Mileage Performance Checkup

[rcnight]

Gents: Did a test run today with 1 ga of gas in a portable tank. Got 3 miles according to my GPS while turning approx 4200 rpms @ 30 mph.. Running a 1997 Evinrude 150 with a 14.5x17 ss prop (I believe the carbs are oversize, not stock) on a 20'SF w/t-top. Lightly loaded, about 20ga in the tank, light chop w/15-20 mph winds. How do those numbers compare to other similiar 20's?

[workinpr0gress]

Whats your wot rpm and speed?

I did not do the one gallon test. However, with a full tank - 47 gallons, just me and some fishing tackle, my GPS said I was doing 36 MPH @ 4100 and my fuel flow meter was registering 9 GPH. That's with a 2010 150 ETEC on my 20SF

[pl99]

I am so totally jealous... I could only wish to get that gas mileage.....

[rcnight]

My topend is 40 mph at 5600 wot - one person w/less than half a tank. I have a 70ga tank and have never had the cash to fill it completely. I was trying to estimate range based on speed & gallons from the pump. I'm going to raise the motor up 2-3 holes & maybe try a 19 pitch out to see how that effects performance.

[Bushwacker]

You'd get a more accurate result if you ran a full 6 gallon tank thru it, but 3 mpg is probably in the ball park. I averaged 2.8 mpg with my ancient 115 crossflow Evinrude over 6 trips to the Abaco's. This was running with a very heavy load, carrying 65-80 gallons of gas, a couple of coolers, dive gear and a couple of weeks worth of grocries.

30 mph is probably above your optimum cruise speed. I believe the "sweet spot" for the 20' hull is about 25 mph because that's where the hull hits minimum running angle. (Check out the Boating Magazine test of a 69 Seafari in the Literature section.) Of course the optimum cruise point for a given rig also depends on engine/prop characteristics as well. Optimum cruise on my 150 E-Tec seems to be at about 25 mph, with rpm between 3500-3800 rpm, depending on what prop and load I'm carrying. Instantaneous cruise MPG from the I-Command system (based on gps speedo and fuel flow from ECU map) varies from about 3.8 to 5.2, depending on load, prop and wind/sea conditions. One neat feature with the E-Tec is that if you're running low on gas and worried about running out, just slow down to hull speed (~ 5 mph), where it's running in the lean burn stratafied charge mode, and gets 8-12 mpg!

[zach]

3 mpg is probably about right. I'd average 2 to 2.5 with my 1989 Johnson 175.

With my new Optimax I do considerably better, in the 4 to 5 mpg range. A recent trip from ft lauderdale to key largo and back yielded an average of a hair under 4 knots per gallon (~4.5 statute per gallon) and that was heavily loaded and cruising in the 27-32 knot range.

[rcnight]

Gents: Thanks for the feedback. At least I know I'm in the ballpark. I'll try 6 ga. thru it at 25 mph & let you know the results. What effect will a 19 pitch prop have on fuel burn?

I am running a 19 on my ETEC.

[Bushwacker]

The 19 will probably be a little better, but make sure you're running the load you plan to carry most of the time. 5600 on that 17" prop will come down when you add more gas, gear and people, so you might want to hang on to that one for heavy load operation. A lot of folks do their prop testing with too light a load and end up picking a prop that's too big (too much pitch) for the load they typically carry!