Diesel used per hour

Rick486 · Aug 9, 2015

Same boat, same engine, 8th year. Mine uses about 1 gal/hr running 2300-2400 RPM.

ice breaker · Aug 9, 2015

My Yanmar 4JH3E, 56hp uses 1.25 gal per hr at 2600

Stu Jackson · Aug 9, 2015

Good to ask advice. Good to start out with an estimate. Good to check your consumption. Good to not trust a fuel gauge. Better yet to start your own fuel consumption log, since only YOUR boat, YOUR use and YOUR hand on the throttle will determine what YOUR boat consumes. Good luck. It takes a while, but you get to use the boat!

Benny17441 · Aug 9, 2015

The fact that you painted the bottom has nothing to do with the engine's burn rate. The formula used is gallons per hour or in your case liters per hour. There is no speed or distance components in the calculations. Your engine should burn approximately 1 gallon or 3.785L per hour. If you are getting 2.2L it seems there is something afoul in the measurements or calculations. Check your hour meter against a good watch or chronometer.

JamesG161 · Aug 9, 2015

About 85% of your diesel consumption is due to the weight of your boat and contents. The other 15% will be currents and wind resistance opposing your course and engine efficiency (by engine designer).

Most small inboard diesel engines are designed for a maximum RPM of 3000 and have a "sweet spot" at about 60%-70& of max (SOG max with min Diesel consumption).

I think one of the safety items on your boat is a reasonable fuel tank gauge, but just like a PFD, it is not the only thing that can assure your safety on your boat.

Start your cruise with a full tank and then estimate your consumption for the trip by your last trip's consumption.

These are facts...

1) Horsepower (Hp) used is directly related to fuel consumption. ( not hours or distance )
2) RPM and Hp will plot almost a straight line. Thus if you have a 40Hp 3000 rpm engine, running at 1500 rpm with be 20 Hp used.
3) Using hours just gives you a best guess time between fuel stops.
4) Keep 5 gallon of spare diesel on board since all of tips by others are estimates.

Fair winds and seas to minimize diesel use...
Jim...

PS: I calibrate my fuel gauge each time I refuel. Gauge reading for each 5 gallons of diesel in your fuel log. The data should be close each time you refuel. That is the reason my Fuel gauge works.

Don Lucas · Aug 9, 2015

I've tracked my fuel use for 4 year now and find if I motor at 5 knots I use about 0.5-gph. If I motor at 6 knots it works out to about 0.65-gph.

So my experience matches the OP for the same engine and pretty much the same size.

Johnb · Aug 9, 2015

I don't believe you can figure out consumption from just one 6 hour run. You need to keep a log over many refills to draw a conclusion. That said, the numbers given above, 0.5 gal per hour at low speed to 1+ gal per hour motoring hard ring true.

My average for 12 years (2000 hours) is 0.65 for a 30 H.P.

The tank level is useful information but frequently goes up after the fuel has sloshed around a bit. Also the tank is a complex shape so 1/32 near full is more than 1/32 near empty.

Schatzi · Aug 12, 2015

I have monitored mine over the last 4 years.
2003 H44AC Yanmar #4JH3E
Fuel usage has been between .66 and .98 gal/hr.

Benny17441 · Aug 12, 2015

For those that are getting readings over a wide margin approximating 1/2 a gallon per hour I would strongly suggest you use the higher reading for your calculations as anything less might leave you stranded. Also do not forget that not all fuel in the tank is usable so leave yourself a sensible reserve of around 15% of your tankage or more in upset seas. Gentlemen, the burn rate calculations will not be exact and do not have to be; they just have to be good enough. I drive my boat in similar fashion on every outing and I use an average calculated figure which consists of time idling, moving at slow speed and running at high RPM. Over time I have found out that my average burn rate is quite consistent at around .43 gph for the 2GM20F. I can consistently take on 25 gallons of fuel and be within + or - 1/4 to 1/2 gallon of my estimated total need. I allow myself a 3 to 4 gallon reserve depending on the condition of the seas. I know that my margin of error of 1/2 gph will be covered by the reserve. Since speed and distance are on a different formula there is no guarantee of the range you will get for your burn rate and tankage. This is where the condition of the hull, wind and currents become significant variables. I carry extra cans of fuel on some crossings not because I do not trust my burn rate calculations but because I do not know how long the crossing is going to take. Range is calculated on the water based on actual conditions and if you ever come into calculations that the fuel you have on board is not going to be enough to reach your destination then you better shut that engine down and sail to conserve fuel for your approach or you may seek a closer alternative destination. There is no big science behind these calculations, yes they are just a good enough approximation and they work. I have not found a fuel tank gauge that gives me the peace of mind of approximating how much fuel I have left. Keep doing your calculations every time you fill up dividing the amount of fuel taken in by the number of hours you ran the engine and keep upgrading that average burn rate.

