A Center board in progress

[Rational Root]

The Center Board (http://davesboat.blogspot.com/2008/08/center-board.html)

The Irish Rainy Season has started. We learned in school that Ireland had warm sunny summers. This was obviously a Blatent Lie. I've been wearing a coat to work in the mornings.

I can still work in the shed though 8-)

I used a router to cut slots at the correct depths base don the NACA foils. This gave me a guide for sanding.

You can see the lines cut in the CB here.
http://4.bp.blogspot.com/_-jLgHzfXWAU/SKIJ4HdznOI/AAAAAAAAAfs/p6wPbZj0bdk/s320/IMG_0106.JPG (http://4.bp.blogspot.com/_-jLgHzfXWAU/SKIJ4HdznOI/AAAAAAAAAfs/p6wPbZj0bdk/s1600-h/IMG_0106.JPG)

Here you get a good idea of how it looks from the endhttp://3.bp.blogspot.com/_-jLgHzfXWAU/SKIJ4b6d4KI/AAAAAAAAAf0/zILX8tVQkKs/s320/IMG_0107.JPG (http://3.bp.blogspot.com/_-jLgHzfXWAU/SKIJ4b6d4KI/AAAAAAAAAf0/zILX8tVQkKs/s1600-h/IMG_0107.JPG)

And here's what it looks like as I start to sand one side.http://4.bp.blogspot.com/_-jLgHzfXWAU/SKIJ3hx5kvI/AAAAAAAAAfk/Pyr6OWSkn50/s320/IMG_0111.JPG (http://4.bp.blogspot.com/_-jLgHzfXWAU/SKIJ3hx5kvI/AAAAAAAAAfk/Pyr6OWSkn50/s1600-h/IMG_0111.JPG)

[Thorne]

Not that you'll want to hear this, but I did the same thing you are doing -==- used non-marine ply for my centerboard. I happily ignored all the sage advice on this forum, figguring that I knew better and that a good coat of epoxy would solve all issues.

Ended up with the CB breaking in half, snagging lines in the harbor and could have lost the boat easily. A friend paddled out in a plastic canoe and grabbed her just inches from the seawall...

Now my CB is two pieces of Meranti epoxied together and covered with glass cloth and epoxy. Sadder and wiser and all that...

Original cheap ply CB -
http://www.luckhardt.com/centerboard.jpg http://www.luckhardt.com/cb-painted.jpg
http://www.luckhardt.com/cb-down.jpg

DOH!!
http://www.luckhardt.com/brokenCB2.jpg

New marine ply CB blank -
http://www.luckhardt.com/newcb2.jpg


http://www.luckhardt.com/newcb8.jpg

[Ray Frechette Jr]

And why not a nice laminated quartersawn solid dimension lUmber cboard?

I like Marine ply and use plenty of it. And I will make rudders out of it, but to date all centerbaords except for a Bolger Elegant Punt leeboard have been either ash or d fir quarterassawn laminates.

Cyclical rolling stresses on plywood centerboards make them rather suspect .

[donald branscom]

Cover with "S" glass for strength.

[wtarzia]

For my outrigger canoe I made both rudder and leeboard out of pine laminate sold at Home Depot for wide shelves and desktops. I was looking for a fast solution when I was totally tired of building and wanted to get on the water. I chose through the pile a relatively knot-free one.

Also, I looked for one where the builder tended (I mean tended!) to alternate the growth layer curves as you are supposed -- just about the first lesson a wood builder learns after sawing to a line, I should think. Saddly I bought another one to build a hiking seat, and I flipped through the whole stack and found not one laminate that alternated the curves! Unbelievable. But at least the foil blanks were ready and dry.

After shaping, I epoxy-glassed the whole thing (6 oz glass). I am only up to my 5th sailing trip, but, so far, so good. -- Wade

[Rational Root]

[quote=Thorne;1916540]Not that you'll want to hear this, but I did the same thing you are doing -==- used non-marine ply for my centerboard. I happily ignored all the sage advice on this forum, figguring that I knew better and that a good coat of epoxy would solve all issues.[quote]

You may well not believe me, but that ply was sold as marine ply, stamped with the BS number an all. (pun accidental, but hey)

Lesson: Bon't buy marine ply at a builders providers, in spite of what is stamped on it, it may well be nothing more than WBP.

