Low HP parallel offset shaft coupling options?

Discussion in 'Inboards' started by swmn, Feb 24, 2017.

  1. swmn
    Joined: Feb 2017
    Posts: 5
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Interior Alaska

    swmn Junior Member

    Looking to build a boat with mostly off the shelf hardware.

    Wetted area pretty similar to a johnboat 1660 or 1668 ish.

    Inboard V twin gas engine. 16hp makes me nervous, 18-20 is OK. If I am going to have a bunch of loss in my transmission I can fit a 22 no problem.

    Common prop diameter, direct 1:1 drive should be OK.

    I really want at least neutral. Reverse is desirable, but not mandatory.

    Prop shaft is coming in 2.5" above the planking, centered over the keel.

    Engine output shaft is going to be at least 5.25" above the keel, on center, before I put bunks under it.

    Probably (negotiable) 1" keyed shafts on both engine output and prop shaft input.

    A Schmidt type offset coupling would give me 1:1 forward, no neutral. I am a bit concerned the disc that mates to the prop shaft would be big, big enough that I would need to hole the planking and notch the keel to fit it over the propeller shaft. http://www.zero-max.com/flexible-shaft-couplings-schmidt-couplings-c-1_8-l-en.html Not sure about corrosion resistance on these either.

    I could maybe find a worn out snow thrower on craigslist, use a cutting torch to free the cage with the shafts and sheaves and belts in it from the rest of the unit, and then figure out what height to make my engine bunks and start upgrading bearings.

    Spur or helical gears don't seem a viable choice since I really want at least neutral.

    Not excited about a centrifugal clutch on the water, though I am 300 miles from the nearest ocean.

    I looked at Velvet Drive Transmissions, they don't really make anything for boats as small as mine.

    I have read a little bit about Robb White's Rescue Minor. My fab skills just aren't up to that. I could pay someone to build that, I guess.

    Looking for options.
  2. gonzo
    Joined: Aug 2002
    Posts: 16,877
    Likes: 1,758, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Seems like you are describing a setup for a surface piercing propeller. Could you post a drawing?
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