Gas Mileage

[JohnnySCV]

Hello and thanks for reading.

I have a 1992 20ft Champion Bass Boat with a 200 HP Mercury outboard Carburated not EFI. I recently purchased the boat in late October and it seemed to suck up gas like no one's business. Since that time I have changed from a 23 pitch 3 blade prop to a 25 pitch 5 blade (both stainless). I had the voltage regulator replaced as it was not working, and the timing was slightly off at WOT so I had that adjusted. Since these changes have been accomplished it seems to be easier on gas to the point that it is very noticable. Could one or any of these adjustments make that much of a difference? My other thought is that the boat was not run very often and now that it is being used regulary it's running more efficiently (not sure if that is even possible)

Anyways, thanks for your thoughts....

 

[Boatist]

Re: Gas Mileage

Going from a 23 pitch to 25 pitch 5 blade will save you fuel as long as it is still in the recomended RPM range.
Best mileage is timed right. Too slow will cost you mileage and power. Too fast may cause it to overheat and blow a hole in a piston.

Best way to save fuel is Slow down. Best fuel mileage is at a fast idel on most boats.
Then the mileage drops off as you increase speed until boat comes up on a natural plane.
As soon as you reach a clean plane add about 100 rpms and this will be close to your best criuseing Mileage.
WOT is the worst fuel mileage so back off at least 1000 rpms and get much better mileage.

You may get more replys in the MerCury fourm.

 

[Mischief Managed]

Re: Gas Mileage

WOT is the worst fuel mileage so back off at least 1000 rpms and get much better mileage.

I have a fuel flow meter and can assure you that plowing speed (just under planing speed) gives much worse MPGs than WOT. My GPH is highest at WOT, but I cover a lot of ground and only see a 20% drop off in MPG from best cruising speed. Plowing along at 15 MPH yeilds a 50% drop in MPGs from best cruise. Sadly, when gas prices were really high in the Summer of 2008, I saw many boats being operated routinely at plowing speed in perfect weather conditions. I assume the captains thought they were saving gas...

 

[JoLin]

Re: Gas Mileage

I have a fuel flow meter and can assure you that plowing speed (just under planing speed) gives much worse MPGs than WOT. My GPH is highest at WOT, but I cover a lot of ground and only see a 20% drop off in MPG from best cruising speed. Plowing along at 15 MPH yeilds a 50% drop in MPGs from best cruise. Sadly, when gas prices were really high in the Summer of 2008, I saw many boats being operated routinely at plowing speed in perfect weather conditions. I assume the captains thought they were saving gas...

At 15mph you're nearly on plane- that's gotta be the worst condition from the standpoint of water resistance. As boatisit SAID, MPG will fall as you approach planing speed, rise again as you come on plane, then fall again as you approach WOT.

get on plane, reduce rpm's but stay on plane. Generally with a 2-stroke OB, cruising rpm's in the low 3000's give you the best compromise of MPG and speed.

 

[triumphrick]

Re: Gas Mileage

Along with the above posts, you're gonna hear that the EFI Mercs, non Verados get some pretty crappy mileage.

 

[dingbat]

Re: Gas Mileage

Generally with a 2-stroke OB, cruising rpm's in the low 3000's give you the best compromise of MPG and speed.

It really depends on the boat. In the low 3K rpm range I'm border line even staying on plane. Most boats I?ve owned have been happiest in the 4.0 - 4.5K rpm range. My 20? had a Merc 200 Hp on it was happy, via flow meter, @ 4.1K RPM. The current boat has a Evinrude 200 HP on it and is in the groove @ 4.4K RPM.

Even then there are times when you have to turn up the radio to drown out the sucking noise come from the back of the boat

 

[QC]

Re: Gas Mileage

Generally with a 2-stroke OB, cruising rpm's in the low 3000's give you the best compromise of MPG and speed.

Yeah, I see this as more consistent with I/O numbers . . . seems a little low for a typical 2 cycle application. Agree with dingbat though, fuel economy usually has more to do with hull efficiency than engine efficiency despite many trends that appear to confirm the opposite.

