durable bottom coat for surf dory

i am ready to repair the bottom of our harvey dory. It has a few quarter size holes wore in streeks back towards the stern...the boat is fiberglass and i have built many surfboards but no boats,,,the boat is 30 years old and would like to do a good job.... do i have to flip the boat to do gel coats whats a good coating that will be real durable for beach sliding? the gel coats on there seem pretty strong...what would you use to fill a good size gash in the chine?polyester and glass clippings with wax paper...will gel coat seal and hold "IN" patches or do i run 6oz glass over the patch 1" over the edges of the hole? this may be a confusing question but i dont know where to start.....

 

You may work alternatively from two sides. When it concerns the bottom, start first to bring the boat on the dry; then let it dry out for some time - depending on weatherconditions, till the hull has thoroughly dried out.
Fiberglass sucks up water by way of the hollow fibers and the whole area around the gash is fully wetted out.

Take a small size grinder and grind the area around the gash till you have sufficient "bite" for the over lap. Seal the outside of the hull clamping a non-adhesive plastic covered board or plank on the gash ans start afterwards to build up layers of glass/epoxy or glass/resin on the grinded area of the hull.

Since you indicate it is the bottom that is wholed, forget about the gelcoat.
There is no reason why you should apply gelcoat on the bttom of the boat.

It is a little job but needs to be done good.

If your repair has been dried and gassed out, sand the sharp edges oof and apply some layers of top-coat.

The repair should be ready then.

 

it looks to me that the spots where the gell coat are missing the fiberglass is wearing quickly...like the gel coat is a better protector than just fiberglass? getting a good bite requires you to sand with no less than what 60 grit? actone wash after grind? how to you get the best mechanical bond? is there any way to get a chemical bond? what would you use to fill many holes from excessive mounting/drilling/rivots..etc...micro ballons? q cell? cabosil? last repair poped after 1 year even though i sanded it real good with heavy paper