Drying your bottom

A week or so ago I posted a question on drying the bottom fiberglass laminate on a Hatteras, buried in a long, old, thread. Having not received any response, I decided to make it a new thread to see if that made it more likely to fetch comments/advice. The former post read:

I have a question on the subject of blisters in GRP Hatteras hulls. I have a 1976 48 LRC that had blisters to a moderate degree. The boat stays in the water year round, except for a bottom paint job every two years. In the Spring of 2007 I hauled the boat for new bottom paint and one thing lead to another and I did a total bottom job. Sanded the bottom down to the gel coat and fixed probably 200 blisters, all between the mat layer and the structural glass. Some as small as a half dollar, a few as large as 3 inches across. Used a hose to wet the hull and sight down it for a reflection. Anything that did not pass the absolutely fair test got opened up, including a few non blisters. All openings were cleared back to good glass, cleaned several time, and dried for several weeks (a drought in the south-east was great at least for this). The cavities were then filled with West epoxy and biaxial glass. The bottom was faired to new boat condition. Next came seven coats of Sea Hawk Tuff Stuff, a thicker barrier coat product. My estimate is a final film coat of around 75 mils. Pettit Ultima was hot coated onto the final Tuff Stuff coat. Boat was back in the water about 10 days later. Last winter I ran two dehumidifiers constantly, and held the humidity level below 50%. At the same time a blower ran to force air to circulate against the hull with a few cabinet doors and drawers opened to provide a complete path. The bilges of the boat are always absolutely dry. Again this summer I run the same dehumidifiers and blower when ever the boat is not being used. When I check the hull skin on the interior with a moisture meter it indicates no moisture. My hope is that the low air humidity circulation, coupled with the barrier coat will over time dry the bottom laminate. So finally my question, am I actually drying the bottom laminate, or just making myself feel better while wasting electricity? BTW, the boat will be coming out in the next month or two for a paint job, so I will get to see what it looks like for the first time since the bottom job. Thanks

Pete

Since the bottom fiberglass is waterproof and very thick, I don't think you can affect the last layer outside next to the water by drying the inside, which is probably also painted with waterproof paint. Just my $.02 Before I got GFO packing, my shaft area bilges were permanently wet with an inch of water, and I never had bottom blisters in that area outside.

Doug

How do you clean your AC stainer without getting water in the boat? Sometimes I have to pull the hose off and run a coat hanger down the seacock. That always lets in a few quarts or gallons.... I have never in six years seen my bilge completly dry....

Captned

Captned, I am an avid user of wet/dry vacs. I have a 5 gallon size in the engine room that gets used for cleaning all strainers. The procedure is to turn off the sea cocks, start the vac, hold it next to the top plate on the lowest point of the diameter, slowly loosen the wing nut, gently pry the bottom loose with the wing nut controlling the maximum gap, suck up the water as it starts to flow from under the top plate, continue until you can remove the top plate without loss of water, then run the wet vac down over the center stud and suck out all of the remaining water and most of the junk in the canister, then hold a small one gallon paint bucket under the opening and remove the canister. Clean the canister on shore, and reinstall. Immediately vacuum up any accidental splashes. Took me longer to type this than to do a strainer in this manner. I also made some top plate gaskets out of sheet nitrile so things come apart and reseal with ease.

BTW, I also use GFO shaft log packing and it works great. I keep a folded paper shop towel under each so I can both see any seepage and to absorb it should any happen.

Pete