[FELLOW-SHIP]

I would do it the right way. Just like all holes to be fill in, the size is not a issue unless it effects the strength of the transom. I would first enlarge the hole on a taper of 30 degrees towards the outside of the boat meaning that your 4” hole will open up to a approx 8” hole on the outside skin of your transom maybe even bigger. Then I would cut a round approx 8” by ¼” thick piece of fiberglass sheeting and epoxy it in the inside of the hole where it still is approx 4” diameter let epoxy get hard then if you have room I would place one or two layers 16”x16” again in the inside over the 8” fiberglass disk for additional strength. Then I would start building the transom back by using ½” thick plywood then two or three layers of glass then another ½” plywood and then more glass cutting the plywood again on a angle to best represent the angle of the bigger part of the hole using filler around the edges of the plywood to help fill in the gap. I would use approx ½ fiberglass and approx ½ plywood for filling in the hole then faring material, sanding, and lots of beer. Then gel coat or paint
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