Fuel consumption and range values for motoryachts

With sample measurements on a Grand Banks 36 MY trawler
Data source: Powerboat & Motoryacht Magazine

Introduction

We all know, we all hear, that consumption, range, noise and engine wear are strongly related to the engine revolutions. The data below show that these relations are beyond the imagination of most of us.

All what has been done is that a boat was run with varying engine revolutions and consumption, speed and noise were recorded.

Data Table

Revs (1/min)
Speed (sm/h,knot)
Consumption per time unit (l/h)
Way made good per unit fuel (sm/l)
Range (1000sm)
Noise (dB)
1.000
6,3
7,6
1,0
1,31
73
1.250
7,5
11,4
0,8
1,03
73
1.500
8,3
22,7
0,4
0,58
74
1.750
9,2
30,3
0,3
0,48
75
2.000
9,8
40,2
0,3
0,38
77
2.250
10,7
53,0
0,2
0,32
78
2.500
14,3
68,9
0,2
0,32
79
2.650
15,7
84,9
0,2
0,29
80

Graphical Presentation
fuel_range
As can be seen in the graphics, 

1. Speed of the vessel is the variable least depending on engine revs. When the engine revs are 1000-1 speed is 6.3 knots. When the engine is revved up to 2650-1 , the speed has increased to 15.7 knots.
2. Range, way made good per unit fuel and hourly consumption are highly dependent on the engine revs. As an example, while at 1000-1 revs the hourly fuel consumption is 7.6 liters. At 2650-1 revs this has increased to 84.9 liters. Thus, the hourly consumption has increased more than TEN fold. At the same time, range and way made good per unit fuel has decreased FIVE fold.
At this example the “good” revs are 1500 – 1750 revs. Specially the green curves show the “hump” at these revs. Above these revs the range drops more significantly.

In summary, whoever runs his/her engines calmly, reduces engine wear, saves money and has the comfort of a larger range. Whoever “beats” the engines harm the environment and themselves..

 

 

Notes:


 

[1]Original tables from PMY magazine

 

rpm
Sea Mile/Gallon
Speed(Knot)
Gallon/Hour
Sea Mile / Gallon
Range
Noise(dB)
1000
7.3
6.3
2.0
3.63
1308
73
1250
6.6
7.5
3.0
2.87
1032
73
1500
9.6
8.3
6.0
1.6
576
74
1750
10.6
9.2
8.0
1.3
477
75
2000
11.3
9.8
10.6
1.1
382
77
2250
12.3
10.7
14.0
0.9
316
78
2500
16.4
14.3
18.2
0.9
324
79
2650
18.1
15.7
22.4
0.8
290
80
Boat Grand Banks 36 MY Test Conditions
Length OA 11.23 m Temperature 21 ºC
Beam 3.86 m Humidity %85
Fuel Capacity 1515 l Wind No wind
Draft 1.22 m Sea Condition Very Calm
Displacement 12.2 ton Fuel ½ capacity
Engines Dual 210-hp Cummins 6B15.9M Water Full
Transmission Twin Disc MG 5050 2.54:1 Crew 3
Propellers 28”x25” 3-blade bronze Load Light

 

The speed has been measured as average of two direction by radar.

Source: Powerboat & Motoryacht, January 1996, page 92