ice breaker · Aug 12, 2015

I believe that this discussion is getting a bit wrong. Speed is irrelevant in determining GPH, as we have tides, wind etc. Suggesting that a certain motor burns X GPH is not a data point with out the RPM that the boat is run at.

For a particular boat configuration( prop, motor size, etc), The only thing that maters for fuel consumption is RPM, as RPM is the proxie for Horse Power. If you run at High RPM, you will burn more GPH because you are producing more HP. If you gooogle Yanmar, you can find fuel/HP/GPH curves. They are not linear. HP is never free. So run low RPM and burn fewer GPH's or red line it and burn exponentially more fuel.

Sorry if this sounds gruff......not meant to be.

Stu Jackson · Aug 12, 2015

ice breaker said:
I believe that this discussion is getting a bit wrong. Speed is irrelevant in determining GPH, as we have tides, wind etc. Suggesting that a certain motor burns X GPH is not a data point with out the RPM that the boat is run at.

................

Sorry if this sounds gruff......not meant to be.

Not gruff at all. You are absolutely correct.

However, in the real world, Benny's analysis is correct. What you NEED to know is what the average use is, which is based on varying RPMs over time. That's all that matters for this purpose. All of YOUR particular cruising/sailing/motoring, OVER TIME, will use the same AVERAGE fuel in GPH. It's based on how you use YOUR boat.

I've been doing this for 17 years:

http://c34.org/bbs/index.php/topic,3841.0.html

Benny17441 said:
I can consistently take on 25 gallons of fuel and be within + or - 1/4 to 1/2 gallon of my estimated total need.

Me, too.

If you want to figure your range, then when you're planning a cruise, figure the constraints upon your forward movement then, and when you know how much time it will take, you know your range.

JamesG161 · Aug 12, 2015

I carry extra cans of fuel on some crossings not because I do not trust my burn rate calculations but because I do not know how long the crossing is going to take

Aye Aye Captain Benny17441! I would sail as crew anytime with you.

Time and Distance calculations are estimates, because of too many unknowns.

I repeat... Only Horsepower Used determines fuel consumption. Period. RMP up HP up.

I am still amazed at sailors and their fuel gauges. My car works great! I use it all the time.

I just recently replaced my level transmitter with its modern day exact version.
http://www.wemausa.com/sensors/level-FuelWater.shtml#.VcvvLXjTQo8
It cost me <$50. I also downloaded my exact fuel tank design from Hunter's website.

The SSS/SSL is 220mm long and reads in 13mm increments. That similar to a foot long ruler reading marked only by 3/4" marks only. No way to read 1/4th inch so you MUST work with that precision.

Shown in my picture is a rough drawing of my 50 gallon tank. Note how I use it, but it still works when checked on each fill and verified by fuel logging.

Your fuel gauge is as much a SAFETY device as a PFD. Get yours working and develop confidence in it telling you information.

This simple pictogram of my tank..
1) Green rod is my sensor ( note that it not on bottom )
2) It is not linear with tank percentage. LOL neither is the tank shape.
3) My 50 gallon tank is really 40 and 5 gallons is kept separately to compensate for Time/Distance variations.
4) Saba is my boat name

, not a scientific term.
5) This is posted near my gauge.

It doesn't take much effort to do the same calibration and service your fuel gauge.
Jim...

