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Subject: TWL: Re. Re. KK 42 calculations
From: Kurt Reno (kreno@XXX.XXX)
Date: Fri Nov 01 2002 - 12:24:04 EST
<<< Assuming a 42,000 pound boat with a 39'2" waterline length and a modern,
>fuel efficient, direct injection diesel engine it would take about 74 shaft
>hp to drive the boat at 8 knots and that equates to about 2.1 nautical miles
>per gallon. >>>
>>My calculations, again based on Keith's formula, show that only 52 hp is
required. Keith's formula is generally accurate within 5% for displacement
boats with clean bottoms and normal powerplants operating in calm
conditions.<<
>I stand by my statement that no KK 42 can average 7.2 knots using 38 hp.
Tossing around high efficiency fuel burn numbers is plenty of fun, but it
ain't necessarily the real world.<
I have only been on the Trawler World List for two months but find it
incredibly fascinating that trawlers are populated with so many techno-geeks.
Planning hulls seem to be populated by non-techno-geeks. Dag-gone, I feel
right at home here.
There are two types of technical personalities. When my type of techno-geek
pulls out from the docks they tend to monitor everything but record little.
We enjoy our run and latter try to fill in the blanks that we didn't record.
Then there is the second technical personality. Them people are technical
personalities that obsessively record everything and has cataloged everything
in every bin. You people know who you are!
The two technical type personalities can clash. We all love a good debate.
I for one, believe in the validity of Keith's formula when taken in it's
proper context. We must remember that Keith's formula is taken in the real
world within the parameters set by the designer. That said, we boaters don't
follow the parameters.
Examples, two Krogen 42's can turn up drastically different results.
One Krogen 42 can normally be operating lightly, in generally calm coastal
conditions with good maintenance, low electrical power requirements and no
stabilizing gear. This Krogen 42 could turn in numbers close too or better
than Keith's formula.
The second Krogen 42 could be grossly over weight, love electrical appliances,
be covered with barnacles, need and engine rebuild, run stabilization
constantly, have laundry hanging all over the exterior of the boat, double up
the dingy as a storage barge and be unlucky enough to buck seas and head winds
often. That Krogen 42 may turn in real numbers more than twice that predicted
by Keith's formulas.
Both Bob and Larry can be virtually correct in their respective arguments
using "REAL" world numbers.
I haven't used my boat yet, as I just got it and we are going into winter, but
I will bet that the numbers that I turn in are closer to the condtions of the
second KK 42.
Kurt
Pious Puffin
Over loaded 26' GlassCraft trawler.
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