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Old 09-10-2007, 02:14   #16
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Epoxy is the only solution against osmosis. it contains no air if applied well preferably with vacuum resin infusion or prepreg ( preimpregnated fiber).A couple of cats are built with epoxy only, Gunboat, Atlantic 44 and 55 , FastCat 405 , 435 and 525.A couple of European monohulls can be purchased optionally in Epoxy.
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Old 10-10-2007, 13:25   #17
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On power boats a cored hull is disastrous. If the hull has water in the core and the power boat has enough power to slam waves, do quick turns and jump waves the water hydraulics the core to shreaded mess. In effect turning it to a weakened void between two layers of glass.
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Old 10-10-2007, 15:30   #18
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On power boats a cored hull is disastrous. If the hull has water in the core and the power boat has enough power to slam waves, do quick turns and jump waves the water hydraulics the core to shreaded mess. In effect turning it to a weakened void between two layers of glass.
Absolutely, what the cored hulled devotees don't speak to is that the core material makes signifigant contribution to the strength of the sandwiched components and that water infusion may not cause rot of the core but once it becomes a water logged mess, the strength of a cored hull (that is not a strong as a well laid up solid hull to begin with) is comprimised.

I would like to address another "opinion" regarding production built boat hulls. In a perfect world everyone would take great pride in their work and strive to build the absolute best product they are capable of. In reality with corporations looking to eek out modest margins, the boat building industry often hires cheap unskilled labor who's attention to detail may not be all that great. All it take is a pinhole around a through hull area that is supposed to be sealed and the water infiltration starts. Then what happens is that this goes on for years undetected and you can figure out the rest.
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Old 11-10-2007, 02:21   #19
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Hallo C Burger

Your story explains why the best way to built a boat is with resin infusion under vacuum because even a solid lay up can have air inclusions if not built very precise, it is advantagious to use Epoxy resin because of no osmosis. Having Balsa under the water line and even over the water line is not a good idea because of the possible chance of water penetration and the rot after that. Closed cell foam is still the best way to prevent any rot and it gives extra floatation with lower weight.
Conclusion is built with epoxy resin infusion and use closed cell foam in the laminate to decrease weight and increase insulation and floatation
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Old 11-10-2007, 02:25   #20
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Hallo Delmarrey

To prevent this from happening a high density foam is used under the water line where the slamming occurs in order to prevent and that the foam becomes a mess. By adding this foam that cannot happen and the boat still decreases in weight by doing so and will give you better speed or a better fuel economy or both and ads to insolate at the same time both for sound and temperature decreasing condensation.
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Old 11-10-2007, 19:18   #21
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Absolutely, what the cored hulled devotees don't speak to is that the core material makes signifigant contribution to the strength of the sandwiched components and that water infusion may not cause rot of the core but once it becomes a water logged mess, the strength of a cored hull (that is not a strong as a well laid up solid hull to begin with) is comprimised.

I would like to address another "opinion" regarding production built boat hulls. In a perfect world everyone would take great pride in their work and strive to build the absolute best product they are capable of. In reality with corporations looking to eek out modest margins, the boat building industry often hires cheap unskilled labor who's attention to detail may not be all that great. All it take is a pinhole around a through hull area that is supposed to be sealed and the water infiltration starts. Then what happens is that this goes on for years undetected and you can figure out the rest.
Trouble is, if you use a solid layup on a multihull it will be so heavy, and sail so badly you might as well have a mono. (well almost)

A 10 mm solid layup will run around 20kg per m2, whereas a cored layup will be around 1/4 - 1/5 of that. So a balsa cored hull, which might weigh around 3 tonnes (empty) would weigh 12-15 tonnes in solid glass. (And it would very likely be less stiff too). Then, because of the weight of the hull, you will need a bigger rig, bigger motors, more fuel etc etc etc...

The answer is a cored layup, but it has to be done properly, or you accept a large performance loss.

There are differences between balsa cores too. Many of them have the balsa made up of blocks which are seperated from each other by a line of epoxy - so if a leak does occur, it can't spread far. And despite what has been said here, water doesn't soak into end grain balsa "like a sponge". While water flows quickly ALONG the grain, it only travels very slowly across the grain.
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Old 20-04-2008, 23:43   #22
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Vinylester is a cure for osmosis

"Epoxy is the only solution against osmosis." This is untrue-vinylester is just as good.
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Old 20-04-2008, 23:56   #23
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Want some facts with that opinion?

