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Old 07-31-2015, 07:59 PM   #32
Bilgewater
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City: New Bern, N.C.
Country: USA
Vessel Name: Lady J
Vessel Model: 1978 Mainship 34 #150
Join Date: Jun 2011
Posts: 272
For a displacement boat, hull speed (most efficient) is computed at 1.34 x square root of the water line length. On my Gulfstar, a water line length of 33 feet gives me a theoretical hull speed of 7.69 knots. When I first got the boat, someone on this forum suggested to increase rpm 100 at a time and watch the bow. When it starts to rise, back off because you're wasting money trying to climb over your bow wave. I found a sweet spot at 1750 rpm on my two 85 horse Perkins, which will give me 7 to 7.5 depending on wind and waves. I plan on 3 gallons per hour usage, and usually do better. Canal cruising at 6 knots or less does even better, hovering above 1 gph. Slow and steady wins the day (and the wallet).
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Bilgewater

"Keep putting off till tomorrow, and you'll end up with a lot of empty yesterdays" Prof. Harold Hill
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