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Old 03-02-2009, 16:55   #1
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balsa cored hull

I've recently developed a love for a 1987 Pearson 39-2. The biggest concern to me is that this boat is a balsa cored hull (below the waterline). I've read the various old postings here and on Sailnet, and read the various options from some suryerors on-line about the subject. Seems that once you get past the "this is a bad idea no matter what" people, that the aguement of the construction method can be presented as a pro or con. I was even surprised by the number of manufacturers that use this contruction (seems Pearson was pretty big into this whole end grain balsa development thing).

So given this I'm looking for options from those who have had a balsa core hull boat, below the waterline, as to thier personal experience. Was this really a bad thing, or did it overall just not matter (from a construction view). Not talking abouts decks, we all know this story and they are in a different world with all the holes in them etc.
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Old 03-02-2009, 18:09   #2
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It's not the core, it's the folks that cored it. It's the same thing with the new synthetic cores. It's easy to screw up! You can screw up synthetic cores really easy.

You can thump it before you buy it and even fix it. A neighbor had an Endeavor 33 and they are known to have core problems. He bought the boat new and they found a few problems in the deck when he recently sold it. The key is they found them and he took a bit of a beating for it too. It is a problem you can look for and find.

I think you really take boats as they come. The potential for an unlimited number of things to be wrong will quickly eliminate a lot of good boats and eventually all boats. You could by virtue of "can any one say anything bad" methodology eliminate enough boats you never considered and end up with one. I don't think it yields the best boat though.

Risk includes the known and the unknown.

You can argue the point if it was a good idea and I'm sure many will but if you are looking at just one boat it really is just a lot of talk. You are not buying every boat with coring below the water line you are only buying just one (unless you really want trouble). You can pass on all the bad ones you thump. It's not a problem that is easy to go undetected.
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Old 03-02-2009, 20:56   #3
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End grain balsa core construction from a quality builder like Pearson is a great material. If it was such a bad thing how come there are so many cored boats still floating?

Get a good survey from a good surveyor and stop worrying. Every surveyor has surveyed a lot of cored boats - they know what to look and listen for.

And the boat you're looking at is 20 years old. If it had a serious core problem, it showed up 10 years ago and was fixed.

As you say, balsa cored decks have more risk from the many holes and are much more expensive to fix. Core problems below the waterline are quick to fix. Just cut the outer skin. Put in new core and some fiberglass. Fresh bottom paint covers all.

Any repair is going to be the seller's problem. And since everyone knows those balsa cored boats are death traps, you deserve an extra $10k discount just for making an offer

Carl
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Old 07-02-2009, 05:42   #4
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As is common the problem with this boat appears to not be the cored hull at all. It is the cored deck that is pegging the moisture meter in the boarding gate areas. So guess will have to wait till it gets warmer to be able to get an idea of the extent of the damage.
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Old 07-02-2009, 07:16   #5
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The core itself it's not the problem. Properly built, a balsa cored boat is great, good strength and good isolation. Many boats builders still use balsa today. If you get water in it, or in severe cases of osmosis, it is hard to dry it out, it could take years, or if you do it actively, require a lot of work. But the same goes for any cored hull. If it gets wet and stays wet, it will rot. That actually makes it a bit easier to find the damaged areas though Get a surveyor, if the hull is good and you otherwise like the boat, buy it. There's no reason not to, just because the core is made out of balsa. Pblais' words are wise
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Old 07-02-2009, 09:04   #6
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Our 28 foot sloop is balsa cored. Never had moisture intrusion problems, depsite blister "pox" and the occasional "deep" blister.

However, moisture DID get in due to a poor dynaplate install by moi, years ago, when I did not epoxy plug the thruhull holes deep enough (I shoulda cut out more of the balsa between the laminate and filled in more epoxy).

Ten years later, found water got in. The good thing about endgrain balsa, is the end grain limits the spread of moisture. It only spread to about 6 inches around the holes.

It is very hard to get balsa COMPLETELY dry. However, a rot problem is likely if the core is SATURATED i.e. moisture weeping from a test hole. If it is merely damp, or even "feels" dry despite high moisture readings, there is a chance rot will not be a problem.
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Old 07-02-2009, 10:23   #7
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It's all in the building, it can be a huge problem. If the builder left a few inches of non core around every hull penetration then it could be OK. I once had a boat that was cored in the topsides(ie:hull sides), but the core ran about a foot below the water line also. There were three through hulls on the starboard side of the boat a few inches below the water line. 30 feet x 16" of the hull had to be removed as the water had migrated that full length between the through hulls. the bill after that and repainting the boat was about $40,000. One problem with cored hulls is that if the builder does not saturate the balsa with resin well enough, it doesnt stick to the inner and outer hull creating an air gap between due to shrinkage as the resin cures. This hull was so thick it really wouldnt have mattered if it was cored or not, but usually the point of coring is to make the boat stiff without a thick layup. If it's that old and you have a very astute surveyor and if it surveys ok now, it's probably good to go.
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Old 01-03-2009, 01:24   #8
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Jedi is a Sundeer 64 built by TPI in Newport... Pierson is the "P" in TPI so we're related ;-)

We have a full balsa core in the hull & decks too and have had no problems at all. The Sundeers are built using the SCRIMP process which might be a factor as each piece of balsa is completely encapsulated in resin and thus protected. They used vinylester instead of polyester and we never have blisters.

