GPH numbers on 18' w/ 115

toadfish · #1 03-08-2003, 11:03 PM

Tom, my 18' Seacraft has a 48 gallon tank from the factory....Toadfish

Tom Bare · #2 03-10-2003, 09:26 AM

Mark-

I think Toadfish solved it-mine is 48 also. I did not want to run it dry due to the age of the boat-God only knows what is in the bottom of the tank, but I'm pretty sure it is not pleasant!

Thanks again,
Tom.

Bigshot · #3 03-10-2003, 05:13 PM

No biggie running it dry, your fuel pickup is at the bottom anyway. You may want to try a 19" prop, I believe that engine redlines at 5500 but double check. If prop is alum, swap into a 17" SS and drop 100 rpm's or so. Your cruise will pick up a few mph.

David Bienvenu · #4 01-03-2004, 06:03 PM

One pound of fuel will produce 2 horse power per hour. Figure a way to do better and you can get rich fast. Gasoline weight is 6 lb/gal.I have 150 Yamaha. Running at 75% is 112.5 Hp. Formula: (112.5 x .5)/6 = 9.38 GPH. Formula works for anything. No mater if it's a lawn mower or airplane.

ocuyler · #5 01-03-2004, 08:04 PM

Mark is right. Run it dry and find out...

Then replace the filter.

Flatline · #6 01-06-2004, 06:50 PM

I have been registerd for a while but do not post much. I have a 78 18ft seacraft and mine too has a 48 gallon tank. But I have a v6 150 rude on it. To my best calculations I get about 2.2 miles to a gallon usually running at 4000 rpm. I want to install the NAV MAN but have not found a good place for it. May I ask where you installed your NAV MAN? Thanks.

Mi Time II · #7 01-12-2004, 07:21 PM

I replaced the tank in my 1975 SeaCraft 18' with a new one same the same size and it hold right at 49gal. As far as MPG goes it get about 2mpg average. It has a 1992 even 175. If your #'s are correct your getting one hell of MPG. Mine is also carb 2stroke. Good luck.

[ January 12, 2004, 06:26 PM: Message edited by: Mi Time II ]