UV Degradation

Gentlemen,

I recently purchased an unfinished 46’ composite hull. There is no deck on the hull and it has been stored in the open for some time. In a few spots, the interior woven material is showing signs of what I suspect to be UV degradation. The lay-up is 3 layers of 13 oz diagonally applied Kevlar-glass hybrid w/ Derakane vinylester resin on both the inner and outer skins over foam.

I believe the inner layer will need to be sanded down to sound material and new material applied. While I believe only the outermost surface is involved, I would be interested in hearing thoughts on the possible integrity of the inner layers, or the outermost layer where it appears to be ok.

Carrying the thought a bit farther, why don't all GRP boats just disintegrate in the sunlight? Is it only the gel coat which protects the resin and fibers?

All input would be very much appreciated.

Best Regards,

Sea Jay

 

The gel coat also gives only partial protection against UV, after each summer you can wipe off quite a lot of powder. I think the secret is in reflection; the areas without gel coat absorb much more so deteriorate faster.
On small hulls lying here along the coast the fishermen crudely repaired holes with a few layers of glass and some clear resin. After a few years in the sun, their patchwork starts leaking again because the resin disappears, while the gel coat around it - albeit dull - is still there.

 

VE resins are less UV resistant than polyesters, so they'll degrade faster when exposed and unprotected. Gel coats typically use more UV resistant base resins, but they mostly rely on the pigments and fillers to protect them from the sun. UV inhibitors can be added to resin and gel coat, but it's not that common, they do help somewhat in resin, but don't do much in gel coat.

 

Ok, I'm getting the picture on the resins and gel coat, but what about the fabric itself. I just read that kevlar can be damaged by UV, but what about S-Glass?

Sea Jay

 

Glass is less effected than most other things.