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Old 01-20-2019, 04:31 PM   #1
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Cored Hull Underwater

This arises because I`m considering a Beneteau ST42 which has a cored hull incl below waterline. According to a boat test video taken at the Beneteau factory, all Beneteau`s are built that way, the core is balsa, the balsa is saturated with resin during the build.
I`d probably not question above waterline coring. But,Beneteau build a lot of boats,all done this way,over many years.
I`d expect known negative experiences if it is a problem. I found comments online like "I`d never buy a cored hull",but nothing specific.
Contributions about experiences or knowledge would be much appreciated.
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Old 01-20-2019, 04:39 PM   #2
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I guess t depends on how much you like the boat. Balsa is not rot resistant at all. So if it gets wet, it will rot. "Saturated" with resin is not worth that much IMO because its not really possible to do that without vacuum infusing, etc. I think we all know that coring below the waterline can definitely cause issues. But if all the hull penetrations are properly sealed, its shouldn't be a problem.

Personally, I would hate having a boat that was cored below the waterline, but if I liked the boat enough, I would live with it.

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Old 01-20-2019, 04:47 PM   #3
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The devil is in the detail. 'Saturated with resin' is a glib statement. Normal resin would not saturate balsa. Some resins will. For example this stuff is amazing:
https://www.whitworths.com.au/norgla...reatment-clear

I would want to know specifically what they used. Because balsa with just a coating of normal 'glass resin on its surface will be a major red flag. Any damage to the hull and the balsa will likely get wet. Once wet it will not dry out, and it eventually will rot.

A hull cored with closed cell foam is different entirely, and would not concern me at all.
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Old 01-20-2019, 04:53 PM   #4
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Saturated with resin probably means maybe a thick coat of resin. I doubt it is resin infused. I am not even sure resin infusion would penetrate the balsa or not. I am not a fan of cored hull bottoms, but if you really love the boat, go ahead and roll the dice. Good luck what ever way you go. Maintain the through hulls if you go cored.
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Old 01-20-2019, 04:59 PM   #5
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My Cherubini isn't cored below the waterline, it starts somewhere up the side. As already mentioned, all protrusions into or through the coring need to be properly sealed, which requires some level of faith in the manufacturer's process.

To give you an idea of rhe potential life expectancy of balsa core when properly sealed: My charter boat is a Bruno & Stillman 35. The entire hull and transom are balsa cored. It's a 1975 (44 years old), still bone dry, and has zero core delamination issues (or so it appears)!

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Old 01-20-2019, 05:01 PM   #6
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Key words “properly sealed”.
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Old 01-20-2019, 05:05 PM   #7
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Bruce, when I started counting below-waterline hull penetrations on my boat—through hulls, rudders, props, bolts for struts, grounding/bonding plates, seachest grate, etc—I quickly ran out of fingers and toes. With each of those as a possible ingress point, I was grateful more than once not to have balsa below the waterline. Beneteau may well have figured out how to build a hull that never takes in water somewhere, but I’m betting they’d be among the first (except, of course, for Ted’s).

Anyway, best of luck with your search. I’m sure whatever you buy will have a world-class sound system.
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Old 01-20-2019, 05:11 PM   #8
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Quote:
. Personally, I would hate having a boat that was cored below the waterline, but if I liked the boat enough, I would live with it.
That is where I am at:
Never cared for cored hulls, bottoms, decks, etc.
Now I got a Albin 28TE that is all of the above.
Had a good survey done with infrared imaging, no leaks, all dry.
The factory changed from balsa to closed cell foam about the time my boat was built (April 2001), not sure what it has for coring and with the factory out of business, nobody to ask.
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Old 01-20-2019, 05:14 PM   #9
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On the boat Bruce is interested in, couldn't a surveyor with a moisture meter check the through-hulls and other penetrations for water in the coring?
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Old 01-20-2019, 05:34 PM   #10
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I have owned two boats with core below the water line. The first was a Saga 43 sailboat that ceased production some years ago. I bought it new and visited the factory and concluded they knew what they were doing with that construction.

At the factory, each thruhull was done with no coring for about 6" around the penetration. During commissioning I had a genset installed and they cut back the core and filled it with thick epoxy before installing the thruhull. I felt that this level of attention to detail was sufficient to minimize the chance of water getting in.

I sure wouldn't want to trust that the balsa was saturated with resin during lamination. That is a last chance barrier to water and I don't trust it. You need to isolate all underwater penetrations with resin, not balsa or plywood to be safe.

The second boat was a used J/32 and they have been building them that way forever and there have been no reports of underwater core failure over maybe a thousand boats built by that builder. So I had confidence in their workmanship.

So look at how they isolate penetrations and don't pay much attention to the claims about saturating the balsa with resin- that is a given. You may be able to see the solid fiberglass around the penetrations. If so that would be a good sign. On my Saga above they were obvious inside the hull since the solid hull thickness was less than the surrounding cored area.


Beneteau is a good boat builder, but I would be careful. Witness the bad injection elbow installation in the boat you are considering that you sent me pics of in a PM. I am also a little surprised by their claim that they build all of their boats with coring below the water line. That is news to me. I thought only performance sailboats were built that way.



