Retiredat38

What diameter prop are you looking to use? Make your cage at least 2 inches bigger.

Do not use plastic. The cage is a safety device intended to control a runaway prop. Plastic will simply shatter and add to the pieces flying through the air.

Brass is heavy. If possible I'd go with aluminum tube. Aluminum can work but it would require more fiddling. You can't solder it and welding I suspect is not in your skill set. Otherwise go with a brass rod for the round edge of the cage and use brass tube for all the supports. 1/8 inch should work. Might even get away with 3/32 depending on prop size but no smaller.

A jig can be simple based on the shape of things. You'll have basically two ends to this cage. A smaller hub which attaches in front of (towards the front of the boat) the prop. Usually in front of the motor too. And the larger back end of the cage. Keep it simple and incorporate the front cage mount into the motor mount.

For the larger end I'd make it an inverted 'U' shape. The legs can then mount to the boat hull simply by insertion into some holes and either glue or set screws to hold it. Bend it first and mount to a piece of wood for a jig. Then determine the front piece size and shape (a 'U' shape works here too) and use another piece of wood to hold it in place in front of the big end. Then start sizing and soldering in the supports between the two. A bit time consuming but overall quite simple.

I can see a side view of this where the support tubes have a 90 degree bend in them. Make a bender for this by deciding how sharp a bend it will be (not very sharp). Take a piece of plywood the thickness of the tubes and cut a circle (wheel) out of it with the bend you want. Then put sides on this ply that overhang the edge. Like a pulley. The sides need to be robust (strong) to control the tube. This is your tubing bender.

Sounds like a fun project to me. If I had fewer projects of my own I'd be tempted to do one of these.

Good luck!