RE: Martin PBM Mariner
The Charlesriver r/c link is a good source, also search the web under hot wire foam cutter for others. A simple hand held bow, strung with .020-.030 stainless steel wire (i've even used multi-strand from Ace hardware) and a 10 amp auto battery charger (you don't need variable current control) will do the job easily. The easiest to construct bows use a 4 " long wood 3 x 2 with 18'' or so of stout threaded rod angled outward to provide the wire tension when strung. Quick and easy. I made mine with a 50" length of 3/4' alum square stock, 3/4 square oak sreaders that pivot on the ends and a spring for tensioning the spreaders, but that much effort is not neccesary. Put your effort nto making good root and tip templates.
Regards,
SC