Monday, May 25, 2009

New centerboard (part 5)

We know a family with 2 homeschooled boys; the older was really interested in working on the boat with me, so we invited them over. I showed him the work and he started planing the bevel. He ended up doing the rest of the side I had started. Later I tried clamping the centerboard on to the work bench in the garage and found that I could plane better there than on sawhorses. I beveled unevenly on purpose. The low point on the centerboard is often the first thing to hit bottom, so I left it thick for strength. (Perhaps a little metal reinforcement would be good here?). I also left it thick around the hook. You can see this in the path of stripes.

When the centerboard is up, it is held in place with a fid.

For the fid there are 3 holes in the centerboard. One is in the full up position, for beaching, trailering, shoals, etc. I've never messed with centerboard positioning very much, but when I have an easy-to-move centerboard, I will have a chance to experiment. I need the holes to be big enough for a 1/2" fid, but I don't have a 9/16" bit. I do have a 5/8" bit (uggh, these fractions are confusing!), but that hole seemed way to big. I ended up drilling with my 1/2" bit, and then wiggling the bit around to make it a little larger. Then I got the advice to put a couple thick layers of epoxy on the centerboard before I paint it, so I figured I should make the holes bigger now, so the epoxy doesn't make them too small. I drilled to 5/8" afterwards. (Yes, the bit kept jamming; it sucked.)

I drilled a 1" hole to hold the stopper knot for the centerboard lanyard, and then a 5/16" hole from the edge to the 1" hole to put the lanyard through. I practiced doing this a couple times on a piece of scrap plywood, and I'm glad, because it's hard to do well. The drill wants to drop to a softer ply, would would make the hole off-center. An awl + a very tiny pilot hold did the trick. Even so, it's hard to drill through the edge of a board and keep it perfectly centered. I was a little off when I came out in to the 1" hole, but not by much. (And it's better than the original centerboard's lanyard hole, so I'm happy with that.) If I ever do this again, I will look in to a jig.

From Jay Bazuzi's personal blog

The plans call for a metal plate around the hook to reinforce it. It says to use 1/8" brass plates, at 3" x 5 1/2". I wasn't sure if I could pull off the old plates without damaging them. The plans say to screw them in place, but the old ones were just epoxied in. Turns out that made them really easy to remove: a prybar under one end and they popped right out. (The alternative was to buy new brass from Amazon; $25 for a 12" square sheet, free shipping with Amazon prime, but without a bandsaw it might be hard to cut.)
From Jay Bazuzi's personal blog

Using a 1/4" bit to provide a starting hole, I used my grandfather-in-law's J.C. Penny jigsaw to cut around the lead sink weight in the old centerboard. Now there's no going back! The lead is held in place with small nails or screws, but the jigsaw only hesitated at these. After cutting 2 1/2 sides, I was able to pry the rest of it out. Wow, it's heavy! Duh. 11 lbs. (The alternative was to buy lead on Amazon, which I was surprised to find.) Now the old centerboard is really light. I suspect the wood I'm using is denser than they old centerboard, so I may not need as much lead to sink it. Hmmm.
From Jay Bazuzi's personal blog

From Jay Bazuzi's personal blog

While cleaning up I spilled the big bin of legos right in the sawdust pile. I don't really want glue, wood, and and metal shavings on the toys that my kids like to put in their mouths, so I hauled the legos inside for a washing. There are piles and bins of drying legos all over the kitchent.
The brass plates are supposed to be set in the plywood. Not flush, but not on top, either. Without that, the brass would scrape the inside of the centerboard trunk. Cut flush would take 1/4" out of the 3/4" plywood (which is really more like 5/8" thick) and leave it weak at the point where strenght matters most.

I bought some chisels and a small mallet, and experimented with cutting a 1/16"-ish deep hole in my scrap plywood. I think it will be fine. However, these chisels aren't as sharp as they could be, so I'll spend some time on the sharpening plates before I cut the holes.
I think I will use both screws and some Gorilla Glue to hold the brass reinforcement plates in place. Belt-and-suspenders, I know. But better to make it easy to remove in the future + more secure now. I brought some #10 3/4" brass screws (like metals, right?) and experimented with drilling a hole in the brass for them. I also beveled the edges of the brass a little, to make the transition to the plywood fairer.
I am worried that the screw heads sticking out would focus the force of the moving centerboard and gouge the centerboard trunk. I plan to countersink the screws, but again, if I sink them too deeply, I'll loose the strenght of the brass. My plan is to sink them 1/16" in, leaving 1/2 the thickness of the brass plate under the screw, and only a little bit of screw head sticking out. Another reason I'm planning to use Gorillage Glue - to alleviate the stress on the screw holes.

I plan to cut the slots for the brass plates to be a snug fit, which should also help.
The lead pouring plan is coming together. I decided not to go for an asbestos plate to back up the hold, instead using a piece of scrap plywood. I will do a test pour in a scrap piece, so I can develop my lead casting skills, and then do it for real. The only thing I'm missing right now is the propane tank, and a friend said he'll loan me his.

Updated TODO list:

- Clean up the cuts that went off the line
- Draw and cut the curve at the top
- Plane down the leading and trailing edges
- Cut a hole and pour in a lead sink weight (first time pouring lead!)
- Cut a gap for the pivot
- Prepare 1/8" sheet brass as pivot hole reinforcement (in progress)
- Drill 5 holes for fid and lanyard (ooh, the easy part)
- Epoxy and paint
- Install centerboard & lanyard
- Put boat back on trailer

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