This large blister on a GRP hull has been opened up to reveal the damaged laminate. Note the dry white glass fibers.

This is serious blistering that has caused a localized weak spot in the hull.

This boat also had a balsa core which was in danger of becoming rotten.

The balsa core can be seen in this photo. Darker patches are where water has damaged the core.

The damaged balsa was removed and the hull dried before laminate repairs commenced.

This is a good example of a deep laminate problem on a production yacht.

The photo shows a pen knife blade inserted under a loose laminate.

The ‘90’ is a chalk mark indicating the moisture reading taken. The pinkish roving is actually a layer of Kevlar®.

Count the blisters. These are small blisters that if left should not affect the hull strength in the short term. But devalues the boat.

In this case the owner opted to repair them with a full bottom gel-coat plane and repair with vinyl-ester resin.

Rudders are often prone to blistering and filling with water.

Even late model production yachts have rudders that blister and this may be because cheaper resin is used in the layup.

Water inside a rudder can lead to failure of the webs welds where they join the stock.

Planed hull with deep laminate blister in centre of frame

The dark spot is moisture oozing from the core. Note the dry white glass fibers at the bottom of the photo.

This hull had a poor wet out of the laminate during construction.