I've spent quite a few hours over the last several months trying to determine what a new centerboard should look like.
Since the plan view is controlled pretty tightly, I've concentrated on and struggled with things such as:
-What wood should I use?
-What width should it be?
-What cross section?
-How do I keep the centerboard handle pin from shreading the wood to shreds?
Surprise is a heavy boat, and there's little I can do to lighten her. Therefore, I am choosing a light wood for the centerboard. I hope that this will not reduce her stability. The wood I have chosen is Sitka Spruce. I have a source for it here in Houston. It's expensive, but hopefully I won't have to make too many of them.
It seems reasonable that the centerboard trunk opening should be the minimum width 1-3/8". Surprise's CB trunk is wider. Therefore, the centerboard should be 1-3/8" maximum, and I will narrow the trunk opening. With a chord length of 14-1/2", This width results in about a 9% width to length ratio.
The advice I've received has indicated that a wider board will "dig in" at lower speeds. At the speeds a Day sailer operates, having as wide a board as possible will be better than any disadvantages incurred by the same... I plan to use two layers of glass - but I will use more if the board as shaped will allow it. I may vacuum bag...
I had originally considered using the NACA four digit cross section, but also considered a Selig-Donovan 8020... I have instead gone with my original choice -NACA 0009.
I bought a bearing plate from Cape Cod. This will be inlaid into the board head and probably through-bolted.
I have made drawings and the plans are set. The workshop is available, the tools are there. With the blessing I should have a new centerboard in time for next year's sailing.
Posted by Bob at December 16, 2003 09:44 AM