripping it with Bio-Blast and, when that did not work, StripEaze. The light-colored region above the keel, forward of the darker, is where I have stripped some. So long as there is a little bit of blueish tint to the white where I have scraped off paint, I know it did not chemically attack the gelcoat. The bluish tint will be fair enough to just apply paint right to it (if no more work is needed).
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