Low rpm prop for high torque diesel engine

Discussion in 'Props' started by NautiPhillip, Sep 6, 2019.

  1. NautiPhillip
    Joined: Aug 2019
    Posts: 26
    Likes: 1, Points: 3
    Location: Seabrook, Texas USA

    NautiPhillip Junior Member

    I know very little about props. Recently I saw a video that I can't seem to find now. The owner of a old wooden trawler with a large pilothouse changed his prop on the advice of a friend. The boat is diesel powered and it's cruising RPM is somewhere around 2000-2200.

    The new prop had large blades with a lot of pitch which pushed to boat up an plane for the first time ever. There was mention of a design patterned after submarine props. Anyone have in info on props for low RPM and high torque diesel engines?
     
  2. Deering
    Joined: Feb 2005
    Posts: 475
    Likes: 22, Points: 18, Legacy Rep: 44
    Location: Juneau, Alaska

    Deering Senior Member

    A cruise RPM of 2000-2200 probably does not qualify as a ‘low RPM’ diesel. I’m assuming its top RPM is significantly higher, 3000+. Overpropping with too much pitch or diameter will damage the engine.

    It comes down to the reduction gear (shaft RPM) and the vessel displacement and speed. Dave Gerr’s Propeller Handbook is the definitive book on the subject if you want to learn the fundamentals. Otherwise contact a propeller dealer to help work through the options. I’ve worked with Pacific Propeller in Anacortes Washington and found them to be knowledgeable and helpful. There are several free online tools available as well.

    Edit: Olympic Propellers
     
    Last edited: Sep 7, 2019
  3. NautiPhillip
    Joined: Aug 2019
    Posts: 26
    Likes: 1, Points: 3
    Location: Seabrook, Texas USA

    NautiPhillip Junior Member

    Deering, thank you sir. I told you I didn't know much. ;)

    I will look for Dave Gerr’s Propeller Handbook. May I presume Amazon would be a good source? If it's not too much of an imposition, could you provide links to the online sources you mentioned? It would be much appreciated.
     
  4. NautiPhillip
    Joined: Aug 2019
    Posts: 26
    Likes: 1, Points: 3
    Location: Seabrook, Texas USA

    NautiPhillip Junior Member

    Btw, this inquiry is based on a yanmar diesel which is a marinized tractor diesel. It is also a transplant from a blue-water sailboat to a VSV semi submersible hull. And before anyone asks; No it is not intended for drug running.

    I am exploring the possibility of marrying the efficiency, safety, comfort and speed offered by the hull design with the advantages of self-tending and power-reefing sails to produce a fast cruising passage maker. My current calculations have produced a hull that more resembles a torpedo with a wave-piercing bow and an enclosed bridge deck/saloon above the waterline than the high-speed planing Darpa version or the low-slung stealthy 'narco' version.

    Right now, this is at the spitball stage and I am busy knocking down the more obvious obstacles, so any help or positive criticism is welcome.
     
  5. Deering
    Joined: Feb 2005
    Posts: 475
    Likes: 22, Points: 18, Legacy Rep: 44
    Location: Juneau, Alaska

    Deering Senior Member


  6. NautiPhillip
    Joined: Aug 2019
    Posts: 26
    Likes: 1, Points: 3
    Location: Seabrook, Texas USA

    NautiPhillip Junior Member

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