Prop mounting with using a safety, cut-off pin on outboards - propose to discuss

Discussion in 'Props' started by Gered, Nov 12, 2011.

  1. Gered
    Joined: Nov 2011
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    Gered New Member

    Hi all. I apologize in advance for my english
    Prop mounting with a safety pin in present time is used on some small power outboards (up to 6-8hp). Previously, 20-25 years ago, such prop mount is widely used on outboards up to 30-40hp and more, as I remember. This mount has some advantages.
    Minimal risk of damage to the blades and, more importantly, the motor gear. Also, this mount has its drawbacks - often uncomfortable process of replacing the prop and cuted pin.
    With the increasing power of outboards and using exhaust through the prop the prop fastening on a shaft became splined connection.
    Splined connection is more simple and convenient to install the prop. But at the stroke risk of damage to the propeller blade and gear box is very high.
    What do you think about the reasons why now is not used fastening screws using a safety pin?
    Is this structural complexity in the case of exhaust through the propeller?
    Is this additional income to producers for the sale of spare parts and screws?
    And second, how this situation (prop mounting with the splined connection) explain by the representatives of the manufacturer? – May be someone knew, heard or read their opinion on this issue?:confused:
    Thanks in advance for your opinion
  2. FMS
    Joined: Jul 2011
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    FMS Senior Member

    If you hit things regularly I can see the advantage of a pin which can be replaced far from home. The pin is cheap, but if it breaks the prop will likely be damaged anyway, so...

    I haven't spun the rubber hub in my prop once in the last 10 years, so I like the ease of taking the prop on and off without needing a pin.
  3. marshmat
    Joined: Apr 2005
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    marshmat Senior Member

    The nice thing about rubber hubs (that replaced shear pins on most outboards and sterndrives) is that, after hitting something, they re-engage. So you can often still limp home at idle with a bent blade, whereas a shear pin would leave the prop free-wheeling.

    I've seen plenty of rubber-hub props damaged, up to ~200 hp. I've yet to see a shaft or gearbox break as a result of banging such a prop.
  4. powerabout
    Joined: Nov 2007
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    powerabout Senior Member

    many companies offer user replacable rubber hubs

    The pin had to go away on big engines as it removes the solid conection which is very tough on the shift dog with an aluminium prop and horrendous with a stainless prop
  5. CDK
    Joined: Aug 2007
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    CDK retired engineer

    There are no commercial reasons for the widespread use of rubber hubs, only mechanical ones.
    The shear pin concentrates the torque load on two small areas, limiting this construction to small engines only because using a larger pin diameter requires a larger hole, weakening the shaft at that point. A splined shaft can handle a much higher torque, so a smaller diameter can be used without the risk of deformation.

    And of course the use of rubber to transmit torque to the prop is much more gear friendly than a metal pin.
  6. Gered
    Joined: Nov 2011
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    Gered New Member

    The prop with pin can be demaged as rule in high roration speed and solid obstacle - but this does not necessarily and depends of many conditions.
    Your situation doesn't need the pin, but it can be very different.

  7. Gered
    Joined: Nov 2011
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    Gered New Member

    But if "something" is enoth solid and big you 'll get geabox crash - I"ll prefer to replace the pin or prop.;)
    I know situations when the geabox was breaked, but prop and blades are ok, with outboards 30-70 hp.
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