MJM Yachts 40z Express - Manual (Page 26)

CHAPTER 5
Propulsion Systems. The NMPG and Range numbers will also vary depending on engines
installed and the relative efficiency of the propulsion unit. It’s anticipated that the standard
sterndrives and/or lighter Volvo D4 or the Cummins QSD4.2 engines will improve the efficiency
by a tenth or two from those shown below.
Range of Efficient Operation It’s interesting to note that it doesn’t particularly matter whether
you are going 9 knots or 27 knots on a 40z, nautical miles per gallon remain fairly constant.
Cruising Speed Volvo Penta suggest that given suitable conditions, 10% below wide open
throttle, or about 3200 RPM at 30 knots is an optimum cruising speed. The data below would
indicate that 2900-3000 RPM in the 28-knot range would be a more efficient range.
Sour Spot The 40z seems to have a huge “Sweet Spot” and just one small “Sour Spot” to avoid
at about 1600-1700 rpm where the most power is applied in overcoming resistance prior to the
boat jumping up on a plane at just over 10 knots. You can see that the boat is no more efficient at
that point than at 30 knots.
Acceleration Tests Volvo technicians commented, “This is a Ferrari!” as I mashed the throttles
forward to hit 20 knots in 5.3 seconds from a standstill. No wonder, that’s on a par with some
“thunder” boats and about what it takes a Mercedes SL550 to hit 60 mph (52 knots).
FUEL EFFICIENCY
RPM
600
1000
1200
1300
1400
1500
1600
1700
1800
1900
2000
2200
2400
2600
2800
3000
3200
3400
3500
Remember that fuel level readings when underway, with the fuel pushing back
in the tank where the fuel level sensor is located, could be reading # tank more than what’s really
there. So, when you get down to 1/3 tank, it’s time to top off.... not roll the dice on finding another
fuel dock open later in the day.
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GPH
0.6
2.3
3.5
3.9
4.7
6.8
7.8
9.5
9.7
10.6
12.7
14.8
17.6
20.5
22.9
26.4
30.5
35.7
38.5
FUEL SYSTEM
KTS
4.8
6.7
7.6
8.0
8.2
9.3
9.5
10.0
13.1
14.3
15.1
17.9
20.9
24.0
26.9
30.0
32.8
36.1
37.7
NMPG NMrng* 0-10 0-20 0-30
7.6
3.0
2.2
2.1
1.8
1.4
1.2
1.1
1.4
1.3
1.2
1.2
1.2
1.2
1.2
1.1
1.1
1.0
1.0
RANGE
2392
937
684
646
555
428
384
333 2.5
425
425
374
380
374
370
370
357
339
319
308
ACCELERATION (secs)
5.3
9.5