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  1. #14
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    Thumbs up Re: How much power/speed loss at altitude

    Quote Originally Posted by fishwrong2 View Post
    My advice is dont overthink it. Greater elevation means less horsepower. Carbureted engines are more susceptible than fuel injected models but it affects them all to some extent. Reducing the prop pitch or diameter is just reducing the gear ratio, same as dropping from 5th to 4th gear in a transmission.

    How much horsepower is enough? Subjective to the individual. So long as you can get a loaded boat up on plane, Id consider it safe. After that, its how much do you want to spend to go faster. Thats a fight my wallet and pride have yet to settle.
    I had some of that trouble with my main, but it has an electric pump & is carb'ed. I only had to adjust the idle jets with a screw driver and timing light....Jetspray
    2003 Alumaweld, 19'6", Chevy vortec V-6, SD-309 american turbine jet, T-8 Yamaha kicker, waiting for the tackle fairy to show up to fill my boxes

  2. #13
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    Re: How much power/speed loss at altitude

    My advice is dont overthink it. Greater elevation means less horsepower. Carbureted engines are more susceptible than fuel injected models but it affects them all to some extent. Reducing the prop pitch or diameter is just reducing the gear ratio, same as dropping from 5th to 4th gear in a transmission.

    How much horsepower is enough? Subjective to the individual. So long as you can get a loaded boat up on plane, Id consider it safe. After that, its how much do you want to spend to go faster. Thats a fight my wallet and pride have yet to settle.

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  4. #12
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    Re: How much power/speed loss at altitude



    Scam !!!

  5. #11
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    Re: How much power/speed loss at altitude


  6. #10
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    Re: How much power/speed loss at altitude

    You will lose 3-3.5% of your horsepower per 1000. So at 5000, your hp will decrease 15-17.5%. Fuel injection engines have computers that automatically adjust lessening the effect. Carbureted engines need to have the idle adjustment and possibly the jets recalibrated if mostly at elevation.

    A lower pitch prop is typically the solution. Every 1 is about a 200-250 rpm gain. You might have to try a few to see which pitch gets you into your max rpms and provides the performance you want. You will lose speed with a lower pitch prop but your engine will perform better and wont bog down.

    My prop pitch was chosen for 5000, hits 5900 rpms and boat goes 28mph. So, when below 5k, Im over-propped and have to watch the rpms to prevent over rev-ing the engine. Still go 28mph though.

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  8. #9
    Member BDuck's Avatar
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    Re: How much power/speed loss at altitude

    I bought my current boat Columbia 20' with a Yamaha F150 from a guy in Everette WA. It came with a 20P stainless prop. After getting it here to the intermountain west altitude was in play in performance. The Salt Lake Valley is around 4000 elevation which I used to base performance conditions with. A lake within 5mi of my house in North Ogden area is where my trial run would take shape. At WOT I was lucky enough to get between 3800-4000rpm at 30mph on an engine that should be more nearer to 6000rpm. After talking with our local prop guy I went with another stainless 15P. This boosted rpm up to where it should be bringing speed to near 40mph. The real test where I fish is at an elevation of 8000'. My rpms now cut back maybe 3-400 off of top end and speed also dropped a little, but not as it was with a 20P prop. Also keep in mind there is a standard day condition for engines to run there optimum which is based 59F outside temp, 29.92 barometric at sea level. The computers installed in our machines will compensate for altitude as well as standard day condition.
    2000 F250 Diesel
    2007 Columbia Fisherman 2018XL Yamaha F150 Yamaha 9.9 Kicker Raymarine Element HV9 4 Electric Walker Downriggers

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  10. #8
    senior member RideNfish's Avatar
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    Re: How much power/speed loss at altitude

    Quote Originally Posted by ppickerell View Post
    Look at Kingfisher while you are at it. I striper plug just fine in my 16 ft KF Falcon.

    PM Sent.

  11. #7
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    Re: How much power/speed loss at altitude

    Quote Originally Posted by RideNfish View Post
    While I'm at it. Is a 17' Alumaweld Stryker a rough ride? Can't find deadrise info as of yet.
    Look at Kingfisher while you are at it. I striper plug just fine in my 16 ft KF Falcon.

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  13. #6
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    Re: How much power/speed loss at altitude

    Any Aluminum boat in chop is going to be a rough ride, North River Seahawk probably the best boat built for overall ride but you pay the premium dollar for them. The older Stryker i think had a 10 or 12 degree deadrise, the bow entry deadrise at the water line i feel is most important. I wouldn't let worry of rough ride be the overriding factor, you can adjust your speed accordingly.

    Nor sure your going to get 40 mph with a 115 with many boats unless it's just two small guy's in it, alot of time water conditions don't let you go 40 mph. If you don't over pay for the boat and after a while don't like it you wont loose much money, they tend to hold value.

    Your doing it right, ask all the questions you want and then try to make a dollar wise decision.

    Enjoy the hunt !

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  15. #5
    senior member RideNfish's Avatar
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    Re: How much power/speed loss at altitude

    While I'm at it. Is a 17' Alumaweld Stryker a rough ride? Can't find deadrise info as of yet.

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