Yamarin 461: Where does it hold water?

Our 14 year old Yamarin gets heavier in the bow each year. We've made inspection holes in the fuel hold and the bow room, but cannot see anywhere that holds water.
My theory is that they used hydroscopic foam (two part PU foam?) between the hulls. But the vendor says they did not. Any idea what to do?

 

Pull a core sample and test it. This is a common ploy to find out what's going on, with these types of issues. A hole saw and a drill is all you need. To defend the manufacture, they likely thought the polyurethane foam they used was not hydroscopic, but in reality, particularly under pressure, can absorb some moisture. Additionally, the foam may indeed not be absorbing water, but has cavities and voids all through it, which do collect moisture.

 

How do you test a core sample of foam?

 

Weigh it, then put it under vacuum and weigh it again after it's sucked dry. The sample is treated as a whole, not just the core.

 

Last year I removed the expansion foam from a Beachcraft runabout. No weighing required. It left wet splats when dropped.

 

Yeah, it's usually pretty obvious . . .

 

But it's solid glass, outer and inner. Don't know where the foam is, if any.

 

It likely has foam between the liner and hull shell. You can cut holes or remove the deck cap/liner and find out, though this is major surgery, just to explore and examine. I see this fairly regularly, where boats that normally performed quite well, suddenly start to slow down, for no apparent reason. They check the engine, prop(s) and other stuff, but nothing seems to be wrong, except it's slower. The last one I did needed it's transom replaced. When I opened up the back of the boat, about 500 pounds of water had collected between the hull shell and the foam under the liner. With the foam removed, repairs made, the little 40 HP outboard was again able to push this 18' boat along at a reasonable pace.