Fuel consumption 75 hp Yanmar

[captainrussj]

Hello,

I'm getting ready to head for Mexico from Pacific Northwest on my Beneteau 473. Has a 75 hp Yanmar. Has a Gori folding prop with overdrive function. Does anybody have a good idea of fuel consumption at 6 knots (around 2200 rpm) and 7 knots (around 2500 rpm)?

thanks,

Russ

 

[Stu Jackson]

Our 21 hp gets 0.5 gph. M35 engines get 1.0 gph. There's almost a linear relationship on horsepower but once you get to your size engine on your size boat, it may not be linear. Soooo: fill up your tank, motor around for two hours, refill it again and you'll know for sure. Of course, two different rpms might make a difference, but IIRC most engine manufacturers suggest to not stay at one rpm for any extended time. My fuel log averages out to 0.423 gph over 15 years, and I never seem to run too often at one set rpm. Point being that overall average is usually more important than trying to nail down the differences between two rpms.

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

Good luck. Have a great trip, safe journey, fair winds.

 

[Benny17441]

I would use 1 GPH as a starting figure for your burn rate. Like Stu suggests you may need to refine that figure based in actual average burn. If you have an hour meter at the time of filling the tank go ahead and log the reading. The next time that you fill the tank go ahead an log the number of gallons taken in and log the reading on the hour meter. Divide the number of gallons taken in by the amount of time in hours and fractions since the previous filling and you will have a very close average burn rate for your engine. Know the size in gallons for your fuel tank but understand that not all of it useful. The tank's pickup tube will start sucking air well before the tank is empty. We try to keep a 20% reserve of fuel for emergency use and to avoid sucking air in rough sea so that when planning refueling stops and range we calculate based on a tank 20% smaller. The burn rate is strictly a formula of Gallons per Hour and does not relate to wind or current nor the weight or the condition of the bottom of the boat. Once you know how many hours your engine and fuel tank will give you then according to the conditions on the water then you can estimate maximum range and time to destination. It has been my experience that small changes in engine RPM do not significantly affect the burn rate and it would be difficult to keep track of time elapsed at different ranges. To maintain an average burn rate is good enough for our needs. After you refine your burn rate you may find that you can predict how many gallons your boat will take when refueling to as close as 1/2 gallon. It is very useful to be able to calculate at any time how much usable fuel you have left in the tank and make decisions to divert or proceed course with the knowledge that you have enough fuel.

 

[Dave Groshong]

Hard to see, but attaching a graph, here's a link to the site:

http://mastry.com/mec/new_products/images/pdfs/4JH4-TE.pdf

 

[Dave Groshong]

graph

I can't get it to load, but it looks like 1.3 gallons/hr at 2200 and 2.1 gallons at 2600rpm

 

[sailaway78]

Same engine

I have a friend who has that same engine in a H45. His burn rate averages just over 1 gal. per hour. 1.1 or 1.2.

 

[Benny17441]

Remember the Average Burn Rate will always be lower than the manufacturers posted burn rate at an specific high RPM. The Average Burn Rate contains periods of idling and low speed manuevers. It is good to know that if you cruise at 2,200 RPM instead of 2,600 RPM that you can save 0.80 GPH but some of it goes in the wash as your speed will be lower and so will be the distance covered.

 

[Stu Jackson]

Benny, very good point. I've been using average burn rate for 15 years and it suffices for all planning purposes. Your post reminds me again of other reasons why that's all that's necessary. Most of us don't idle or do much low speed traveling, at least around here, and, as you say, if you're running slower, you have MORE fuel left! , although you're no nearer to your destination. Thanks.

 

[Eddie7045]

I found that when I opened up the throttle and then

throttled back until I lost a tenth of a knot I was at a very economical high speed. I suppose that you could get an optimal burn rate at another speed but that is a pretty good place to start and suited my needs well as it was virtually top speed with good economy.

 

[Ray Bowles]

We had a Yanmar 50hp 4cyl in our 1990 Island Packet 38. When we were loaded and leaving for the Bahamas we used .75 to 1.0 gph at 2200 rpm. At 2450 it went down to 1.3 to 1.5 gph. Sea state and breeze also affected burn rate. Motor sailing really helps.
Ray