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Old 11-28-2014, 09:01 PM   #26
Tacomasailor
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All of the following is probably old news to many of the trawler fans here but no one has laid out the data in this forum for this potential new diesel operator.

Most engine manufactures provide BSFC curves or at least fuel used per hour and the horsepower delivered. From the latter you can calculate BSFC. The interesting thing about this is how much the BSFC varies based on engine RPM.

For example on a Cat TA (435 HP) the following are representative numbers:

1500 RPM 67 HP .381 pounds diesel per bhp per hour (BSFC)
2000 RPM 159 HP .340
2200 RPM 211 HP .339
2600 RPM 348 HP .357

You can see that at max efficiency the 3208 TA is 12% more efficient that at a low trawler speed of 1500 RPM.

The Lugger 6108 is another example where you can see very detailed BSFC numbers and their significant variation based on RPM. The continuous power curve (300 HP) shows the following BSFC numbers:

1400 RPM 220 HP .379 (less than 80 prop HP)
1800 RPM 280 HP .360 (120 prop HP)
2000 RPM 292 HP .358 (160 prop HP)
2300 RPM 300 HP .368 (295 prop HP)

But, as shown for the Lugger – the prop curve is really where you need to be looking at the power and BSFC. So the Lugger is 5.8% less fuel efficient at low RPM than it is at 2000 RPM which is the minimum BSFC.

A little research will show you similar data for almost any available marine diesel.
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