# Fuel consumption question



## tireman (Apr 3, 2011)

Just bought a new Jeanneau 42DS with a 54 hp yanmar. I'm trying to get an idea of fuel rate consumption at different power settings so I can guage my range for trip to home port (plan to motor quite a bit as time is a problem). Boat holds 63 U.S. gallons. I've tried yanmar website and I've been through the Yanmar engine manual but no clues as to what I can expect. Can anybody point me to a source for this information or give me even an estimate of this engines range.


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## kd3pc (Oct 19, 2006)

I have an older hunter similar in size to your J, with the Yanmar 4JH2 57-65hp depending on who you like.

I use a gallon an hour for budgeting fuel, actual use is closer to .6 gal per hour as I use 2200-2400 rpm for most motoring, as you near top rpm, 3000 in my case...it approaches the 1 gal per hour.

Enjoy your new boat, they are excellent, I had an '84 jeanneau and loved her most of any boat since.


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## tireman (Apr 3, 2011)

*This forum is great*

Thats the first time I've ever posted to a forum and within 5 minutes I get a good answer. Thanks


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## Minnewaska (Feb 21, 2010)

I find the last knot of boat speed will increase fuel burn by 25%-50%. Said differently, you can substantially extend range by pulling back a little on the throttle. To get these precise burn rates, I suggest a real life test. Fill the tanks and go cruising at a standard power setting. Top them off and do the math.

To be accurate, this takes many hours of cruising. Not sure how far your delivery will be, but it could be done on an early leg or two that are well within safe estimates.


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## sck5 (Aug 20, 2007)

it also depends a lot on sea state. and if you can get any help at all from your sails it will make a big difference. Keep the main up if you can.


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## rbarkas (Dec 25, 2001)

We've put 250 hours on a 42I performance model with the same engine as your 42DS since October. Our overall consumption has been 0.82 gallons per hour.

We run our engine (after the breakin period) mostly at 2000 RPM and get about 7 knots from the boat. I can run it at 2400 and get between 8 and 8.3 knots depending on Sea State. The fuel consumption really goes up and the fuel cost to get more than 7 knots is pretty steep. Not only that but engine noise and vibration go up over 2000 rpm too.

Your speeds may vary due to the prop on your boat - we have a MaxProp classic 3 blade on ours.

We've motored far more than we wanted to in the first 6 months we've had the boat as we've done quite a bit of coastal cruising (circumnavigating Tasmania) where for some reason the weather gods haven't smiled on us (either 30 knots right on the nose or 4 knots up the stern).

I was pleasantly surprised at the low fuel consumption. Yanmars fuel graph indicated that we should expect to use quite a bit more fuel than this.

The engine has been 100% reliable, with low noise and vibration. The engine compartment exhaust blower is sometimes the most objectionable noise on our boat.

I agree with what Minnewaska said - gather your own data and understand that the fuel consumption / speed curve gets pretty steep toward the top end.


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## dhays (Jul 9, 2010)

I have a Catalina 400 with a Yanmar 4JH4E engine which supposedly produced a max 54hp at 3000 rpm. Actual fuel consumption will depend on hull, transmission, prop, auxiliary equipment, wind, and sea state. 

I've not used mine enough yet to get a good feel for fuel consumption. However, Catalina lists fuel consumption to be 1.25 gph at 2800 rpm. Looking at the fuel consumption graph from Yanmar, it appears that fuel consumption at cruising rpms of 2400 to 2500 would be closer to about .8 gph.

As always, YMMV.

Dave


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## tireman (Apr 3, 2011)

*Fuel Graph?*

Where's this fuel graph you're all talking about? That's what I've been looking for. Not on website and can't find it in Yanmar engine manual that came with boat.


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## CaptainForce (Jan 1, 2006)

I have 5,175hrs on my Yanmar 4JH3E and I typically push my 26,000lb Morgan at 6.5kts running at 2500rpm with a 3-blade 18x13 prop at .9gph.


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## rbarkas (Dec 25, 2001)

Here you go - found near the bottom of the brochure that the URL takes you to.










