Centerboard

Graham has redesigned the centerboard for EC22. He wanted to remove an annoying touch of lee helm. which became worse when the board was partially raised as when sailing close hauled in shallow water.

The new centerboard has a lead tip sized to make the board sink and stay on the bottom but kick up readily if an obstruction is encountered.

First task is to laminate a dozen or so boards to make a 61 inch by 16 inch blank. Laminating from a lot of small sticks is time consuming but allows you to select for good straight wood and control things like grain orientation. Hopefully this results in a centerboard that has little inclination to twist, bow, warp, crack or mess up.

There needs to be enough lead on the board to make it sink and stay down even when the boat is at speed.

 Graham suggested about 15 pounds of lead. Someone else used about 18 pounds for a similar board.

 I decided to try to calculate the weight of lead needed and the amount of the board that should be lead.

That is should the bottom 2 inches of the board be lead or bottom 4 inches or 6 inches?

I could figure this out empirically by taking the completed board out into the water and piling weights on it until it sank. Then add a few pounds for good measure.

Another way involves calculating the volume of water displaced by the board and using the density of the board and the density of water to arrive at the amount of lead needed.

I carefully measured and weighed my centerboard blank to determine a density or 0.017 lbs/cubic inch.

The density of water is 0.036lbs/cubic inch

The density of lead is 0.409lbs/cubic inch

The density of my Douglas Fir centerboard is about half of the density of water.

After the blank was glued up and smoothed I cut it to shape in two dimensions. Then I marked the edges in preparation for shaping the board in the third dimension.

Did I mention that some centerboards are flat, however a board with a air foil like shape is more efficient.

 

Heading North to escape the snow.

I have been looking forward to heading back to Rhode Island so I could get back to work on SKORPA.

Putting up firewood, felling saw logs, sawing lumber, erecting a fence all tasks that needed to be done. None of them made easier by the beautiful white stuff. A couple of weeks later than I had hoped we left Virginia and headed for my long silent boat shop.

Everything was just as I had left it. Not a thing had been done.All the work I had done last summer looked pretty solid. Nothing had sprung apart.


First order of business is to glue in the mid transom beam. It was already fitted just needed some creative clamping arrangement to hold it in place.

I need to put pressure on the beam running down the center inside of the transom, way too deep for any clamp I own to reach.

With some scrap lumber and my ordinary C clamps I have an arrangement that can put just the right amount of pressure just where I want it.

Here as the clamps are being removed you can see that the mid transom beam is laminated from two pieces and wraps nicely around the king post or whatever that big board going up the center of the transom is called.

High on the list of things to do is the centerboard and centerboard case.