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Fuel use rate comparison

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delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Initially Posted - 05/30/2007 : 15:07:59

The other day we burned about a gallon an hour running directly into a 20 mph wind & 5-6' waves. This was with our Johnson 8hp Sailmaster. I have no idea if this is a lot or a little. We could only make about 3 mph (GPS) against the wind & waves. Theoretically we should have gotten a push from the outgoing tide, but not sure how I would have calculated that.

I'm curious how other outboards perform, do you guys have burn rates you've figured out for your engines? Do you carry spare tanks? I'm thinking a 3 gallon reserve tank isn't a bad idea, but not sure where I'd put it.

David
C-250 Mainsheet Editor

Sirius Lepak
1997 C-250 WK TR #271 --Seattle area Port Captain --

Edited by - on

Bill Arden
1st Mate

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USA
83 Posts

Response Posted - 05/30/2007 : 15:37:07

I find this question really interesting, and I haven't been able to find out much hard data either - so let me add my invitation to everybody to dive in with comments.

Manufacturers generally talk about a gallon an hour at full throttle for motors in the 8 - 10 HP range, as far as I've been able to determine. Does anybody have any better data than that?

Personally, I carry 2 three-gallon tanks for my Nissan 9.8. It's got a high-thrust prop for power rather than speed (I know, that's another thread

). Where we sail, Sunday had 25-30 kt winds and Monday afternoon was so flat I had to motor home - so I carry some insurance.

Thanks and regards,

Edited by - on

dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 05/30/2007 : 18:08:20

My personal rule of thumb while cruising with my 2 stroke, 8hp Merc is a gallon an hour, but actual fuel economy is probably closer to 3/4 gallons per hour.

Edited by - on

delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Response Posted - 05/30/2007 : 18:32:18

So it sounds like maybe my engine was doing well at 1gph. I still like the idea of a reserve somewhere, I hate the thought of running out of gas in a situation like that, very scary.

Edited by - on

Ben - FL
Admiral

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880 Posts

Response Posted - 05/30/2007 : 19:45:58

I have a six gallon fuel tank and keep a six gallon jerry can just in front of the board ladder on my C-250. The good thing about a sail boat is if you run out of gas just put some canvas up and you'll get there sooner or later.

Edited by - on

ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 05/30/2007 : 21:05:36

With my Honda 'Classic 8', about 2/3 throttle gives me 'near hull speed' (5.5 to 5.7 kts) and burns approx 2/3 of a gallon per hour. Putting more twist on the throttle gives a couple more tenths, squats the stern, and makes a lot more noise and vibration. I can't tell you what fuel consumption is in that mode as I don't run there very often or long.

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atgep
Master Marine Consultant

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1009 Posts

Response Posted - 05/30/2007 : 23:47:43

My Nissan gives me .5 gph at half throttle 4000 rpm. That is usually my setting unless I have some urgency. At full throttle I burn .9 gph at 4950 rpm. I always plan for 1 gph and have never come up short. I have the low pitch 3 blade prop BTW. Your figures are about right.

Edited by - on

JimB517
Past Commodore

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USA
3285 Posts

Response Posted - 05/31/2007 : 08:50:03

I figure about 3/4 gallon per hour for my Tohatsu 9.8 4 stroke. With the main up and even a little wind assist, I get between 10 and 20 nautical mpg.

I have a 7 gallon main tank and a 3 gallon emergency reserve spare tank. I keep the spare on the floor of the lazerette.

You did real good going into those winds and waves!

Edited by - on

Arlyn Stewart
Master Marine Consultant

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USA
2980 Posts

Response Posted - 05/31/2007 : 10:40:21

I've used two different motors on my 250 w/b. The first was a Honda Classic 8 hp four stroke ls and it yielded 2.25 hrs per gal @ 5 kts.

The second is the current Honda 8 4 stroke xls high thrust and it produces 1.6 hrs per gal, again at 5 kts.

