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Old 03-26-2021, 10:42 AM   #21
City: Boston
Vessel Name: Adelante
Vessel Model: IG 30
Join Date: Nov 2016
Posts: 1,208
Originally Posted by DavidM View Post
I don't think so. More like 2,600 for the Lehman. Check both in neutral (no load) and in gear. If it can't make rated rpm at wot in gear then your bottom or prop is dirty or you have too much prop pitch. If you exceed rated rpm then your prop is under pitched.
I believe he has a Perkins. Sounds like he might be a bit overpitched but first he should use a photo tach to check engine rpm's and transmission output rpm's to make sure there is no slipping.

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Old 03-26-2021, 11:29 AM   #22
Nomad Willy's Avatar
City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 18,117
Check rated rpm from the manufacturer and marineizer.
“rated” sounds like some kind of maximum ... it isn’t. It’s a minimum.
You will be reducing pitch to achieve rated rpm.
I like to be 100rpm over. Especially on an application like yours.

You have truck like weight and trucks do well in lower gears. Lower pitch will be your lower gear.


North Western Washington State USA
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Old 04-02-2021, 02:07 PM   #23
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City: Sidney, BC
Vessel Name: Raincoast Gypsy
Vessel Model: Cheer Men 38
Join Date: Sep 2010
Posts: 37
Final word on this - when all else fails, read the manual PROPERLY. It turns out the WOT for the Perkins 6.3544 is not 2250 as stated earlier, but 2800. So, after owning the boat for 13 years, it's like discovering an extra gear in the gearbox of my car! I have been running at 2000 rpm and wondering why I wasn't making hull speed. It transpires I can crank her up to 2600 rpm and reach over 8 knots (> hull speed).

Thanks again for all your input. Together they made me re-check numbers that I had incorrectly assumed years ago. Now, who wants to go waterskiing?
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Old 04-03-2021, 10:17 AM   #24
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City: Chocowinity, (Cypress Landing) NC
Vessel Name: Boatwright
Vessel Model: Camano 31
Join Date: Dec 2017
Posts: 129
Prop evaluation

I put my Camano's numbers into Victoria Propeller's prop calculator, and the answer came out remarkably accurate for how my engine and propeller perform. That's a free and easy way to get an independent evaluation starting point. Data: 200 hp turbo, 20x18 four blade prop, 3700 to 3900 rated max WOT, actual recent 3/4 fluid load, actual max SOG both ways of 14.4 kt at 3750 WOT - 2 year old bottom paint, cleaned by diver 2 months before. Model suggested something like 14.7. Model said to achieve 15 kt. I needed 25 more hp. My purpose was to see if I could go to a 20x20 prop and get more speed, but evaluation convinced me to stick with what I have. Will check again after May haul out.

See what Victoria Propeller's model tells you, and determine your next step.

Good luck!

Build me straight, O Worthy Master,
Stanch and Strong, A Goodly Vessel,
That can laugh at all disaster,
And with wave and whirlwind wrestle. (Longfellow)
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hull, power, propeller, speed

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