Must replace high altitude prop with sea level prop. What do I need?

[Muttonchops]

I just bought a 2001 Trophy 2052 walk around cuddy cabin fishing boat. The boat probably displaces about 4000 lbs fully loaded. It came with a Mercruiser 4.3 Liter EFI 210 HP engine and an Alpha 1 outdrive at a gear ratio of 1.62. The boat was setup for use above 6000 ft altitude in Idaho and reportedly worked well there, but now that it's in San Francisco Bay the prop is apparently the wrong pitch. The prior owner and I test drove it at sea level and he said the engine RPM was too high for the speed we were getting.

My question is, given all of the above info, how do I figure out what size and pitch prop I need? Where do I begin? Is there a table where I can look up the answer? Thanks for any advice.

 

[fishrdan]

Re: Must replace high altitude prop with sea level prop. What do I need?

For any of the prop guru's to help, they will need to know what your existing prop is, diameter, pitch, aluminum or stainless steel, any numbers off the prop (might be under the washer/nut).

You could try Mercury's prop selector too.

 

[Muttonchops]

Re: Must replace high altitude prop with sea level prop. What do I need?

Thanks, it's a Quicksilver Mirage stainless steel stamped as follows: 48 19838 A41 15P

 

[Leardriver]

Re: Must replace high altitude prop with sea level prop. What do I need?

So the current prop is a 15 pitch. You probably need a 19. There is a little bit of trial and error involved. Does the manufacturer have a website that shows what prop it came with?

 

[steelespike]

Re: Must replace high altitude prop with sea level prop. What do I need?

The 19 will get you to an rpm range you can test in even if you have to over rev momentarily to
get an rpm and speed reading.You may be able to find a dealer that will let you try some props to find the right one.This will require a deposit and assume you will buy the prop selected.
To get more predictable results you should stick with the same brand, model and material.

 

[Muttonchops]

Re: Must replace high altitude prop with sea level prop. What do I need?

Yes, I'm beginning to understand that there's some guesswork (hopefully of the educated type) and approximation involved, and that "It all depends..." is the underlying principle. But I also know that the prop is the most important part of the engine & drive train and I want to be as sure as possible that I get it right. The "Prop Selector" page of the Mercury website recommended 3 different props for me. 2 of them were 4 bladed. One of these, a "Vensura," has a pitch of 19.0. The other, a "Revolution 4," has a pitch of 17.0. It is also bit larger in diameter than the Vensura at 14 5/8" vs 14." The 3rd recommendation was for a 3 bladed prop at a pitch of 19.

Does anyone have any info or opinion on the Revolution 4 prop?