Edit: Hmmmmm . . . this seems to confirm JoLin's rule of thumb. 20 foot Aluminum Lund with a 175 Opti. This is from a Merc product bulletin. Also saw simialr results from an independent test of the same.

 

[Philster]

Re: Gas Mileage

Hello and thanks for reading.

I have a 1992 20ft Champion Bass Boat with a 200 HP Mercury outboard Carburated not EFI. I recently purchased the boat in late October and it seemed to suck up gas like no one's business. Since that time I have changed from a 23 pitch 3 blade prop to a 25 pitch 5 blade (both stainless). I had the voltage regulator replaced as it was not working, and the timing was slightly off at WOT so I had that adjusted. Since these changes have been accomplished it seems to be easier on gas to the point that it is very noticable. Could one or any of these adjustments make that much of a difference? My other thought is that the boat was not run very often and now that it is being used regularly it's running more efficiently (not sure if that is even possible)

Anyways, thanks for your thoughts....

Lacking specifics, I am still left thinking that those changes can add up to MPG improvement that are very noticeable. You get more bite with the 5-blade (less wasted slip when accelerating), so low- to mid-end economy will improve... and I will never forget about how a bad Volt Reg ruined the performance of a few boats. Combine those two, and sure, you get better MPG that you can notice.

Not too surprising -- just refreshing.

 

[JoLin]

Re: Gas Mileage

Mea culpa- I stand corrcted. RPM's in the low 3000's ARE consistent with I/O's. I mixed 'em up.

My 21' Pro-Line with Johnson 175 was happiest at 4000 RPM.

 

[dingbat]

Re: Gas Mileage

Yeah, I see this as more consistent with I/O numbers . . . seems a little low for a typical 2 cycle application. Agree with dingbat though, fuel economy usually has more to do with hull efficiency than engine efficiency despite many trends that appear to confirm the opposite.

Edit: Hmmmmm . . . this seems to confirm JoLin's rule of thumb. 20 foot Aluminum Lund with a 175 Opti. This is from a Merc product bulletin. Also saw simialr results from an independent test of the same.

As I said, it depends on the boat.
My boat with a Yammi F250:

RPM MPH GPH MPG
1500 6.4 1.9 3.46
2000 7.7 2.9 2.64
2500 8.5 4.3 2.0
3000 12.9 6.1 2.11
3500 23.8 7.4 3.23
4000 28.9 8.9 3.25
4100 29.7 9.0 3.29
4500 33.9 11.6 2.92
5000 37.6 14.0 2.69
5500 41.8 17.3 2.42
6000 46.0 21.5 2.14
http://www.gradywhite.com/popup/specs.php?boat=226&file=F250

This time with a F225

RPM MPH GPH MPG
1500 6.2 1.9 3.24
2000 7.1 2.8 2.56
2500 7.7 4.8 1.59
3000 13.2 6.5 2.05
3500 18.0 7.6 2.38
4000 28.0 10.0 2.80
4500 32.7 12.4 2.64
5000 37.3 14.5 2.57
5500 41.0 18.6 2.2
5900 43.1 20.4 2.11
http://www.gradywhite.com/popup/specs.php?boat=226&file=F225

Same boat, F225, this time bracket mounted motor.

RPM MPH GPH MPG
1000 5.2 1 5.2
1500 6.7 1.56 4.3
2000 8.3 2.35 3.5
2500 9.2 3.6 2.6
3000 14.1 4.25 3.3
3500 20.1 6.26 3.2
4000 27.2 8.06 3.4
4500 31.75 9.91 3.2
5000 35.7 12.51 2.9
5500 39.7 16.4 2.4
6000 43.2 19.02 2.3

http://www.gradywhite.com/popup/specs.php?boat=228&file=F225

As you can see in all three test, this hulls starts the transition to plane @ 7-10 mph

 

[JohnnySCV]

Re: Gas Mileage

I will never forget about how a bad Volt Reg ruined the performance of a few boats.

Serioulsy? Would be able to elaborate on why this is? I only mentioned it on the off chance that it may matter, but I really can't seem to figure out why.