Chapter 5 fuel system, Fuel consumption – MJM Yachts 34z Express User Manual
Page 20
CHAPTER 5
FUEL SYSTEM
- 20 -
34z
5.3 CHECKING
THE
SYSTEM
Your engine needs clean fuel to operate. Be sure to buy diesel fuel from a reputable marina. Also,
check the primary fuel filter regularly. The primary fuel filter has a clear bowl that will allow you to
inspect for water and sediment accumulation. You should be able to see thru the fuel in the bowl
at all times. Cloudy fuel indicates a problem. Also, you should not see bubbles passing through
the filter while running. This would indicate a leak on the suction side of the fuel system.
5.4
FUEL CONSUMPTION
To assist you in estimating fuel usage and range, the following table is provided by the engine
manufacturer for the Yanmar 6LY2A-STP 440hp, 6-cylinder engine. Yanmar states that these
numbers are accurate to within +/- 3%. The actual speed achieved is a function of the weight
carried aboard, condition of the bottom (barnacles/slime), prop design, etc. If your top speed is 31
knots (35.7 mph) at 3300 rpm, then the approximate fuel efficiency is 31 divided by 22.59 (from
the table below) or 1.4 nautical miles per gallon.
Diesel engines are more efficient when run at about 85% of maximum rpm. The maximum rated
rpm of this engine at propeller load is 3450 rpm. If you selected 2500 rpm and realized a 23 knot
cruising speed, the theoretical fuel consumption would be 2.3 nm/gal. Using not more than 90%
of the 150 gallon fuel capacity, the cruising range would exceed 300 miles. It’s advisable keep
the accompanying log of engine hours and gallons on each fill-up to best predict fuel usage.
It’s rare that the boat is operated constantly at higher speeds. Average recreational fuel
consumption between fill-ups on GRACE is generally 4-5 gallons per hour of engine time. The
34z averages better gph figures than shown on the following Yanmar chart.
3.
94
4.
49
5.
87
7.
3
4
8.
96
10.
89
13.
32
14.
66
16.
0
6
17
.9
9
20.
18
22.
59
0
5
10
15
20
25
1700
1800
2000
2200
2400
2600
2800
2900
3000
3100
3200
3300
RPM
GA
L/H
R
FUEL SHUT-OFF
VALVES
(SHOWN OPEN)
ENGINE FUEL SHUT-OFF
GENERATOR FUEL
SHUT-OFF (Option)