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Old 01 July 2007, 11:35   #1
Country: USA
Town: barrington nh
Make: HBI
Length: 5m +
Engine: evinrude 115 hp
Join Date: Nov 2006
Posts: 102
weight to power ratio

New to the sport my question is at what add. weight do you start to lose speed or take longer to plan? I know there are alot of variables, my rib is 18 ft with a 115 hp evinrude with a 14 X 19 prop. Empty she will run 39 miles at 5000 rpm, 2 divers and gear 34 to 35 mph at 4900 to 5000 rpm. I have added more chain to the anchor,add. prop safety gear, onboard weight belts for add weight anchor etc. a few other safety items(total additional weight 150 lbs). Now about 32 to 33 mph and 4700 to 4800 rpm. Is that about right in lost mph and rpm. The engine seems to run great but I have not had it tuned but schedule for tune up in a couple of weeks or is it time to throw the additional diver overbroad and that damn safety gear?

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Old 01 July 2007, 12:33   #2
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Country: UK - England
Town: Fareham
Length: 6m +
Join Date: Sep 2003
Posts: 7,855
Well the easiest way to compare weight related performance is with different numbers of crew aboard, I like many find that weight is a big killer of performance. I used two different pitched props to help me get the best possible performance for a given application.


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Old 01 July 2007, 15:54   #3
Country: UK - England
Town: Gloucestershire
Boat name: Osprey
Make: Osprey Vipermax
Length: 5m +
Engine: E-tec 300 G2
Join Date: Dec 2006
Posts: 4,016
Originally Posted by 603doug View Post
Now about 32 to 33 mph and 4700 to 4800 rpm. Is that about right in lost mph and rpm.
That RPM is too low I think you will find that the recommended RPM for that engine is between 5200 and 5500 It might be worth looking at a 18" Prop or possibly even a 17" one.

Are you trimming the engine out when on the plane to get the most out of it?

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