Hello, I have been looking through your web sight vary informative. I
have a 1989 52’ Jefferson Marquessa that has will over a thousand little
gel coat blisters on the bottom. The marina sand blasted the bottom and
now is suggesting I have them gel coat strip the bottom. They then want
to put five coats of a barrier coat on the bottom, then the primer and
then finish. My question is should I have them fill the blisters or
strip the gel coat. If we take the gel coat off will this hurt the boat?
Thank for your time, J

First, let me state that surveyors should not dictate how repairs are made.  In addition to the
obvious blisters, has the wetted surface been checked by a surveyor for moisture incursion
and/or delamination?  
I can tell you that in the case of severe blistering, (boat pox- see photo below), which you
appear to have, that the common approach is to strip the gelcoat back to healthy laminate,
routinely wash with soap and water to remove the glycol (chemically produced when water and
resin mix) while the laminate is drying over a period of several months, then fair the surface
and use a barrier coat such as
Interlux Interprotect 2000.  Finish with your favorite anti-fouling
paint.  This unfortunately can be a long and expensive job, but your motor yacht is well worth
the job.  Note; the drying process can be accelerated by a mild, dry climate or inside storage
with heat lamps, etc.  
Marine surveyors commonly supervise the drying process by routinely testing the laminate as
it's drying for moisture content.  It will be a waste of money if the laminate is not dried properly
before restoring the surface.
Thanks for the question and good luck,
Peter Spang, AMS

Photo of "boat pox"