Little props for little outboards

Discussion in 'Props' started by jakeeeef, Sep 11, 2009.

  1. jakeeeef
    Joined: Sep 2009
    Posts: 141
    Likes: 27, Points: 28, Legacy Rep: 16
    Location: Hamble

    jakeeeef Senior Member

    I have a 16 foot light plastic Canadian canoe which I have fitted some low drag stabilising hulls and crossbeams to that I have knocked up out of stitch and glue plywood. It's now a trimaran I suppose! I'm going to put some sails on it later (so the stabilisers are very deep v to provide lateral resistance, but I digress) The stabilisers are set so they only rarely touch the water but are there when you need them.

    At the moment I've got a 4.5 hp johnson 2 stroke outboard on it. (It's a '95 model year long shaft with the black plastic prop with rubber / nylon bush mounting with 9 splines on it). I use it to go out fishing on calm mornings, as it's a self sufficient launch job, fits in my front garden etc. It feels like it is trying to plane as its a wide canoe with a flat bottom, but never quite gets there whatever we do with our weight (theres usually 2 of us in it). I would like it to plane and guess the prop needs optimising to kick off with.

    I guess the standard prop supplied with this engine is a one size fits all applications pitch and diameter, and many people would buy a motor like this to push a heavy displacement dinghy or even a small racing keelboat like a J24 in and out of harbour. I guess for my lower drag, higher speed application I probably don't have enough pitch, and this is bourne out by the fact that it screams away on the back at high revs without pushing me at more than about (guessing ) 6mph.

    I don't want to get a bigger engine as the hull is rated to 5 hp max (probably to stop irresponsible people from making it plane:( ). I want to try to set it up right with the engine I've got. Also the only other thing I use this motor for is a small zodiac yacht tender, and it would be nice if I could get this planing with it too!

    1) I've just removed the prop and nowhere does it have any pitch numbers stamped. Is there any way to roughly work it out?
    2) Do manufacturers or aftermarket manufacturers make alternative pitch props for little motors like this? I've not seen them.
    3) It's plastic. It looks like that stiff black plastic that they make some automotive components like inlet manifolds out of. Can I heat it up and bend the blades to alter the pitch? Any one done this. Any advice as I don't want to wreck it.
    4) It looks very old fashioned shape. Like props on little outboards looked in the 1960s, with very pronounced spiral to the blades when you look at it hub on. I'm guessing thats to increase blade area
    and thus make it better for pushing heavier boats??? Or maybe to make it pick up weed less? Either way, not properties I need for my application.
    5) It's a bit bendy when I grab a blade. Would a stiffer aluminium prop make noticeable efficiency gains?
    Many thanks
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