New (to me) 5 hp 80 gallon compressor to aid me in my endeavour. Just need to install breaker install switch and run conductor.

Going to cut the last 10" of the stringers out to replace the transom. Has anyone done this if so where should I make my cuts as I don't want to cut into the hull.

My suggestion would be to cut the top of the stringer back from transom 8 - 10" (parallel with the transom). Then cut both sides of the stringer towards the transom along the top. Remove that glass, then remove the foam. Now you can see where stringer and hull meet. Angle grinder with a cut off wheel is your new BFF. This assumes you have the large box stringers.

I used an angle grinder with a cutoff wheel to cut it about 1/2" from the hull because I was also worried about slipping and cutting into the hull. Then I used a multitool like this to cut it almost flush to the hull so I could finish smooth it with a 80 grit flapdisc on the angle grinder.

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The multitool blades that come with it (shown in pic) get destroyed by fiberglass; I ended up getting the the abrasive bit for tile and that worked much better.