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  1. #1
    Join Date
    Jan 2016
    Location
    Long Beach CA & Cape Town
    Posts
    297

    Default Prop pitch for 80s 60hp 3 cyl - inflatable rib 16ft - skiing and fishing

    Hi there, having a hard time deciding what pitch for my outboard? spun a hub last week and replacing mine with a mercury spitfire prop..

    will a 13 be revving very high? 14 sold out here, so have to choose between 13 and 15 pitch.. If anyone has REAL world experience with plz share -

    thanks

  2. #2
    Join Date
    Sep 2006
    Location
    Baton rouge, La, USA
    Posts
    2,501

    Default Re: Prop pitch for 80s 60hp 3 cyl - inflatable rib 16ft - skiing and fishing

    the hub can be repaired by a prop shop....the dealer will try to sell you a new one but its fixable much cheaper than a new one..common problem...

  3. #3
    Join Date
    Jan 2016
    Location
    Long Beach CA & Cape Town
    Posts
    297

    Default Re: Prop pitch for 80s 60hp 3 cyl - inflatable rib 16ft - skiing and fishing

    Quote Originally Posted by papyson View Post
    the hub can be repaired by a prop shop....the dealer will try to sell you a new one but its fixable much cheaper than a new one..common problem...

    i thanks - well after realizing the problems one could have with a bust prop on the water im happy to have a backup onboard.. Ive pinned this one - the local workshop owner is a very friendly and knowledgable guy said better to get a new one.. these old things can shatter trying to insert a new rubber -

    I can buy used props here for $60 easily, but looking forward to the spitfire prop - ive read many many good stories about it.. plus I can keep it if/when I change boat/motor..

  4. #4
    Join Date
    May 2007
    Location
    Inverary, Ontario, Canada - The Great White North Eh!
    Posts
    9,114

    Default Re: Prop pitch for 80s 60hp 3 cyl - inflatable rib 16ft - skiing and fishing

    So you currently have a 14 pitch (whatever diameter)?

    If so is your motor getting into it's WOT range with that propeller? (which I would guess is 5000-5500 depending on your exact year/model).

    If you know what rpms you are getting now then you can simply do the math to see if a different pitch OR different diameter will work for you.

    Some basic rules of thumb:

    If you increase EITHER the pitch OR diameter by 1 your revs will "go down" by 200 rpm at max (so opposite true - go from 14 to 13 and they "go up" 200 rpms

    If you go from a 2 blade to a 3 blade OR 3 blade to 4 blade (so add a blade) you will drop your rpms by 100 (go the other way and gain 100 rpm)

    If you go from straight blades to cupped blades you lose about 50 rpms

    If you go from composite or aluminum to stainless steel you likewise lose about 50 rpms

    So, as an example, if you currently have a 14P13D (so 14 pitch 13" diameter) and you make 5200 rpms then you could replace that with a 15P12D and get exactly the same rpms (because you increased the pitch by 1 but dropped the diameter by one - so they cancelled each other out).

    OR if say you have that same 14P13D (and I'm just picking numbers here - not specific to your model) and you are only making 5100 rpms with that prop you could drop to a 13P13D, which would increase your rpms by about 200 giving you a new max rpms of 5300 - still "within the range" your motor is rated for.

    Trying to pick a prop without having a "baseline" on your exact set-up (knowing what your max rpms are using your rig how you typically use it) is not the best way to pick a prop. Even if Bob has exactly the same boat/motor, if he carries more or less weight or it distributed differently what "he needs" in a prop will be different than you. And that's why looking at a chart or asking someone will do nothing more than "get you in the ballpark".
    Graham

    A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it :)

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