I am sure your will get many similar thoughts but I have stripped bottom paint on my M-23 and done gelcoat repair on large section of my M-17 and under the water line you want to use barrier coat.   Either Interlux or Petit would be fine but there is no reason to go to all the effort of gel coat if you are going to paint over it, as you will below the water line.All the best! Robbin -----Original Message----- From: Gerry Lempicki via montgomery_boats <montgomery_boats@mailman.xmission.com> To: For and About Montgomery Sailboats <montgomery_boats@mailman.xmission.com> Sent: Thu, Apr 25, 2019 9:12 am Subject: M_Boats: looking for input on gelcoat application on M-17 To add gelcoat or not?  Here's the deal; we stripped all the paint below the water line since we didn't know what it was, and it needed refreshing.  I also removed a through hull, and redid a couple old through hull patches I found because I didn't like the looks of them.  As we removed paint we found many areas (particularly under the lapstrake edges) where the gelcoat had been previously been sanded through.  And of course I have the new repairs I did.  Should all this have gelcoat reapplied over the fiberglass?  I will be using Interlux 2000e primer, and maybe Bottomkote NT over it (not sure on that yet).  The boat will be moored in fresh water for 5-6 months.  Any thoughts on what should be done for proper protection/longevity of hull?