Centre boards

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Frank Frank
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Centre boards

I have a little problem.would appreciate some advice.
I have snapped the centreboard on my ELEVEN PLUS  sailing dinghy! Well it was old.!
It. Was ply. I am not sure whether to replace with marine ply, expensive, ... Laminate hardwood, even more expensive, or find a table in oak,teak or pine, and cut to suit.possibly cheapest option.
Are laminate hardwood ones stuck together as vertical strips or flat sheets like ply.
If using table top is pine too easily warped being soft and knotty?  Hope somebody can help  would like to practise more capsizing soon!
Timmo Timmo
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Re: Centre boards

Not got vast experience, but my tuppence worth:

Replacing like for like with marine ply seems sensible. It's a critical piece of kit so worth investing in. You've got a limited width in your centreboard case for the board to fit so my thinking is that each part of the board should be as strong as it can be for it's width.

I've made a dagger board from iroko. Not cheap but cheaper than some alternatives. That was made from vertical strips laminated together and is holding up very well. Strips were reversed and inverted after cutting to stabilise the structure and avoid warping.

Like the idea of using a table top as the source for hardwood. Would personally avoid pine and look for something stronger and more resistant to rot. I'd cut the table up and re-assemble the strips you make. Be sure to remove any old glue lines (i'm assuming the table was laminated originally.) The old glue is unlikely to be of marine quality... that's learned by experience!

Not yet done this (though the build I'm working on does require it so I'll do it soon) but sheathing the plate in epoxy and glassfibre will make most choices of wood stronger and more water resistant, though the pivot hole will require thought if it's not going to be a point where water gets under the sheathing. Means deducting the thickness of the sheathing from the thickness of wood, so there's trade-offs.

Now for others with wider experience to contribute...


On 1 Mar 2016, at 23:23, Frank [via UK HBBR Forum] <[hidden email]> wrote:

I have a little problem.would appreciate some advice.
I have snapped the centreboard on my ELEVEN PLUS  sailing dinghy! Well it was old.!
It. Was ply. I am not sure whether to replace with marine ply, expensive, ... Laminate hardwood, even more expensive, or find a table in oak,teak or pine, and cut to suit.possibly cheapest option.
Are laminate hardwood ones stuck together as vertical strips or flat sheets like ply.
If using table top is pine too easily warped being soft and knotty?  Hope somebody can help  would like to practise more capsizing soon!


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NAML

simplesimon simplesimon
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Re: Centre boards

In reply to this post by Frank
Check the class rules first. They may require a particular construction (like ply ...)
Chris Waite Chris Waite
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Re: Centre boards

I reckon TimmO has it just about on the button

He's covered every angle and all the pitfalls

Happy sailing

Chris W
Paul (admin) Paul (admin)
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Re: Centre boards

In reply to this post by Frank
Unless you are seriously interested in racing, or might sell it to a racer I would ignore the class rules. But if racing is important class rules are paramount.

Otherwise Tim has given great advice. If the boat is out of the water during the week or most of the time then rot on the bottom sides should not be a problem - any absorbed moisture will slowly dry out. But the top sides need protection from rain and sun.

A Lloyds warranty on marine ply is void if the edges are not sealed. Given the life of a centreboard permanent sealing is impossible. The tip will drag and scuff the sea bed exposing end grain.

Many of us have successfully built centreboards and rudders from external ply (at 1/3rd cost) by carefully sealing any voids with epoxy and aligning the leading edge with a "good" piece of ply when cutting out. I fill voids with liquid epoxy, wait 10 minutes and add more, until gravity fills the voids. You could test the board supported by bricks with your weight.

I coated my centreboard with Jotun 2 pack epoxy grey primer and 2-pack Jotun polyurethane white top coat. It's messy to apply but dries rock hard. It is laminated from 2 layers of 9mm ply, opposite grain as Tim said to increase strength and avoid twisting.

Painting the centreboard and case interior white was one of my best decisions. Every surface is well lit and clearly visible down to the water. If jammed with stones or mud the solution will be clear. In other words, I know how hard to hit it with a big hammer.

-Paul

Port-Na-Storm Port-Na-Storm
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Re: Centre boards

If you can find an old table with a solid top for less than the price of plywood then good luck.
In this neck of the woods it would be given a quick thin coat of emulsion, rubbed back a bit and sold as shabby chic for a small fortune.
I wouldn't use pine, too soft and lacking in strength.

My preference would be ply, sheathed in epoxy/glass with a metal strip on the corner for protection from scuffing. Drill the pivot hole way oversize and fill with thickened epoxy, then drill through to form an epoxy bush.
Grum.
Chris Partridge Chris Partridge
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Re: Centre boards

One of the advantages of a daggerboard is that it is available for inspection every time you get the boat out of the water. If it is damaged, warped, bent, spavined or hogged, it is very simple to make a new one.
Frank Frank
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Re: Centre boards

In reply to this post by Frank
Many thanks to all contributors, I don't think any class rules apply, too few boats made, too long ago .I have a set of drawings ,aren't specific  re materials .like the idea of a metal strip on the base, Regarding laminating strips of hardwood,apart from the criminal expense,would you just butt them up together, or some sort of joint ,?
 Probably have to be ply,  that's about £90 a full sheet, still it would give me enough for when the second boat gives up.
Currently have my eye on two oak tables ,for about 30.   30 mm thick tho .that's a lot of sanding down to 22mm .
Take the point about furniture glue not being marine quality.
Timmo Timmo
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Re: Centre boards

I just butted the vertical strips when laminating hardwood. Others have reinforced with splines. Centre boards aren't subject to particular stresses across the board, mainly vertically, so the butt join seems suficient.

I think Robbins does half sheets of marine ply, but I've not checked their prices recently.

On 3 Mar 2016, at 23:42, Frank [via UK HBBR Forum] <[hidden email]> wrote:

Many thanks to all contributors, I don't think any class rules apply, too few boats made, too long ago .I have a set of drawings ,aren't specific  re materials .like the idea of a metal strip on the base, Regarding laminating strips of hardwood,apart from the criminal expense,would you just butt them up together, or some sort of joint ,?
 Probably have to be ply,  that's about £90 a full sheet, still it would give me enough for when the second boat gives up.
Currently have my eye on two oak tables ,for about 30.   30 mm thick tho .that's a lot of sanding down to 22mm .
Take the point about furniture glue not being marine quality.


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NAML

Port-Na-Storm Port-Na-Storm
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Re: Centre boards

If you are going the ply route and are sheathing in glass I would go for good quality WBP ply as opposed to Marine. Its pretty much all the same once its encapsulated. A local timber merchant might sell you a half sheet.
Grum.