Prop calculators - is there a difference between electric and diesel drives?

Discussion in 'Props' started by RayThackeray, Nov 14, 2011.

  1. Joakim
    Joined: Apr 2004
    Posts: 892
    Likes: 53, Points: 28, Legacy Rep: 422
    Location: Finland

    Joakim Senior Member

    As Ad Hoc stated propeller power demand is ~RPM^3, thus propeller torque demand is ~RPM^2. All diesel engines have a decreasing torque near rated RPM. If you don't reach rated power, you will have more torque available than at the rated power. If you lower from rated RPM to 90% of it, your propeller power demand drops almost 40%, torque demand drops over 20% and your diesel can output a few % more torque and maybe 95% of the rated HP. Thus missing the rated RPM by 10% is a huge error in propeller selection.

    Bollard pull or getting into plane can be a problem for some planing boats, not for displacement boats.
     

  2. tugboat

    tugboat Previous Member

    yes i see that, by definition of hp, torque is included...thanks
     
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