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Yamaha Outboard Prop Question

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  • Yamaha Outboard Prop Question

    I have a 2005 8HP Yamaha 4stroke outboard model T8ELHD on my AB dinghy model 3.20 VS, LOA 10"6", LWL 9", normal displacement 750lb, maximum displacement 1400lb. The standard Yamaha propeller for my outboard is an 11-3/4" x 5-3/4" - R, 7 tooth spline, model 96GF-45941-00-EL. It"s my belief, seemingly confirmed by propeller calculations, that this outboard/propeller combination is a high thrust unit designed for much heavier displacement boats than my dinghy. According to my calculations I should have a propeller of size about 11-3/4" x 11.5"-R. However when I search online I can not find a propeller anywhere near this size. Also Yamaha advertise Propellers for an F8 outboard with a gear ratio around 2:1 whereas I cannot find any advertising for my T8 outboard which has a gear ratio around 3:1. Can anyone help advise me please as to what I should best do? Thanks.

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    Re: Yamaha Outboard Prop Question

    Easiest way to check ratio is to remove the plugs put a mark on the flywheel , rotate and count the revolutions to make the prop turn once. Best way to estimate prop pitch is to get a tach, Tinytach will do).Do a light test run and get the rpm and speed hopefully it will plane if you can get in the middle seat.Is the hull shape intended to plane.Most dinghys have a lot of rocker and don't plane well.
    Hull is designed to handle well at the end of a rope.
    While diameter usually doesn't directly affect pitch/prop selection at almost 12" on a 8 hp that is huge and the pitch numbers reflect that.
    A 50 hp Evinrude with a 2.42 ratio has an 11 3/4" X 12" in the middle of its prop list.