you can either goomm a new thruhull in there with 5200 b/c it has good adhesion or,
grind the inside and the outside around the hole, just a little being carefull not to get into the kevlar, just thru the gelcoat layer , (if you go too deep the kevlar will turn to a fuzzy material and really suck to glass over). On a peice of cardboard wet out 1peice of chopped fiberglass let it soak in then apply it to the bottom of the boat working out all air bubbles. when it hardens cut a lot of small circles (probably 1'' thruhull size)out of glass to fill the hole , wet one out ,apply it in the hole work out bubbles , do this untill the hole is filled flush with the insde of the hull , then apply 2 or three more peices of glass to overlap the 1'' hole , probably a 3'' circle let dry . you can then grind the bottom flat and gelcoat. Be careful not to get into the kevlar you will know bc it will start to furr up , use a small sander and 80 grit and take your time
Karl, good input! Do everything that he said to do, except skip the first step of grinding the bottom of the hull.
Instead, take a piece of thin wood, like luan or door skin, and over it in mold release, then screw it to the bottom of the boat so it covers the hole.
Use small screws into pre-drilled holes in the hull so you dont crack the gel coat. This is where the thin wood part comes into play. It seams yo have a bit of a curve where the thru hull is located and the thin wood will bend some to conform to it.
*** NOTE, you can also just hot glue the wood to the bottom of the boat as well, this way there is no holes to fill latter on.****
Once the wood is in place then fill the hole like he said to do.
After the glass cures, pull off the wood on the bottom. Now you are just left with two small screw holes to fill. Or if you used the hot glue, all you have to do is sand that area and then blend in some more gel coat and you are good to go!
This way you dont have to worry about gong to deep into the kevlar, plus there is less work on the bottom side to make it pretty again where you would have ground away all the gel coat.
Remember that it is just something temporary to hold the glass from sagging. I have even seen people use a piece of duct tape just stuck to the hull, then filled the glass form the other side. Let it dry, pull it off and then dremal (sp) where the tape stuck to the new glass they laid. Saves allot of work on the bottom side!
I hope this helps you! Lets see some pics of the progress!!