The trick is the extra work for thru-hulls, fasteners etc. The core must be replaced with solid before doing that. I use 2 methods:

1. big holes like for thru-hull: I use the final size holesaw and make the hole. Next, I use the bigger diameter drum-sander on the dremel to remove the core between the fibreglass layers as far as possible. I fill that space with 3M structural vinylester filler and run the holesaw through again to remove the excess. Works great.

2. small holes like for fastener. Trick is to leave the outer-layer of fibreglass intact. Use a holesaw to cut through inner layer and core and remove these (breaks out quite easy). Sand clean and fill; drill holes for fastener.

Check this post on our blog for an example: s/v Jedi: Mounting deck hardware (English)
I worked from the outside here because this was on deck and I didn't fancy working upside down belowdecks. The cleats cover it all. I also bevelled (is that the right English word??) the edges of the top fibreglass layer for more contact area with the filler and opted for epoxy with high density filler because of the forces involved.

We love the insulation the core gives us and the stiffness and weight savings (we're very light).

cheers,
Nick.
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Old 01-03-2009, 05:29   #9
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In my opinion, there is nothing inherently wrong with cored construction, when it is done right.

As other Cruisers have indicated, a properly built cored hull, using the correct materials, and methods, can be a great advantage in providing a light, stiff, strong boat.

Anytime a hole penetrates a balsa cored hull or deck, the hole needs to be epoxy lined (either under cut, and filled, or plug taken out and undercut and filled, or solid glass around the hole/fitting). Nick (s/v Jedi) offered a good basic description of the process.

Notwithstanding, there are opposing experts, such as David Pascoe, who bemoan the practice of coring hulls.

Cored Hull Bottoms

Sea Ray and Balsa Core Bottoms - by David Pascoe, Marine Surveyor
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Old 01-03-2009, 06:43   #10
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A good build will have solid layup for all thru hull areas and areas of high stress. You want to have a material that does not wick moisture which might find a way in to migrate. Balsa end grain works great for this purpose.
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Old 01-03-2009, 13:34   #11
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I read the links Gord provided and the links on those pages too. After taking that in, my current thoughts are:

The surveyor is obviously having a problem with Sea Ray. As he also writes that even the plywood cores of the stringers rot on these boats, something most/all other builders can do right, I think he might be right. One should master the required techniques before attempting advanced layups.

His core objection is that builders use a core as a cheaper replacement for more expensive material, like fiberglass layup. The resulting hull is cheaper to build but of less quality than a non-cored design. Indeed, a child can understand that this is not good.

He also writes that there are many designs done good until owners or contractors mess it up later, because they don't understand what they are doing. Yes, I see that happening around me.

But, there is no disagreement in those pages that if ones intention is to create a hull that is superior to solid fiberglass, and the knowledge and implementation is good, the end-result will indeed be a stronger and stiffer hull. Such a hull will have many parts that are still solid: deck-hull joint, keel area, thru-hulls, bow, chainplates, frames etc. When doing all that right, the hull will also be more expensive than the same hull build in traditional solid fiberglass. For example, the balsa core on Sundeers tapers out towards solid fiberglass around the keel over a considerable length; this prevents hard spots and distributes forces well. This is also very labor intensive and thus costly.

But this isn't all to be said; the pages also describe solid glass layup's that are done very bad (like his Grand Banks example). Delamination isn't something exclusive for cored hulls! Thru-hulls for discharge are always a cheap solution and inferior to standpipes molded or welded into the hull and the list can go on and on. We're talking about total build quality of the hull and all attached to it. (I have seen failures on the solid glass laminates on a Irwin 50 that brought tears to my eyes... cardboard!

The OP was asking about a Pierson. How is that one build? How many owners did have problems with the cored hull? I must admit that even though we met many Piersons on our travels, I don't know which ones were cored or not or even when they were build... but I never heard a complaint.

The SCRIMP process developed by TPI is well known and proven for many items including balsa cored hulls (but also 30' blades of big wind generators). I don't think Pierson used that before becoming part of TPI but they clearly were working towards it and I would feel positive about buying a cored Pierson if the survey gives the green light.

cheers,
Nick.
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Old 02-03-2009, 09:25   #12
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Yes, my TPI built Lagoon 42 was 10 years old when I sold it. It had never had even a bb size blister.
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Old 26-02-2013, 19:39   #13
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Re: balsa cored hull

I don't believe for a moment that a cored hull will end up being more expensive than a non cored hull. It is done this way to save cost so why would it be more expensive
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Old 26-02-2013, 21:46   #14
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As pointed out above, it is more often the deck core that is the problem. Over eager owners with a electric drills are the biggest problem.

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Old 26-02-2013, 21:55   #15
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Re: balsa cored hull

Quote:
Originally Posted by edwmama View Post
I don't believe for a moment that a cored hull will end up being more expensive than a non cored hull. It is done this way to save cost so why would it be more expensive
Actually coring is done to make a structure stronger and stiffer while keeping weight down. Nothing to do with cost.
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