8 HP 4 Stroke Yamaha / 15'4" Gheenoe

Discussion in 'Prop Shop' started by makovec, Mar 19, 2009.

  1. makovec

    makovec Frequently fish in the New Smyrna Beach area.

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    Yamaha suggests one (any?) of these 5 for my 8hp 4Strk:

    9 x 7
    8.5 x 6.5
    8.5 x 7.5
    8.5 x 8
    8.5 x 8.5

    Any experience with this motor and a 15'4" Gheenoe in order to offer a suggestion? My local prop shop said 8.5 x 7.5, but also gave some erroneous information, so now I don't trust their expertese any longer. Could also use some guidance on a good vendor for the prop as well. I am on the Treasure coast.

    Curtis
     
  2. The_Skiff_Shop

    The_Skiff_Shop Well-Known Member

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    You'll need to install a Tiny Tach and give data from the prop you have. Then you can make an informed decision.

    I suggest doing your own research and buying from your local dealer for anything under 9.9 hp.

    TSS/CR
     

  3. makovec

    makovec Frequently fish in the New Smyrna Beach area.

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    Thanks for the quick reply.

    I would love for it to be that easy. I am not starting with a prop in good condition. I just bought the motor/gheenoe, and the previous owner had run it through the mud and flattened the blades out of shape. So since the prop isn't shaped as it is supposed to be, I have to either pay to repair and then do this procedure, or buy one and start from there with the test.

    Shall I just take a stab in the dark or do I have options that I don't know about? My local folks don't keep props this small on hand for me to test with.

    Curtis
     
  4. Brett

    Brett > PRO STAFF <

    I'm running an 8 inch diameter with a 9 inch pitch
    on a Nissan 5hp 4 stroke. The closest I see to that in your list
    is the 8.5 x 8.5 That would be my start point. Get the tach,
    install it, try the prop, if the top rpm's fall in the middle of
    the engines recommended top end you're fine. If not swap to
    a different prop.
     
  5. The_Skiff_Shop

    The_Skiff_Shop Well-Known Member

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    In that case I would go to my local Yami dealer, check which prop comes on that motor from the factory and start with that. Tach it and hope for the best. If you need to adjust, you'll have a great spare.

    TSS/CR
     
  6. makovec

    makovec Frequently fish in the New Smyrna Beach area.

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    Thank you both. Much appreciated.
     
  7. TomFL

    TomFL Well-Known Member

    I can solve this pretty handily if you have the patience to wait till Saturday.

    I have an 8 horse 4-stroke Yammy that I've run on a 15.4 hi-sider and have GPS speed #'s for both 1 and 2 people, which I've posted here. That was with gear both times.

    The motor was sold and is in a warehouse waiting for a forum member to pick up. I can get over there and let you know what prop is on it, I would think it'll give you a great starting point as the motor ran like a top.

    -Tom
     
  8. The_Skiff_Shop

    The_Skiff_Shop Well-Known Member

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    Thanks,
    That would be the best data to minimize his expense.[smiley=1-thumbsup1.gif]
     
  9. TomFL

    TomFL Well-Known Member

    Curtis, the 8hp 4-stroke Yamaha I have has the 7.5" prop on it. On a 15' 4" hi-sider it'll run as described below:

    19.5 mph with one person (175lbs) and battery, fuel, trolling motor, (giant) fishing gear bag, rods, large cooler & ice/drinks and anchor.

    Adding a second smaller person (120lbs) drops it to right about 17 mph.

    I have no idea what the RPM's are, but installing a tiny tach and swapping to a different prop might get a little bit more out of it. I doubt it would get much unless you change from the above weight loads, as the motor seemed really happy at whatever RPM's it was running.

    Hope this helps.

    -T
     
  10. makovec

    makovec Frequently fish in the New Smyrna Beach area.

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    Thanks for the help. Excellent assistance. I went with the 7.5 RPM's work out well on the tach. Weight distribution turned out to play the biggest part here, and I learned a bit while working it out. Thanks again.