A Hole in the Roof

My wood burning stove is the popular cubic mini stove.  The cubic mini stove model is the "grizzly"  and is able to heat a 40' boat, around 250 sq. ft.  Punching a hole in the roof proved difficult - I bought a 4" hole saw to puncture the roof and with little success.  I would suggest buying a metal blade for a jig saw.  I have 4' of flue and a 3" marine cap.  Really love the cap!