Benny17441 · Aug 13, 2015

James, I do not have a horsepower meter on my instruments nor the desire to keep track of the length of time I ran at a particular RPM figure. I do question the accuracy of my tachometer. The use of an average for the burn rate is a simple, effective and proven method to calculate fuel consumption . I agree it is an estimate but it is also good enough for the desired purpose. A car is different as the wheels are mechanically engaged to the road and as wheel revolutions are counted it yields a pretty accurate MPG figures. Now days car computer gives you an update anticipated range in miles. Water is a fluid surface and a different method is needed to calculate fuel consumption. I have a fuel gauge and use it in my home area to tell at a glance if I have fuel or not but when doing a crossing to the Bahamas I do my calculations based on the hour meter and a proven burn rate for my engine and my use of the boat. You are correct in your assertions and I'm glad the method you have chosen works for you but understand that a fuel tank gauge is not the most exact instruments in a rolling and pitching boat. There should be no need to carry a 5 gallon can of fuel on every outing. I do my trip planning a week in advance but only calculate range on the day of the first leg and based on actual conditions. These calculations are updated every couple of hours as I move through the track line. Any adverse changes are dealt with while I still have a reasonable amount of fuel in the tank with no surprises.
I do appreciate your vote of confidence and will guarantee that I would get you to your destination without accidentally running out of fuel. Fair winds and let's be glad we drive the most perfect hybrid powered machine.

JamesG161 · Aug 13, 2015

Captain Gunni....

The use of an average for the burn rate is a simple, effective and proven method to calculate fuel consumption .

PERFECT!!

A tach is a simple and easily fixed/added sensor. My engine habits are so repeatable, using the estimated value, standard RPM and of course fuel tank gauge, I have never been off by more than 10%. Therefore, I keep 10% spare on board.

In harbor ~1000rpm no WAKE. ( 17 hp and normally about 30 min in and out)

At sea 2000rpm (34 hp for the vast majority of the time 98%)

I don't worry about a RPM log, but habit. By your time average you are essentially doing the same thing (like me).

My key point is all using all of the above works and each verifies the other.
Thus...

Reliability ==> Safety

Bahama crewing

hmmmmm?
Jim....

PS:There is no need for 4 PFD's on board with a 3 man crew. Or is there? Take some extra fuel as back up.

Rob38 · Sep 15, 2015

Nice discussion. Some of us have generators on board that use fuel from the same tank supplying the engine. I usually don't think much about fuel for the genset but this thread has inspired me to get a handle on its consumption. I'd guess for average electric loads while it's running at anchor (house bttery full charge, air conditioner, hot water, watching a movie etc.) we're in the 1/4 to 1/2 gallon per hour range.

mz4wheeler · Sep 15, 2015

ice breaker said:
I believe that this discussion is getting a bit wrong. Speed is irrelevant in determining GPH, as we have tides, wind etc. Suggesting that a certain motor burns X GPH is not a data point with out the RPM that the boat is run at.

For a particular boat configuration( prop, motor size, etc), The only thing that maters for fuel consumption is RPM, as RPM is the proxie for Horse Power. If you run at High RPM, you will burn more GPH because you are producing more HP. If you gooogle Yanmar, you can find fuel/HP/GPH curves. They are not linear. HP is never free. So run low RPM and burn fewer GPH's or red line it and burn exponentially more fuel.

Sorry if this sounds gruff......not meant to be.

Sorry, I disagree. I think a dirty bottom ABSOLUTELY affects your gallons per hour. Why?

Most of us have a certain sweet spot that we run our engine. In my case, I like 2600 RPM. So, the only thing that is static is RPM. If you have a dirty bottom, you *WILL* have extra drag, which your engine WILL feel. For instance:

1) Clean bottom, 2600 RPM, 6 knots, throttle POSITION is at 55%, GPH=.50
2) Dirty bottom, 2600 RPM, 5.0 knots, throttle POSITION is now at 65%, GPH=.65

[The above is just an exaggerated example]

Why? Because we always set RPM to be 2600 RPM, or whatever you use.

Your THROTTLE POSITION will vary based on how much DRAG your boat is creating on the engine and WILL change your GPH calculations (and speed).

Diesel used per hour

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SBO Weather and Forecasting Forum Jim & John

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SBO Weather and Forecasting Forum Jim & John

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SBO Weather and Forecasting Forum Jim & John

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