Fuel usage

[Mischief Managed]

Also at a place like Lake Powell where places to buy gas are few and far between, you want to conserve as much as possible. The first time I was there with this boat, I ran around all week at a fairly low speed thinking I was conserving fuel when actually, I could have been going much faster to get better MPG.

I see people do that around here when gas prices peak. They'll run I/O runabouts at 10 to 15 MPH instead of 25 to 30 MPH thinking they are saving gas, but they are using almost twice as much per mile.

A fuel flow meter can save you a lot of money if you boat often. I cover about 1000 to 1500 miles and use 400 to 600 gallons in a typical a season in my boat. I can easily save 10% on fuel by carefully trimming and running at optimum speed based on real-time MPG measurements and the flow meter paid for itself in less than two years. I've had the flow meter for 7 years now and it's saved me 350+ gallons of gas. I think I paid $250 for it with the flow and speed sensors. I love that it's an ultra-accurate gas gauge too, that lets me keep my 74 gallon tank only filled with 50 gallons for the start of a typical day out, and the weight savings (150 lbs or so) of that alone saves gas and makes the boat perform better.

 

[java230]

my typical run is right about 12 miles, do it at least 2-3 times a week. 80% of the time im at WOT, 13' whaler clone, 82 40HP 2 cyl merc, WOT for me is 4680 RPMS, a bit low for the motor, right at 25MPH WOT. Use right about 2 gallons every time. Or 6 MPG. not very accurate, but ok.

 

[kjsAZ]

This http://www.boat-fuel-economy.com is a pretty good guideline IF the prop is set up right.

 

[H20Rat]

rough number is horsepower/10 = gallons per hour at WOT. It varies some for different engine types, but not as much as you would think. For the OP, there is no way a 1977 70hp outboard averages 2 GPH, unless half the cylinders aren't even running because the carbs are plugged up. No modern engine comes anywhere close to that economy, so something else is completely wrong...

 

[bruceb58]

rough number is horsepower/10 = gallons per hour at WOT. It varies some for different engine types, but not as much as you would think.

I hardly ever run my engine at WOT but now I need to try it and see. Would mean mine is getting around 1.4MPG which may be possible. I get around 2.8 to 3.0 If I get everything trimmed up perfect.

 

[Cptkid570]

Bruceb58 - I'm very jealous of you guys that have the gas flow meter. I'd love to have one for at least a day or two. I think all of us would like to see if what we think is the sweet spot is really the sweet spot. What is yours? Can we get an example of your ideal cruising speed and trim? For example: "I put the drive all the way down and then tap on the "up" button xxx amount of times and then cruise at xxxx rpms that is xxxx mph"

 

[bruceb58]

I have a lowrance gps/fish finder and a fuel flow meter that attaches to the NEMA bus. Its an older unit unit now.

I pick a speed and trim up until I get best economy. Have to use small increments. I can then change speed again up and down to fine tune it. Problem is, every speed has it's best trim setting. This would basically be a math nightmare if the GPS wasn't taking the fuel flow and the speed to compute the MPG.

 

[UncleWillie]

My 220 HP MPI MerCruiser uses ~16 gph at WOT according to the Fuel Flow Monitor.
Under exceptional Lake Erie conditions that yields a little over 50 mph. ***

The rule of thumb formula indicates I should be using 22 gph but I'll assume the Fuel Injection gives the improvement. (7.3gal/Hr/10HP)
That also calculates to 3.1 MPG. It would suck my 28 gal tank dry in 105 minutes if I kept it up an went the whole 87 miles WOT.

Half throttle at ~25MPH yields ~6GHP and ~4.5 MPG at a ~120 mile range.

*** Trimming up to absolute max speed and RPM is seldom possible due to Lake conditions are never flat.
Higher speeds at higher GPH and a lower MPG and closer to the formula would be expected.
WOT yeilds ~4400 rpm due to the non-ideal trim. It just gets too light in the water.

 

[bruceb58]

It would suck my 28 gal tank

Yikes...28 gallon tank! My 21' Bayliner had a 50 gallon tank in it!

 

[UncleWillie]

Yikes...28 gallon tank! My 21' Bayliner had a 50 gallon tank in it!

It is fine for my boating style. I spend 95% of the time under 25 MPH.
It will take me over 8 hours to go through 20 gallons.
By that time I am ready to call it a day.

 

[tpenfield]

I wish I had flow meters on my engines . . . maybe next year I'd like to connect it to my GPS and get a true mpg reading.

All I know is that I ran about 50+ hours last year and used 400 gallons of fuel. So, it averages out to 8 gallons per hour.

Twin 310 HP Mercruisers (620 hp total)

Generally run at 2600 rpm which gives about 28 mph

I used that boat fuel economy app (link given a few posts above) as a guideline . . . I think it is OK, but with twin engines, you tend to do a little better per engine than with a single.

My WOT fuel usage would be about 60 gallons per hour. . . . :faint2: