Monday, March 30, 2009

New centerboard (part 1)

My boat (12' Bolger-designed plywood catboat, called a Bobcat or Tinycat) has centerboard trouble. It sticks badly, and I have to work hard to push it down and pull it back up.

Getting it out is a bit funny: you have to pull it out of the bottom of the boat. The boat is in the 400-500lb range, so getting it off the trailer, on to the ground, and rolled over is not something I can do solo! I finally got some friends over and 4 of us were able to lift the boat, roll it on to its side, and pull the old centerboard out.

My first plan was to use an orbital sander to lower the high spots, put a layer of fresh paint on it, and put it back in. Progress was slow at first, so I bought lower, and then still lower grit sandpaper. I then found that one side had been epoxied. I think that means the other side got soaked, and the board warped from the uneven wetness. I also did some measuring and found that the centerboard is about 1/8" thicker than specified in the plans. I decided to go for a new centerboard.

Original plans suggest laminating 2 or 3 layers of 3/8" or 1/4" plywood to make a 3/4" centerboard. I also want to make a new rudder at some point, and it's laminated to 1 1/2" (6 layers of 1/4"!). Instead I bought a single 8' x 4' sheet of 3/4" marine plywood at Edensaw Woods for $120. (I bought it with all 3 kids in tow, and we strapped it to the top of the minivan. Home boat building, yeah!)

Plenty of things stopped me from attacking the new centerboard, including lots of uncertainty about how to do it. I spent a while trying to cut and plane a small piece off the corner of the plywood, just for practice, and did learn that working with 3/4" plywood is hard work.

I eventually read some thoughts about overcoming procrastination with action, and decided to get cutting. I placed the old centerboard on the plywood & traced a line. Then I attacked it with my small cordless circular saw (not quite powerful enough, and won't cut a curve) and my grand-father-in-law's old J. C. Penny jigsaw, which will cut a curve but slowly, and it likes to splinter the veneer as it goes. I also decided to curve (a 4" semi-circle) the top point of the centerboard, instead of cutting it straight like on the plans. I think it'll look nice. (Maybe I'll discover why it was specified to be straight.)

It took 3 sessions of cutting, but today I finally finished separating the new centerboard from the rest of the sheet. What's left:

- Clean up the cuts that went off the line
- Draw and cut the curve at the top
- Plane down the leading and trailing edges (need a low-angle plane)
- Cut a hole and pour in a lead sink weight (first time pouring lead)
- Cut a gap for the pivot
- Cut some 1/8" sheet metal to reinforce the pivot
- Drill 5 holes (ooh, the easy part)
- Paint (no epoxy)
- Install centerboard
- Put boat back on trailer.

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