Vacuum Bagging Question

I've got a question about vacuum bagging very thin foam core laminates.

I did my second foam core hull on the weekend, and it's worked out really well. The only puzzling thing is on the inside surface of the part. It looks as if the foam has been cracked or buckled in two places about waterline height, maybe 12' long.

I'm using a very simple 6mil vapour barrier bag, and what I think has happened is that these lines were formed under longitudinal pleats in the bag - the pleated edge was a bit harder than the rest of the bag surface, and this got forced into the sides of the core.

Has anyone else seen this happen? It should be relatively easy to fix, either by using a different bag or a bit more padding.For an idea about what I'm doing with these hulls, go to :

http://www.turnershells.com/construc3.htm

This part is under construction, but should make it easier to visualize. The finished weight of the hulls is about 8.5lbs, and I'd like to get the interior surface consistent.

Regards,

Matt Turner
Turner Racing Shells Ltd.