Yanmar Fuel "hourage"

[Tom Boles]

Subject to survey, I am about to purchase a 1999 Hunter 380 with an original equipment Yanmar 36HP engine. It has seemingly been very well maintained.
My previous sailboats have had Universal 18's. I will have to get it home on the Intercoastal, about 90 miles away. What can I expect from a hours-per-gallon basis at a 6-7 knot speed with this engine.

If anyone would know it would be this group.

Thank you

T

[Mr Fox]

My experience with my yanmar 3gm is that it burns about 0.5gph at 2700 and 1gph at about 3100. My boat has a 21.5 foot length at waterline, and 2700 gets me 6kts, opening it up gets me about 6.5kts.

Since I don’t have a hunter 380 I am not sure what your rpms would be at your desired speed, sorry if I am obfuscating things; hopefully someone with a 380 and the same motor will reply with a more precise answer for you. If not I hope this gets you a ballpark to start with.

[sailorboy1]

My 4jh3e 54HP uses about 0.65gph at about 1600 rpm (5 knots in calm conditions) and 0.8gph at 2000-2200 rpm (6-6.5 knots in calm conditions).

[tkeithlu]

Tom, take a look at this web site,

https://www.boatingmag.com/calculati...l-consumption/

which gives you a formula for computing your burn, at least as well to not run out of fuel. By this formula, if you are developing a full 36HP, which is not likely under ICW conditions:

GPH = 0.4 x HP/7.2 = 0.4 x 36/7.2 = 2 GPH

0.4 = finagle factor for a diesel engine
7.2 = pounds per gallon for diesel fuel

Another approach to this issue is to know the limits of efficiency for traveling under power. First, calculate your hull speed, the fastest you can go without "plowing" up your bow wave:

Hull speed in knots = 1.34 X square root of length waterline in feet

or for 36' = 8.04 knots, 38' = 8.26 knots.

Then, do an experiment. Measure your speed in knots at increasing RPMs. You will see a point somewhere around your hull speed in which adding RPM doesn't add much speed, and your bow may slightly rise. Now you've got you maximum efficent cruising speed/RPM.

Have fun getting to know these details of your new boat. You'll find the knowledge useful.

[Group9]

Originally Posted by sailorboy1

My 4jh3e 54HP uses about 0.65gph at about 1600 rpm (5 knots in calm conditions) and 0.8gph at 2000-2200 rpm (6-6.5 knots in calm conditions).

Pretty close to what our 4JHBE did (we actually burned a little more fuel) on a 42 Catalina.

[Lnewman]

I own a 1994 Ericson 380 with a 2012 Yanmar 3JH5E 38 hp three cylinder diesel. Boat has an Autoprop. My boat has a 55 gallon fuel tank. My engine burns about .87 gallons per hour when I cruise at about 6 knots, which is at around 2000 - 2200 RPM.
So if I do my math right I figure I have a range of ~379 or so miles per tank.

Most sailboats should have a range of at least 300 miles per tank. But I guess some boat builders might skimp on the fuel tank size.

[desodave]

My Hunter 38 with a 40hp 3jh4e burns between 0.6 and 0.7 us gph mostly running at a 2700rpm cruising speed. The variance is based largely on how clean the bottom is but also includes a little diesel heater (espar) usage early and late in the season.

[redsky49]

Originally Posted by tkeithlu

Tom, take a look at this web site,

https://www.boatingmag.com/calculati...l-consumption/

which gives you a formula for computing your burn, at least as well to not run out of fuel. By this formula, if you are developing a full 36HP, which is not likely under ICW conditions:

GPH = 0.4 x HP/7.2 = 0.4 x 36/7.2 = 2 GPH

0.4 = finagle factor for a diesel engine
7.2 = pounds per gallon for diesel fuel

Another approach to this issue is to know the limits of efficiency for traveling under power. First, calculate your hull speed, the fastest you can go without "plowing" up your bow wave:

Hull speed in knots = 1.34 X square root of length waterline in feet

or for 36' = 8.04 knots, 38' = 8.26 knots.

Then, do an experiment. Measure your speed in knots at increasing RPMs. You will see a point somewhere around your hull speed in which adding RPM doesn't add much speed, and your bow may slightly rise. Now you've got you maximum efficent cruising speed/RPM.

Have fun getting to know these details of your new boat. You'll find the knowledge useful.

The waterline on the Hunter 380 is 33'. So the actual hull speed max works out to 7.58. This will only be obtained at maximum rpm assuming that propeller/pitch is in the correct ball park, and sea state is not an issue. I would posit that a reasonable cruising speed would be in the 6.5 knot (or less) range, likely consuming (for planning purposes) approximately 1 gallon per hour. Six knots might be a good compromise on speed/economy.

Clean prop and bottom, as well as loaded weight, also important to fuel discussions. This could easily cause a 1/2 to 1 knot per hour penalty.

Do a quick test during sea trial to determine speeds at various rpm settings and extrapolate from that data.

[tilostahl]

On a Jeanneau 37 with a Yanmar GM3 I use 0.5 gal per hour at about 5+ knots and about 2700 rpm. Note: don't trust the fuel gage until you've checked it by running it down to half full and then refilling it.

