I am trying to calculate MPG

[greg2648]

I am hoping someone can help me on this. I have a Lund Angler 1700. It has a Mercury 75hp 2 stroke. 2 guys and pretty loaded FOT is 38 mph (gps). Can anyone give me their best guess on miles-per-gallon. Thanks for your help. Greg.

[Jerryv]

I would guess 4 - 5 MPG at 3/4 throttle. Slightly less at WOT.

Jerry

[greg2648]

Thanks, Jerryv. I was actually thinking 4.5 mpg @4400rpm. WOT is 5200rpm. Thanks for the help. Greg.

[Hot Runr Guy]

here are my numbers. I have a 17' Lund Explorer tiller, with a 75 Opti on it. In the spring, I spent a week on the Turtle Flambeau Flowage in WI, and put on 5.9 hours, and used 8.2 gallons of fuel. There was no trolling involved, so the rig is either idleing and warming-up, or on plane, usually running in the mid-20's speed wise. If you take a low average of 20mph x 5.9 hours / 8.2 gallons of fuel, you get a tick over 14mpg. My hours and fuel used were similiar last year, so I am fairly confident in the numbers, which came off my SmartCraft tachometer. I've never looked at the gph value while running, my tach is somewhat out of my line of sight, so I can't tell you what the fuel burn at WOT is.
HRG
found a chart for a 75 Opti on a 18' Lund.

[Rapala Paul]

if u have a lowrance U can put a fuel meter on it. Mine tell me gph gallons used.

[1625rebel]

Usually your WOT fuel rate is approximately 10% of your horsepower.

So 7.5 gallons per hour. If your max rate of speed is 38 miles per hour, your fuel economy is around 5 miles per gallon at WOT (38 / 7.5). The 10% rule usually applies to modern 4 strokes/DFI 2S's though, so you are likely lower with a 2 stroke.

My guess would be around 3.5 mpg at WOT and agree with mid to upper 4's for a steady cruising speed.

[greg2648]

Thanks for the help. I kinda thought that this motor was a "gas pig". I know that the boat weighs alot. Right now I have a 4 blade aluminium prop (19p). Could I get better performance (not gas but speed or handling) out of the boat with a 17p or 18p? Thanks, Greg.

[1625rebel]

What are your RPM's at now, and what is the max for the motor?

I don't think your motor is that bad. Assuming it's not one of the newer direct injected 2 strokes (Optimax or Etec) then you are right where you are supposed to be. I had an '84 Evinrude that could blow through some gas. But you can buy ALOT of gas for the cost of a new outboard.

[greg2648]

Trimed perfectly, WOT is 5100rpm. My GPS says 38-39 mph with 2 guys and some gear. The motor is a 2000 Mercury 75 hp, 2 stroke. I would try a different prop just to play around, but I dont know which wat to go, up or down. Thanks, Greg.

Originally Posted by Hot Runr Guy

here are my numbers. I have a 17' Lund Explorer tiller, with a 75 Opti on it. In the spring, I spent a week on the Turtle Flambeau Flowage in WI, and put on 5.9 hours, and used 8.2 gallons of fuel. There was no trolling involved, so the rig is either idleing and warming-up, or on plane, usually running in the mid-20's speed wise. If you take a low average of 20mph x 5.9 hours / 8.2 gallons of fuel, you get a tick over 14mpg. My hours and fuel used were similiar last year, so I am fairly confident in the numbers, which came off my SmartCraft tachometer. I've never looked at the gph value while running, my tach is somewhat out of my line of sight, so I can't tell you what the fuel burn at WOT is.
HRG
found a chart for a 75 Opti on a 18' Lund.

If you divide 8.2 gal. by 5.9 hours, you get about 1.4 gal. per hour. That's what you're burning. Looking at the chart you included, and your speed, that's right in line with getting around 6 mpg.