Re: Specific Fuel Consumption

Mark Erdos


This is great. Thanks for sharing.

I'm a little confused about the 0 to .9 on the Onan table. What does this represent? Load?

With best regards,


Sailing Vessel - Cream Puff - SM2K - #275
Currently cruising - Santa Marta, Colombia

-----Original Message-----
From: [] On Behalf Of David Vogel
Sent: Friday, March 15, 2019 5:34 PM
Subject: [AmelYachtOwners] Specific Fuel Consumption

Hi all,

Just a quick contribution for the benefit of those who are operating a Yanmar 4JH3-HTE and ONAN genset.

I developed the attached look-up tables to assist me with keeping track of diesel consumption. Each time either the ONAN or YANMAR is used, I create a line-item in a hand-written fuel-log. When I significantly change revs on the YANMAR, I also create a new line-item (so, in essence record 1.5HR@1,600, 2.0HR@2,200, and so on). The figure for the fuel USED column is derived from the quick-lookup-tables attached, a laminated two-sided copy of which is held in the back-cover of the fuel log.

All figures in the table are rounded UP to the nearest whole liter. This means that, over time, I am actually over-estimating fuel usage. Which periodically I correct by dipping the tank. I never want to see less fuel in the tank than I have calculated as remaining.

The figures for the YANMAR are come from the ideal performance curves for the YANMAR engine, which were put into an excel spreadsheet and a theoretical fuel-use curve derived. This curve was then adapted/adjusted on the basis of actual fuel consumption observed, the resulting formulae being derived by EXCEL. This second formula was then used to populate the table.

The speeds were derived on the basis of an actual run in still-water over several hours in calm conditions; but with moderately dirty prop and hull - so probably in the ball park for real-world use, but not rough seas. I have not seen the need to adjust anything using these speeds in two years since initial calculation.

I am interested to hear about other's experience. In the meantime, this is about as complicated - and as simple - as I need to get and, once I take the round-up errors into account, have found these fuel figures to be remarkably consistent over 2 years.

Please note that range and endurance figures are based NOT on the full-tank 600 liters, but on 510 liters, leaving roughly 15% always as a "fixed reserve", at least for planning purposes.

I hope this helps someone else out there.

Shelter Bay Marina, Panama,
Bound for the South Pacific

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