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new prop sizing


SJRwake

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2 minutes ago, wdr said:

You can safely get a 14.5 on that hull with some safe space and not loose that much performance from a 15”. JM2C

You can go 15" on that hull (and ALL Vdrive Malibus) and have a safe space.  No good reason to go with a 14.5" prop unless it is scored used and cheap.

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I think we all agree (so long as you have at least 3/4" between blade tip and gelcoat) that a 15" diameter prop will not hurt, it will only help...what we differ on is to what degree you pitch down.  I'm certain that anything near 14" is much too high for what you do, as that's what I'm running now and it could definitely be lower; the same pitch with added diameter would make it even worse.  Also keep in mind that cupping is critical: .050" is roughly equivalent to 1" of pitch, so make sure you factor that in.

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  • 4 weeks later...

So I installed my new prop and there is about an inch gap between the gel coat and the tip of the blade so no rubbing there. I did notice that when I would go in reverse there is a humming noise like metal rubbing on metal. Then when I go forward the sound continues for a moment and then stops. Could it be the lock bolt setting in place(I tighten it down really good)?

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On 1/18/2020 at 4:49 PM, formulaben said:

Could be the key got jammed up when you installed the new prop. 

https://marinehowto.com/lap-fitting-a-propeller/

Skip down to Step 8 (Install the Propeller) and note the 2nd & 3rd items explain how a dry fitting without the key is done to make sure you have a tight fit.

I checked it without the key in place first and then put the key in and eye balled it to see if it was as deep. I should have marked it. I feel bad now after reading this cause when torquing the bolt on I had the tip of the prop resting on wood instead of wedging the wood up against the bore. The grinding noise I mentioned also seems to have stopped after a day of running the boat on the river. 

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11 hours ago, SJRwake said:

I checked it without the key in place first and then put the key in and eye balled it to see if it was as deep. I should have marked it. I feel bad now after reading this cause when torquing the bolt on I had the tip of the prop resting on wood instead of wedging the wood up against the bore. The grinding noise I mentioned also seems to have stopped after a day of running the boat on the river. 

What prop did you go with and what are RPMs like? The 381 on my dad's boat like yours hits 5100 RPM WOT which is right in the sweet spot for the Monsoon. 

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  • 3 weeks later...
On 1/20/2020 at 11:08 AM, UWSkier said:

What prop did you go with and what are RPMs like? The 381 on my dad's boat like yours hits 5100 RPM WOT which is right in the sweet spot for the Monsoon. 

I went with the ACME 2949 4 Blade 15" x 11". It has a lot of torque to it and is so smooth. I lost around 8-10mph but i dont even notice it cause i never go over 35mph anyway. I sit at about 2900-3200RPM to surf now with a fully loaded boat of 8500lbs displacement. It has even made my wave smoother and more crisp. I love this prop!

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