When they lay their eggs
Your talking about gel coat cracks right? It is pretty much cosmetic. The gel coat serves a role in sealing but isn't really a structural element. We've done some experimenting with no gel coat hulls to save weight. Biggest disadvantage of no gel coat hulls is that they do not slide over rocks worth a darn.
If you had extensive spider cracking on the deck gel coat (ie. pretty much every New Wave boat older than 10 years) you can expect that perhaps some water might be wicking into the laminate anywhere the fibers are stressed underneath but not really in a consequential way. With a hull- gel coat that has been chipped away (like on a chine) can lead to some water getting through but that also has something to do with the fibers being stressed at that point.
Another way to think of it is that water sits inside your boat all the time and it isn't a concern for de-laminating it or causing damage.
Did that answer what you were asking?
