Join Date: Feb 2012
Location: New Orleans Louisiana
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Re: De-watering wet core
The only way to do it right is to cut open one layer of laminate and remove the wet core, replace it, and repair the cutout. Honestly it sounds more daunting that it is. A cutting wheel on an angle grinder will cut out the section pretty quick, the core comes ready to apply, and then you just need to bevel the edges of the old skin and reapply. Use epoxy for the work, and take it slow.
Trying to place a core under vaccume can cause major headachs, and really doesn't work. The thought behind a vaccume is that it will lower the boiling point of water enough that it actually boils in the skin and vaporizes, allowing it to be removed easily. In practice fiberglass doesn't hold a vaccume very well, and the core won't at all. Which means you have to pull a vaccume over the entire inside of the hull. And it has to be a very strong vaccume. Figure 29" or so to get the boiling point of water down to room temprature. This is roughly the same preassure used during vaccume infusion, and requires a very strong pump to hold it. Combined with the fact that every pin hole in the laminate, screw hole, ect can act as a leak, and has to be sealed... It just isn't worth the time.
If the area involved is very small (an inch or two around) you can bore out the core and replace it with thickened epoxy, but over large areas this is poor practice. What you are doing here is replacing the designed in core with an epoxy core. Which will be much stiffer and heavier than balsa/foam. Because of the differences in material properties you will generate major stress risers in the deck. If it has to ever absorb significant blown (like falling off waves) you can actually draw a line on the deck where the epoxy core is, and that is right where the laminate will break.