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Go Back   SailNet Community > On Board > Gear & Maintenance > fuel consumption gas vs diesel
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Thread: fuel consumption gas vs diesel Reply to Thread
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Topic Review (Newest First)
05-11-2013 07:28 PM
bubblerings
Re: fuel consumption gas vs diesel

Thank you, everyone!
I will have to seriously consider a small diesel, now... I had no idea!!!
And, yes I will eventually be sailing, one day.
Up until now, my life revolved around being IN the water... freediving.
I do love ON the ocean, as well... maybe I just won't have a car!
I need a boat more than wheels.
05-11-2013 08:14 AM
copacabana
Re: fuel consumption gas vs diesel

My Yanmar 3GM30F burns 2 liters/hour at 2500RPM, pushing the boat at 5.5 to 6.5 knots, depending on sea state. Does that jibe with other owners of 3GM30F engines?
05-11-2013 07:12 AM
SimonV
Re: fuel consumption gas vs diesel

My Perkins 4.108 should burn about 2.5 l/h @2400 revs giving 6.5 knots. When trip planning, I use 3 l/h and a speed of 5 knots, and a max running time of 100 hrs. As I carry 420 litres, my workings should give me a decent safety net.
05-11-2013 06:17 AM
jameswilson29
Re: fuel consumption gas vs diesel

Quote:
Originally Posted by bubblerings View Post

Hello, new to your forum...
By "normal sailing operations", did you mean your motor is running to assist your sails, or running alone, under full load???
Is your diesel motor really that efficient?

A dumbfounded gas user.
-Planning to build a fuel efficient trimaran for inter-island travel, Hawaii.
-Mahalos from Maui.
Yes, diesels are that efficient. My 3 cylinder 24 h.p. burns about half a gallon per hour running alone under full load:

05-10-2013 10:06 PM
miatapaul
Re: fuel consumption gas vs diesel

[quote=bubblerings;1028438]
Quote:
Originally Posted by JohnRPollard View Post
An old thread, but what the heck...

Over the course of 8 seasons, our current 3 cylinder 27hp diesel has consistently burned about 1/3 gph during normal sailboat operations. We push it hard (2700-3000 rpm whenever we're motoring, except when docking and during warm-up/cool down).

Our previous 2 cylinder 18hp diesel burned about 1/4 gph during normal sailboat operations.


Hello, new to your forum...
By "normal sailing operations", did you mean your motor is running to assist your sails, or running alone, under full load???
Is your diesel motor really that efficient?

A dumbfounded gas user.
-Planning to build a fuel efficient trimaran for inter-island travel, Hawaii.
-Mahalos from Maui.
That sounds about normal for gph under power alone. What have you used that was gas powered? Remember sailboats are generally displacement hulls, so you are not talking about speed, likely 7 knots at most depending on length. I don't see inter island travel to be that patient, unless it is for tourists and is a stay aboard. Why spend a whole day when you can get a cheap flight for short money (especially with the kamaaina rates). Now if you are talking typical ferry speeds you will spend a lot more!
05-10-2013 07:43 PM
bubblerings
Re: fuel consumption gas vs diesel

[QUOTE=JohnRPollard;521105]An old thread, but what the heck...

Over the course of 8 seasons, our current 3 cylinder 27hp diesel has consistently burned about 1/3 gph during normal sailboat operations. We push it hard (2700-3000 rpm whenever we're motoring, except when docking and during warm-up/cool down).

Our previous 2 cylinder 18hp diesel burned about 1/4 gph during normal sailboat operations.


Hello, new to your forum...
By "normal sailing operations", did you mean your motor is running to assist your sails, or running alone, under full load???
Is your diesel motor really that efficient?

A dumbfounded gas user.
-Planning to build a fuel efficient trimaran for inter-island travel, Hawaii.
-Mahalos from Maui.
09-12-2009 09:01 PM
negrini ... gallons, littlers, miles, kilometers ..... I just messed up as I don't think imperial. John, redoing the math to my engine, you're correct. Shame on me.
09-12-2009 08:03 PM
jrd22 Negrini- I realize that I am not using all 62 hp when at 2500 rpm on an engine that will do 3500, but do the math, it still does not equate. Even if I were only using 40 hp to push Laurie Anne (40' - 24,000 disp.) by that formula I would be burning 2.2 gph which is over twice what in fact it uses. By this formula I should only be using 18 hp at cruise speed since I only use 1 gph. In fact, using that formula it is wrong for any of the scores of diesel engines I have owned and have paid for the fuel bills on, so I know how much they use. My current crab boat, for just one more example, has 200 hp, 190 at the prop, and I run it at 3400 rpm. WOT is 3800 and I average betweeen 6 -7 gph at that speed(I log every gallon that goes into it). According to this formula it should be burning close to 9 gph. The Volvo fuel consumption graph is close to my actual burn rate, a little higher. All I am saying is that this does not seem to be a reliable formula to use to estimate anticipated fuel consumption, and therefore required tankage.
09-12-2009 06:49 PM
negrini JimsCAL, very good point to remember. Also, many new diesels does provide an average chart for rpm/HP (like you say, clearly not linear), so you can beter estimate fuel consumption if you balance against speed.
09-12-2009 04:55 PM
JimsCAL One thing to keep in mind: the power doesn't vary linearly with speed (and RPM), it varies with about the cube! So at 3 knots, you need about 1/8 the power you do at 6 knots. Reduce the speed by only 20% and the power is only about half of what it was. That explains the differences between the calculated fuel consumptiong based on rated engine power and actual consumption at cruise speeds.
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