Originally posted by rdpierce:
Is there any core around the keel joint? I would think that area would be solid glass. Yes, there's vermiculite filler everywhere, but that's not core per se.
I'm doing an extensive recore of the bottom of my J/30 (70% starboard, 30% port under the water line), including all around the keel sump. Core extends right up to the edge of the keel sump, but not down into it (I suppose this could vary by production year). The inner laminate glass over the coring is over 1/2" thick at the edge of the sump and tapers down to about 1/8 as you get to the settee. I've removed the floor to recore from the inside, so gravity is on my side. As several people have mentioned if you have significant moisture in your hull, it will be wettest around the keel sump since the water migrates downward. In my case, the core around the keel was the texture of a firm sponge. Let just say, it was 'no longer structural'. Fortunately, the glass over the inside and the three stringers across the sump prevented this area from developing cracks. I also think that the resin between the balsa squares helped keep the core layer from completely collapsing (think 'resin rivets').
I decided to recore based on a sample of the core (vs simply drilling a hole and poking around). When I cut a square of core out of the bottom it was not well bonded to either laminate (inner or outer) and had greatly diminished compressive strength. And it was wet, which means it would only get worse over time. I tried 'drilling and drying' this fall and winter with no success at all, even with a dehumidifier and heat lamps. I've been told by a source at Waterline that core that is wet with salt water will not dry with this method... I'm not sure if I believe this, but it seems plausible. I think it was simply too wet to dry this way. Even if it dried, I'd still be left with badly weakened core. Its a nasty project, but its going to be as good as new.
I've read a lot of posts about water problems in J/30s (or all
J/Boats of this era). This is definitely a common issue in any balsa cored boat with polyester resin and no barrier coat. I'm sure a large portion of the fleet has been sailing for years with a lot of wet core. These boats are rugged, but at some point wet core will get substantially weak and we'll hear about more delamination, blisters that reappear every year, or water weeping out of unexpected places. My boat was infiltrated by simple blistering that was never thoroughly dealt with by the previous owner. The result is a repair that would cost more than the value of the boat at a yard, but one that is manageable if you are crazy enough to do it yourself. I estimate I'll spend about 2k in core, glass and epoxy; god knows how many hours I'll burn up... If you don't have barrier coat, do it now.
I use a Protimeter Aquant moisture meter and I've found to be utterly reliable at gauging the real situation inside the laminate. If it reads over 200/1000 its significantly wet (you can press water out with your fingers and a good hard pinch). If your meter is over 800/1000, it is truly soaked (think sponge before you squeeze it out). I've used it to map out all of the core issues on my boat on both the deck and hull - its always spot on. Be advised that metal will make this kind of meter read false positive.
http://www.gesensing.com/products/aquant.htm?bc=bc_ge_protimeter Here's some information about this project visit
http://www.6degrees.com/j30/underthefloor/ , which features revealing shots of under the floor, the keel sump and in the core space. Enjoy.
Also see the thread "Dewatering Aft Bilge - Need Advice" for more information about this project.
Wee!
Rich
Tres Cosas
#294
