Lets talk about rotten balsa in the hull...

[Noah]

I know of two very nice boats built by TPI using the scrimp method that have delam/rotten balsa in the hulls. Neither of these boats are more than 15 years of age, and the hulls haven't been breached in any way. IE no cracks, etc, and no blisters. On general inspection these hulls looked ok, with good paint, and well bedded through hulls. I did notice that on the inside of one of the hulls there were screws drilled straight into the hull used for attaching wires, etc. If the bilges were full of water then the screws could have leaked. Furthermore, one of the boats has only been wet sailed for 4 years. Before that it was put in the water each time it was going to be sailed.

Anyway, enough with the nasty details...How hard is it to repair a wet hull. Lets say that 30% of a 30ft boat has a soggy core. Give the boat a $75k value...how much time and effort would it take to do the job? Can you even do a good job?

I know that many of you have re-cored decks, but I haven't heard much about hulls stuff. This is probably because you all have "classic" fiberglass hulls with no silly wood that is prone to rotting.

Noah

[Tim]

Are you sure these boats were built using SCRIMP tecnhology? That hasn't been in use for as long as 15 years--perhaps 5 or so. Older boats built by TPI did not use SCRIMP. The newest models of J-Boats are built with SCRIMP, but only quite recently. Hinckley now also uses SCRIMP.

TPI has built many boats, including many cored hull boats, and their success is checkered. Many of the TPI boats (Pearsons, Freedoms, J-Boats, and a host of others) have some questionable construction techniques, mostly surrounding poorly-installed hull fittings and so forth. Older J-Boats in particular are notorious for having hull core issues stemming from poorly-bedded through hull fittings. This is more a result of time-saving installation techniques rather than a problem with the cored construction itself.

The difficulty and expense in repairing cored hulls varies, of course, and is highly dependent on the situation. Evaluating the true condition of the core is one of the most challenging jobs there is. On what evidence are you basing this assesment of the core condition? There's a vast difference between core that might contain slight levels of dampness (even a small amount will tend to nearly peg a moisture meter), and core that has rotted away, thereby destroying the structural integrity of the structure. Core that is damp, or even wet, but that remains bonded to the skins has been shown to be as strong as dry core.

Remember that wood is very strong when wet--think of living trees, which are far wetter than any wood used in boatbuilding. Wet, by itself, does not necessarily indicate a ruined structure. This is not to say we should be happy to find moisture in a hull--of course not. But the possible presence of moisture is not the kiss of death. Still, any boat containing moisture must be approached with substantial knowledge of the possible ramifications, and with knowledge of and preparation for whatever repairs might be necessary.

If enough water enters a cored structure, particularly if the core is not well bonded to the laminates (leaving a wide-open path to the core's end grain), it may lead to rotting, which of course destroys the core and leads to debonding. (Note that delaminating technically refers to the separation of various layers of fiberglass from each other, while debonding refers to what happens when core separates from one or both of its fiberglass skins. It is an important distinction, although it is frequently breezily dismissed by many. Also, the presence of moisture does not always equal debonding either.) This sort of damage is frequently seen near some sort of hull penetration--from a screw hole, or through hull, or any other opening where water can get into the core.

Water can also get into the kerfs cut into the core material, which might allow the water to migrate for large distances--but if only the kerf are open, the water will have a harder time getting into the structure of the wood itself (as opposed to migration between the core and the skin). Water in the kerfs would of course send a moisture meter wild, but in an overall sense, this is a far less significant issue with few ramifications from a structural standpoint.

Core repair is very labor intensive, and repairs are always expensive, at least when labor is taken into account. One can do a very successful job on most hull core repairs, depending, of course, on the severity and nature of the damage. It's impossible to generalize, because each case varies so significantely. Of course the price of any boat with a known core problem would have to be discounted to allow for repairs to be carried out. The basic repair process is identical to what we might do on the decks. Obviously a hull truly needing a full core replacement might be one ready for the scrap heap--but most are not actually this bad.

I continually defend the concept of cored hulls, but do not condone the poor construction practices that lead to preventable core failures. Coring is always a hot topic, and frequently brings up uninformed and blithe responses that are of little help, and which perpetuate bad and untrue information and myths. The issue is very complex, and to automatically shun all boats with cored hulls would be unfair. There is no question that many boneheaded construction techniques were employed that have led to core failures, both in hull and deck. Many builders have learned from these mistakes, and now do a better job in this respect. Sadly, cost-cutting will always be an issue in the industry, and there will be builders who still fail to properly deal with core penetrations. This is not an acusation of the cored structure itself, however.

One might ask: why ever build a boat using a cored hull? Well, a cored hull is lighter and stiffer than a solid glass hull can ever be, at least within practical limits. The stiffness inherent in a cored structure is the main driving force behind their use. Stiffer is better--less flex in any structure, over the long haul, will prolong its life. In the most general terms, lighter is also better--with all things remaining equal, any weight removed from the hull can be replaced with additional ballast (for a stiffer boat), and/ or increased interior accommodations without a weight penalty.

The benefits of cored structures are easily negated by poor construction, which can lead to the failure of the structure. But the poor construction used by some builders should not automatically mean that all cored hulls are bad. Neglect--whether by the builder, or by a subsequent owner--causes most boat-related failures. On occasion there are true construction deficiencies that the most meticulous owner could never foresee, but in general that's not what we're talking about here.

[bcooke]

Wet, by itself, does not necessarily indicate a ruined structure.

So how then does one go about saving the structure? Assuming the core is wet but not debonded. Can the moisture be drained, dried, or flushed? Or is removal the normal course of action? I have heard of these techniques over small portions of decking but how far can they take you?

-Britton

[Tim]

It's not always necessary to remove core that has become dampened. Sometimes, the condition is such that eliminating the source of the moisture ingress will stabilize the situation successfully. Smarter people than I have come to this conclusion under a variety of testing circumstances. I am paraphrasing statements I have read in trade and consumer publications, and adding my own experience and opinions to the mix as needed.

This issue is extremely complicated, and I could spend all day covering the various ins and outs of it all--there are simply too many variables at hand in any given situation to provide blanket statements one way or another.

Therefore, if we can, let's stick to specific instances, if applicable, and try to address what to do in that instance. My points above were merely to illustrate the difficulty in automatically condemning--or, conversely, providing a stamp of approval to--any boat with a cored hull. I am not an engineer or forensic expert on cored hulls, and can only point to a variety of articles on the subject, as well as my opinions based on personal and widespread experiences.

Unquestionably, solid glass hulls simplify the whole situation! Solid glass isn't perfect either, but at least you eliminate the possibility of core failure.

[Noah]

Thanks for the detailed response.

Perhaps one of the boats wasn't built using SCRIMP, but I believe one was. They are both very different designs. The one boat which I have seen up close and personal was "debonded" and the core rotten to such an extent that is was easy to push in the outside of the hull an 1/8" with very little effort. This debonding was located on the side of a hull with no through hulls, and probably ran for 10ft or more. I know that water travels a long way before it can make it's self known...I suppose it got in from the inside, but it's hard to know. The owner had no idea, and was pretty shocked as he just re-did the paint and a number of other things.

One friend that has some knowledge of how to do these things said that he has successfully used a vacuum bagging system to pull water out of damp balsa. Once they have pulled the water out he goes for core samples to see what the condition of the balsa in various areas. Then you can go out and start replacing the core either from the inside or the outside depending on the boat.

I don't want to go into more specifics of the individual boats because they will both probably try to be sold after repair, and I don't want to get involved. I just enjoy watching from the sidelines as I toil away on my wooden boat with it's own challenges.

Thanks,

Noah