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Go Back   SailNet Community > General Interest Forums > Gear & Maintenance
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  #11  
Old 11-03-2009
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Personally I'd stick with marine ply under a deck stepped mast. Were it my own job, I'd probably run one piece the thickness of the core to replace the balsa with a generous lap, say two or three times the area of the actual step. Another piece of 3/4, cut to the shape of the step with the edges chamfered would provide a pedestal of sorts to avoid the potential for water to find its way in.

Again, it's your project so it's your call, but balsa isn't commonly used in area where there's point loading like under cleats and winches but is 'fine' in areas where the entire panel is loaded (like side decks, cockpit seats, etc)
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So even if I go with wood don"t use balsa but use marine plywood. But what is it's advantage over fiberglass? I should mention that I will go in from the top since the deck requires repair where the outer skin cracked due to the compression. As far as the sugestion of stopping into a boat yard or Fiberglass place there are none here. There is a boat yard 140 km away but they don't do this type of repair anyway.

Last edited by superiorvoyager; 11-03-2009 at 11:16 AM.
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Old 11-03-2009
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Quote:
Originally Posted by superiorvoyager View Post
to answers, "SOlid is the way to go" and "it's probably not the best choice" what are your reasons. As far as experience I have a lot of experience with fiberglass (west system) over the years (boat and car repair, canoe construction built a 16' glass over wood boat years ago etc.) I also have a lot of experience with wood (finishing carpenter, fine furniture and Luthier). one problem with wood is If I am going to use Balsa or Coosa I'll have to order it in where as I have everything I need for west system
It would help if you quoted your intended target... I had to go searching as to whom you were asking .

IMHO... The only reason it was not soil to begin with in your and my boats is the builder was to cheep to do it..A lot of top of the line boats have a sold core where intended deck penetrations are..cheaper built bots not so much.

You ask why...Simply water intrusion ....intrusion and compromise of the core material rather wood or foam that you are currently facing and would not and will not ever be a future issue with solid glass core in that area.
a
The only reason for any plywood or balsa core in the first place was for a stiffner..and cheap stiffening at that...There is an exception when an insulating factor is desired in the hulls construction..but a modern sandwich is ultra light and ultra strong..but still generally solid glass where penetrations are engineered to go through either their decks or hull.

I have no clue as to why it was suggested as a bad idea to go solid in your mast step area..maybe he will respond to his answer.

FWIW...repairing it from the top will be WAY easier..just way harder to get your top gel-coat looking factory nice that's all..as you will have gravity working for you not against you...as I said earlier practice with 2 or three goes at mixing and saturating some scrap pieces together to get the hang of saturating and working with mat and resin..it ain't rocket science..learn to work all the air and excess resin out of the mat..gobbing on way to much resin is a beginners fist mistake..you dont want any unsaturated areas but you dont want it swimming in the stuff either..it will be brittle and crack.

You say you have lots of experiance with glass...Then Go For it!..If I was there I would help you.
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Last edited by Stillraining; 11-03-2009 at 12:18 PM.
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Old 11-03-2009
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I'd go solid not wood core of any kind under the mast. Stillraining is right - the only reason builders use plywood is that it is cheaper and is also faster than multiple layers of glass. I'd use epoxy (West as I know it well) and rather than mat and cloth or roving I'd use 1708 biaxial - stitched as opposed to woven roving with mat already attached to one side. It's easier to use and fully compatible with epoxy - some mat isn't epoxy compatible. If your deck is already needing repair going from the top is always the best way - it's easier and the job will turn out better. I'd paint after instead of gelcoat. For a good rundown of this see Tim Lackey's site - Northern Yacht Restoration | Tim Lackey:* One Man, One Boat at a Time. He recores decks on a regular basis in his restoration business and documents everything with lots of pics. Just click on one of his projects and follow it along.
Hope this helps.
Brian
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Old 11-03-2009
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try this....?

