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Old 08 July 2012, 15:50   #1
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Make: Bombard SB420
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Yamaha F40 propeller

Hi, i am beginner in RIB boats and i need some help.

I have RIB Bombard SB420. Now i have secondhand engine Yamaha F40 (2008) with prop 11 3/8 x 12.

i would like to find solution for my following problems:

- max RPM is only 4800-4900
- max speed is "only" 25 mph (3000 RPM - 12,5 mph)

speed by GPS on my iPhone

I don't know on which boat was engine use before my RIB.

I think that i have wrong propeller for my Bombard ....
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Old 08 July 2012, 15:53   #2
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11 3/8x12 SHOULD have higher revs than that. Is your engine ok?
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Old 08 July 2012, 20:37   #3
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Agree with NOS. Hard to believe you'd need a shorter prop.

Are you sure your throttle is actually opening all the way? Might have to pull the cowl and see what moves when you open the throttle, then take the boat out and manually actuate it while running (ideally with a couple of people, so you can do the motor stuff while someone else drives.)

Luck;

jky
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Old 09 July 2012, 14:45   #4
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I checked today engine and throttle is full open.

I think that engine is ok.
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Old 11 July 2012, 18:11   #5
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Do you have a tachometer on board? Does the motor spin up past 5000 at all?

The recommended WOT range for your motor is 5000-6000 rpm. Ideally you want to be in the upper half of that range. That would mean (rule of thumb - probably not that accurate) a prop shorter by about 3 inches (9" pitch.) That sounds ridiculous for a boat that size.

Make sure your tubes are inflated properly, and the boat isn't loaded down with a bunch of extraneous gear that you don't need. Check the hull and make sure it's clean and smooth. Ditto the lower unit. Make sure you remove the trailer from the boat before speed testing (yeah, just kidding.)

jky
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Old 11 July 2012, 23:24   #6
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My Yamaha 40TLR (2006) runs a 10 5/8 x 12-G prop. This gives 5600 rpm at WOT.
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Old 12 July 2012, 01:39   #7
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What kind of boat?

jky
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Old 12 July 2012, 20:42   #8
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Quote:
Originally Posted by jyasaki View Post
What kind of boat?

jky
Zodiac Pro II 470 console.
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