Range question 69 20' & 97 200 OX66

[SteveH]

My father ordered and purchased (subsequently it became my boat) our 1978 20 ft master angler in 1978. I sold it in late 90s..... anyway, I believe the standard tank was 40ish gallons. We went offshore (up to approx 35 miles) and he had a 70 gallon tank installed at the factory, which was an upgrade. How thirsty is the 200?? Don't forget that a 40 gallon tank may only have about 35/36 or so usable gals.