Mileage Performance Checkup
 

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?

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Whats your wot rpm and speed?

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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

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

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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.

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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!

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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.

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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?

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I am running a 19 on my ETEC.

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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!

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X2

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Let's see if I hook mine up to a gas tank with 1 gallon in it I'd still be close enough to the dock to throw someone a line when it ran dry. Old merc's love the pre-mix

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Hehe.....Yea, seriously with my Twin 225's I would make it out of my canal to the Manatee River. Maybe [img]/forum/images/graemlins/tongue.gif[/img]

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A little late to get into this conversation but I have a question???

Why is everyone so concerned about how many miles per gallon they get? Or is this just a different way to get the information then hours per gallon?

Now let me explain. When I was running a 30 ft Allura with a 350 inboard I put on over 1400 hours and I could not tell you what my mpg was.

However I could tell you what my burn rate was per hour and almost any speed. I use to log my hours and every fill up. So if I was going port to port my burn rate would be 8 gph. If I was doing fishing cruising or cock tailing my burn rate was 6 gph. So by using the hour meter and the high end of the burn rate I could always tell how much fuel I had left, and there was confirmation at every fill up.

Anyway that is my story and I am sticking to it. :D :D

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Probably just different ways of thinking about almost the same thing. For example, I could care less what I burn per hour; as variable as my engine use is, it would be hard to keep up with anyway. But, since I go way out back of beyond where there ain't no fuel and want to stay as long as possible, mpg is important.

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I was thinking ahead to this summer when I hope to join other CSC'ers head across to the Bahamas. Since I've never made the crossing, I figured a good way to estimate fuel needs would be to factor gallon per mile at a fairly constant cruising speed.

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I think I hear another boat going to Bahamas this summer!!!!

I think everyone is talking the same thing - GPH + MPG.
Back in the "Old Days" we didn't have the electronics to know the miles travelled so it was hours and gallons.

Hmm, thinking about the old days - I can't remember the last time I used the mop handle to stick the tank.

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Wow. That brought back memories. When I was a kid, my grandfather had an old 43' Rybovich with the twin 300 gallon saddle tanks and fuel fills on each gunwale. No fuel gauges. He had a 1" square wooden stick about 7' long, with measurements carved into the wood.

Those twin Chrysler Imperial "Majestic 8" inline-8 motors sure did suck the gas down. And all of 150 hp each.(I remember one of the engines was reverse rotation.) I know those motors were out of a pre-WWII Navy patrol boat.

Memories, Memories.

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In the old days if the gas gauges stopped working then there was always a site gauge on top of the tank. ;)

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My first SeaCraft was a 79 Seafari with a mechanical guage on the tank. It had a plexiglass window in the floor to peer thru. Worked better when it was wet - due to all the scratches.

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Many a big boat has sight tubes on there tanks. The best fuel setup ever IMO on those bigger boats is below cockpit/bilge fuel fills directly on the tanks with a wooden stick on the bottom side of the cap and no sighttube to break...sticking the tanks is very accurate if they were done right I have pulled into Fernidena Beach from Pamlico on a 60' custom with nine gallons in each rear tank...lol...Plus if you have a fuel spill while filling , just shut off the bilge pumps and clean it up when you can instead of it dumping overboard and having your tiny problem turn into a huge ordeal

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On that trip just running to places you know have fuel is the deciding factor and that will be within 100 miles. WPB to WE - then to Foxtown. So you shouldn't be stretching it

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Short answer, gas was cheaper back then?

For us I'd say its because miles per gallon is a way of measuring efficiency in relation to time, and with gas getting more expensive; it's not about how much you burn each hour but how little you can burn on a given trip. If gas gets crazy expensive, those getting the best miles per gallon will be the ones still fishing, IMHO, which is why we have a 70 safari, with a mercrusier alpha and 4.3l :-)