Wednesday, April 1, 2009

Boat Balks At Building Pace; Builder Gnashes Teeth

Boatbuilding on a schedule? What a comical notion! Capital! Thank you for the laughs, Dr. Humorous Droll.

Getting everything assembled (and glued, and bolted, and final-shaped, and sanded, and sealed) for this weekend was going to be a tight schedule anyway. But things slipped off the rails last night with the discovery that my pivoting centerboard does not pivot. This is like having a car's wheel that does not turn.

Luckily nothing's been put together yet, and some careful work with a belt sander will remove enough of the pivot area to enable the hell-blasted, snicker-snack, thunder-and-death, red-gobbled centerboard to swing freely. Once everything is loose and movable, I can put the board inside its case, insert the pivot pin assembly, and bolt/glue the whole thing together.

The pivot pin is an interesting conundrum. It consists of a steel tube that fits snugly through a hole leading from one side of the well, through the board, and through the other side of the well (the well is like the casing for the board; the bread that sandwiches the ... peanut butter ... that is the board). Then you thread a bolt through the tube, slather it with grease, and tighten nuts down on either end to forestall leaks.

Here is the question that make me wrinkle my brow at work and set up miniature tests with business cards and pencils. The bolt is designed to turn inside the tube. But the tube doesn't know it has a bolt in it, and the bolt isn't attached to anything except the tube. What pivots?

I mean, obviously the board swings up and down and something is turning. Either the board pivots on the tube, or the tube sticks to the board but pivots inside the holes on either side of the well.

For the life of me I cannot understand what function the bolt provides besides keeping water out. But if that were the case why not go with solid rod?

Hulk confused. Hulk crush!


Peter S said...

I think I've got it. The hole in the centerboard is slightly bigger than the diameter of the tube. The centerboard rotates on the tube, as you would if you swung from monkey bars. The threaded rod is there to transfer the load from the tube, on which hangs the centerboard, to the well sides and down through the hull. The threaded rod/tube setup gives you two chances to get your waterproofing right. Since there's a lot of stress and movement, waterproofing is important.

Or I could be totally wrong.

S R Wood said...

Sigh. Unfortunately, the tube is taking all the weight.

Ostensibly the bolt is the real pivot for the whole thing, and the tube is just there to prevent the well sides from collapsing inward when the bolt is tightened.

Because the tube fits snugly (though loose enough to turn) in both the centerboard and the well sides, the weight of the board is transferred through the tube. The bolt just sits there. I think. Uh oh, Hulk angry! RNGNRRRGRRRR