2 miles per Gallon vs typically 1 mile a Gallon!

S

stuartdmc

Member
Joined
May 1, 2006
RO Number
21081
Messages
97
Two years ago I would run to Catalina Island 65 miles round trip port to port, and return to my home port (NPB)with just under a haft a tank of fuel. Well this past weekend I ran to Catalina and on the way back we ran out of gas 5 miles from the jetty.
By the time Vessel assist got to us which took them 3-4hours with fuel, we had drifted further out to sea approx 7 miles it took 15 gallons to make it to my slip which was just over 8-9 miles. This is unheard of for a 7.4 454 penta.
My question is;
What could be wrong that would cause the engine to burn so much fuel?
 
- Hull has growth
- Prop and/or shafts have growth
- Prop is damaged/bent
- Lack of air to engine
- Poor ignition or combustion
 
Might have something to do with your poor fuel consumption mentioned in your other post?
 
First of all real boaters talk GPH, figure you time with wind, sea conditions taken into account. Then always include a 20% reserve.
 
REAL BOATERS! ARE YOU KIDDING? DO ME A FAVOR AND DON'T RESPOND TO MY POST, EVER.
quote:
Originally posted by JimPend

First of all real boaters talk GPH, figure you time with wind, sea conditions taken into account. Then always include a 20% reserve.

Click to expand...
 
Thanks for asking, I get her bottom cleaned twice a month, my diver keeps the her pretty clean if that's what your alluding to.
quote:
Originally posted by KiDa

Has she been hauled in the last 2 years?

Click to expand...
 
You may have hit the nail on the head. What do you think about "blow by" would that also cause plugs to fail? and thus not burn the fuel.
quote:
Originally posted by Gregory S

Might have something to do with your poor fuel consumption mentioned in your other post?

Click to expand...
 
in addition to decrease in compression, consider ongoing weight gain over time due to accumulated onboard "stuff"

RWS
 
quote:
Originally posted by stuartdmc

Thanks for asking, I get her bottom cleaned twice a month, my diver keeps the her pretty clean if that's what your alluding to.
quote:
Originally posted by KiDa

Has she been hauled in the last 2 years?

Click to expand...


Click to expand...


Didn't know about your diver. I experienced a similar problem due to a dirty bottom and running gear.

That's one we can rule out.
 
Just a suggestion....anytime you are in a low fuel situation with the possibility of not making it back to the dock, slow down to hull speed, 6-7 knots. You will double your range.
That 15 gallons you burned going 7 miles...you probably could have covered it with 7-8 gallons, maybe less.

Any chance your secondaries opened up sucking down all the extra fuel?

BTW, I also much prefer MPG over GPH.
 
Is this a carb or fuel injected? The reason I ask is I have fuel injection and my ECM went bad on one engine well suddenly that engine starts burning ridiculous amounts of fuel. After the usual process of elimination all done by a Mercruiser shop a new ECM was installed and the engine runs like new with a normal fuel burn.
Rob
 
Any chance the tank wasn't full when you left? Sounds like you got your regular 2mpg once vessel assist got more fuel in your tank.
 
quote:
Originally posted by stuartdmc

REAL BOATERS! ARE YOU KIDDING? DO ME A FAVOR AND DON'T RESPOND TO MY POST, EVER.
quote:
Originally posted by JimPend

First of all real boaters talk GPH, figure you time with wind, sea conditions taken into account. Then always include a 20% reserve.

Click to expand...


Click to expand...


While you may take exception to the way it was stated, you should be measuring in GPH anytime the vehicle is subject to currents, winds etc. This is because while the route distance is fixed, the things that effect the total trip time are not. In aviation, which has the same issues, fuel consumption is always measured in GPH because you may make your regular trip of 150 miles, but if the airplane is doing 100 knots into a 100 knot headwind, it matters little what your mpg is, you are going to run out of gas no matter what your tank capacity is, unless it is infinite.
 
I can't imagine a boat burning twice the fuel without showing any sign...

If the running gear was dirty you d have notice sluggish performance. Slower acceleration, harder to get on plane, slower speed
Any mechanical issue would also have been noticeable with vibrations, smoke, etc.

What speed were you running at? Same as in previous trips?

Was th boat fully on plane? For instance if your boat burns 30gph at 18kts, if you re running off plane but above well hull speed, 15kts, you will burn close to the same fuel for a slower speed.

The only other thing would be that didn't start with full tanks. Either the gauge was off (common on boats) or you thought the tanks were full because fuel spat out the vent refueling which could be due to clogged vents

Key question: what speed ?
 
The subject of this thread, "2 miles per Gallon vs typically 1 mile a Gallon!" doesn't make any sense when compared to your explanation. Perhaps you mean "2 gallons per mile vs typically 1 mile per gallon". Gallons per hour in my opinion is meaningless without knowing RPM and speed.
 
No it is not meaningless. Any powerplant engineer will tell you that flow per hour is an important measure of propulsive efficiency and the only direct indication of horsepower being developed. Typically an ICE gasoline engine will burn .46 pounds per hour per hp. Thus if you have say a 300 hp engine at WOT throttle that is burning signifigantly more or less than 23 gph regardless of speed you know you have a problem. Equally so if you know what are typically speeds though the given mass, in this case water, for a given RPM, high fuel flow is a warning of problems because a higher than normal hp is required to develop the same given speed. Since we don't have "HP meters" on our engines, fuel flow (gph) is the only true indication of how much power is being required to develop a given speed. If you don't believe me, ask why fuel flow is the most important variable charted in engine condition trend monitoring.
 
I use MPG too. I also use a simple vacuum gauge to determine the load on the engine which is a better indicator, IMO, of how efficient you're running. No fancy, expensive flow meters.
 
I use MPG. Over the past 2 years and 2 major (for me) trips, it's been the most consistent measurement.

Case in point... this summer I made a week-long, 244 mile round trip through the Great South Bay, Peconic Bay and Long Island Sound, stayed over at 4 different marinas along the way, and made 4 refueling stops. Variable wind and wave conditions. Speeds varying from extensive no-wake zones, to full planing speed, to slogging along at 12 mph getting the crap pounded out of us, to everything in between. Here are the results I logged at my refueling stops. I filled the tank each time and used the logging features of my GPS to record distance and Avg SOG. Distance is recorded in statute miles

Refueling 1 - 69.8 miles , Avg SOG 12.1 , 65.4 gals , 5.75 hours , 11.4 GPH , 1.07 MPG
Refueling 2 - 61.7 miles , Avg SOG 12.2 , 59.7 gals , 6.25 hours , 9.9 GPH , 1.03 MPG
Refueling 3 - 51.0 miles , AVG SOG 19.6 , 49.1 gals , 3.25 hours , 15.1 GPH , 1.04 MPG
Refueling 4 - 62.0 miles , AVG SOG 15.6 , 57.1 gals , 5.50 hours , 10.4 GPH , 1.09 MPG

Makes a lot more sense for me to use MPG for planning purposes. The MPG figures are very consistent. My GPH is all over the place.

My .02
 
INCREDIBLE. The OP asks a question about fuel consumption and it morphs into a class on semantics.
 
You must log in or register to reply here.
Back
Top