2 3/4" to 4" exhaust holes

[OLD MAN ON THE LAKE]

I am going from 2 3/4" to 4" exhaust thru transom.
Since I won't have a pilot hole for the hole saw,I am concerned I will screw it up.
Anybody have a tip to do this properly. Thanks

[Moneypitt]

I am going from 2 3/4" to 4" exhaust thru transom.
Since I won't have a pilot hole for the hole saw,I am concerned I will screw it up.
Anybody have a tip to do this properly. Thanks
Put a wooden doubler inside with some screws, find the center and drill/cut away, repeat...............MP

[BDMar]

You can also take the 4" hole saw, drill out a piece of 1/2" plywood. screw or glue the piece on the transom over the 2 3/4" hole centered. Then you have your pilot hole. After you have a good start, about 1/4" deep, remove your pilot and have at it. Use a 4 1/8" hole saw instead of 4". The tips will fit better and you can seal the wood with resin.

[SmokinLowriderSS]

Use the new tips as guides, draw a circle arround them with sharpee, cut it out with a jigsaw or reciprocating saw, sand to finish with a drum sander, and resin seal them.
Masking tape a few layers on the glass to avoid scratching it with the saw shoe.
Cutting thru masking tape helps reduce splintering of the 'glass a bunch too.