How far can I go?

[ctbarbarian]

I have a 24 ft Premiere tritoon with a 34 gal gas tank
115 4 stroke Yamaha.

How many miles can I go down the river at quarter speed?
best guess,
I'm hoping at least 65 miles to get across Lake Pepin.

Huck Finn trip 2016

[BoatCop]

A lot of variables, but here's one.

65 miles at 1/4 speed (about 7 MPH) = 9.2 hours to get across. I would guess this is unsatisfactory, so let's bump it up to something reasonable, like 15 MPH. That would take you 4.3 hours.

At 15 MPH (3,500 RPM) with a 115, you'd be getting approx 3 MPG. That would use about 21.6 gallons.

That coincides with the est. 5 GPH you'd get at 3,500 RPMs, which would be 21.5 gallons.

This is considering no wind and no current. With the wind and/or current, you'll do better. Against the wind or current, a lot worse.

Remember the rule of thirds:

1/3 fuel to get there
1/3 fuel to get back
1/3 fuel for contingency/unforeseen problems

[BoatCop]

If the 9 hour trip is OK, then you'd be closer to 1.5 GPH or 13-14 gallons.

[ralph]

A lot of variables, but here's one.

65 miles at 1/4 speed (about 7 MPH) = 9.2 hours to get across. I would guess this is unsatisfactory, so let's bump it up to something reasonable, like 15 MPH. That would take you 4.3 hours.

At 15 MPH (3,500 RPM) with a 115, you'd be getting approx 3 MPG. That would use about 21.6 gallons.

That coincides with the est. 5 GPH you'd get at 3,500 RPMs, which would be 21.5 gallons.

This is considering no wind and no current. With the wind and/or current, you'll do better. Against the wind or current, a lot worse.

Remember the rule of thirds:

1/3 fuel to get there
1/3 fuel to get back
1/3 fuel for contingency/unforeseen problems

[Onegun]

Good math, but just say the hell with it! Carry 2 five gallon gas cans and go!!

[rancherlee]

should be fine, My Suzuki 140 is a bit more thirsty and I can JUST do a lap around Lake Vermilion cruising @ 22mph which is ~70miles with a 22 gallon tank. I usually put in ~18 gallons after the loop. I'm running 4000rpm at that speed, around 1/2 throttle.

[ctbarbarian]

Thanks for the help
I will carry 2 5 gal gas cans, just in case


But you built my confidence on my trip planning

[mpilot]

I can't give you mpg numbers but I can give you a rough estimate as well as gph at certain RPM's. Then you just need to know your MPH and you can calculate MPG and range.

Below is the data from a 24 foot bennington, but the GPH should be fairly constant across 115 four stroke motors. It looks like on this boat the optimum cruise speed is 3500 rpm at 17.2 mph. If you are running near that speed then these numbers might be pretty close to yours and you'd be getting 5.38 mpg. Otherwise, just take the fuel burn numbers and take your MPH at any one of these RPM readings (preferably via GPS) and divide your MPH by GPH and it gives you the MPG you are getting. Multiply that times your tank and then subtract 10% and that's what a manufacturer would call your maximum range. As the other poster said though, because you have currents to deal with it sounds like I would take my 100% range calculation and multiple it by .75 or .66 to give yourself a buffer.

RPM MPH GPH MPG
1000 3.6 0.6 6.00
1500 5.2 0.9 5.78
2000 6.7 1.3 5.15
2500 8.2 1.8 5.56
3000 13.1 2.6 5.04
3500 17.2 3.2 5.38
4000 20.7 4.4 4.71
4500 22.9 5.9 3.88
5000 27.0 6.8 3.97
5500 30.4 8.6 3.54
5850 32.7 10.1 3.24