Except for not having an extra long shaft, the Honda 8 Classic was the better motor and as far as I know, they had to reintroduce them by demand and they can still be had new if asked for... though they don't advertise them.

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 05/31/2007 : 10:56:43

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Arlyn Stewart
 Except for not having an extra long shaft, the Honda 8 Classic was the better motor...<hr height="1" noshade id="quote"></blockquote id="quote">
That's a big "except"!

I had the same high-thrust Honda 8 Arlyn has, on a C-25 FK. A little over half throttle (who knows exactly) gave me a between 5 and 5.5 knots burning about 2/3 gallon per hour. More throttle was pretty useless--just more noise as the stern squatted.

When going any significant distance, I carried 6 gal. and 3 gal. tanks--the three by the transom. That'll take me farther than I ever go in a day. The ethanol issues suggest to me not leaving the same gas in the spare tank all season. One way or the other, manufacturers and mechanics are saying to stabilize all of your fuel these days, especially for 4-strokes.

Edited by - Dave Bristle on 05/31/2007 11:01:50

Chris Z
Captain

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452 Posts

Response Posted - 05/31/2007 : 13:46:26

I would like to be able to give my usage on my 25, however it has not been in the water yet. still finishing up some things before it goes in. I can however offer some differences to think about. My 16 foot fishing boat had a old evinrude 2 cycle that would usually burn about a 6 gal plus on a typical day of trolling and motoring around. I changed a while back to a new mercury 4 stroke. The dealer gave me a 3 gallon tank stating that I should burn about half of what I did prior. Well over the past three years I can say he was wrong, it seems to burn less then half.

Also, anothe side note, the 4 strokes provide more torque then a 2 cycle. This means that under a load, it can maintain more trust.

Got to love not mixing the gas, no oil smell and how much quieter the four strokes are in comparison.

I wouldn't own another 2 cycle ever again.

Edited by - on

tinob
Master Marine Consultant

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USA
1883 Posts

Response Posted - 05/31/2007 : 13:55:27

Hope I remember this acurately,I don't write things down, but when my Nissan 9.8 was new and not broken in fully, I did a run out and back of ??I think 7 nautical miles miles. and burned 63 ounces of gas. The fuel usage was quite acurate, having filled the tank right to the opening and then upon returning measured gas used with a graduated beaker to refill the tank to the same point and it used 63 ounces. I remember NOT remembering the time it took to run the test.

. Probably because I was impressed with the distance that I had run and the amount of gas that the then new motor used to do it, while memory of the old Johnson sailmaster was fresh in my mind.

Admittedly not an acurate statement, but when considering the variables, it was still impressive.

Val on Calista, #3936, Patchogue, N.Y.

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 05/31/2007 : 18:18:51

Val, that's a pretty remarkable number--almost double the mileage of my Honda, and more than double Jim B's identical Tohatsu. Exactly what are you putting into that fuel tank

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JJM
Navigator

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USA
170 Posts

Response Posted - 05/31/2007 : 18:53:10

I remember when I first got my boat and we moved it from Marina Del Rey up to Channel Islands Harbor. Left MDR at the crack of dawn (5 AM...) with lots of coffee and motored up the Pacific coast. The engine, a Honda XLS 4-stroke, was new at the time. The motor was pushing the boat at 5.5 kts and I remember having to refill the 3 gallon tank at a bit after noon. So we went about 7 hours on 3 gals of gas. I thought that was pretty impressive, especially since the wind picked up in the mid morning, and we were heading into it pretty much the whole way.

Edited by - JJM on 05/31/2007 18:54:13

JimB517
Past Commodore

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USA
3285 Posts

Response Posted - 05/31/2007 : 19:12:27

It is so hard to say because of winds and currents. 10 mpg would be 1/2 gallon per hour. I've done about 25 mpg coming down wind, down swell, down current in calm conditions at 5 knots. 5 miles per gallon in the reverse direction with big seas. It gets worse if you need to push it up to 6 knots. Much worse.

