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Old 03-12-2007, 12:45   #1
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Core Material

I am going to have to do some deck and core work. Appears to be about a 2'X3' section in front of the cabin (probably a leaky stanchion). There is a lot of great information about doing the work on several threads.

However I have not been able to find any discussion concerning core material balsa, marine ply or Nico-honeycomb. Any experince would be appreciated.

Oh this is on a 27 foot 1970 Tartan which I have no intention of racing so weight is not criticial.
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Old 03-12-2007, 13:05   #2
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Back in 1991 I started a similar repair on my Passport 45 (it had teak decks). I found that it was originally constructed with small (maybe 3"x3") pieces of bolsa wood. The small pieces were put together like a jig-saw puzzle, then filled with polyester resin. I guess this is a typical Tawain deck material.

Anyway, I cut off the top layer, in the place that I suspected some problem. It took me about 30 minutes to realize that the problem was much worse that I suspected. Water had made channels all through the deck and the bolsa absorbed it like a sponge.

I ended up taking a small circular saw and cutting the entire top layer of FG off (teak deck & all) and removing the entire core. Every single piece of bolsa was entirely soaked. The deck weighed a ton.

I replaced the core with 3/4" marine plywood (cut to fit) in about 4' sections (1' wide to maintain a small amount of curvature on fore & aft decks), laying each section in epoxy resin. I faired out the deck with epoxy filler, glassed it (with epoxy), faired it again and that deck is strong as can be and one heck of a lot lighter than the wet Bolsa that was in there. The entire project only took me about a week (with an assistant).

I would NEVER own another boat with teak decks. Why anyone would take a perfectly sealed FG deck and drill 2000 holes in it is beyond my comprehension.
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Old 05-12-2007, 06:22   #3
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If you have an area where there was a leaky stanchion and you feel the core may be stuffed (it should have been de-cored when made), I would be inclined to remove the damaged core and replace with whatever was used before leaving a 100mm dia. section out.

I would then be mixing up an epoxy resin, gluepowder and small strands of glass to make "Hairy Bog" to fill the area, sand, glass and finish.

When holes are re-drilled you have a hard area to spread the load and no core to cause problems.

Dave
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Old 05-12-2007, 06:35   #4
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my question is the weight above the waterline for 3/4" ply! But I suppose if you've taken off all that teak it would pretty much even out.
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Old 05-12-2007, 10:47   #5
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I am finishing up repairs of a similar nature. The core in my deck was 3/8 marine ply which I replaced with the same. I made an incision with a cut-off wheel on a Makita 3" grinder and peeled the innerskin off. I then would cut the ply to shape and take a circular saw and make incisions in the ply. This allows the thickened resin to create a bridge between the two layers of glass. In areas that had hardware mounted (chainplates, stanchions, windlass) I replaced the core with G10 Structural Glass (McMaster and Carr). Where I could I re-used the original skins, the last step was to grind a shallow V around the seam and add glass and tape to reconnect the surfaces. I did find that where I used fresh glass the is a noticable difference in rigidity. If I had to do it again I would scrap the inner skins and lay fresh glass (XMat). At the end of the project I started playing with a synthetic core material you use like glass, BaltekMat. It's fairly expensive but builds quick and is more resistant to rot and water intrusion than natural materials. I am not sure how it rates for weight. It is lighter than ply, but probably heavier than balsa and definately heavier than honeycomb. Good luck!

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Old 05-12-2007, 11:28   #6
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my question is the weight above the waterline for 3/4" ply! But I suppose if you've taken off all that teak it would pretty much even out.
Remember, I was working on a 45' center cockpit boat with a large fore and aft deck. I doubt that you would need to go that thick. My deck was pretty flat too (just a slight curvature). If your deck has any curvature in it, it will have a lot more structural strength.

You were right though, I felt like I need to build my deck a little stronger because I remover the teak. However, in reality, most decks are built without concidering the "Optional" teak for strength.

Did I mention.....I HATE TEAK DECKS!!!
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Old 05-12-2007, 11:56   #7
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The other option for buidling strength and keeping weight down is to laminate stringers under the deck, given you have the head room. The do not really need to be that thick, say 1.5 to 2 inches. The material does really matter as it's the layers of glass (use XMat) that give the real strength. I also have large, fairly flat decks and just laminated in a grid using 3 strips of 1/4 ply and 2 layers of fabric. It gives me something to attach my ceiling material to and not penetrate the core I worked so hard on. It really stiffend up the decks but maintained some flexibility. It did not add more than 6 pounds.
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Old 05-12-2007, 12:25   #8
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More then likely it is a ply core. If you can peel of the deck in one or two pieces you can save it and re-use the skin. If you do the work from above a ply core can be used. I alway hold down the top skin with drywall screws, others use weight.

If you choose do the work from inside it may be easier to repair with a vacuum bag and epoxy and use balsa as the core.

Good luck, easy to do but not much fun.

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I am going to have to do some deck and core work. Appears to be about a 2'X3' section in front of the cabin (probably a leaky stanchion). There is a lot of great information about doing the work on several threads.

However I have not been able to find any discussion concerning core material balsa, marine ply or Nico-honeycomb. Any experince would be appreciated.

Oh this is on a 27 foot 1970 Tartan which I have no intention of racing so weight is not criticial.
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Old 05-12-2007, 12:27   #9
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Oh, I hate teak decks also! But... I love looking at other peoples boat with lovely teak decks
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