A couple of questions on osmosis and buying a boat

[pillars]

How worried should one be about osmosis/boat pox on a 12 year old catamaran?
Let's say that you are looking at a 12 year old boat that's sitting on the hard for months. Everything checks out. You put her in the water an go for a test sail and everything is good. Do you then haul her back out to check for osmosis - would it even show up having been in the water for a day or two?

[Suijin]

No they would not.

No boat ever sank from blisters. Don’t worry about it on that boat if the bottom looks good when hauled.

[Bean Counter]

Your surveyor should be able to identify any serious osmosis related issues like delamination.

[44'cruisingcat]

Buy a boat built of epoxy.

[Segelschulzi]

There are some models, which are prone to heavy osmosis. You will find them very quickly with google. I would check that before buying.

[sailcrazy]

Also know that the gelcoat does ..."wear out", and at some point in the boat's life the bottom will need to be stripped, refeathered, and re-sealed(based on advice from a F/G professional). Our boat was built in 1989, we had numerous small, shallow blisters every time we hauled. We took the pro's advice, had the bottom stripped and resealed, and have not had a blister issue since-now going on 10 years.

[NevisDog]

I'm no expert but I do know osmosis will not show up after days in the water if it wasn't visible before launch. A good surveyor will check the hull (and the deck - even more prone to water intrusion into the core and just as costly to repair) with a moisture meter and tell you if the readings are even or localised; he'll know roughly what the readings should be on a hull depending on the time it's been out of the water. Just remember - not all surveyors are so knowledgable or reliable, so find a good one.

[YachtBroker]

Some Cats are cored hulls. So hull below waterline could be cored as well. Blisters on cored hull can be worse than a non cored hull because the laminates are so thin. A non cored hull is a lot thicker.

No boat ever sank from blisters but any boat that is cored below the waterline, like J/boats for example, have to really be checked for delamination and any water instrusion.

[Cadence]

If they were not there previously, after 12 yrs., a couple of days in the water isn't going to cause them.

[rabbi]

Originally Posted by pillars

How worried should one be about osmosis/boat pox on a 12 year old catamaran?
Let's say that you are looking at a 12 year old boat that's sitting on the hard for months. Everything checks out. You put her in the water an go for a test sail and everything is good. Do you then haul her back out to check for osmosis - would it even show up having been in the water for a day or two?

A 12 year old boat either has osmosis or not. 2 days in the water don't change anything.

What catamaran are we talking about?
The ones one can read about are Foutaine Pajots of certain model years. For example we had a late 2006 Mahe, which had been treated in 2009 IIRC and she was doing well when we sold her. I never really figured out if/when FP finally found a solution for the problem (other than fixing under warranty).

For Lagoon, Leopard, Privilege I never heard of particular problems with osmosis.

[Rumlater]

Originally Posted by YachtBroker

Some Cats are cored hulls. So hull below waterline could be cored as well. Blisters on cored hull can be worse than a non cored hull because the laminates are so thin. A non cored hull is a lot thicker.

No boat ever sank from blisters but any boat that is cored below the waterline, like J/boats for example, have to really be checked for delamination and any water instrusion.

I have never witnessed enough water asbsorbtion from blisters to soak a cored Jboat that caused delamination of coring and skin, but I have repaired some core in the hull under the floor that was from screwing things into the hull and not sealing them with anything, and badly sealed through hulls. Blisters are a gel coat problem that needs to be looked after, usually sooner than later but as they said they never sank a boat just a boat sale.

[Bean Counter]

What brand model and year cat are you looking at?

[Cheechako]

If it had blisters they would either be evident sitting in the yard, or may have been filled and painted over so you wont know.
I always assume when someone advertises "new bottom and barrier coat" that it's a blister boat until proven otherwise. Or even if it just happens to have new bottom paint, you need to delve into it.

[gdecon]

Originally Posted by Rumlater

I have never witnessed enough water asbsorbtion from blisters to soak a cored Jboat that caused delamination of coring and skin, but I have repaired some core in the hull under the floor that was from screwing things into the hull and not sealing them with anything, and badly sealed through hulls. Blisters are a gel coat problem that needs to be looked after, usually sooner than later but as they said they never sank a boat just a boat sale.

What the core material is can matter. All the southern cross boats are cored, but it is with a closed cell material, so water intrusion at one point will not spread( at least not through the coring)

[boatpoker]

Originally Posted by Rumlater

I have never witnessed enough water asbsorbtion from blisters to soak a cored Jboat that caused delamination of coring and skin,

in 4,586 surveys I've seen dozens of them.