You are looking at a simple, but very effective jig for making angled cuts with a hole saw. This is the brainchild of Cory McMahon of Triton Marine. We were in the process of installing a fresh water pick up for the new air conditioning cooling system when Cory suggested this to Chris Martin.
This jig is made by drilling a pilot hole through a block of wood, and then making a cut with the hole saw in question.
You then use double sided carpet tape to position the jig. Now, when you begin to make your cut with the hole saw it is held in line by the block of wood.
Because you are cutting a circle on an angle, in this case 45-degrees, the cut out is oval shaped. This plug is from the engine room bulkhead which also forms the aft end of the fresh water tank. The inside, after almost seven years, is shiny and clean.
With the installation of an updated air conditioning system we are plumbing the aft fresh water tank to be used for cooling the condenser coils. We want the pick up for the pump to be right on the bottom of the tank, thereby minimizing the amount of water that needs to be carried. The 45 degree angle allows the tank penetration to well above the highest point of the bilge in normal operation. We are expecting both more efficient an d quieter operation from this new Marine Air gear.