When I restored a Huntsman l remember that the transom is curved and set at a slight angle. look at pictures of the real boat and I would suggest using two pieces of ply and while gluing together set the curve you require in a vice, with blocks supports.
note the curve needs to be very slightly more than you require as some of the curve will be lost when the vice is released, once the glue has set.

regards Roy 🤔

I have use 3mm ply for my hull

Thanks for that.
The plan seems to indicate that the hull should be planked. If I were to use ply sheets instead what thickness would you suggest??

Hi I enquired what was in a wood kit from Sarik and they said all the parts shown as outlines in the plan. I ordered it and when I opened the package I thought it a good bargain.
Sometimes on a plan the transom if angled is shown as a projection, is it a curved one? Get a piece of ply the same section as the hull sides just put in place when hull is constructed and draw round it for size.
regards
Roy