How do I check the structural integrity of a bulkhead or interior plywood surface?
Dan Dickison responds:
Thanks for your question. Most of the damage to bulkheads or other interior surfaces will come from water leaks. Collisions are actually pretty rare, but they can definitely stress a vessel's bulkheads and other load-bearing surfaces. Your boat might also sustain damage to bulkheads from a serious grounding, being thrown against a dock or sea wall by a particularly vicious sea, or from by a severe pounding in a seaway over and over again. (About a decade ago, a brand new 60-foot aluminum racing boat suffered severe oil-canning after pounding its way through the Gulf Stream on an initial test sail.) Often, the damage done isn't readily apparent.
Most of the time you can make a simple visual inspection to ascertain the status of a bulkhead or a span of plywood like a cabinet face or side. If the plywood or the surface of the bulkhead is bulging out in an extraordinary fashion, it's likely that it has wicked up moisture or is suffering from a leak. If there's damage from standing water, then you're likely to see a discoloration in the plywood and perhaps some delamination at its edges.
There are instances, however, where water damage may exist, but it's not noticeable. These, of course, are the worst kind of problems because the longer they go unchecked, the more damage they do. There are two ways to get a better handle on the condition of the bulkhead or surface in these instances. The first would be to check it with a surveyor's tapping hammer. The tone produced by the hammer tapping on the surface should be relatively uniform except where there's additional structure behind the surface or where the bulkhead has been compromised. It takes a little getting used to, but after you've spent about 15 minutes listening to the different tones, you should be able to use this method of detection fairly effectively.
The other approach is to use a moisture meter to determine if you have water damage that's not visible. This too is tricky as your meter may be picking up water that's in the bilge or moisture in a tank nearby, so you first need to rule those possibilities out.
While you're having a look at the bulkheads, the other area to check is the joint along the hull. If the tabbing or the fillet is loose or broken, then the structural integrity of the bulkhead is most likely compromised. This might not mean immediate problems, but certainly eventual ones and it's best to remedy the situation as quickly as you can.
Here's hoping that this information is useful to you. If you still feel uncomfortable with your findings, consult a professional marine surveyor or at the very least an experienced boatbuilder.