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Recommendations for avoiding hull blisters

Jan 1, 2003

Tom Zydler's recent informative article on blisters ("Battling blisters," Issue No. 95, Jan./Feb. 1999) prompts me to suggest some comments based on my 30 years of yacht surveying experience. Hands down the most effective way to avoid blisters is to haul the boat in the winter, coupled with an epoxy barrier coat at time of manufacture.

I'd recommend that all owners of used fiberglass boats purchase a professional moisture meter and carefully examine their entire hull surfaces at periodic intervals. (Sovereign and Tramex meters, costing about $400, are sold by J.R. Overseas Co. of Kent, Conn.; phone is 860-927-3808.) Also, I'd recommend avoiding the use of epoxy-based bottom paints since I believe they trap moisture already in the hulls at haul-out time. In contrast, the newer ablative bottom paints allow some moisture to evaporate.

Our experience has been that a full six months is required for moisture to evaporate fully after the gel coat is ground away. The best time to do a bottom job is in the summer. For indoor heated storage, three months is best. Again, a moisture meter is essential.

In our experience, most boats, no matter the manufacturer, will eventually experience osmosis problems in tropical waters. However, it is very unusual to find a hull laid up with epoxy resins incurring problems. The best way to learn about osmosis is to walk around the boatyard each winter with a moisture meter. It is not unusual to find a boat with a fancy, flag-blue awlgrip paint job that has a really wet bottom.

Finally, it's worth noting that the really interesting osmosis repairs involve cored hulls. Which is why Lloyd's had traditionally specified solid hulls below the waterline, as do most warm-water charter fleets.