Balsa-Cored Bottoms

[Joe S]

Deal breaker? In the past i've walked from boats with balsa cored deck issues. Balsa cored bottoms scare the ....out of me.
Thanks for your thoughts/comments.

[Dockhead]

My boat's hull is entirely balsa cored.

I did a lot of research before buying it. That research seemed to indicate that well constructed balsa cored hulls are not troublesome. "Well constructed" includes, among other things, the use of end-grain balsa blocks which are individually encapsulated in resin. My research seemed to indicate that in a boat with a well-constructed balsa core, any breach of the hull will create only localized damage.

Cored hulls are lighter and stronger. They also have the advantage of better insulating properties (so less condensation in cold weather, a very significant advantage if you plan to be aboard much in cold weather) and much better sound insulating properties. The latter thing is really striking -- how quiet our boat is down below.

Disadvantages include difficulty of installing new through hulls, and cost -- well-constructed cored hulls are much more costly than solid ones.

Poorly constructed balsa cored hulls include the notorious Sea Ray power boats, which are extremely troublesome. This has unfairly blackened the reputation of cored hulls, I think.

Part of my research included finding out whether there were any reported problems with the cored hulls from my boat's particular maker. I couldn't find anyone who had ever heard of even one reported problem.

So that made me reasonably comfortable buying our boat. I can't say yet whether we'll never have any problems, but I can report that we are enjoying the advantages. The hull is tremendously stiff, extremely quiet, and does not suffer from condensation (we sail year round).

You will need to do your own research, and particularly, on that model of boat you are considering. Older = worse, I think, as earlier cored hulls did not generally use end-grain encapsulated blocks. That technique appeared only in the '90's, as far as I know.

[GordMay]

That's a good "solid" review of the issue, Dockhead.

I tried to send you a "thanks" but got told:
You must spread some Thanks around before giving it to Dockhead again.

[skipmac]

Purchased a 1984 Pearson 42 last year knowing I would do a bottom peal after purchase but did not know the hull was balsa cored. When we shaved the gelcoat below the waterline the end grain, balsa mat was clearly visible through the glass. The core is not in the very bottom of the hull, roughly from the bilge area down to the keel.

The boat stayed in the water since new and was a bit neglected for the last few years by the PO. However, moisture meter tests show no difference between the cored and non cored areas. Visually there are no areas in the core that look darkened from water saturation of the wood but also noted that Pearson used solid glass in a large radius around all through hulls. Tapping found no areas that sound soft or delaminated.

I know that this is a data sample of just one but no problems with my cored hull.

[Mule]

Very well addressed above. If the Balsa is COMPLETELY encapsulated in resin and the through hulls are dough-nutted big time then I think balsa could be OK, even a plus as outlined by Dockhead. He does have a Moody, not a production boat.

And now for the big "But". The voids between the blocks need resin from glass to gelcoat with no voids. EVERY through hull needs a solid glass collar around it perhaps as much as 3 inches wide from the outer edge of the through hull to the end of the solid glass. Every time a through hull is added the installer of same needs to do it right.

As an owner of a solid glass hull and poorly done balsa cored decks with ignorant, inattentive or uncaring installers and/or previous owners I can attest that I would be very careful in dealing with anything balsa. My hull is in great shape, no blisters but the decks have been an expensive, labor intensive nightmare that I can assure you had I know how bad it was to be I would have NEVER bought this boat. 82 Mainship 34. The gaps between the balsa blocks was not filled with resin so it gave little channels for intrusive water to migrate and do its damage every where. So much for localized repair. For me, the term Balsa-cored is is about appealing as the term gonorrhea,divorce, sick child or Republican.

