This process definitely works, but it isn't fast. At this point in time after 2-1/2 days of pulling vacuum while heating I may have removed about 8 to 10 oz. of water from the area I have been working on. I'm on my 2nd setup for this area and basically the difference was that I enlarged the area I am actively pulling vacuum on. This 2nd setup has struggled to maintain 15 inches of Hg. and is often slightly less than that. What I do know is that the vacuum extends well beyond the immediate area under the plastic. The area that I had cut out the balsa core last fall is about 4' from the vacuum line. I started wondering if that open area was degrading my sealed area, so I battered up some new foam core and started pressing it into place and then started battering the transition edge between the new core and the existing hull. I was prepared to deal with the epoxy wanting to sag out, but instead it kept getting sucked into the cracks. I was finally able to batter over the entire area and I think that did make a difference in the amount of vacuum I was pulling. But this section still only gets to 15 inches of Hg., so there is either some leaking in my lines or more places in the hull that are helping to lose vacuum.
This morning I left the same setup in place and just lit the infra-red burners and turned the pump back on without changing anything. What is interesting is that there are areas above where I am pulling vacuum that have dried to to the desired level, but there are also areas directly under the vacuum that still seem to read high as well as areas that have acceptably dried out. So tomorrow I will pull the plastic and sealing tape off and cut a couple of new kerfs through those stubborn wet areas and then reseal and start again. I would like to stay with parallel kerfs, but I am wondering if a cross pattern might work better in terms of spreading the vacuum out better. I also will try using more breather cloth.
I have used one 7# tank of propane so far and just switched to the next tank. One part of the setup I did change was to add another 25' of coiled airline in front of my T moisture trap trying to condense more moisture out of the line before it hits the trap and that seems to be helping a lot.
So we are on our way to a dry hull, but I do have a lot of work to do before claiming total victory.
For anyone interested in pursuing this same approach here are some of the items and their approximate cost:
New vacuum pump, $350 plus about $100 for pressure switches, reservoirs etc.
Plastic film and Breather cloth, $100+
Two burner infra-rd Mr. Heater, $100
Propane, Estimated at $50
Moisture meter, $350
Infra-red thermometer, $20
Probably some other things I'm not thinking of. In my case the pump has utility well beyond drying the hull and doing glass work, so that was easy to add to the tool collection and I also had the Mr. Heater from other outdoor adventures. All of this is not inexpensive, but if I can restore the dryness of the core to normal levels and then keep it from getting soggy again the life of this hull will be dramatically extended.
Again it is important to know that the balsa in my boat has not decayed significantly, likely due to being in colder and milder climates and cooler water. Drying out molded core would be a waste of time, effort and money.
This process will be going on for some days. I will do another update with images in a few days when there is more to show for the effort.
