miles per gallon.

leslie riggan

leslie riggan

Well-known member
I have a 16 ft extra wide boat with a 1992 25 2 stroke merc. I have two batteries 1 extra can of gas 2(gallons)probably 150 pounds of "stuff" removable seat/ box, anchors, decoys, wood floor, etc. I weigh 175, my partner 250+ i'd geuss. Left the dog home this river's too dangerous. 5 person cap. on this boat. I ran approximately 25 miles day before yesterday. I ran out of gas about 1 mile from ramp. I had my spare can though. What is your normal range on a tank? I have ran that far before but never ran out. I had 5 gallons in a 6 gallon tank. I know stupid me, fill it up, wont be like that again. It seemed like my range dropped drastically this trip out. It was the first time I had someone else on a trip this far. The river had a heavy current due to a water release raising from 3ft to 9 ft in about 10 minutes. Does this range sound right? That's only about 4.7 mpg. It seems awful low to me.
 
If you were running wide open you can figure about 2.5 gph at whatever speed that gets you. Current flow will factor in also along with the load an balance of the load. If you can't get the boat on plane with that load, you'll suck gas big time. What sped were you getting?
 
Yep, boats are figured at gallons per hour....on plane at the most efficient rpms. Usually the most efficient is 2/3 of wide open throttle ...IF you are on plane. A rulr of thumb is 10% of horsepower equals GPH so your 25 should suck 2.5 gallons per hour at ideal cruising speed, on plane, set up correctly and well tuned. Like Ken said, if you are using all motor power to push water it will suck big time.
 
That agrees with what I have always thought. Move the decimal point and get gallons per hour. Learned the lesson the hard way once , invloved walking a long ways in chest waders and a tore up lower unit. Got about 35 min out of a 25 hp and 3 gallons. Best lesson yet is a spare can.
 
Thanks, on the trip down river it was mid to slow go because of the low water, and it being dark thirty. I know the stretch pretty good, but things change almost overnight on a river. Like I said earlier the NC dam cut loose and water flowed heavily all morning. It washed out our dekes twice and we had to round them up. I always keep a spare can of gas no matter how far I run. I guess the extra weight played a factor along with super swift currents. I ran 2/3 to 3/4 throttle on the way back. It looks like I'll be putting an extra 6 gallon tank in the front. I didn't smell the tell tell of the motor running rich. I pulled the plugs and they were good and dry. I dont know what speed I was running down but I was on plane half of the time on the way back.
 
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I'd say if you went 25 miles on 6 gallons of gas....you have a hell of a engine.Sounds like pretty good gas mileage to me.
 

Harker,

Is the rule of thumb the same for 2 and 4 strokes? I'd heard the 4 stores were a lot better on gas. If it is different, do you know what the rule of thumb is for 4 strokes? I'm still running a 2 smoker...

Thanks,
Charlie

Yep, boats are figured at gallons per hour....on plane at the most efficient rpms. Usually the most efficient is 2/3 of wide open throttle ...IF you are on plane. A rulr of thumb is 10% of horsepower equals GPH so your 25 should suck 2.5 gallons per hour at ideal cruising speed, on plane, set up correctly and well tuned. Like Ken said, if you are using all motor power to push water it will suck big time.
Click to expand...
 
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I'm not sure, I've never figured it out. But I do know that i have run 10 miles up river and back and still have ~2 gallons left in a 6 gallon tank. Thats with an 18 Nissan 2 stroke on a 1440 mv jon boat loaded.
 
Charlie, I know that with a 2 1/2 gal tank and my old 9.9 Honda that Scott O. bought....on my 1750MV...I could go all day and have gas left. On my 18' pontoon with a Honda 25, I only put about 10 gallons in it all summer. They get Horrendously good gas mileage. I don't know if there is a rule of thumb on the 4 strokes or not. I would say that they get at least 2 times the mileage as a good running, well trimmed 2 stroke. I remember Hank Garvey saying that when they first got their Bankes Boats, they let it idle all day long because it was below zero where they were hunting.
 
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