Trying to figure out GPH on my boat & engine

[thomas3120]

Hello,
I have a 1989 17' Boston Whaler Super Sport Limited which has the same exact hull as the Montauk but instead of the center console it has a "drop-in" gunwale to gunwale console with a large rear hatch. Probably slightly heavier than a Montauk.
The engine is a 1989 Johnson GT 100 (max. rated for my boat). It's a V4 with 2 carbs.

If I remember correctly on a good day, going with tide and wind and also trimmed up I got 48mph @ around 5200-5300rpm. WOT is 5000 (trimmed all the way down).

Wondering what GPH I can expect on various rpms, or at 3000rpm on plane?

Any info appreciated.

thomas

 

[papyson]

the rule of thumb is you will use one gallon of fuel for every 10 hp running wot...so you can expect to use 10 gallons an hour...the exact fuel used at different rpms will vary depending on engine condition and boat etc... but your max efficiency will probably be 4000 rpm or in that range...for me its hard to make a long run at that speed but the price of gas kinda dictates it...