I thank you all for the replies, however I have no idea how to make a jig, can you direct me to a source how to plot out the arc, how to make the jig, as a model builder its one thing to use a balsa knife, scroll saw and the like now I'm up with the big boys. Can I impose further the rear cockpit had several variations on Riva boats they could be opened for seats, or as a sun lounge, or as in my case a hatch for the engine access. The hatch has round corners sowith out teaching you to suck eggs you will know the hinges are not regular butt type.They were a curved casting with pin held flanges. I made loads in paper, then ended up with then fashioned from brass and silver soldered. Because this model is scratch built from line drawings no details. Not having during construction made provision for the hinges now I can not figure out how to get the correct arc for the hinges or how to install them, I can not take the deck off for access, pretty stupid of me, any ideas
I have added a picture of my Ariston bow, I have pictures of the hatch and hinges I have made.
Disregard heading of pictures.