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From: (no name) (no email)
Date: Fri May 30 2008 - 11:32:13 EDT
Since we are perseverating on the fuel price thread, it might be appropriate
to consider how the characteristics and operation of a typical trawler
displacement hull affect fuel usage.
At a given speed, fuel consumption is directly proportionate to displacement.
If you increase the weight of a trawler by 10%, power requirements and fuel
usage rise 10%. DECREASE the weight by 10% and fuel usage DECREASES by 10%. Get
those spare tools off your boat and load only as much fuel and water as you
reasonably need.
For boats of the same displacement, at any given speed below hull speed, fuel
usage is inversely proportionate to the square root of waterline length. If
the waterline length of a trawler is INCREASED by 10%, fuel usage DECREASES by
about 13%. You can't do much about the length of your boat but you can keep
the bottom clean. It reduces skin friction at slow speeds.
For trawlers of a given length and displacement, power and fuel usage changes
as the cube of the speed change. DECREASE the speed by 17% (i.e., from 6 kts
to 5 kts) and the fuel usage DECREASES by 42%. Slow down for best fuel
consumption.
Thus we see that saving weight has a relatively minor effect on fuel economy
compared to cruising a bit slower. Dropping your cruising speed from 8 kts to
7.8 kts will save as much fuel as paring 10% off the displacement of your
boat. At the slower speed, a 100 NM trip will take only 19 minutes longer. What's
the hurry?
Larry Z
**************
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