osmosis advice

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Alrob

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looking at a trawler yacht just now and have been told by a friend of a friend who knows the boat that it has very mild osmosis although he says nothing tom worry about but the word osmosis frightens me
the chap that told me is a professional skipper

what advice can anyone give me as to what to look out for

can maybe get some photos (boat is out of water) if I know what to look for (I have not seen any blisters of such)


cheers
 
osmosis

‘Osmosis’.
Osmosis is one of the processes by which water is absorbed into the laminate and it can be and is reversed when the vessel is left to dry out on the hard. The word is, however, among the boating fraternity, aided and abetted by the popular yachting press, usually and totally incorrectly used to describe gel coat blistering formed as a result of the chemical and structural break down of the resin matrix as a consequence of water absorption whether this is by true osmosis or not.

The first of these main defects is fairly obvious and is usually found by simple observation of the hull and any voids in the lay up can be found by the familiar technique of the hammer test and a well tuned ear. The second defect is also found by simple observation and experience soon shows the Surveyor where to look.

By far the most important defect in plastic hulls, however, is gel coat blistering, popularly but incorrectly called osmosis, or, more vulgarly, the boat pox!

Gel coat blistering can be found by simple observation if it is a fairly advanced stage but the early stages are often difficult to locate and, if not noticed, can develop with remarkable rapidity later leaving a very unsatisfied client and a possible law suit on the Surveyor’s hands.

If the boat is located inside a shed or the side of the hull is dark, a bright torch shone along the hull will often show up the blisters by means of the shadows cast. It is also useful to carry a hand mirror so that the sun’s rays can be deflected along the hull to highlight blisters.

Finally it should be noted that all plastics suffer from ultraviolet light deterioration and boats left lying in the sun soon loose their pristine shine on the side or end lying toward the south.

this is what some expert reckons, as for myself I have never heard of a boat sinking because of osmosis.
 
Wow! Thats an oversimplification.

Suggest the OP reads up on the subject, for example PBO ran a series a couple of years ago.

If interested in buying the boat, discuss it with a qualified surveyor who can advise on the various defects in GRP which go under the general heading of osmosis.
 
there is about 8 in total
I am led to believe that the hull was epoxy treated in 1996

also current owner tells me that it has not got any worse in the 3 years he has had it (he is a very honourable person)
 
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look carefully at the waterline, & waterline of similar boats, find out their age & if possible their speed, a heavier boat as you know will perform, & sit differently
 
alanrob said:
there is about 8 in total
I am led to believe that the hull was epoxy treated in 1996

also current owner tells me that it has not got any worse in the 3 years he has had it (he is a very honourable person)
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then scrape the blisters off, sand the area, and re do with gel shield, prime and antifoul, like I said earlier they will not sink you.
A surveyor would probably advise the whole boat be done with some fancy concoction to remedy it, but he is covering himself re any claims
 
how old is the boat?
how long has she been on the dry?
before gelshielding epoxying the boat I would be careful to be sure to dry the laminate 100%
if you gelshield the bottom and the Resin is not fully dryed out you can find out yourself in twice more problems in a few years time
if you have only 8 blisters, I would dry them out, epoxy them and see what happens in a season or 2, always if the remaining of the laminate looks dry
 
Hi boat is 20 years old and has been on hard for at least 3 months

I am happy to treat the blisters but what worries me is trying to sell the boat on in a few years also how much should I be getting off the price
 
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alanrob said:
Hi boat is 20 years old and has been on hard for at least 3 months

I am happy treat the blisters but what worries me is trying to sell the boat on in a few years also how much should I be getting off the price
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You only need to grind and epoxy a few small dimples, just ensure the area is dry, grind out all sign of stains or white areas and re glass using epoxy, after curing just sand them and apply 4 to 5 coats of epoxy wet on tacky to avoid more sanding; allow to cure and apply a coat or two of high build epoxy primer the antifoul.

Do this whenever the boat is lifted out, small blisters are a fact of life on 20 year old glass boats, think on it as a fraction of the work required with a steel hull. Keep up with it and it should not be a problem, ask anyone with a cast iron keel how much work is needed if tended each time it's lifted out.

The cost of a full Osmosis treatment would be a good percentage of the total value and probably make any resale a heavy loss.

Avagoodweekend......
 
alanrob said:
Hi boat is 20 years old and has been on hard for at least 3 months

I am happy to treat the blisters but what worries me is trying to sell the boat on in a few years also how much should I be getting off the price
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They do not look a big problem. However, if you are buying the boat - this is where your surveyor earns his keep. Get a proper report and recommendations for action. If the cost is significant and the defect was not declared then it is grounds for negotiations on price.

As others have indicated if it is only a few local blisters and moisture readings come out OK then it is not a deal breaker. I would not worry about future resale - if the boat is a good deal and you follow the professional advice on making good - what have you got to lose? buy it and enjoy!
 
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