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post #1 of 7 Old 05-24-2018 Thread Starter
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Osmosis Impossible?

I came across this statement in a Yachtworld desription:

"The ships hull is constructed in a sandwich method: built on a core, a layer of foam and then finished by hand using a layering method with polyester and fiberglass material and afterwards the vessel has been evened out. This ensures a maintenance-free ship without risk of osmosis."

I understand cored hulls and cored decks, usually with foam or wood.

Is there a special method that this boat has used to avoid the possibility of osmosis? How?

Is there a construction (GRP) that can avoid it?

Here is the listing to reference:

1983 Van De Stadt one-off Sail Boat For Sale - www.yachtworld.com

Many thanks.

Martin
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post #2 of 7 Old 05-24-2018
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Re: Osmosis Impossible?

Osmosis is the disease of polyester. Whatever method is used there is always a risk of water passing to the grp. There will be voids and chermicals which will cause hydrolysis. The manufacture date is when more osmotic polyser resin has started being used for boat production.

If there is a constuction method to avoid osmosis why some other producers do not use it.
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Re: Osmosis Impossible?

written by a yacht salesmen what do you expect? there are many ways to protect the polyester. not all polyester resin will get osmosis and the boat can be over coated or built with with vinyl ester or epoxy resin

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post #4 of 7 Old 05-24-2018
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Re: Osmosis Impossible?

Quote:
Originally Posted by celenoglu View Post
Osmosis is the disease of polyester. Whatever method is used there is always a risk of water passing to the grp. There will be voids and chermicals which will cause hydrolysis. The manufacture date is when more osmotic polyser resin has started being used for boat production.

If there is a constuction method to avoid osmosis why some other producers do not use it.
This is not even close to correct. What is correct is that there were almost no FRP materials and methods during that era that would "ensure a maintenance-free ship without risk of osmosis."

But today and shortly after this boat was built, there are resins and laminating techniques that can eliminate the possibility of osmosis. In the production boat world, the use of vinylester resin coupled with careful resin ratio control will pretty much eliminate the possibility of osmosis since the perm rate for vinylester is extremely low, and vinylester is more ductile than other polyester types. Vinylester is more expensive than conventional polyesters and so production builders often only used vinylester on the outer layups. Only adding an exterior barrier greatly reduces risk, but it does not eliminate it entirely.

Epoxy resins also cannot have osmotic blistering. Epoxy resins are much more expensive than either vinylester or polyester and so are typically only used on custom boats or on cold molded wooden boats.

It is very difficult to achieve a blister resistant laminate with conventional polyester resins or with a hand lay-up. That said, properly applied epoxy barrier coats reduce the possibility of osmotic blistering.

Jeff


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post #5 of 7 Old 05-24-2018
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Re: Osmosis Impossible?

Quote:
Originally Posted by Freemotion View Post
"The ships hull is constructed in a sandwich method: built on a core, a layer of foam and then finished by hand using a layering method with polyester and fiberglass material and afterwards the vessel has been evened out. This ensures a maintenance-free ship without risk of osmosis."
"Until it is put in the water."

That part got accidentally left out.

Mark

Manta 40 Catamaran "Reach"

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Re: Osmosis Impossible?

It is practically impossible to completely eliminate any possibility of osmosis. There are a lot of things that can be done to dramatically reduce the probability of osmosis. So, "without risk of osmosis" is salesman-speak. At best, what it really means is "with very little risk of osmosis." Though to assess just how much they have reduced the risk, you need more details about exactly what they did, and precisely what materials they used.
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post #7 of 7 Old 05-25-2018 Thread Starter
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Re: Osmosis Impossible?

Lesson to be taken with a grain of salt: A salesman has to say what a salesman has to say.

I've heard of over epoxying that can create a higher chance of osmosis too, is this correct?

So, while it is not "impossible", it seems that one can vastly reduce the chance of osmosis through using new resin and epoxy products that hadn't yet been introduced.

Of course, salesperson mentions poly which is the weakest of all resins, compared to vinyl/epoxy.

Maybe he's trying to make a regular process seem better than it is.
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