I am a little concerned about it, and I suspect that this one will be a build test, and may never see water.

I was also thinking that I should cut the cb diagonally from the sheet, giving 2 plys at 45 degrees to the force, not one at 90 and one parallel ?

Another thought was 2 sheets of 3 mm, tape them together at one end, run a piece of wood top to bottom, bevel the back to meet nicely, clamp it up, fill it with A/B foam and led shot for weight, and then glass it all up. Like so.

I've seen a web site where somone did the same for foils for a big Cat.

http://lh5.ggpht.com/dave.tolan/SKKPoiu45pI/AAAAAAAAAf8/xCZcXzJUnMM/s400/cb.JPG

[Thorne]

Wot, the local Texas store doesn't carry boatbuilding supplies?

;0 )

I'm certainly no expert on marine ply (the CB is the only piece o' ply in me little boat), but most of the stuff I've seen has a lot more layers -- at least 5 per piece. As you can see in the photo above, with two pieces of Meranti glued together, there is at least 7 per piece.

Unless the boat is huge, I'd certainly avoid any hollow foils == seems like a recipe for disaster. Plus you usually want weight in CB's, so why go to a lot of work to make it lighter? And CB's often double as depthfinders -=- so they need to be strong and impact-resistant.

[Rational Root]

Wot, the local Texas store doesn't carry boatbuilding supplies?

;0 )

I'm certainly no expert on marine ply (the CB is the only piece o' ply in me little boat), but most of the stuff I've seen has a lot more layers -- at least 5 per piece. As you can see in the photo above, with two pieces of Meranti glued together, there is at least 7 per piece.

Unless the boat is huge, I'd certainly avoid any hollow foils == seems like a recipe for disaster. Plus you usually want weight in CB's, so why go to a lot of work to make it lighter? And CB's often double as depthfinders -=- so they need to be strong and impact-resistant.

It's a lot less work, you get a fair curve by just clamping the wood and gluing it all up. Much easier than sanding and fairing.

Not quite NACA 0012, but neither is my sanding.

Then pour in some lead shot, some two part foam and slap on some glass. Happy Days.

[JimConlin]

For any but the smallest, slowest boats, I prefer not to use plywood for foils. Boards need longitudinal strength and in plywood, half of the material is oriented the wrong way. Furthermore, boards get dinged on their edges and the cross-grain of plywood carries water into the body of the board, accelerating its deterioration. It's hard to improve on DF or mahogany.
Glass is useful in boards for two purposes. A sheathing of glass cloth makes the board more stable and resistant to dings and unidirectional glass (or carbon), applied longitudinally to the thickest part of the board, will stiffen the board greatly.

[Rational Root]

What if I cut the board from good ply, but cut it at 45 deg to the grain. Then both plies will be in play ?

Ps a Glen L 14 is not exactly a Foiling Moth :rolleyes:

[Ray Frechette Jr]

Is there a aparticular reason you WANT to use plywood instead of solid dimension lumber laminated centerboard?

Solid wood is not going to cost you all that much more nor takle considerably longer.

Is there some particular reason you feel it would be better to use ply?

[JimConlin]

What if I cut the board from good ply, but cut it at 45 deg to the grain. Then both plies will be in play ?...

Actually, both plies are oriented in a wrong direction and you'll waste a lot of ply in the process.

[Jay Greer]

I butterfly, book match, the plywood and bury carbon fiber strands in the middle as well as the two out side surfaces along the length. for added strength. The inner strands would be too close to the center of flex if it were not for the outer strands working in conjunction with them. I have yet to have a board break.
Jay

[Rational Root]

Is there a aparticular reason you WANT to use plywood instead of solid dimension lumber laminated centerboard?

Solid wood is not going to cost you all that much more nor takle considerably longer.

Is there some particular reason you feel it would be better to use ply?

Me no, that's just what the design calls for.

[Rational Root]

For a one off boat, not a big deal.

Also - not nearly as much ply as I will waste if it breaks 8-)


Actually, both plies are oriented in a wrong direction and you'll waste a lot of ply in the process.

[Rational Root]

Making it up from solid wood is starting to appeal to me.

Sanding Ply sucks.

Planing Ply is no fun either.

I think I may try this new fangled hi tech "wood" stuff 8-)

[donald branscom]

What about a steel centerboard?

[Martin O'Halloran]

What part of Ireland are you in