I've done this before. If there is only a 1 ft area use stiff wire to dig out all rot wood. Attach vacuum to small tube to help. Get west sys epoxy in a empty caulk tube and attach small tube to end of caulk tube end. Stick tube in access hole and pump away. Don't peel away cabintop. Unless U R a fbgls pro it will never look right
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I think gwp is wrong. The area is over 1 square foot. That's a large area to fill with epoxy that way. Besides, there is little strength to epoxy without fibreglass imbedded in it. And this will be under a mast so it requires strength. You will have to paint, but it's easy to get a fair surface. Just build it up layer by layer (1708 biaxial is about 1/8" per layer I think) and when you are almost level with the deck surface, sand and squeegie a fairing coat of epoxy mixed with fairing filler (West #407). sand and refill any low spots with fairing again until there are no more low spots. Sand lightly and finish with a coat of straight epoxy put on smoothly. Then prepare for the paint you choose. It isn't hard to do it just takes a bit of time. If you can read instructions you can accomplish this.
Brian
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I suggested you replace with core material so that deck structure with similar qualities of stiffness and flexibility as originally designed can be maitained.Also,a heavy,solid lay-up can be difficult to fair without removing glass again. Since it is mast step area,all epoxy and 17 oz. material will definitely do the job-I missed the size and type of boat-just be aware if cabin top is lightly built and supposed to give a bit ,it probably won't anymore
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george
The cabin top is not supposed to give under the mast step. It should be a solid step supported by a bulkhead, compression post or beam belowdecks. If it was solid from the date of manufacture he wouldn't have this problem.
Brian

Last edited by mitiempo; 11-03-2009 at 07:42 PM. Reason: addition
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Old 11-03-2009
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Quote:
Originally Posted by mitiempo
the only reason builders use plywood is that it is cheaper and is also faster than multiple layers of glass
Respectfully Brian, I think you're forgetting about about the intent of laminate construction being to provide two skins held at a fixed distance apart to provide MORE panel stiffness than the same amount of material as a single skin. The key to that stiffness lies in the compression strength of the core.
Also, it's not faster...it adds time because it has to be added as it's own step which disrupts the layup timing. Then it has to be flood-coated before the inner lams start going on.

Another take on gwp's suggestion: remember here that the OP wants to use West System because that's what he's got (or what he's most familiar with). Ignoring the cost of filling 1/2" void left by the core, the exotherm will at least cause the glass to print through the gel and will at worst cook the gel, permanently discoloring it.

With that in mind, the exotherm will also make a solid casting a tricky job for someone who is fairly new to it. While they add a ton of strength, fibers don't do much to dissipate the heat. Remember that the heat vs cure curve for epoxy is much different that poly based resins.

Also, given the temps he's likely to see over the next while, he will NOT get a sufficient cure to re-step the mast, re-rig, and sail the boat anytime soon. Personally, I wouldn't feel comfortable restepping the mast on a solid epoxy layup that hadn't progressed very far beyond initial cure. I think it's important to point out as well that the exotherm enables the initial cure. Sure, it may feel hard, but only time can fully cure epoxy.

I can't really think of any issues with a solid layup of epoxy and cloth, again as long as the exotherm is dealt with. A continuous layup (always adding the next layer while the previous is cool but still green) will give all the units a primary bond but should allow the heat to dissipate. Once you compare the added cost to the properties gained, I'd still go with plywood core.
Just different strokes I guess.

Plywood has more compression strength than solid wood in this application unless he wants to cut short pieces and use the endgrain similar to the way a butcher block is made (and the way the balsa is laid).

Plywood has more panel strength than solid wood, so will do a much better job of spreading the loading evenly all around the step. THAT is the primary reason it's used in decks and steps, where balsa is used in cabin sides and coamings. Core materials are an insignificant proportional cost in any well-found production boat. Balsa is easier (read:quicker) to work and lighter than ply.

Again, this is just what my experience has shown me, for right or wrong.
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I doubt that Hinckley, Morris or other premium builders put ply under the mast step. Cost really isn't a factor for these builders - quality is. I suggested using multiple layers of biax. Not all at once. Even if you wait until one layer is hard it's easy to wash the amine off with a nylon pad and some water. Exotherm is not an issue if done this way. West epoxy is usable down to 35 degrees f. At these cold temps exotherm is less of an issue. Plywood does have more compression strength than solid wood - of the same species. Fir or mahogany plywood still compresses and under a mast fully rigged it will eventually happen. If any moisture gets in it will deteriorate and that's where we started. As far as core material where core should be used, balsa is far superior in several ways than plywood. Less chance of moisture travelling with end grain balsa, less weight with balsa where the weight is not an advantage, and better bonding to curved surfaces with balsa than with plywood. The following is taken from West's fibreglass repair manual which is free on line here.http://westsystem.com/ss/assets/HowT...aintenance.pdf
Brian
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