leaky fibreglass?

[BogMonster]

Further to my other thread on my potential purchase of either a RIB or a speedboat, I have heard when discussing it with people, that older fibreglass hulls can suffer horrible diseases and doing a bit of a search on here on "osmosis" brings up a few relevant threads which suggests it is something I should be wary of.... and certainly something that is way outside my level of ability to deal with.

How do you spot it? The boat I am looking at has been stored out of the water most of the time for a number of years that I know of, so would it develop osmosis under those conditions or does it only develop when boats are stored in the water? Whatever I get, I plan to store mine in the water for at least a few months of the year so it seems like something I should worry about.

From what I have read it appears that the hull would look "blistered" which I don't think it does (though I will go back for another closer look) so assuming it is OK, if it is painted or covered in epoxy or whatever the recommended prevention method is, will that then guarantee it will be OK?

What about areas of damage to the fibreglass - can these be "hot spots" where osmosis can develop? there are a couple of small places on the keel where it has been scraped, these need repairing, but the damage didn't look to be serious and appeared confined to the area that had talked to the rock.

What is the worst case with this disease - threads I read suggested that some sort of acid develops from uncured resin when the water gets at it, does this ultimately dissolve the entire hull?! be a bit of a PITA if you jumped in one day and went straight through the bottom.....

From what I have read on here it also appears that GRP quality has improved in the last few years so that might be another plus to buying a 3/4 year old RIB rather than something much older?

Does anybody have a photo of a hull that is seriously suffering from this disease so I know what I should be looking for?

Many thanks (again!)

Stephen

[roycruse]

You need to use a moisture meter to measure the water content of the hull - dont know a huge amount about it myself - but google does.

check here

[Mark Halliday]

Hi StephenThis may help.
http://www.turbolink.co.uk/jlasurveys/osmosis.html

I doubt it will be a problem with a hull that has been dry stored.

[BogMonster]

Thanks - I did a google but there seemed to be conflicting information like

http://hometown.aol.co.uk/__121b_gR7...tenNYfdbyzzP5E

which says it is a serious problem which must be treated immediately while

http://www.insightmarinesurveyors.co.uk/blisters.htm

suggests it is mostly said to be a serious problem by those who are trying to sell you the repair jobs! (like the first link I posted!)

hence just after some independent opinions

[codprawn]

Osmosis in hulls usually only effects boats left on moorings - it takes years to develop and even then it isn't the end of the world.

Blisters develop that smell a bit like vinegar when they burst.

Even if the boat DID have blisters all over it if the boat isn't being kept on a mooring there is nothing to worry about.

[Scary Des]

I have yet to see a boat that has failed because of osmoses and I know of one particular yacht that failed survey 15 years ago because of osmoses and is still no a mooring and still in regular use

With the type of boats you are looking at I don’t think you would have an issue Des

[jwalker]

Originally Posted by BogMonster

...Does anybody have a photo of a hull that is seriously suffering from this disease so I know what I should be looking for?

Stop worrying about it. There may be seepage of moisture at the damaged area and that is best fixed but that's not osmosis. In osmosis, the gelcoat becomes a semi-permeable membrane which the water penetrates.

The quality of the original moulding process will determine how far water is able to penetrate along the glass fibres. It a top quality moulding, resin will surround each fibre filament and water will not be able to wick along the fibres. If there is damage, it is likely that there will be some localised cracking in the resin adjacent to the damage and water may well penetrate this area.

[BogMonster]

Thanks. Since posting the question I have researched it through Google and seen quite a few photos - nothing like that is apparent on the boat I have been to look at and I don't suppose it will be on the RIB I am going to look at tomorrow since that is only about 4 years old I think.

I guess my main concern was that if it was happening the hull would become "rotten", structurally very weak and likely to fail spectacularly, but that seems to be very unlikely in all but extreme cases.

[Searider]

Hi Stephen,

To check if you have blisters take a sharp scraper or 1" chisel and scrape off several 4" square patches of the bottom paint - if there is any. Blister heads should then show quite easily.

If you see blisters we would normally recommend that they are treated when they are bigger than your little fingernail, and Must be treated whn they are as big as your thumb nail. The bigger the diameter of the blister the deeper into the laminate it goes. I have seen blisters 10" in diameter - this means serious delamination within the laminate and a loss of strength - it was on a 1970 river cruiser that has been in freshwater all of its life apart for one week per year though!

No blisters on a boat of the age of the one you are looking at pobably means no problems.
Often a moisture meter will just confuse matters. Some old hulls can be "wet" and never develop actual blistering

Hope all goes well tomorrow.

[BogMonster]

Thanks - I think I'll be shot if I start digging holes in a boat I haven't bought yet but I'll bear it in mind for when I do have one

I am pretty sure there was nothing visible on the speedboat even with the age it is.

Why is fresh water worse than salt water for osmosis?

[Searider]

It's normal practice to scrape off antifouling paint as part of a survey - don't remove any thing else though!

Osmosis is all about difference in contrations of solutions either side of a semi permeable menbrane.
The resin and gelcoat is the membrane.
The liquid in the blister site is the concentrated solution.
The water is the weaker solution.

The blister forms and enlarges because the water will migrate into the concentrated solution until the solutions are equal in concentration. This never happens though.

Fresh water is a "weaker" solution than salt water. Hence a greater difference in pressures driving the blistering process.