Which is better in high altitude?

_chris_

Chief Petty Officer
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Jul 9, 2009
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439
On my new to me Four Winns 5.0 OMC I have a 14-1/4 x 19p SS prop, I also have but not ever run 14-1/4 x 19p Aluminum prop. This weekend I am going to running it at above 6,000 feet and am wondering which would be better as I do not know the differences if any between SS and Aluminum.
 

fishrdan

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Jan 25, 2008
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6,989
Re: Which is better in high altitude?

I'd think the aluminum prop will perform better at altitude since (from what I've heard) a 19P SS prop will perform close to a 21P aluminum prop. Going up to 6000' you will notice a loss of power and the easiest way to compensate is to run a prop with less pitch.

When I used to take my ol' 140HP Mercruiser up to 9000' I'd drop from a 17P to a 15P prop (both aluminum) and lean the carb out. It was still doggy, but made it to where the boat could plane. Without the modifications the boat wouldn't plane, just plow through the water.
 

_chris_

Chief Petty Officer
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Jul 9, 2009
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439
Re: Which is better in high altitude?

Thanks fishrdan I thought the same but I didn't know which way the SS prop went or even why they are different, this is my first time running this boat at this altitude but I do go to this lake alot so next year I will be picking up a prop just for this reason.
 

fishrdan

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Jan 25, 2008
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6,989
Re: Which is better in high altitude?

Since you have the V8 I'd see how it performs with the aluminum 19P prop, you might have enough engine to run that prop up there. Weight will be a killer though, too many people on board and it'll might be doggy, unable to plane. Move weight forward to see if it helps pop the boat up on plane.

When I adjusted my carb for high altitude I didn't have to do anything with the idle screws, just replace the main jets with smaller ones. Kind of a PITA removing the carb top off to replace the jets, but that's what needed to be done in my situation at 9000'.

Only thing I haven't tried yet is bumping the timing up a 1-2 degrees, next trip...
 

_chris_

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Jul 9, 2009
Messages
439
Re: Which is better in high altitude?

I will be bringing both props, I just didn't want to switch it out in the water but not a big deal I guess the only way to know for sure is to try it out. I wil probably have a full boat this time. I didn't want to mess with the carb because I use the boat at sea level alot as well and for me switching a prop seems the easiest solution. My only issue was that it already takes a good amount of time to get on plane at sea level, I probably also need a set of trim tabs but that is also in the future. Thanks for your help and let me know if you think of anything else.
 

Randybeall

Petty Officer 1st Class
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May 2, 2008
Messages
319
Re: Which is better in high altitude?

Since your going to go there again, and you mention that your boat is slow to get on plane now. As well, you say that you will be having a full load.....This all adds up to, you should consider a 17 inch prop. At altitude you will loose horse power, have a full load and want to have fun. There is little fun in a boat that won't go when you push the lever.
 

_chris_

Chief Petty Officer
Joined
Jul 9, 2009
Messages
439
Re: Which is better in high altitude?

I will probably end up with a 17p prop but this is the last time this year that I am taking it out up there so I will use what I have and then work on figuring the perfect prop for the altitude.
 
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