[Scubaseas]

Lots of variables like wind, waves, growth on hull, etc. but if you use 1 gal/hour you should have some left in the tank after your 90 miles. 0.8gph would be my guess with efficient (fixed) prop, clean bottom and 2200ish RPM. Feathering and or other style prop may or not burn more fuel. The difference between 1800 rpm and 2400 rpm could be substantial in consumption. Good time to fill it, run it noting speed/rpm and fill it at the end of the trip so you will then know how much for those conditions. Sailboatdata shows you with a 30 gal tank.

[MicHughV]

...their are so many variables involved in determining this....it would be hard to say....
1) prop size, diameter and pitch...is the boat propped properly.
2) Hull configuration...ie, long keel, fin keel, etc...planing hull, displacement hull....etc..and is the hull clean or fouled.
3) Besides 1) above, is the prop two bladed, three bladed, maxprop or other feather style prop.
4) Are the fuel filters clean ? Dirty filters can cause lotsa fuel burn problems.
5) Is the engine running properly..ie, no smoke, etc..
6) Getting back to the prop...is it clean, fouled, partly fouled, etc...
7) At what speed do you plan to run....most diesel manufactures can provide you with a spec sheet detailing optimum rpm and fuel consumption.
8) Older boats may have an accumulation of slime/sludge in the tank, and it's a worthwhile exercise to have your tanks cleaned by a pro. Nothing worse, than having your engine stop working due to contaminated fuel
9) While I'm at it. Your #1 protection against bad fuel, is a good Raycor fuel filter with clear bowl so you can visually inspect the fuel. Even better is to attach a vacuum gauge to the filter. A vacuum gauge will tell you right away if there is a problem with the fuel or filter.

Having owned 3 sailboats I can tell you that to run at " hull speed" requires a BIG diesel. At " hull speed" you are basically trying to push the hull over the bow wave.

Your average 38' sailboat probably has a " hull speed" approaching 8 knots.
I doubt very much that a 36 hp Diesel on a 38' sailboat can do that.
Don't confuse max. hp with cruising hp....at cruising rpm' your diesel may only provide around 21 hp......so factor in a " cruising " speed of 5-6 knots.
Most marine diesels will run about 3,000 rpm wide open. A good check is to run your boat at max. operating rpm for a short burst to see, if indeed, you can get the diesel to that rpm. If you can only attain, say, 2,700-2,800 rpm, that will tell you your prop is fouled, the hull is fouled, the prop is not pitched correctly, etc...
A 3,000 rpm diesel will likely have a cruising rpm of around 2,100-2,300 rpm.
At that rpm you can run all day long.
Diesels have different power ratings, too complicated to explain here.

But for you....Based on 35 years of sailing, I think a 0.5 gallon/hour is likely a good estimate for you. This is cruising up the ICW. If you are offshore and have to deal with waves, that will likely go up to 0.8 gal/hour.

There is nothing stopping you from bringing spare diesel aboard in 5 gallon jerry jugs...Always a good idea to filter this as you pump it in.

Hope this helps.....

[Tom Boles]

Thank you everyone for the great information. I am having as bottom job done just before leaving, which should help. The trip to my home base should be a good learning experience as I get to know this boat.

Tom

[Cheechako]

My guess is you wont be over 5/8 gallon per hour max. May be 1/2 gallon per hour.

[a64pilot]

I have a 33’ waterline length boat with a 40 HP Yanmar 4JHE
I get 6.5 kts at 1800 to 2000 RPM difference is wind and sea state.
I burn about 2/3 a gallon an hour.
I’m surprised when I see people running these things over 3000 RPM and aren’t going much if any faster.
I guess it’s the Autoprop?

[Lnewman]

Originally Posted by a64pilot

I have a 33’ waterline length boat with a 40 HP Yanmar 4JHE
I get 6.5 kts at 1800 to 2000 RPM difference is wind and sea state.
I burn about 2/3 a gallon an hour.
I’m surprised when I see people running these things over 3000 RPM and aren’t going much if any faster.
I guess it’s the Autoprop?

I doubt the Autoprop brand prop is causing anything negative. My prop does a great job. Cruising speed/RPMs typically depends on all the other stuff people mentioned. Boat, tides, fouled prop and bottom. Wind. Of course they could have the wrong prop for the boat, but it would seem odd that all previous owners would not have addressed an issue like that. Of course you can't rule out anything when dealing with a boat. I have met several clueless boat owners. I sometimes cruise at 6 knots and it is only requiring 1600 - 1800 RPM. But then with heavier seas, wind, tides, the RPM needs to be at 2000 - 2200 to maintain 6 knots. And sometimes you just can't maintain 6 knots if it is too crazy out.

I don't like to cruise at a much higher RPM. Just want to take it easy on all the running gear. When I first got the boat I ran it harder, cruising more in the 7 - 7.5 knot range (I think 2400 - 2500 RPM or so). Later I decided it was just better to back off a bit. Take it easier on the boat. When I am running at 7.5 knots it produces a sizable wake and the stern squats a lot.

Once I am getting ready to shut down I rev the engine (per Yanmar instructions) several times, sometimes holding it revved for several seconds, to blow out any carbon before then idling a few seconds and shutting down.