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  #1  
Old 08-01-2009
CKH CKH is offline
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Blistering

Blistering seems to be a big issue, and a serious problem, with sailboats.
And because I have no knowledge, training or experience in the subject matter, any explanations, simple or scientific, will be wasted on me.
This brief survey, however, will help me greatly.
Thank you in advance for your help. This could be a teachable moment for me.
Would all boat owners who have had their boat sink due to blistering as the original causal factor simply list here the:

Length - Year Keel Laid - Manufacturer - Date Of Loss
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Old 10-05-2009
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Blistering

The short answer to your question is that it is extremely rare for a boat to sink due to blistering. If you pull and inspect your boat on any reasonable periodic schedule it will be quite plain to the eye if blistering is present. A surveyor can yelp you too if you search out one with a trained eye for that sort of problem. If you are looking at any boat older than 1990 you can almost bet on some blistering. Structural blisters are large and tend to be quite obvious to a trained eye.

Most blistering I have delt with shows as a visible pox of small bumps where the gel coat is popped loose from the underlying matrix. These bumps are typically anywhere from ocasional to very dense and range from BB size to abut tripple that size. West Marine has a West System video that will show you how to handle these. In short, grind them out into a region of good confirmation, dry them extensively, fill with an appropriate epoxy filler and fair flat. The important step will be to remove ALL antifouling paint, dress the surface and apply a sealer such as INTERPROTECT 2000 or other sealer rated against blisters. We were fortunate that the yard where our boat was would permit sand blasting to remove all previous paint. The added effect is that it will expose most surface blisters. You could also get your hands on a device called a peeler if the hull is in bad enough condition to warrent a total replacement of the gel coat.

You must plan in advance what antifouling paint to use since effectiveness of its bond to the sealer may require timing its application to the hardening of the sealer. The Interlux and Pettit gurus turned out to be really helpful on this for us and even consulted one-another to suggest the best choice for us. Go figure!

Some boats may have some really impressive blisters between the laminations of glass. These are not cosmetic and will require some re-building of the damaged area. We found 8 such major delaminations on our bottom job of a 1984 vintage boat that spent 100% of its life in the water in the tropics. (worst case for a boat). These were seperations in a layer about 1/4" to 38" deep and over 6 to 12 inch diameter. Pressure inside was enough to shoot trapped fluid up to 30 feet when lanced with a drill bit. I cut these out with a right angle grinder and faired them out up to 24 inch diameter looking for totally dry matrix and to leave a 15 degree tapered edge. these were then built up using West epoxy and glass. Once faired, treat as above with seal layers.

Really big blisters can be detected with a moisture meter or you can sight the hull in varying light levels and direction every time you are there. If it looks like it's sticking out - it probably is.

One note, the rudder was so bad I have stripped it for a total do-over right down to the stainless skeleton.

If you are dealing with an old boat and you are not confortable with your own abilities to inspect then I strongly suggest a survey. condition will depend greatly on the care the boat had.

OLD: any glass hull made before the causes of blistering were learned and the manufacturers reacted. Better compaction of the matrix, vacuum bagging and better resins imporved the situation. I am not sure of my dates but I think things got better in the late 80's to mid 90's.

The break came when they changed from polyester resin to vinylester resin which is markedly less prone to blistering. Many owners also never sealed the bottom, or maintained the sealer. Sealers have improved too. some manufacturers never got the message and continued to make polyester resin boats.

View my photo log here on the sailnet (Nicholson58) where I have a lot of pictures showing a badly blistered bottom and some of the tools. We scraped off the soft VC tar layer; blasted the underlying friable other paints; ground out all blisters by hand with a carbide grinder, filled using West System; faired the entire hull with a 40-grit flexible wheel, applied 6 coats of Interprotect and finished with 3 coats of VIVID yellow. If I did it again, I would start with a peeler.

http://www.sailnet.com/photogallery/.../ppuser/159746
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Old 10-05-2009
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The original poster, whatever the heck his actual intent is, made it very clear that any explanations would be wasted on him.

CKH, you will find, provided it's not wasted on you, that this is an excellent forum with contributors from all over the world.

Given that one member has already taken time to try to help, do you think you could tell us what your point is?

Obviously, you and I know that the bottom of the sea is not littered with blistered boats, so what's up?

Last edited by Siamese; 10-06-2009 at 10:29 AM.
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Old 10-09-2009
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I'm convinced the multi-million $ blister business was fabricated soley so you would buy expensive products and work your butt off. Back in the early 70's I noticed fabricators spraying on the gelcoat, rolling out the bubbles on the sprayed on matt, laying on the roving, wetting, then rolling out the bubbles. Layer upon layer with a slow cure polyester was used. The heat from the resin caused the tiny rolled around bubbles to expand. Duh! Coming out of the mold the bubbles didn't show, but walla in time there they were. My boat the 23 ton 50' Daedalus (I have no financial interest in this ship I designed and hand built and launched in 1977, except my humble ego.) never had a blister, not one after 32 years of hard sailing and daily groundings, so my charter folks could climb down and swim. I sold my boat in '02 and you can find her on biophilia.net amongs other things about this newbe. I repeat we are not open to the puplic and I have nothing to gain financially. I digress. I painted my homemade mold, rolled on the release agent, layed out 2oz 36"X60" matt, generously wet it then layed a 36x60 roving over that. Wet it and now the secret. I simply squeejeed out every bubble. Lapped 8" and started again. Each piece required a little less than a gallon of resin. Squeejeed all the mess into the bottom of the keel, which was 14'' wide, preparing for 2 blocks of steel 12"x12"x14'+/-, but that's another storey.

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Old 10-09-2009
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CKH I can't think of one boat that went to the bottom due to blisters Maybe an owner opened a valve or two to send his one time pride and joy to the bottom All because he didn't want to deal with the blisters. but can we blame that on the blisters? They can in time and I stress a very long time cause a breakdown in the structural integrity of the hull. I know you don't want the science behind blistering But if you ever find you can't sleep at night MIT has a paper on their study of blistering. It's guaranteed to put you to sleep.
There are plenty of very effective products and methods to deal with blistering. from popping them one by one to bead blasting the hull. then it isa matter of filling and applying a barrier coat before allying bottom paint.
My favorite method was to fill all the blisters with an epoxy fairing compound sanding that down then appling a couple of coats of west system eppxy. Then the expoxy is just a littel tacky to the touch apply your bottom paint.
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Old 10-09-2009
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Blisters may affect purchase and resale values, but generally the dangers of blisters are overblown.
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