gas mileage

[blackhawk180]

Re: gas mileage

I boat downhill all the time..... in my drift boat. It would be a lot more relaxing if they would remove those darn rocks from the river. And from experience, the steeper the downhill, the less relaxing it becomes. I realize many prefer the steepest parts but I'm not out there to pump myself full of adrenaline, just trying to catch some steelhead.
But my MPG is phenomenal.

 

[john cole]

Re: gas mileage

Nice,
we have the salmon river here, i just hit the holes, no boat for that.

 

[agallant80]

Re: gas mileage

I think the closest you can get without doing the math yourself which will require several trips and fills along with logging your trips is to find a boat like yours at boattest.com and see what they came up with.

 

[john cole]

Re: gas mileage

"Assuming the engine is in proper tune:

Take the top speed, square it, then divide by the rated HP, call the result X.

Take the speed at 3000 RPM, square it, then divide by X. The result is the HP required to cruise at 3000 RPM, call that Y

Multiply Y times .08 and that will give you the GPH in fuel burn at 3000 RPM.

Divide the speed at 3000 RPM by the fuel burn to get MPG."

Holy Crap, that just drove me to drink , i believe that i will just take the time to do it by the time tested, run it for x number of miles and fill it back up and see what I got.
not a math guru, still have a hard time using my micky mouse watch, but thanks anyways.

 

[Mischief Managed]

Re: gas mileage

Let's assume it will go 45 MPH at WOT and has 190 HP, that means it would burn roughly 15 GPH at 45 MPH and therefore get 3 MPG. If it goes 28 MPH at 3000 RPM, it will burn roughly 6 GPH and get 4.66 MPG. I would be very surprised if these numbers are off by more than 10%.

 

[dingbat]

Re: gas mileage

I would be very surprised if these numbers are off by more than 10%.

I've run a fuel management system for 3 years now.

My numbers vary by:
10% - running with or against a wind.
30% - with or against a tide.
50% - flat calm to 2' seas.
15% - one person or three on boat

That averages out to a little over 26% variance on daily, if not hourly changes in conditions.

200HP - 27 kt. cruise - 2.3 GPM @ 4200 RPM in ideal conditions. Percentage of consumption taken from that figure.

Anything other than checking actual usage under varying conditions is a WAG at best.

 

[Mischief Managed]

Re: gas mileage

I've run a fuel management system for 3 years now.

My numbers vary by:
10% - running with or against a wind.
30% - with or against a tide.
50% - flat calm to 2' seas.
15% - one person or three on boat

That averages out to a little over 26% variance on daily, if not hourly changes in conditions.

200HP - 27 kt. cruise - 2.3 GPM @ 4200 RPM in ideal conditions. Percentage of consumption taken from that figure.

Anything other than checking actual usage under varying conditions is a WAG at best.

I know what you are getting at, but he won't be running 3000 RPM is 2' seas and there's very little tide on Onieda Lake in NY.

 

[Slip Away]

Re: gas mileage

Fisherman.....

 

[john cole]

Re: gas mileage

Let's assume it will go 45 MPH at WOT and has 190 HP, that means it would burn roughly 15 GPH at 45 MPH and therefore get 3 MPG. If it goes 28 MPH at 3000 RPM, it will burn roughly 6 GPH and get 4.66 MPG. I would be very surprised if these numbers are off by more than 10%.

thanks for figuring that all out, i'm hoping to get that much at cruise, I will see this spring.

 

[dan02gt]

Re: gas mileage

Let's assume it will go 45 MPH at WOT and has 190 HP, that means it would burn roughly 15 GPH at 45 MPH and therefore get 3 MPG. If it goes 28 MPH at 3000 RPM, it will burn roughly 6 GPH and get 4.66 MPG. I would be very surprised if these numbers are off by more than 10%.

Mischief,

I have a 4.3L MPI in my Stingray with a MercMonitor that can tell you fuel burn and MPG to the second. Your numbers are slightly optimistic from what I see but not too far off. Best I can remember I burn ~7GPH at 3000RPMs and around 8GPH at 3500RPMs.

 

[john cole]

Re: gas mileage

At least all these suggestions and answers are giving me a ball park figure to work with. For the moment, at least until I can run it again, I will err on the side of caution on coming up with a basic cost of running it on this approx 140 mile trip this summer. Plus I believe I will see some mileage improvements and performance improvements after I upgrade to an electronic ignition (my distributor is about shot). It's tough to really say what I have been getting because usually my outings usually are not very long and involve, fishing, trolling, some cruising and tubing with the kids.

 

[bruceb58]

Re: gas mileage

Plus I believe I will see some mileage improvements and performance improvements after I upgrade to an electronic ignition (my distributor is about shot).

Unless your engine was completely out of time, you likely won't notice much difference.

 

[Mischief Managed]

Re: gas mileage

Mischief,

I have a 4.3L MPI in my Stingray with a MercMonitor that can tell you fuel burn and MPG to the second. Your numbers are slightly optimistic from what I see but not too far off. Best I can remember I burn ~7GPH at 3000RPMs and around 8GPH at 3500RPMs.

The MPI engine should burn more gas than the carbureted engine for a given RPM because it is propped for more peak HP and under more load in general. The MPI engine will probably be more fuel efficient for a given HP, but not dramatically so.

 

[lg260ss]

Re: gas mileage

Gallons per hour is a much more realistic way of measuring fuel use on a boat.

here is an interesting link to a site that gives you fuel burn for all of Volvos and Mercs engines along with some outboards.
Boat Fuel Economy | MerCruiser | Mercury | Evinrude | Yamaha | Suzuki | Honda | Volvo Penta Diesel Marine engines

 

[bruceb58]

Re: gas mileage

Gallons per hour is a much more realistic way of measuring fuel use on a boat.

I disagree since you also need to know the speed. 12 gallons per hour at 40 MPH is way better than 6 GPH at 15.

I have a fuel flow meter on my boat that measures the GPH and uses the GPS to give me MPG so I can change the speed and/or trim and see what the affects are. Having only GPH on a meter and having to convert constantly to see if you have improvements is not practical.

 

[Scott Danforth]

Re: gas mileage

lets confuse the thread

the BSFC (Base Specific Fuel Consumption) for various motors in #/hp-hr is

0.40-0.48 for Fuel injected four-stroke gasoline automobile engines

0.48-0.60 for Carburetor four-stroke automobile engines

0.55 or more for Two stroke gasoline engines (not direct-injection)

0.29-0.35 for Diesel engines

so how much power do you need for how long?

 

[Mischief Managed]

Re: gas mileage

Gallons per hour is a much more realistic way of measuring fuel use on a boat.

here is an interesting link to a site that gives you fuel burn for all of Volvos and Mercs engines along with some outboards.
Boat Fuel Economy | MerCruiser | Mercury | Evinrude | Yamaha | Suzuki | Honda | Volvo Penta Diesel Marine engines

GPH knowledge is very handy if you want to know, umm, how many gallons of fuel you are burning per hour. MPG is handy of you want to know how far you can go on a given amount of fuel or how much fuel it will take cover a given distance.

 

[john cole]

Finally got out and did a nice long run with it today, after doing some major modifications to it, but looks like I will be running at least 3 mpg with it at cruising speed if not a little more, so overall I can't complain. And it sure beats .8 mpg