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.

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.

Ken

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/norglass-norseal-wood-treatment-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.

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.

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)!

Ted

Key words “properly sealed”.

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.

. 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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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.

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?

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.



David

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.

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.

Jim

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.

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.

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 !

djmarchand said:

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

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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

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.

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.

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.

HiDHo said:

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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QUESTION: Why does a "state of the art" boat get blisters?

Apologies for not posting the video earlier,and confusing some of the build procedures.
Does the video add to anyone`s understanding and opinion?
I`m holding off making an offer, I could go lower than I planned, but the kernel question is, do I want to own it, at all? Which is what this thread will help me resolve.

Bruce, you seem quite keen on this one, and I can understand why. I'll do some thinking out loud as it were, in case it might help you.

The video does not really help. Although, it refers to the balsa being encapsulated, which IS NOT saturated or sealed. Any delamination of balsa from the fibreglass (either side) will provide a pathway for water. Once water is in, it cannot be removed, you cannot dry out wet balsa. You have to cut it out, re-core and replace the 'glass skin. In theory stress flexing could delaminate the balsa. How well your surveyor will be able to test for delamination or sections of wet balsa, I don't know. That is the cautious angle.

Beneteau have been in business a long time, and have built many boats. There does not appear to be many core failures, or it would be readily found by searches and on forums. Maybe their designs manage the stress regime well, and their resins and manufacturing methods ensure very good bonds to the balsa. As others have noted, balsa used in boat building when this boat was built, as opposed to the 1980's Taiwan learning period, can be perfectly fine. More than likely Beneteau did it well, but surveying to look for delamination would be prudent. The hammer test by an experienced person I guess. This is the 'trust the brand' angle.

Ideally I would want to remove underwater through hulls to inspect for correct fitting (oversized holes with thickened epoxy etc) but in particular search for any non-standard, potential DIY fitting work, topsides as well as below the water line and check those carefully. Including the portlights you mentioned. Moisture meter at minimum if removal is not feasible pre-purchase. Factory-fitted penetrations might all be fine, later DIY ones might not be. You might only be able to do this after your offer, subject to no material adverse survey results, has been accepted. I'd make it clear that any areas found defective will result in the offer being lowered, but clearly it would have to be a material issue highlighted by the surveyor that could take real money to fix.

BruceK said:

Apologies for not posting the video earlier,and confusing some of the build procedures.
Does the video add to anyone`s understanding and opinion?
I`m holding off making an offer, I could go lower than I planned, but the kernel question is, do I want to own it, at all? Which is what this thread will help me resolve.

Click to expand...

.

Hi Bruce,
I have read your numerous posts over this boat,starting from the hull blisters noticed around the transom to yesterdays post.
You seem very wary and ill at ease over this boat !!
Walk away from this boat or you will never feel relaxed and always be thinking of some negative. Your spending huge money here. Go find another fish from the ocean.
Regards to you both.
Brett

Hi,


I have checked the single ST42 purchase intention, but the hull sides very much liike a spider network (stress cracks) and the risk of water to move kapilar in the core.


I didn't look at the other ST42, so whether this individual had experienced a hard or type of failure?


NBs

QUESTION: Why does a "state of the art" boat get blisters?

Which era of "state of the art?"

Cheap resin choice ,thinned too far for quick wet out , poor workmanship , dirty work area poor layup schedule ,to name a few.

THe use of balsa instead of foam that will not get saturated with water is done purely foe economic reasons.

Price AIREX , one of the best core materials to see price of quality. .

People forget that water can enter a cored hull from inside as well. Anything screwed into the inside of the hull is cause for concern.

There are many cored hulls afloat that seem OK but I don't need another thing to keep me awake at night.

There once was a KK type( I don't know the actual brand) trawler in a yard near me that was having the entire bottom replaced because of balsa core rot.


I would not own balsa cored hull. Synthetic cores however are fine IMO. I also did the experiment of soaking synthetic core samples for many months without any apparent change or damage.

I think that the early adapters of coring below the waterline experienced a learning curve. 90's era Sea Rays were a horror story. weirdly enough Bayliners and many other builders cored their hulls below the waterline without issues if proper precautions were used when installing hull penetrations ... From a design perspective the weight reduction is needed to achieve performance at a reasonable cost.. The building techniques have improved... If this is "the boat for you" and the survey is good, a cored hull would not be a show stopper for me

I think if you have to ask on here if you should buy a particular boat because of its construction technique then you have answered your own question....

If in doubt move on...

Good luck in the search, we found it fun....

I don't think that using balsa today when synthetics are available is defensible.