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Old 07-10-2007, 20:02   #1
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Admiral 40 Balsa Below Waterline

I had the opportunity to look at the new Admiral 40 today at Annapolis. It is a very nice boat with an extensive list of options and an attractive price. I'm still learning about hull construction but one thing that concerned me is that Admiral uses a balsa core below the waterline while most manufacturers seem to have moved to solid glass below the waterline. Granted they do have solid glass at any through hulls. Should having balsa core below the waterline be a concern?

Thank you for any advice.
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Old 07-10-2007, 21:43   #2
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If it was me I would stay away from a cored hull, much greater chance of osmotic blistering and future hull delamination. All it takes is one imperfection in the glass at a through hull and you have the formula for
disaster. Balsa core wicks water like a sponge.

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Old 07-10-2007, 21:50   #3
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If done with the proper skill it could be OK. But that's the question, skill. In one respect balsa would be better then foam in that if done properly a puncture or damaged area would only be restricted to that area. In foam the water would seep through out the foam area. A solid hull is even better but heavier and more expensive.

Balsa is little cubes of wood. When laid up over the outer hull the space between each cube should be filled with resin before the inner layer of glass is started, making little independant structures like a bee hive. This is important especially in bulsa decks. If you install a fitting and the gaps are not filled, which are like reinforcements, the two outer layers of glass will crush together.

A common practice on a bulsa deck before installing a fitting is to drill the holes thru the first layer, ream out extra bulsa with a cut-off allen wrench, fill it with epoxy filler then re drill the hole all the way thru after the cure. This secures the bulsa from water intrusion and adds more strength between the layers.

So in effect, if the thruhull fittings are not sealed properly or one were to get a puncture water intrusion could cause some major problems. Foam is more forgiving when it comes to repairs below the waterline.
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Old 07-10-2007, 22:03   #4
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Originally Posted by laser View Post
I had the opportunity to look at the new Admiral 40 today at Annapolis. It is a very nice boat with an extensive list of options and an attractive price. I'm still learning about hull construction but one thing that concerned me is that Admiral uses a balsa core below the waterline while most manufacturers seem to have moved to solid glass below the waterline. Granted they do have solid glass at any through hulls. Should having balsa core below the waterline be a concern?

Thank you for any advice.
Lot's of boats built in Australia have balsa cores. Solid glass = heavy = slow. Balsa is actually the best core material from a stiffness/weight standpoint. If the laminate is done with epoxy, not polyester, then osmosis won't happen. As Del said, balsa cores are divided into small squares, seperated by a glue line, so water won't travel far if it does get into the core. Also the balsa itself is very resistant to flow across the grain.

As long as all hull penetrations are done correctly a balsa core boat will last forever, and will sail much better that an equivalent boat done in solid glass.
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Old 08-10-2007, 00:32   #5
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As has already been stated there are many boat builders using cored material, I am at present building solid hulled Rigid Inflatable boats between 27-40ft and Catamarans between 40-45ft, The catamarans I am now going back to solid hull below the water, because of problems that have arrisen from cored hull tests in extreemely cold waters.

History points towards major problems with Cored material below thew water, but history does not account for the advances in resins and application techniques, I am just playing it safe.
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Old 08-10-2007, 03:48   #6
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Having a balsa cored underwater laminate is a recipe for disaster , one leak that you do not know about and the rest of the hull wil slowly absorb water .
If it was closed cell foam and epoxy resin infused it would be ok but Balsa acts like a sponge once exposed to water so the creap starts. Polyester is not water proof so even if you get a damaged gell shield it will start.
Why not ask the Admiral people to make the underwater part solid ?
I am sure they are willing to oblige
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Old 08-10-2007, 07:17   #7
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Thank you to all for your quick and very detailed replies. They certainly were a big help. What I read was that 'IF" done correctly, a balsa core can add strength and reduce weight and can be very reliable. Of course most risks of osmosis problems go away with solid glass below the waterline. I am at the show still and will try to get more of an education here while wandering about the other cats I am interested in.

The internet is a wonderful resource because you can quickly uncover problems that certain boats and manufacturers have. I searched for quite a while and was unable to find anyone who has had hull problems with the Admiral cats. If anyone has any specific Admiral related comments that they would be willing to add I would be appreciative.
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Old 08-10-2007, 08:03   #8
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Many (at least new ones) Leopard/Mooring catamarans have balsa-cored bottoms and they do not seem to have problem with it. But I did not see any long-term data. Few years later it could be a different story.
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Old 08-10-2007, 10:33   #9
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Hell, I don't even care for in my deck, but I'm learning to live with it. As for below the waterline, no way would I consider it. Soaked deck core is one thing but a soak core below the waterline, yikes...
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Old 08-10-2007, 10:58   #10
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cburger...thanks for all that information. That's some scary stuff. Balsa cored boats will not be on my list of boats to consider.
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Old 08-10-2007, 11:58   #11
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One of the reasons I bought a MANTA 42!! Solid below the waterline!And NO Balsa at all!
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Old 08-10-2007, 12:07   #12
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An excellent choice . lovely boat with good handling and sailing ability,s and niced lines.Also good quality workmanship a bit heavy and slow but a good choice overall
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Old 08-10-2007, 14:22   #13
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Originally Posted by laser View Post
Thank you to all for your quick and very detailed replies. They certainly were a big help. What I read was that 'IF" done correctly, a balsa core can add strength and reduce weight and can be very reliable. Of course most risks of osmosis problems go away with solid glass below the waterline. .
Nope. Osmosis risk goes away if you use epoxy instead of polyester for the construction. The type of core makes no difference to osmosis. There are hundreds of solid glass boats with severe osmosis problems.

The article posted above is interesting, but IMHO has limited relevance to this topic - for one thing it discusses powerboats, not sailboats - powerboats experience far more severe pounding compared to sailboats.

Even then it is hardly conclusive in favour of solid glass layups -

"People usually think that a balsa cored bottom would be far worse because of the wood's ability to absorb water. So far, the evidence at hand does not support that idea. Foam, because it is much softer, and not at all fibrous, breaks down much faster under hydraulic pressure. In fact, in all the test borings taken on this boat, the balsa itself was yet to break down. The actual failure occurred because the cored bottom panels were not properly terminated at the keel. In this instance, the major ply separations occurred within the solid laminate (containing a LOT of CSM) first."

If a solid glass layup contains CSM then it appears it could just as vulnerable to failure, and I would be surprised if any production boats with solid glass didn't use CSM as "filler" - it's so much cheaper.
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Old 08-10-2007, 14:38   #14
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Hell, I don't even care for in my deck, but I'm learning to live with it. As for below the waterline, no way would I consider it. Soaked deck core is one thing but a soak core below the waterline, yikes...
Actually soaked deck core is likely to be worse. Rot will happen much faster if the water is fresh. Salt water will do damage, but much more slowly.
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Old 08-10-2007, 23:36   #15
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Repairablility is my concern. Puncture a balsa hull and you absolutely have a drying out issue.

I am sure that a cored hull can be made strong but I am extremely happy with 3/8" or so of solid glass under my feet.

One of our club J24s was holed by lightening this year and sunk. It's been drying out since around April but a decision was made recently to scrap it. Of course it is a bit different than balsa but cored hulls are not on my list of desireables for cruising.
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