GPH Estimate - The Hull Truth

VtWarthog · 07-23-2003, 08:51 AM

36' Mainship Sedan 1988

I have twin crusader 270 hp non-injected engines w/ straight drives. boat cruises at 3200 rpm at 17-18k, max speed around 4000 rpm at
25-26k, dry weight 20,000lb, Semi-displacement hull 36'mainship 240 gal fuel 100 gal water

Anyone with similar equipment want to guess what the gph would be at cruise speed? What do you think the most efficient speed/rpm (MPG) might be?

I have just recently purchased the boat and
would like to get some idea of the most efficient speeds without the expense of a flow meter.

VtWarthog

dry doc · 07-23-2003, 09:05 AM

14-15 gph would be my estimate....i have a
friend with the same vessel, but single
cummins burns about 6 dan

cabosn · 07-23-2003, 10:38 AM

30 cruise and 45 WOT

SN

AlexT · 07-23-2003, 11:50 AM

The fact that you are hesitant to add a fuel meter based on expense is a big bold sign that you really needed one.

On a boat that size a flow meter is going to pay for itself almost immediately in terms of fuel savings. It would literally be the first thing I would add.

Capt. Dan · 07-23-2003, 12:15 PM

You just bought a 36 foot boat and you are worried over the expense of a $150 fuel flow meter? Doesn't bode well for other needed repairs or upgrades!!

CABSON's comment of 35cruise and 45 WOT is nuts.

You should, however, be able to turn those motors to 4,400-4,600 rpm, check the specs. If the engines seem to be runnning right and the bottom is clean, you may have incorrectly pitched props. Better get out the check book...

jobowker · 07-24-2003, 09:04 AM

Actually it may not be that far off, if Cabosn was referring to the total, not each.
I have a 250hp carbed 5.7, and at WOT 4400 RPM I burn about 19-20 gph. I cruise at closer to 14 gph.
If you double those nubmers for twins, you would get 28 cruise and 40 gph for WOT. I figured it out once and it took about half a season before the flow meter paid for itself.
I realize that it's a different engine, but consumption figures are fairly well predictable based on developed HP and of course fuel type.
In other words gas engines are fairly close on the gph burn per developed hp.

cabosn · 07-24-2003, 12:00 PM

Thanks for silencing my critics jobowker. Talking to boat owners about fuel consumption is more dangerous than talking to a fat chick about her weight..
SN

Capt. Dan · 07-24-2003, 02:08 PM

CABOSN--My appologies, I thought you were refering to MPH.