I think it is also important to consider the damage that may be imparted to the stringers after all those hits. Remember that the wood is flexed everytime the boat hits a wave and even plywood could develop small cracks throughout the structure. Once the rigidity of the structural members is compromised the glass begins to overflex and that would compound the problem. Eventually you are going to reach a point of too much flex and the entire assembly will give up. Unfortunately this would be impossible to see prior to failure so there could be no preventative maintenance.