hollow centerboard?

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hollow centerboard?

Postby fred4936 » Tue Feb 28, 2006 1:19 pm

We've had a Daysailer (II?)for a couple of seasons now and enjoy sailing it very much. One thing about this boat that seems odd is that when we lift the boat out of the water using the hoist after sailing, water drains out of the centerboard itself. I've never seen a hollow centerboard, and have a feeling this one shouldn't be either. Has anyone else have this issue?
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Postby Bob Damon » Tue Feb 28, 2006 1:27 pm

Yes. My first Day Sailer was a II. It had a hole in the cb and it seems it was designed to do this to provide more stability to the boat. It also makes a slow boat even slower. I eventually pulled the board and drilled another small hole as far down as possible to let the water drain, then let the board sit for a month to dry out. I then used some small wooden dowels to plug the holes and refinished those spots with marine tex. I understand these holes are in all DS II standard centerboards.
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Postby deadreckoning » Tue Feb 28, 2006 2:11 pm

Intriguing. How would a hole in the CB provide stability?
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water in cb

Postby Roger » Wed Mar 01, 2006 12:55 am

There has been some thought that a hole near the top and a hole near the bottom of the cb will allow water into the board to make it heavier than the air it displaces, thereby adding additional weight to the board, creating more righting moment, and allowing the boat to sail more upright therefore faster. The trade off is that placing the bottom hole in the flow of water actually acts on the water within the board to draw it out by suction. Water flows in the top hole to replace the vacuum. Theoretically this water movement acts to slow the boat down, hence the trade off. The maximum wieght of the cb is 25# according to the class rules.
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Postby fred4936 » Fri Mar 03, 2006 5:04 pm

Thank you all! I'll plug them up this spring!
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Re: hollow centerboard?

Postby bilbo » Mon Sep 21, 2020 2:00 pm

I noticed this hole in my CB while underneath yesterday looking at how the CB rigging cleat was attached to the trunk. My first thought, since I live in the frozen North, was the effect of contained water's expansion as it freezes. Assuming the board is original, it's seen winters for 40 some years and apparently not had an issue, but still made me think why didn't they build it solid in the first place? Cost I suppose. Anyway, has anyone seen issues from freezing in these boats centerboard or otherwise? Are there places I need to make sure to get extra dry before winter?
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Re: hollow centerboard?

Postby GreenLake » Mon Sep 21, 2020 7:22 pm

Wow, you have been taking my advice and gone way back in the old posts! Good for you.

The reason to make the CB hollow is the limit on total CB weight. This way, you can build a heavy (strong) skin w/o worrying about enclosing volume that leads to buoyancy (which would negate the effect of the allowed weight).

Looks like the drain is working as it's supposed to. Other than trapping water in the bilge, I'm not aware of places that need to be drained. Not all trapped water will cause damage; I had soggy foam that did not cause issues. I guess other than really tight spaces like inside the CB or inside the rudder (the latter only if cracked), there's usually room for the ice to expand.

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