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Old 01-20-2019, 05:34 PM   #11
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Assuming no grounding or other hull damage. We saw a cored boat go aground in Mission Bay inlet in San Diego. Had foam coring hanging out like spaghetti. Not sure how they repaired it.
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Old 01-20-2019, 06:17 PM   #12
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Cored hulls scare the bejeebers out of me.

Here is a link to a David Pascoe article on cored hulls.

One of my favorite sailboats of all time is the Nonsuch 30. It does, however, have a cored hull and thus I would likely not buy one, even if it passed a survey.

Is there a Beneteau Owners Forum that is independent of the factory? If so, it might be work asking the question of that group of owners.

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Old 01-20-2019, 06:22 PM   #13
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I had a Sisu 26 years ago with a balsa cored hull and if any penetrations like a thru hull are treated correctly it shouldn't be a problem, but if you do get water in it's a mess the balsa just disintegrates over time.
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Old 01-20-2019, 07:11 PM   #14
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I'd definitely keep a cored bottom boat away from hydraulic trailers that lift the weight of the boat with pads against the bottom of the hull. There are more and more of them showing up in yards and they are a menace. A 39' diesel Sea Ray in our marina had a hole punched in the aft bottom from one of those things. Think crushed coring and cracks in the outer laminate at a minimum.
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Old 01-20-2019, 07:16 PM   #15
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Our Krogen Manatee 36 has closed cell pvc coring from the rub strake down to the keel. The coring doesn’t absorb water, I saved the plug from a thru hull we added, I submerged it several days in a glass of water and the closed cell pvc did not absorb water. The cored hull compared to a previous solid f/g hull is quieter and the coring insulates in cold weather so no condensation problems.
The hull showed no deflection when hauled out and blocked up. Last block up was for several weeks while the bottom was blasted clean, blisters repaired and epoxy barrier coatings applied. The coring is very rigid which might be why no block up pad deflection occurs. I can however see how a hydralic trailer might be a problem putting the total weight of the boat on the small pad area.
Thanks Rufus I will definitely avoid hydralic trailers !
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Old 01-20-2019, 07:18 PM   #16
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Quote:
Originally Posted by djmarchand View Post

The second boat was a used J/32 and they have been building them that way forever and there have been no reports of underwater core failure over maybe a thousand boats built by that builder. So I had confidence in their workmanship.

David
Never seen a J (any model) more than a few years old that did not have significant moisture in the hull. Attached are a couple of pages from a very typical J-boat survey
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Old 01-20-2019, 08:11 PM   #17
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Appreciate the comments.Here is the video I found which was taken in the Beneteau factory. Without looking at it again I think they moved to vacuum bagging, but well after the 2004 manufacture date.
It`s not an entirely academic discussion. Apart from the numerous thru hulls our boats have, this one has leaking around the portlights either side of the bow cabin. Due I`d say to failed sealing; it`s not recent, there is corrosion on the inside plate and seepage down the interior wall to a wooden shelf below discoloring the finish. There might also be a minor leak in the companionway ceiling below,maybe coming through the deck.
It`s a shame,otherwise an attractive boat, most other issues are likely to be overcome, well kept and I think well serviced, with surprisingly low hours. However, someone should have picked up on those portlights.
Sadly,this may be the deal breaker.

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Old 01-20-2019, 08:23 PM   #18
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Re the video above, click the "Watch this video on YouTube" and it plays. Reviewing it I see it was injection moulding which was introduced subsequent to this ST42 build in 2004. The other steps, incl vacuum bagging, should apply to this hull, which appears to have been built in France.
Surprising,our 1981 IG has foam cell cored decks, it`s not the only one of its vintage though some still had the traditional teak offcut sandwich core.
The David Pascoe article is scary but on point. Most worrying is that survey will likely not reveal a defect.
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Old 01-20-2019, 10:06 PM   #19
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Any balsa hull coring can be disastrous! I was looking at a older 1993 Lagoon 42 Cat. The Surveyor found the hull topsides full of water moisture! This was built by Person Tillotson with a infused hull . Supposed to be state of the art--- LOL!!! What happened was a prior owner wanted rub rails. He installed a aftermarket rub rail himself with screws into hull every 6 inches -no caulking! Well over time rain and deck washing water ran into the hulls balsa ---rotting it, as once in the water cant get out.
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Old 01-20-2019, 10:09 PM   #20
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Our Krogen Manatee 36 has closed cell pvc coring from the rub strake down to the keel. The coring doesn’t absorb water, I saved the plug from a thru hull we added, I submerged it several days in a glass of water and the closed cell pvc did not absorb water. The cored hull compared to a previous solid f/g hull is quieter and the coring insulates in cold weather so no condensation problems.
The hull showed no deflection when hauled out and blocked up. Last block up was for several weeks while the bottom was blasted clean, blisters repaired and epoxy barrier coatings applied. The coring is very rigid which might be why no block up pad deflection occurs. I can however see how a hydralic trailer might be a problem putting the total weight of the boat on the small pad area.
Thanks Rufus I will definitely avoid hydralic trailers !
QUESTION: Why does a "state of the art" boat get blisters?
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