The great controlable pitch prop debate.

Discussion in 'Props' started by Mik the stick, Dec 12, 2012.

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  1. Mik the stick
    Joined: Dec 2012
    Posts: 189
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    Location: Devon

    Mik the stick Senior Member

    I read as much as I could and stopped reading about page six. I am a new commer on this sight having much I want to learn about boats. BUT I DO KNOW ABOUT PROPELLERS.

    My knowledge is about aircraft but a prop is a prop. Aircraft can have fixed, controlable or Constant speed prop. For get constant speed for the moment.

    For aircraft and boats controllable pitch props work the same. Early WW2 aircraft had controllable 2 pitch props fine pitch for take off/landing allowed revs and therefore acceleration to build up quickly. Once airbourne a change to coarse pitch allowed maximum speed. I'm not certain but I think props can be had which are infinitly variable.

    A constant speed prop works on load If you are cruising at say 150mph the prop will be in coarse pitch if you suddenly have to accelerate cause there is a bandit on your tail you slam the throttle forward and the hydraulics in the mechanism senses the load and reduces the pitch so you accelerate faster. when you are up to speed the prop automatically goes to the best pitch.

    THERE IS NO ENGINEERING REASON YOU CANT HAVE THAT ON A BOAT BUT IT WILL COST MUCH MORE TO BUY AND MAINTAIN.

    I know much less about boats, I assume a CPP is infinitely variable and reversable. And the way to use one is this.


    Available Power
    1200 RPM 15 SHP 4kts

    1400 RPM 24 SHP 4.5kts

    1600 RPM 35 SHP






    0.395 pounds/hph


    93 SHP

    2400 RPM


    7.0 gal/hr


    0.408 pounds/hph


    121 SHP

    Speed / Range:
    Speed (knots)

    S/L

    HP

    Gal/Hr

    Hours

    Range (NM)

    6


    0.97


    18.00


    1.08


    1018


    6108

    7


    1.13


    36.75


    2.20


    500


    3500

    8


    1.29


    67.55


    4.05


    272


    2176

    9


    1.45


    112.00


    6.72


    164


    1476
     
  2. michael pierzga
    Joined: Dec 2008
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    Location: spain

    michael pierzga Senior Member

    Sure...many different adjustable props for boats. Even Autoprops .

    They all share the same characteristic....expensive !!!!!

    For some boats they are a worthwhile expense . I particularly like them on motor sailors.

    Reversible props give good power in reverse gear. Great for maneuvering.
     
  3. Submarine Tom

    Submarine Tom Previous Member

    Double post thread.
     

  4. Boat Design Net Moderator
    Joined: Feb 2010
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    Location: www.boatdesign.net

    Boat Design Net Moderator Moderator

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