Osmosis Treatment

[Willallison]

My brother-in-law is considering purchasing a 40ft yacht that was US-built in the 80's.
Like many of those built by the same yard, it reportedly suffered from osmosis and was repaired (in NZ) with epoxy some years ago. The broker has sent the attached pics along with a certificate of repair.
I have suggested that he ask for a copy of the full report, but any comments based on the attached pics?

[Landlubber]

Wil, there are thousands of boats repaired just like that one, as long as the price is OK, then the laminate is most likely reset in the epoxy as the Kiwis are generally pretty good at what they do. I personally reckon they are better than us, they have a lot of experience and it is only 50 miles from anywhere in NZ to the water, so lots of them have played boats for a long time. I have done dozens of repairs the same, and not had any come backs in over 30 years of doing them now.

[Willallison]

Yes - it's difficult to tell from the pics, but the damage looks to be fairly extensive. In the cases I've been involved in, the damage was only in the outer two laminates ( a result of them being laid up in the mold some time prior to the remaining laminates, so they didn't have to re-surface the mold). Once these were peeled off, the inner laminates were in very good condition.
No question, if it's done properly, the repair will be fine.... was just wondering if the damage looked more extensive than normal...?

[Landlubber]

...well, from the pics, certainly not, that is quite "normal"....

[Willallison]

Ok - thanks....

[michael pierzga]

Locally they sandblast the hull .The picture looks like that hull was blasted. After the blasting they wash the bottom with fresh water, let the hull dry out for a long period of time...weeks....then apply an epoxy based paint schedule. This seeems to be the prefered way to deal with the problem.

[CDK]

One quick way to assess the damage is measuring the hull thickness and integrity using ultrasound.
The appearance itself is a bit weird but says little about the quality underneath. On an alligator nobody would expect the animal to be seriously ill.

[gonzo]

If the hull is sandblasted for repair, then you need to have it checked for delamination. If that happened from osmosis, that is the worse I've ever seen. Osmosis, is caused by many things. It is not always capillary action, but trapped solvents and catalyser will absorb water and blister the laminate. If the hull has been sandblasted, do you have photos of before?

[mastcolin]

I know from having worked with International Paint (depending when job was done in NZ, International Paints were called Epiglass) that yards were allowed to give a repair certificate on osmosis repair if they followed spec. This included drying of hull to appropriate level.

West Systems and Hempels operated similar systems. In distant past the work was also insured via independent insurer.

The fotos are from the blasted hull. It appears to me to be the matt exposed under the removed gelcoat, where the osmotic blister normally are/were. (I am pretty sure but not that easy to see). So long as the hull is dried after blasting there are few problems. The spec was normally 500micron epoxy, some yards used a layer of cloth as well depending on owner's wishes which meant more epoxy. Then filled and primed and antifouled. You end up with better hull than the original. (stiffer, tougher, more water resistant)