I could spend hours on this subject write ten books and still have room to debate the why’s and wherefores for years to come. There are differing views of this phenomena but I will try and summarise some of the information for you.
Osmosis is a chemical reaction that takes place naturally and unfortunately sometimes in GRP hulls. It is not a disease or the Pox as it is sometimes called, neither is it terminal if dealt with appropriately. In some cases the best thing to do is leave it alone. It will not go away but sensible maintenance and some remedial works are often all that is required to continue sailing for years. Only in extreme cases does it become a problem. While moisture is required for this process to take place, it does not follow that moist hulls are Osmotic.
The best people to ask about any specific hulls are Yacht Surveyors. We have no vested interest in declaring the boat a wreck requiring work that will cost thousands. We have no axes to grind and can give you sound advise. To generalise here could prove counter productive so I have resisted the temptation of writing yet another piece on the subject.
I will be happy to answer any questions you may have just drop me a line or Email.