Last Outboard Thread - Does My Dream Outboard Exist?

Discussion in 'Propulsion' started by CatBuilder, Feb 11, 2012.

  1. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

    OK, send cheque asap, or used $100's, they start pretty exxy, there's a barge firm nearby with one they swap between platforms/pile rigs etc apparently saves money on tugs, so you buy & I'll hire it out for ya;)
     
  2. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

    No wurries CB, I'll vote for the Honda 20 then, x 2........ or 3 & maybe a spare so 4
     
  3. Willallison
    Joined: Oct 2001
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    Willallison Senior Member

    Let me preface this by saying that I haven't read the 'ganging outboards' thread, so I', coming to this rather late...
    The reality is that outboards are designed primarily to push fairly light loads at reasonably high speeds, so no matter which one you choose, it'll be performing a job that it wasn't really intended for.
    High thrust ob's go some way to addressing this with lower gear ratio's, lower pitch props etc.
    Anyway... I guess you've covered all that... what I really wanted to do was to relate my experiences with a high thrust prop. This was a very simple arrangement that we had on a 10hp Mercury outboard that was fitted to our tender. The prop's hub was shorter than the shaft, such that when in fwd gear the exhaust went out thru the hub as usual. But when in reverse, the prop would slide aft on the shaft, onto a "plug" that was just in front of the prop nut, forcing the exhaust out between the gear casing and the hub. This ensured that the prop always operated in solid water, not 'aerated' by the exhaust. We were able to comfortably use the tender as a 'tug' for its 48 foot, 20+ ton mothership.
    The prop had a low pitch and high blade area, so the tender wasn't exactly a rocketship, but it was quite able to plane still - and with a heavy load to boot! In reality though, we used to run with a normal prop and change over to the high thrust on the odd occasion it was needed...
     
  4. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

    Will, that use of an outboard as a tug for larger vessels pretty much mirrors what we do at work with them- with a rib & a runabout using mostly reverse with the steerable thrust we move up to 68 foot boats with care & easily although we "pick" our weather. Your exactly right on the outboards being a compromise of sorts but but offset by being in a very neatly engineered package at reasonable cost & weight. I read an account some where of the exhaust exit being modified to by pass the prop & exiting the leg higher up.
    Regards from Jeff.
     

  5. Willallison
    Joined: Oct 2001
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    Willallison Senior Member

    Yes - this was an off-the-shelf prop from Merc. I have no idea if they are still available, but somthing to improve the ability to get sensible thrust is essential for Cat's application IMHO
     
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