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Old 05-04-2008, 16:27   #1
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To balsa core or not to balsa core?

I have had warnings against balsa core construction. Seems the main caution is that if leaks occur, say around a stanchion base or any fitting in the deck, water will find its way to the balsa core and wick its way through the core eventually causing you a big mess. Easy solution, avoid balsa core, but it seems many of the South African cats, especially Moorings (a.k.a. Leopard) are balsa core construction. Especially those in my price range (350-450k). Any thoughts/suggestions?
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Old 05-04-2008, 16:58   #2
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With any core, hull/deck penetrations need to be done right or problems can occur. Balsa has some advantages as a core material - probably the best physical properties in terms of sheer and compressive strength, and like anything it has it's disadvantages.

I'm sure there will be people telling you to avoid balsa like the plague, (you'll get people imploring you to avoid multihulls as well) and citing various horror stories - but the lessons have been learned and as long as these lessons are applied during construction - ie. decoring and epoxy filling around EVERY penetration, balsa will work perfectly well.
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Old 05-04-2008, 17:11   #3
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Not for me anymore.

Having owned a couple of balsa cored boats and seeing others working on their's (cutting out wet balsa and re-glassing in new) I would be very carefull about the long term durability. It does make for a very stiff and well insulated hull but if there is any water intrusion it will most definitly migrate thru end grain balsa (I know from first hand experience). That is why I went with a foam cored boat this time.
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Old 05-04-2008, 17:13   #4
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As 44CC says, if it's done properly it is a tremendous core material. End grain balsa will not wick water into the core but the passages between the blocks of balsa must be filled with the proper material to stop any water migration. Also each and every core penetration must be treated properly and that goes for foam core as well. Foam core will eventually absorb water and deteriorate if it's allowed to get wet so the precautions you must take with balsa you also must take with foam core. Plywood.would be my last choice as a core material.

Dave Gerr has a good description of how to use balsa core in his book "The Elements of Boat Strength".
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Old 05-04-2008, 17:18   #5
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I have a balsa core in my deck areas that are close to 30 YO and it's doing just fine. I've had to cut out a couple areas around a couple winches and pad eyes but that's due to that the PO's that knew nothing about caring for a boat. Like 44 stated, if done properly, it's OK stuff.

When putting thru bolts/screws thru an area cored with balsa (winches and deck fittings) be sure to pre drill the holes, spin out the core with a shortened Allen/hex wrench and fill with epoxy filler, then re-drill thru.

And be sure to seal the edges of and open area with epoxy, like below!

BTW Absolutely NOT below the waterline!!!!
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Old 05-04-2008, 17:49   #6
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Honeycombs are an option, such as polyprop honeycomb, Not as stiff, or fire proof, but sealed cells, and better resilience, quieter and easier bonding,
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Old 06-04-2008, 16:43   #7
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Thanks

Quote:
Originally Posted by 44'cruisingcat View Post
I'm sure there will be people telling you to avoid balsa like the plague, (you'll get people imploring you to avoid multihulls as well) and citing various horror stories -
Never considered one hull after I sailed my first beach cat and later crusing cat.

We are most likley going for a used boat, will a good survey be able to identify any problems with the core? So much to learn and just one lifetime-

Thanks for all the info
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Old 06-04-2008, 17:27   #8
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Owning a boat with a balsa cored foredeck, I can say that it doesn't take much to turn the core to mush. I had one bolt break on an inner forestay. Just one bolt... and by the time I discovered it and repaired it, balsa core damage was already done.

Short of removing every bolt in a used boat and expoxying the holes, I'm not sure this can be prevented. Eventually, you will have core repairs to deal with.
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Old 06-04-2008, 17:31   #9
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I'm sure there are surveyors who test for water content using thermal imaging or something similar. (The only boat I have had surveyed was steel)
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Old 06-04-2008, 17:35   #10
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Quote:
Originally Posted by rickm505 View Post

Short of removing every bolt in a used boat and expoxying the holes, I'm not sure this can be prevented. Eventually, you will have core repairs to deal with.
That's exactly what should be done at the time the bolts are fitted. It's not difficult, or even particularly time consuming to do. I would have hoped that any production builders using balsa would be doing this by now.
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Old 06-04-2008, 17:41   #11
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Originally Posted by 44'cruisingcat View Post
That's exactly what should be done at the time the bolts are fitted. It's not difficult, or even particularly time consuming to do. I would have hoped that any production builders using balsa would be doing this by now.
I'm in complete agreement, but who knows what they did with the current crop of used boats when they built them 10-20 years ago? I was very sorry to see that my drilled holes were not sealed and am slowly rectifying this as I rebed everything on the boat....one item at a time (sigh).
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Old 06-04-2008, 18:12   #12
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Yes, unfortunately, it is not just how the builder treated the holes through the core, but also what any other installer of equipment has done. I saw pictures of rot where a contractor had installed a spray hood using screws into a cored deck. But you need to watch for this problem no matter what your core is. As I said earlier, foam will disintegrate if it gets wet, especially if it's subjected to freeze/thaw cycles.

Look for discoloration around fittings and on the bulkheads and ceilings below decks. Step around fittings on deck to see if you can see water or brown gunk ooze out. Check for soft spots on deck. A surveyor should sound the deck and topsides with a plastic hammer to detect soft spots in the core.
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Old 06-04-2008, 18:29   #13
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Just out of experience (not taking a position, really):

I looked at a number of cats from the 90's recently and most of them had serious delamination issues both on deck and above the waterline on the hulls (I didn't haul them).

They may have had water incursion as well - some definitely did, others, I can't be sure...

Anyway, because I saw so many problems with these boats that were made of laminated materials that were separating (sp?), I decided to go for a solid glass hull.

Huge weight penalty on a cat, but I was hoping this would be the last one I bought. I didn't want mine to be one of those ones falling apart.

BTW: They basically all have cored decks, so there is no escaping it. Also, most (if not all?) modern boats are cored.
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Old 06-04-2008, 21:43   #14
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In my own opinion, I believe that 90% of the boat owners out there have little to no knowledge about installing deck gear. And that goes for some manufacturer's, as well!

It is up to the buyers to be aware of this common problem! Out of all the boats I've been on, this has been one of the most common errors I've seen. Ignorance is a costly attribute in which we have all been subject to at one time or another.

It is a craftsmanship failure, not the materials. Once a boat leaves the show room, how many more qualified personnel, if any, actually work on the boat? Unless one has tonnage of $$$, not likely.

So, a used boat is going to have all the combine errors of owner(s) past. Leaving the prospect buyer to know what to look for. For the inexperienced this is where having a GOOD surveyor is important!!!!!

What I shy away from are ply cores, even the treated ply's, especially above the waterline. Saltwater will preserve the wood but still causes de-lamination.

Once water starts in, it wicks it's way thru the wood and travels down hill until it's full, then works it way back up.

To dry out a ply core is almost impossible. One has to drill a bunch of holes on the under side and keep it in a warm dry environment with fans blowing across the holes. Adding wicks helps.

Adding sealer to a thru bolted cored hull/deck isn't enough. They need to be epoxy re-cored to keep from crushing and water intrusion. And any screw that goes thru just one layer should be double sealed and checked bi-annually.

Here's an example of craftsmanship failure...................._/)
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Old 06-04-2008, 23:28   #15
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End grain balso has two advantages over foam, The first being the price is less, and secondly as stated before it is stronger/stiffer than foam of equivalent weight. If the hull is done using vacuum infusion and and all penetrations are epoxy cored, you have a great boat.
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