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Raised my OB

Old 07-03-2007, 07:17 AM
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Default Raised my OB

The boat is a 2005 18' Palm Beach 90 hp Yamaha 2-stroke.
I figured I'd post my results.
With the motor mounted in the top mounting holes, sitting right on the transom, I was maxing out at 4900 rpm and 32mph at WOT.

I raised the motor up one bolt hole(about an inch) and now I get 5100 rpm WOT, didn't notice much of a top end speed increase, maybe 1/2 mph or so.

I did notice a 3-4 mph speed increase at 4500 rpm, which was unexpectable.

I didn't notice any cavitation, but I did test it in flat calm water.
I will test it in rough water and post results.
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Old 07-03-2007, 02:55 PM
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Default RE: Raised my OB

See it works check to see where the cavatation plate is in relation the hull bottom, should be 1" for alum prop maybe a little higher with SS maybe you can go another hole. RPM could be a tad higher stll
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Old 07-03-2007, 03:25 PM
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Default Re: Raised my OB

I bet your fuel economy went up a little as well.
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Old 07-03-2007, 03:54 PM
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Default Re: Raised my OB

I did notice a 3-4 mph speed increase at 4500 rpm, which was unexpectable.

Unexpected


or

Unexceptable
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Old 07-03-2007, 04:17 PM
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Default Re: Raised my OB

Unexpected..Sorry.
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Old 07-03-2007, 04:29 PM
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Default RE: Raised my OB

Unexpectable is good word....I'm going to start using it.
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Old 07-03-2007, 05:12 PM
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Default RE: Raised my OB

truepursuit - 7/3/2007 4:29 PM

Unexpectable is good word....I'm going to start using it.
Hey, as long as get all the credit...
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Old 07-03-2007, 08:00 PM
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Default Re: Raised my OB

You are over proped by 2"
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Old 07-03-2007, 08:07 PM
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Bullshipper - 7/3/2007 8:00 PM

You are over proped by 2"
Ya think? I believe I have a 16 pitch stainless.
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Old 07-03-2007, 10:56 PM
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Default Re: Raised my OB

5100 is too low, I would want around 5700 to ge full horsepower
1" = 300 more rpm.
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Old 07-04-2007, 06:44 AM
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Bullshipper - 7/3/2007 10:56 PM

5100 is too low, I would want around 5700 to ge full horsepower
1" = 300 more rpm.
Max HP is at 5000-5500 rpm according to Yamaha.
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Old 07-04-2007, 07:30 AM
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Default Re: Raised my OB

A Few Dollars - 7/3/2007 3:54 PM

I did notice a 3-4 mph speed increase at 4500 rpm, which was unexpectable.

Unexpected



or

Unexceptable
Thank you!
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Old 07-04-2007, 11:58 AM
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Default RE: Raised my OB

Well I raised my motors one hole and seen a 150-200 rpm increase but am still overpropped as I'm only seeing 4850 rpm on twin 225 hondas at 45 mph.( 14 3'4 x 21 Solas Titan props)
When you say the cavitation plate should be 1" above the hull , this is on the outside of the motor on a level line from the cavatation plate to the hull, Right??
I still think I'm low, as the water is up on the smaller plate above the cavatation plate when i'm running and shouldn't be , Right?
Thanks for the thread.
ken
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Old 07-04-2007, 01:23 PM
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Default Re: Raised my OB

I didn't really pay attention to where my cav plate is in relation to the hull, I think it's way more than 1" above the bottom of hull. I do know that know at WOT, the cav plate is above the water surface.
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Old 07-04-2007, 01:34 PM
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Default Re: Raised my OB

fishaholic18 - 7/4/2007 6:44 AM

Bullshipper - 7/3/2007 10:56 PM

5100 is too low, I would want around 5700 to ge full horsepower
1" = 300 more rpm.
Max HP is at 5000-5500 rpm according to Yamaha.
Sorry, I assumed 6000 rpms was wot.
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Old 07-04-2007, 01:38 PM
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Default RE: Raised my OB

Triple Jack - 7/4/2007 11:58 AM

Well I raised my motors one hole and seen a 150-200 rpm increase but am still overpropped as I'm only seeing 4850 rpm on twin 225 hondas at 45 mph.( 14 3'4 x 21 Solas Titan props)
When you say the cavitation plate should be 1" above the hull , this is on the outside of the motor on a level line from the cavatation plate to the hull, Right??
I still think I'm low, as the water is up on the smaller plate above the cavatation plate when i'm running and shouldn't be , Right?
Thanks for the thread.


ken
The 1" above will vary and should be just taken as a begining reference point.

Now that you can watch your motor run at a low to high cruise speed, the cavitation plate should plane right on top or a tiny bit under the surface of the water below it.
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