"As resin infusion continues to infiltrate composites, fabricators across the market spectrum drive materials and process developments in pursuit of process control." (from article by G. Gardiner))
A Technical Paper by ResinNavigator: Blistering of gel coated surfaces below the water line is a major problem in the watercraft and swimming pool industries. The manufacturing technique is sometimes the culprit, however changing the type of raw materials, such as the resins used in constructing the composite, can reduce or eliminate the problem. (from the site)