I think the seamanship estimate of 3/4 to 1 gallon per hour gives you an excellent reserve capacity.

I carry 10 gallons for a planned 100 mile trip, knowing I'll be sailing much of it.

Edited by - on

Bubba
Admiral

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USA
542 Posts

Response Posted - 05/31/2007 : 20:17:32

I'll chime in with the same 3/4 to 1 gph with my 8 hp 2-stroke.

I have two identical 3 gal. tanks. The spare sits under the lazerette on my 250. When the one being used is empty, I switch tanks. Having the second tank complete with fuel line fitting made for a very quick switch the one time (so far) I was caught by surprise.

The empty gets refilled and stowed until the other tank is empty. That way the fuel doesn't get very old.

Edited by - on

Champipple
Master Marine Consultant

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USA
6855 Posts

Response Posted - 05/31/2007 : 20:33:13

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by dlucier
 My personal rule of thumb while cruising with my 2 stroke, 8hp Merc is a gallon an hour, but actual fuel economy is probably closer to 3/4 gallons per hour.
<hr height="1" noshade id="quote"></blockquote id="quote">

I would agree with this

Edited by - on

Oscar
Master Marine Consultant

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USA
2030 Posts

Response Posted - 05/31/2007 : 20:39:38

There is one thing that needs pointing out here. Fuel consumption vs speed is NOT a linear relationship. I can give you some numbers for illustration, they are for Lady Kay's 44hp Yanmar diesel....(and they are severely rounded.....) Note that hull speed is approx. 8.2 knots.

2200 rpm 5 knots .5 gph
2700 rpm 6.5 knots .75 gph
3100 rpm 7.5 knots 1 gph.
3500 rpm 8 knots who knows....haven't done it long enough to measure consumption...

So you can see that an increase in speed of 50% DOUBLES consumption.
Thus it follows that if you somehwat accurately want to compare engines, you need to motor the same hulls at the same speed.....

Food for thought.

FWIW, I put the 6 gallon tank on our 250, and had a small (2.5) gallon spare can below for longer cruises. I usually motored at 5 or so knots and figured .75gph on the Honda 9.9
Pushing it up to 6 (near hull speed) would increase it to 1gph+

Edited by - on

ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 05/31/2007 : 22:42:31

>"Except for not having an extra long shaft, the Honda 8 Classic was the better motor..."

The Honda Classic 8 was available in XL shaft length... at least back in '94 when I bought mine.
Dunno if they offer the XL shaft in that model anymore.

Edited by - on

Champipple
Master Marine Consultant

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USA
6855 Posts

Response Posted - 06/01/2007 : 06:50:47

Or you can just bring qty 4 five gallon gerry cans along and not worry.

With the exception of being in a marina or no wake zone we had 2 different modes for our outboard. 3/4's of max throttle or off.

We very rarely paid attention to our gas consumption away from the dock because we very rarely went anywhere where a gas station wasn't within 2 hours at any given time and if we did we brought 15 gallons. Generally thought when we did have reason to pay attention at 3 quarters throttle (no idea of the RPM's) we would eat up all but a quarter tank (3 gallon tank) in 3 hours...or about 3/4 gallon per hour.

Edited by - on

britinusa
Web Editor

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USA
5404 Posts

Response Posted - 06/01/2007 : 07:18:10

You can dramatically reduce fuel consumption by leaving the fuel tank vent screw tightened down(closed). After a while, fuel consumtption stops completely!

We were in the middle of returning down the channel into John Pennekamp State park when the engine stopped: flipped up the fuel locker lid, plenty of gas, squeezed the bubble.. ah haa! .. opened the vent screw, squeezed fuel into the line, press the button and we were back in business. Phew!

