Fuel Consumption

Geoffs

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Did some trials with the boat at the weekend, thought it might of interest. As a reminder boat is Larson Cabrio 240 with Volvo D4 260.

Trials done in slack water of Swanage bay with speed average of two runs in opposite direction, SOG. Fuel consumption data taken from Volvo web site for D4 260.

Speed.jpg


Sort of interesting, shows most economical speed is about 2400 rpm about 23.5 knots. About 1.1 nM per litre. Probably a bit optimistic, overall I get about 1 nM per liter.
 

jfm

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Good to have this data. Can you plot mpg vs speed or vs RPM? I would have thought most economical is at tickover rahter than 23kts, I mean I'd expect mpg just falls and keeps falling as you open the throttle (apart from just around the hump). That's what seems to happen with ours (we have diesel flow rate combined with SOG fed into the Volvo computers, so we get a mpg read out)
 

Geoffs

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I'll plot MPg vs SOG, probably look similar.

Red line is miles / litre vs Engine speed. Volvo fuel data only goes down to 1600rpm, but as you see curve is zooming up as it goes down towards tickover. Would expect it to flatten out at low rpm.

This curve is typical of what I have seen of (small) planing boats. As you say high mpg at tickover speed, decreasing as you reach hump speed. Mine would indicate a hump speed of about 13 knots at 2000 rpm.

As it comes on plane drag decreases and mpg increases, until under water drag starts to dominate (2400rpm 23/24 knots). MPG drops rapidly until WOT.

That's my analysis, anyway, someone can say it's all wrong. /forums/images/graemlins/laugh.gif
 

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