you need to cut out the inside of your whole well area of your transoms glass. then cut out just the outter layer of wood same way cut a piece to fill just the center area then cut a piece to fit the whole well area you cut out that goes to the top all the way across. cut the skin off the outside of your transom too but cut it about six inches below the top ot the 20" area. straight across. yours should look like this say the black in cut.
cut out the fiberglass skin and first or outter layer of wood in the red area.
do the same to thearea in here whole back area of glass and the outer layer of wood. this should leave a center area of wood.
now cut a center piece of wood to fit in the center area you want to build up. and glass it in.
Then cut a piece of wood to fill the inside of the transom where you removed the skin. and cut a piece of wood to fit the area you cut out of the backof the boat, no that you have the 2 inner and outter pieces of wood cut to fit and fill the 20to a 25. glass in the new wood. then grind the blue area pictured of the old transom and put your fiberglass you cut out inside and outside back on with resin too.
now clamp it till the wood and old glass dry's then glass the whole area you ground and the center area with long glass. with several layers of glass like 5 or 6 layers inside and out whole area.