Blisters on hardtop - Osmosis?

[kennyh]

Hi all

I've a 2008 Jeanneau Prestige 30s with a hardtop and sliding roof.

I've noticed that I've a handful of minor blisters that have appeared on the hardtop frame and wonder if it could be Osmosis or something else?

Any thoughts on cause and cure (should I feel the need to resolve it - although it is only currently noticeable if you look very closely)?

Thanks
Kenny

 

[rafiki_]

While the boat is out of warranty, why not pose the questions to Jeanneau?

 

[petem]

If it's a frame could it be powder coated aluminum?

 

[kennyh]

If it's a frame could it be powder coated aluminum?

Sorry, I should have been more clear; when I refer to the frame I mean the GRP structural frame for the hardtop assembly.

So it's GRP and not aluminium.

 

[omega2]

Have a dig at it, see if it was constructed out of glass matt, or maybe plywood. If it is the latter then I suspect it's rotted.

 

[petem]

Might be worth posting some pics.

 

[P4Paul]

Hi all

I've a 2008 Jeanneau Prestige 30s with a hardtop and sliding roof.

I've noticed that I've a handful of minor blisters that have appeared on the hardtop frame and wonder if it could be Osmosis or something else?

Any thoughts on cause and cure (should I feel the need to resolve it - although it is only currently noticeable if you look very closely)?

Thanks
Kenny

I worked on another Prestige of the same age with similar blisters but in a different place.

In their location it was unlikely for them to have been a result of osmosis so after a quick conversation with the customer I popped one open to find (as suspected) an air void behind the gelcoat. A quick gel repair later and the decision was to leave the rest for now and only address as and when individual blisters caused any concerns.

Personally I would do the same on your boat - pick a blister, open it and then use the resulting knowledge to inform your decision for the rest. I suspect, as you already suggested, you will decide they are not worth worrying about.

Just be mindful about putting an aggressive polishing mop over that area of the frame, if it is an air void behind the blister, it can heat up quicker than the surrounding GRP and run the risk of looking worse or even breaking through.

 

[boatmike]

There is much misunderstanding of the term "osmosis" that by definition is the permeation of a fluid through a membrane. Often this is caused by salt water permeating the gel coat and/or first layers of structural GRP below the water line often caused by voids in the layup beneath. This obviously can't happen above the WL but there can still be voids in the layup and often are where there is a ply, balsa, or foam sandwich construction. These voids can fill with a cocktail of chemicals involving styrene and above the WL, especially on a roof can cause a pressure build up which is exacerbated by the heat from the sun which "cooks" the cocktail and causes pressure. If it's not a structural problem and there is not extensive delamination of the deck above causing weakness or creaking when walked on it's only effect is cosmetic. Often it can be solved by just drilling a small hole in the blister to remove the pressure. A word of warning though. Wear eye protection when drilling the hole as a spurt of styrene under pressure is not friendly to eyes. If you can, inject some resin through the hole, or just fill with gelcoat. More extensive
delamination requires more drastic measures of course but your problem does not sound serious and is frankly not uncommon especially on boats kept in hot climates. Hope this helps!

 

[kennyh]

Thanks all for your comments / advice.

I've had a chat with the local Jeanneau dealer and his view is, as many have said here, just ignore it/leave it.

It certainly is not in any load bearing position and it is (at present) only a cosmetic issue.

So I will leave for now, at worst I'll burst the larger blisters (which are raised probably no more than 1mm), and reseal.

Thanks all.

 

[ari]

There is much misunderstanding of the term "osmosis" that by definition is the permeation of a fluid through a membrane. Often this is caused by salt water permeating the gel coat and/or first layers of structural GRP below the water line often caused by voids in the layup beneath. This obviously can't happen above the WL

I've seen osmosis in the cockpit of an old yacht caused by standing water lying in one area over long periods of time. (Basically it pooled every time it rained and took a long time to evaporate so through the winters there was water stood in the area almost permanently, eventually causing osmosis).

I can't imagine it could happen in an area not subjected to being effectively immersed in water though, so unless the water pools in the area affected, I can't imagine it could be osmosis in the instance described.

 

[A_8]

Its probably just pockets of air in the gelcoat, as have been suggested open them and fill with gelcoat if you want it fixed. I had a few of these on my P34 as well, different place though.