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Roy M 08-12-2009 16:21

Building a Composite Searunner Centerboard
Okay, I've actually started back to work on my own boat after too many months. The big project, at the moment, is replacing the aged and waterlogged centerboard. I'm doing this now because I'll need it this summer when I haul out, and I don't want to be rushed in the production. I'll be taking pics of the process, should anyone be interested. The Searunner centerboards were all built of solid laminated plywood. Despite adding apitong strips at the leading edge, and lots of glass tape with graphite powder epoxy, I have managed to bash it enough times to allow water to enter into the plys. This makes it swell, crack the glass at the feather edges of the trailing part, and make the board hard to raise and lower.

The new design, by my friend and amazing multihull colleague, Bob Dixon, uses clear redwood, vertical grain planks in the axis of the axle pin. The entire leading edge is laminated redwood planks. The entire aft section, over half the width, is laminated 4# polyurethane foam. Ten layers of 12" wide graphite unidirectional cloth, vertically aligned will be layed atop the redwood axis core. Graphite bidirectional cloth will then be laid atop the faired structure. Then, Kevlar/graphite tape will reinforce the impact zones. All sealer coats will be graphite powder in epoxy resin. I used the graphite as my external coat for all below waterline surfaces when I built the boat, and I love what it does for dragging the boat onto shore when the opportunity arises. Total thickness of the centerboard will remain under 4", as the original.

I've purchased the redwood, ordered the glass materials from FiberLay in San Diego, and will be using WEST System epoxy. Construction begins shortly, and I'll be taking photos of the process if anyone wants to see how it works out. When completed, the board should be easily half the weight of the unwaterlogged original, even fairer, with some design changes on the upper bearing surfaces to spread loads to the centerboard trunk more evenly. I've even changed the locking cord and "fused" position latch. Now, if only I can figure out how to close up the "slot" of the trunk to reduce cavitation, I'd really be jazzed. I will also be adding a cavitation plate and end foil to the rudder when I haul out. Should help when I get to twenty knots and begin to feel the "spongey water".

drew23 09-12-2009 02:08

here here!

looking very much forward to this, Roy!

Jmolan 14-12-2009 12:50

Very Very cool Roy!.....I had a friend with a CC 32' who took the entire rudder and carved out the inside, leaving a frame of the old rudder, the filled it with foam and glass. Not sure of the weight saved, but he stern was higher out of the water when he got done.
I am going to hold you to the posting photos thing....keep us stoked in the slow boat times here:banghead:
I was wondering, have you (or anyone) heard of this bottom application? Or know of any others. I think it is a small co. just starting out, but am not sure.

Marine Eco Coatings

Maren 19-01-2010 07:22

I'm very much looking forward to seeing the process. Please keep up updated.


Originally Posted by Roy M (Post 370796)
Now, if only I can figure out how to close up the "slot" of the trunk to reduce cavitation, I'd really be jazzed. I will also be adding a cavitation plate and end foil to the rudder when I haul out.

I'm sending you a PM on the above.

Roy M 20-01-2010 20:58

1 Attachment(s)
Thanks for waiting! See my album, under Centerboard Evolution ( for detailed pictures. Click on the photos for larger versions. Here's a taste:

Solecito 31-05-2016 15:21

Re: Building a Composite Searunner Centerboard
Roy, I'm in the process of addressing a leaky center board on my Searunner. How did this board work out for you?

UNCIVILIZED 31-05-2016 17:34

Re: Building a Composite Searunner Centerboard
I know that Bob Dixon is very good. And have had a few good chats with him about multi's, as well as composites. But to me, 4lb/cuft foam seems awfully low density. At least if it's going to be anywhere that it's subject to either; shear or compression.
Usually 6lb is the minimum in hulls, & 8lb+ in foils. And far, far higher in some.

I know that it's probably too much to type, but I'd be curious to see the numbers behind this, if it's possible.
Ditto on posting the layup schedule, if it's not too much trouble :)

Also, is the graphite on the hulls really that big a benefit when beaching, even though it has bottom paint overtop of it? Or are your boat's coatings configured differently?

Roy M 06-06-2016 19:26

Re: Building a Composite Searunner Centerboard
No numbers. We'll be installing the CB next April so we'll find out if our seat of the pants engineering works. The graphite on the bottoms has seen plenty of action while beaching on soft shores. Bottom paint hasn't been damaged, so I can't confirm that it will hold up well against a rocky shore, as I like to avoid those. My previous experiences with graphite as an admixture have been very successful. I used it on a lifeguard surf dory, in the days when we used such craft, and it won first prize in the dory races, with virtually no palpable damage to the hull when pulled on cobble beaches.

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