[rourkeh]

.
Jos s has the right idea about cored hull bottoms, except he should run not walk away. Manufacturers of production boats that use coring below the water line use it for one reason only. To save money. And I have never heard of, or seen one instance where it has been done successfully. Viking, Sea Ray, and others use end grain balsa below the water line because it is much cheaper than glass mat and resin. The structural integrity of sandwich construction can have benefits as applied in race boats with carbon fiber or Kevlar, and vacuum bagging under controlled conditions. I have been to numerous manufacturing plants and seen the layup schedules in hull production. The hit and miss quality is scary. Coring in hull bottoms requires meticulous saturation and attention to layup that does not exist in production boats. The level of bonding required to construct a good hull with coring is just not possible in a production facility where cost is paramount. You are bound to get the odd cored hull that can go for many years without failing completely, but internally given the flexing and twisting that occur in any boat there is going to be catastrophic failure. And what you don't see can't hurt you applies best here. I have seen hulls with cored bottoms weighed against factory spec and have gained as much as 25% due to water intrusion. The whole concept is stupid, and typical of manufacturers trying to save money with little regard for the consumer’s safety or well being. There are some good articles out there on this subject you should read before thinking about any boat that has coring below the water line.
Cored Hull Bottoms

[shipofools]

Originally Posted by rourkeh

.
Manufacturers of production boats that use coring below the water line use it for one reason only. To save money.

or weight.

[phillw]

Originally Posted by rourkeh

.
Jos s has the right idea about cored hull bottoms, except he should run not walk away. Manufacturers of production boats that use coring below the water line use it for one reason only. To save money. And I have never heard of, or seen one instance where it has been done successfully. Viking, Sea Ray, and others use end grain balsa below the water line because it is much cheaper than glass mat and resin. The structural integrity of sandwich construction can have benefits as applied in race boats with carbon fiber or Kevlar, and vacuum bagging under controlled conditions. I have been to numerous manufacturing plants and seen the layup schedules in hull production. The hit and miss quality is scary. Coring in hull bottoms requires meticulous saturation and attention to layup that does not exist in production boats. The level of bonding required to construct a good hull with coring is just not possible in a production facility where cost is paramount. You are bound to get the odd cored hull that can go for many years without failing completely, but internally given the flexing and twisting that occur in any boat there is going to be catastrophic failure. And what you don't see can't hurt you applies best here. I have seen hulls with cored bottoms weighed against factory spec and have gained as much as 25% due to water intrusion. The whole concept is stupid, and typical of manufacturers trying to save money with little regard for the consumer’s safety or well being. There are some good articles out there on this subject you should read before thinking about any boat that has coring below the water line.
Cored Hull Bottoms

The article was written in 2002 and I note that more and more builders are going to cored hulls whether it be foam, balsa or even polypropylene honeycomb. Schionning's have this to say comparing balsa to foam;

Balsa can absorb water. It needs extreme neglect to rot (very unusual). Water soaks along the end grain quickly and travels very slowly across the grain. We use balsa under the waterline especially because of its high compression strength for beaching etc, any core types must be sealed. Damages to all cores result in the same sort of repair. Notice a damp spot when drying out to antifoul.... simply grind back the surface glass exposing the core, dry it out and re-glass - its that simple.

[John A]

Once again I must say, "it depends". In this case it depends on the manufacture.

My 1981 Cabo Rico 38 has a balsa core of end grained blocks 2" square (dipped and covered with resin), about an inch thick, mentioned above. When I replaced the two inch thru hull I decovered that the outer layer of fiberglass was over 1/2 inch thick and the inter fiberglass layer was about 3/8" thick. The hull survived a couple of serious bounces off of rocks.
When I drilled a hole thru the cabin top for my Force 10 heaters chimmey the outer fiberglass was about 1/2" the balsa was about 1/2" thick and the inter layer was about 1/4", when I drilled a 2" hole in the side of the cockpit, to install a receptacle for the TV/phone, the thickness was about the same.
Of course. including the 7000+lb encapsalated keel, the boats factory displacement is 22,000 lbs.

[gonesail]

a balsa cored hull is a definite deal breaker for me .. a solid hull means one less thing to worry about.

