Here's a typical day at the lake. - This does not include the monthly
payment, maintenance, insurance or possible repairs needed after the
trip on either the boat or the tow vehicle, only the expense for the
day.

If we're on the lake for about 8 hours and cruise (~35-40 mph) about
25% of the time and approximately 10% of the time we're running wot
to pull a skier or towable and the other 65% the engine was off and
we're relaxing or swimming, we would burn about 35 gallons of gas.
That will cost us about $112. And I used to think the beer and ice was
the big expense.

(8 x .25)9.0=18 x $3.25 = $58.50
(8 x .10)20.5=16.4 x $3.25 = $53.30
34.4 gph 111.80
Park entrance fee 7.00
Food/beverage/ice 38.00
TOTAL= $156.80

Fuel consumption figures for Mercruiser marine engines:
3.0 L: 6gph at 3500 cruise, 11.5 gph WOT
4.3 L (2 bbl): 8.5 gph at 3500 cruise, 16.7 gph WOT
4.3 L MPI: 9.0 gph at 3500 cruise, 19.5 gph WOT
----- 5.0L (2 bbl): 9.0 gph at 3000 cruise, 20.5gph WOT ----- My
category
5.0 L MPI: 10.9 gph at 3500 cruise, 22 gph WOT
350 Mag MPI: 12gph at 3500 cruise, 22gph at (5000 rpm) WOT
MX 6.2L MPI: 13.2 gph at 3500 cruise, 25.1 gph at 5200 WOT
496 Magnum: 16.0 gph at 3500 cruise, 30.5 gph at WOT
496 Magnum HO: 18.5 at 3500 cruise, 33gph at 5000 WOT.