We normally carry 3 fresh gallons in the in use tank, and another 5 gal in a jerry can. I use the left over fuel in our trucks between trips so that each trip has fresh fuel.

Paul

Edited by - on

aeckhart
Master Marine Consultant

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USA
1709 Posts

Response Posted - 06/01/2007 : 07:43:46

I've never really caluculated this to any degree of accuracy but I believe I once estimated that my 88' Evinrude Saildrive made 6 miles on a gallon of gas at about 5 knots in a flat calm. Frankly I wasn't impressed so when cruising I carry a 12 gallon tank strapped between the seats under the tiller and a 6 gallon tank in the fuel locker. This is enough fuel, with a good reserve, to get me to any port of refuge in Michigan, Wisconsin, or Minnesota, in most sea conditions. Ports of refuge are usually 20-30 miles apart. I have an additonal 6 gallon tank if crossing the Lake to Canada, which has far fewer places to fuel up.

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zeil
Master Marine Consultant

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Canada
1314 Posts

Response Posted - 06/01/2007 : 10:59:01

Last week during two occasions we used with our 8 hp Honda a little less than half (about 8 ltr) of a 3 gallon (12 ltr) tank during 4 hours of continues, a little above half trottle, canal cruising.

The fuel was purchased on the road (not marina gas) and was high octane. We carry one 3 gallon and 3 2.5 gallon (10 ltr) tanks for a total of 10.5 gallon (42 ltr) to be suffcient for about 20 hours total. Valve adjustment seems to make a huge difference...

At the beginning of our 400 km Trent/Severn Canal trip we had the motor serviced, oil changed and valves adjusted. After about 90 miles (130 km) of motoring the oil is still the color of honey. Is it the valve adjustment that seems to make the difference...??

The Honda mechanic told us at that time to:
1) use 10W40 instead of the recommended 30 and... before filling the engine with oil shake,
2)shake and shake some more to make sure no lubricants and additives stay behind in the can...
He insists that shaking the can will add thousands of hours to the service of the motor.

Edited by - on

dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 06/01/2007 : 11:16:50

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by zeil
 Last week during two occasions we used with our 8 hp Honda a little less than half (about 8 ltr) of a 3 gallon (12 ltr) tank during 4 hours of continues, a little above half trottle, canal cruising.<hr height="1" noshade id="quote"></blockquote id="quote">

If my math word problem skills aren't too rusty, that's approximately 1/3 gallons per hour...impressive!

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tinob
Master Marine Consultant

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USA
1883 Posts

Response Posted - 06/01/2007 : 12:05:12

Think I'll redo the initial test of the Nissan mentioned up top soon and see if it stands. This time I'll watch the WATCH for a time element inclusion. The one change is to the prop(POWER PROP. It is a pitch lower than the prop that came with the engine, and the one in use for the original test run. I felt little difference in the two props performance mainly because I never run any thing at max rpms. So theoretically the lower pitch prop will have my motor max at a lower speed, but not usually running wide open I wouldn't know.

If this keeps up I might become one of those writer downers

...EGAD or better yet DAGNABIT

Val on Calista,# 3936, Patchogue, N.Y.

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Arlyn Stewart
Master Marine Consultant

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USA
2980 Posts

Response Posted - 06/01/2007 : 12:40:59

Clam...You're right, the Honda 8 Classic was available for a while in XLS but not many knew it. My dealer didn't know it. I didn't know until after I bought a 2001 to replace the Classic and obtain an XLS. The web site never listed the XLS Classic 8. There aren't a great many of the XLS out there.

When they reintroduced the Honda 8 Classic, they did not reintroduce the XLS. I called and talked to a lady at Honda Atlanta marketing and asked why not reintroduce the XLS as well and she said there was very little demand for it as almost everyone who wanted XLS wanted an electric start and 9.9 hp.

Heck...I would gladly have given up electric start to save the back breaking thirty extra pounds of the later model but I'm greatly in the minority obviously.

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