YANMAR Diesel Power - JH3/JH4 Series Marine Engine


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## JohnRPollard (Mar 26, 2007)

Not sure exactly which model you have, but here's another spec sheet with fuel curves for a 53 hp Yanmar: Yanmar 4JH5E

Lots of variables, so best to observe closely and figure out what your boat uses over time. But given some of the feedback here, it sounds like you could conservatively figure on about 500 n.m. for range under power at about 7 knots, with a little reserve. But keep an eye on the fuel gauge!!

P.S. Welcome to Sailnet


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## SlowButSteady (Feb 17, 2010)

rbarkas said:


> Here you go - found near the bottom of the brochure that the URL takes you to.
> 
> 
> 
> ...


Note that the x-axis doesn't originate at zero here. This makes the chart a bit deceptive, at first glance anyway. But, if one compares the fuel consumption at 2000 rpm (a bit less than 4 liters/hour), and 3000 rpm (a bit less than 12 liters/hour), it's obvious that the last third to half of the available throttle just about triples fuel consumption. I get a similar result with my 2GM20, albeit on a much smaller boat. At 2000 rpm I can do about 75% of hull speed; while at about 3000 rpm I'm just about at hull speed.


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## dhays (Jul 9, 2010)

SlowButSteady said:


> But, if one compares the fuel consumption at 2000 rpm (a bit less than 4 liters/hour), and 3000 rpm (a bit less than 12 liters/hour), it's obvious that the last third to half of the available throttle just about triples fuel consumption.


I think the it is the shape of the graph that is important, as Slow noted above. Most of the folks who own boats of similar size to mine are getting around 1gph consumption give or take. Catalina says 1.25 gph at 2800 rpm. Yanmar's graph would indicate twice that. So the importance of the graph isn't the absolute values but the relationship between speed and fuel consumption. Just by eyeballing the graph 2400rpm looks like where the speed/efficiency slope starts to get steeper.

Dave


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## JohnRPollard (Mar 26, 2007)

SlowButSteady said:


> Note that the x-axis doesn't originate at zero here. This makes the chart a bit deceptive...


SBS,

I see your point, but I think the reason it starts at 1K rpm is because that is idle speed (+/-), below which the engine would not be consuming any fuel at all. With the engine shutdown, the the "curve" would plummet at that point. 



SlowButSteady said:


> ... But, if one compares the fuel consumption at 2000 rpm (a bit less than 4 liters/hour), and 3000 rpm (a bit less than 12 liters/hour), it's obvious that the last third to half of the available throttle just about triples fuel consumption. I get a similar result with my 2GM20, albeit on a much smaller boat. At 2000 rpm I can do about 75% of hull speed; while at about 3000 rpm I'm just about at hull speed.


This is a good discussion, even if it's getting more general than the o.p.'s specific question about the range of his boat. Our results with the 3GM30F are similar to SBS. Usually, the objective is to find the best balance between fuel consumption and boat speed to yield greatest range, in a reasonable time period and without running the engine too slowly.

When looking at these engine characteristics, I like to study the Betamarine performance graphs. The characteristics are similar, but I think Beta (marinized Kubota engines) does a better job than Yanmar in overlaying the curves onto one graph, so you can see more easily the trade-offs between fuel consumption and power output. Here's an example for the Beta 50 hp model:

EDIT: Sorry guys, I tried to insert the image but it came out super-sized. Follow the link instead:

Beta 50 HP


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## rbarkas (Dec 25, 2001)

Cost per mile goes up quite dramatically on our boat with the same Yanmar engine while speed doesn't rise nearly as quickly. (speeds are approximate, depend on sea state, phase of moon, etc). I am pretty confident about the 2000 rpm fuel burn because I've measured it. The other burn rates are based on the graph and my knowledge of approx boat speed for different RPM's)


RPMGPHHours to burn 25GSpeed (Kts)Distance (NM)




18000.634396.224420001.003257.017424001.585168.112826001.981138.3105


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## SlowButSteady (Feb 17, 2010)

JohnRPollard said:


> SBS,
> 
> I see your point, but I think the reason it starts at 1K rpm is because that is idle speed (+/-), below which the engine would not be consuming any fuel at all. With the engine shutdown, the the "curve" would plummet at that point.


Actually, idle speed should be about 850, so the curve itself should begin there. However, it is always best (if at all possible) to include the origin (0,0) on an x-y plot. I realize that this is rarely done when data are presented for general consumption, but it is still the least biased presentation. (And, that's the way my Statistics students damned-well better present their data.  )


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