Toroidal Propellers (e.g. Sharrow) for Human Powered Boats?

Discussion in 'Props' started by FroudeAwakening, Jul 14, 2023.

  1. FroudeAwakening
    Joined: Jun 2023
    Posts: 1
    Likes: 1, Points: 3
    Location: Tennessee, USA

    FroudeAwakening New Member

    Could developments in toroidal propellers help low-speed human-powered boats break the 20kts speed threshold?

    Toroidal props got a lot of press this year after MIT published a report touting noise-reduction and huge efficiency gains for some quadcopter prop designs they studied. For me it was news, but sounds like the idea has been commercialized for a while, particularly the Sharrow Propeller.

    The efficiency gains are modest but it sounds like this is the first exciting development in propeller geometry in a while. And minute gains are all that separate record holders from record attempters. The design space for outboard-equipped vessels is so very different than that of a pedaled hydrofoiling catamaran, for instance, so my question to you designers and dreamers alike is:

    “Could human-powered boats benefit from a toroidal propeller optimized for its design constraints?”

    and “If money were no obstacle (lol), how would a serious designer go about answering that question?”

    BlueBell likes this.
  2. Skyak
    Joined: Jul 2012
    Posts: 1,459
    Likes: 142, Points: 63, Legacy Rep: 152
    Location: United States

    Skyak Senior Member

    In a word "NO".
    Since the MIT paper on toroidal propellers there has been a click bait flood of stories claiming breakthrough efficiency. This is clearly an indication of human gullibility since the MIT paper found no such efficiency gains.
    The Sharrow propellers have been produced in sufficient quantity to give some real world experience. No there is no massive efficiency gain. Yes there is a significant gain in efficiency at some midrange speeds. The gains come from different matching of torque curve of the motor and the efficiency of different props in a LIMITED DIAMETER PROP.

    Human powered boats don't have the torque curve matching or limited prop diameter. The human power is so limited that the best setup is to swing the largest high aspect two blade prop you can. The toroidal propeller reduces tip vortices, but it has a significant amount of surface area passing water at high speed at angles that cannot contribute to thrust. A large diameter high aspect prop also reduces tip vortices, but with far less surface area and with greater angular separation of the blades (180 vs 90 for TP).
    BlueBell, Heimfried, baeckmo and 2 others like this.
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