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On power boats a cored hull is disastrous.
Even underwater it's OK with good quality materials like linear or SAN foam and vinylester or epoxy resin. In the topsides and deck, balsa is fine, as well. Lots of really expensive high speed boat builders will tell you this. Just because some el cheapo builders like Sea Ray have abused the concept doesn't make it inherently unsound.
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Old 21-04-2008, 02:24   #24
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And despite what has been said here, water doesn't soak into end grain balsa "like a sponge". While water flows quickly ALONG the grain, it only travels very slowly across the grain.
Totally agree, having done repairs on balsa cored (duflex epoxy) boats that had compramised underwater outer skins for 4 mths prior to repair, water may have gone an inch past the initial damage and needed removal anyway for an effective repair



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Old 21-04-2008, 03:21   #25
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I propose to use polypropylene honeycomb. It has excellent resilience and shock absorbance in pounding conditions. Some people have used a double sandwich. glass/core /glass/core/glass on bigger boats.
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Old 10-11-2009, 18:57   #26
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We work on many differant cats, and I can absolutely guarantee in the boats we have worked on, that the foam core boats are not as good as the balsa core, namely in that we have seen many foam core delaminate once wet. We have had a few balsa core boats that have had their hulls punctured, one in particular was punctured, another hit by a whale, and both boats were in the water for 1-2 months after the damage, the water had migrated less than 4" in both boats. I used to be a sceptic in regard to the balsa, but as long as the boat is built properly, the hulls will be in better shape than a foam cored hulls in the long term.
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Old 21-11-2009, 16:08   #27
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Quality and Follow through at the Factory is KEY

For Cats, it's the factory and the people who work there that is the most important. We're forgetting that it's not a perfect assembly line. There are Mondays, Fridays, and differing weather days. I have been on 2 year old South African Cats that screamed poor workmanship... and it wasn't a Charter Cat! I have also opened up 16 year old French cats with a foam core and found absolutely perfect adhesion between all layers, even after 1 year of water intrusion around a thru hull fitting. It's all due to the craftmanship of the factory laborers. Just like the "experts" who flock to Ft Lauderdale for the high pay in the marine industry talk a big talk, but can't walk the walk. Last year they were rennovating apts in Europe and this year they're an expert, but with no licenses or affiliations. Summary; do your homework on the factory and it's history, service personnel and their resumes, and get references! I've spent the last 14 years going to boatyards in FtL/Mia with cats, monos, and aluminum big boys so if you need an opinion.... don't get fooled by the "nice" guys.
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Old 08-06-2010, 11:58   #28
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Having just removed ALL the balsa from my deck, and squeezing out water from blackened balsa like a sponge as we removed it, there is no way in the world i would ever purchase any underwater cored hull, no matter what the core. I would rather have a boat for years and years and years that cost me a bit in performance, than one which i would have to do extensive (=$$$$) repairs to. And besides, once it soaks up water (and it will), you won't get the performance anyway.
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Old 08-06-2010, 17:01   #29
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G'Day All,

My, but there are a bunch of wildly divergent opinions here on foam vs balsa vs solid!

I think that the observable fact that there are long term success stories from all camps tends to support the idea that quality of workmanship is more important than the specific materials used. Unfortunately, unless buying a new vessel, getting info about the workmanship involved is very difficult, and one is reduced to anecdotal evidence as repeated above. IMO, not a very reliable data source! Big problem.

And on another subject -- comparing decks and hulls in terms of core reliability doesn't work well. Hulls have few penetrations, and once built, hulls are seldom modified by owners. Decks, on the other hand, have dozens of penetrations and are frequently modified by owners (additional deck hardware, etc). Further, many of the deck penetrations (chain plates, genoa tracks, main sheet travelers etc) are subject to cyclical and severe loading which tends to break down sealants, and thus lead to water intrusion. Consequently, I reckon that extrapolating from the fairly common deck balsa mush to condeming cored hulls is a bit extreme.

My own contribution to anecdotal evidence follows: Had a foam cored hull, balsa cored deck boat built by Palmer Johnson (Standfast 36). Had water intrusion around very poorly done chainplate penetrations when the boat reached around 20 years of age (and 70,000 miles traveled under my ownership). Not hard to repair since the water had only spread a few inches from the chainplate. When I sold the boat at age 29 years and 86,000 miles, the foam cored hull had no detectable water intrusion according to a fairly critical surveyor hired by the buyer. FWIW, it had never had any osmotic blistering problems either, despite being polyester construction.

So, instead of blanket condemnation of a form of construction, I believe that one must evaluate the specific boat in question. If a new boat, a visit, possibly accompanied by a knowledgeable surveyor, to the builder during hull construction stages could ease some worries... maybe!

It's a vexing problem for sure...

Cheers,

Jim and Ann s/v Insatiable II lying Pt Stephens, NSW, Oz
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