Help with Propulsion

Discussion in 'Boat Design' started by standman, Nov 27, 2021.

  1. standman
    Joined: Mar 2015
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    Location: Cebu

    standman Junior Member

    Hi All,
    I enjoyed a 16ft. boat I built and decided to built a 49' version. I am now at the stage where I need to install the propulsion.
    Power will be from twin 360HP 2200 RPM Diesel
    ZF V drive 2.06:1
    Waterline length 45'
    draft 2ft
    beam at waterline 12'
    vessel weight about 13 tons loaded
    Target max speed 24 cruising 18 knots
    propeller 28 x 34.8 x 3 (55% coverage) (recommended size by prop maker)
    So what I have available are 2 or 2.5" Stainless 304 shafts. I'm worried with 2" ( should I be?)
    rudder is twin 3.06 sq. ft. - adequate?
    The propeller strut i need to fabricate, single or v type?
    about 6' of the shaft is exposed - will this need 2 struts?
    30KG Delta anchor ok?
    TIA for the input
    propulsion.jpg
     
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  2. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Quite a step up in size, shall we say about 30 times ? Any pictures or drawings ?
     
  3. standman
    Joined: Mar 2015
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    Location: Cebu

    standman Junior Member

    will resize pics and video as I can't seem to upload them boq-2.jpg boq3.jpg
     
  4. standman
    Joined: Mar 2015
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    standman Junior Member

    boq5.jpg
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    OK, that gives a fairly good idea, what is she made of ? Is it a scaled-up version of the small boat ? My initial thought was she might slap on those very wide chines.
     
  6. standman
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    standman Junior Member

    FRP, very close to the design of small boat. I thought too the wide chines would cause slamming but the much deeper kiln actually push water to those chines and somehow acts like a suspension and allows to plane quicker.
     
  7. tonipu
    Joined: Dec 2014
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    Location: croatia

    tonipu Senior Member

    With 3 blades 55%
    Some cavitation problem and strenght
     

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  8. tonipu
    Joined: Dec 2014
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    Location: croatia

    tonipu Senior Member

    4 blades 67% blade area
     

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  9. tonipu
    Joined: Dec 2014
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    tonipu Senior Member

    4 blades area 75%
     

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  10. tonipu
    Joined: Dec 2014
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    Location: croatia

    tonipu Senior Member

    i will go with 2.5 shaft, and if you can find with aisi630
     
  11. tonipu
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    tonipu Senior Member

    and 4 blade prop
     
  12. tonipu
    Joined: Dec 2014
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    tonipu Senior Member

    from the strut to propeller is better to go out, no more than a shaft diameter
     
  13. tonipu
    Joined: Dec 2014
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    tonipu Senior Member

    Prop and strut
     

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  14. standman
    Joined: Mar 2015
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    Location: Cebu

    standman Junior Member

    First, thank you for the input. I'm not familiar with aisi 630 but a google check says it is equivalent to stainless 304 which is what I will use. I wonder why the prop maker gave me those specs? Is it because they are confident with their material? ( Hypothetical) As for the strut to propeller, anything beyond shaft diameter cause vibration? TIA BTW, How's your boat coming along?
     

  15. tonipu
    Joined: Dec 2014
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    Location: croatia

    tonipu Senior Member

    it is about 3 times stronger than 304
     
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