What does Osmosis look like?

[m1taylor]

I am scraping off thick brittle layers of old anti-foul and think I see nothing sinister on the gel coat underneath - nothing that I, as an amateur would recognise as "blisters". I just wondered whether anyone has a photo or a web site link with pictures that would show me what to look for.

Thanks

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[Shakey]

Have you tried Googling it under the images search? You might need an advanced search otherwise you'll probably end up with lots of biology diagrams.

<hr width=100% size=1>It could have been worse - it could have been me.

 

[PaulS]

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[Birdseye]

Real blisters like the photo are later stage. It could be no more than a crescent moon shading where an otherwise invisible blister has lifted the blade of your scraper off the surrounding gelcoat and left a thou or two of antifoul behind.

I had it just like that, and found it difficult to spot at first even after my surveyor had pointed it out.

The blisters are the cosmetic outcome, just like the spots show measles but arent the disease. So you need to check the moisture content of the laminate, and whether it dries out over a period. If you have a moist laminate that doesnt dry out, you potentially have the disease even if you cant see the symptoms. Because the disease is the strong solution of acids and other chemicals that can eventually turn you laminate to mush. This solution wont dry out naturally any more than a bowl of wet salt will dry out in the open, and the blisters come about because you have a weak solution on the outside and a strong solution on the inside of a semi permiable membrane. So water enters the microscopic holes of the gelcoat to dilute the strong solution inside, and the extra volume of fluid in the small interlaminate holes breaks the gelcoat / laminate bond and forms blister.

Apologies if this is "granny and eggs".

<hr width=100% size=1>this post is a personal opinion, and you should not base your actions on it.

 

[Stemar]

Lots about blisters on <A target="_blank" HREF=http://www.yachtsurvey.com/blisters.htm>http://www.yachtsurvey.com/blisters.htm</A>. The bottom line is that a few small blisters on the bum od your boat wouldn't be anything to worry about. It's almost never of major structural significance unless you've got big blisters in the layup.

IMHO, A significant factor in all the hoohah about it is the ability of companies to charge a fortune to treat it and buyers to gouge a price reduction.

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[m1taylor]

Thanks - that's an excellent web site, presenting a very balanced view of the subject.

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[oldharry]

I could not agree more. There's a whole bunch of boatyards fattening their pension funds at the expense of boat owners panicked by the first sign of blistering into spending a fortune for inappropriate treatments.

Its been asked on these pages before: does anyone know of a boat that has actually been lost due to blistering?

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[m1taylor]

The yacht survey web site says:

"In 30 years of surveying and examining around 4000 hulls, I have seen less than 10 cases where blisters have resulted in serious structural degradation of a hull where it was weakened to a point where some type of failure was immanent"

That seems pretty comforting.

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[Birdseye]

Never heard of one sinking myself, but I did once open up a blister in the hull of a Sadler belonging to a friend, and the crater of mush underneath was of the order of 3 to 4 mm deep. Presumably the process would slowly continue until penetration occurredif nothing were done.

If I remember correctly, Tony Staton Bevans' book on Osmosis shows an example of a boat where the prob had been ignored and it was easy to put a screwdriver through the hull. I might remember wrongly (in which case apologies to the author whos name was taken in vain) but I dont think so.

And in any case, you will have to pay up if its found on survey when you sell the boat so why not do the job now and have the peace of mind. Might not be worth it on a cheap and old boat I suppose.

<hr width=100% size=1>this post is a personal opinion, and you should not base your actions on it.

 

[PaulS]

From the web site of a manufacturer of polyester, vynlester and epoxy resins.

"If the upside is cheap pricing, the down side includes poor adhesions, high water absorption, high shrinkage, and high VOC's. Polyester resins are only compatible with fiberglass fibers. Polyester is best suited for applications insensitive to weight and do not require high adhesion or fracture toughness..... If shape accuracy is not critical, resistance to water is of no concern, and ventilation of the workspace is excellent, then polyester's a great candidate."

Makes one wonder why boat manufacturers continue to use polyester, doesn't it?

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[oldsaltoz]

<< Makes one wonder why boat manufacturers continue to use polyester, doesn't it? >>

G'day Paul,

"Most" boat builders are now using Vynalester, however there are the still a few of the back yard boys using the old stuff.

The better builders even add an epoxy coating over the vynalester below the waterline.

Items like tenders and some internal fixtures/mouldings are still made using standard resins.

Vynalesters are very easy to work with to.

Avagoodweekend.

<hr width=100% size=1> Old Salt Oz /forums/images/icons/cool.gif Growing old is unavoidable. However, growing up is still optional.

 

[PaulS]

I stand corrected then.

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[scuby]

Gell coat blisters can be very difficult to see, especially in good quality hulls, their abscence doesnt mean nothing nasty is happening deeper in the hull. Take a look at http://www.osmosisinfo.com and then assess your hull.

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[oldharry]

The Surveyors dodge for spotting potential blistering is to get down near the keel and look up towards the light. Any blistering is much more visible that way.

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