[MacG]

It is as Dockhead explains. You need to have a boat from a good maker because of the particular characteristics of fiberglass and the used resins.

In itself fiberglass is far from watertight as is the used gelcoat. So a balsacored bottom needs a very professional way of manufacturing at a very trusted yard. The bigger Contest Yachts are of same way of construction as apparently the bigger Moody's and they are far from being idiot. From a top yard I would say yes.
Delamination is the biggest danger and once it starts it causes many problems of which the foresaid delamination is the biggest and most expensive to repair. Even repaired the hull will loose some of the original stiffness for obvious reason.
So from Moody, Contest, yachts from the topend of the production boatmaking, I would say yes. Others I would definitely investigate. Nevertheless delamination in balsacored decks are common problems. Even with brands like Swan and Baltic. Specifically the older ones.
Watch the type of used resin. The ortho resins are less 'bonding' than the current vinylesters.

[Dockhead]

Originally Posted by rourkeh

.
Manufacturers of production boats that use coring below the water line use it for one reason only. To save money. And I have never heard of, or seen one instance where it has been done successfully. Viking, Sea Ray, and others use end grain balsa below the water line because it is much cheaper than glass mat and resin.

I'm not sure that this is true. In fact it sounds like to an erroneous oversimplication to me.

A cored hull is much more complicated and more labor-intensive to make. I doubt that it could be cheaper than a solid hull, even in production boats.

I think the reason is to lose weight and gain stiffness, and not to save cost. Balsa-cored hulls are expensive extra-cost options in a number of high-end boats, and are standard on some of the very best sailboats like X-Yachts and Contest. I think most of the new Swans are fully cored hulls (I think Swan uses foam, however, and not balsa).


Planing power boats have their own different design goals. They have very large flattish surfaces underwater which desperately need stiffness. They don't have keels or the profiles which our sailboats have which naturally give stiffness. At the same time, weight is crucially important to planing ability. It's probably very difficult to achieve the right stiffness without sandwich construction. A planing power boat in the 40 or 50 foot range would probably not even float, much less plane, under the weight of a solid hull with the required stiffness, and I am not aware that any even exist with solid hulls.

The problem is that, like someone wrote, it does require more care and precision, than laying up a solid hull. So when a manufacturer like Sea Ray tries to do it with mass production techniques, with unskilled labor, on the cheap -- well, like many other things, the results are not so good.

[MacG]

This is undoubtly true. I am familiar with the Contest production facilities and it is a fact that cored hulls are substantial more expensive.
In the older Swan's and Baltic's you will find balsa decks only. No fully cored hulls - as far as I know.

It is done for the reason of gaining stiffness, not so much for the weightfactor. It does not pay to save weight below the waterline. Topsides and superstructure, yes.

As I wrote before, delaminiation is the big issue. Once it happens, you might have a sincere problem.

[S/V Illusion]

For someone who thinks a solid core hull is preferential to a balsa core, this too is a mis-perception and as we know, sometimes perceptions are peoples' reality right or wrong. Solid core hulls can and do suffer from water intrusion just as much if not more so. Water intrusion in ANY hull is a bad thing and to a large extent, it matters little what the coring is. Regardless of the real issue, some folks simply don't want a cored hull despite evidence to the contrary they are in some cases preferable for certain design reasons.

We had a Mumm which had core rot but it was much easier repaired than what would have been required of a solid hull with the same malady. Each to his own beliefs but just because a boat has a balsa core hull is no reason to dismiss it as a purchase candidate.

[zeehag]

i love my formosa. hull is solid. in my ericson, with cored decking, i found the balsa doesnt turn dark as does teak--was WET only. very freeking WET. i will NOT buy a cored anything anymore.. i dont care who builds it.



btw--i fixed it--isnt easy. as i said--i LOVE my FORMOSA 41, and i also love my ericson, but i will NEVER buy a cored anything on a cruising boat again.