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Comparing Thrust from Electric Prop Devices


(Bret Howe) #1

I thought that there would be some small difference between propeller devices as far as efficiency of converting power (watts) to force (lbf). I wanted to compare thrust from from different trolling motors with the T200 thrust.

My research showed that most of the trolling motors I could find required about 600 watts for 55 lb thrust (they usually leave the f off, but I think they are meaning lbf). The T200 generates 11 lbf for 320 watts.

Am I misunderstanding something? Why the huge difference in efficiency?

Thanks for any help with this !

Bret


(Adam) #2

Hi Bret,

Different propeller and motor designs can have significant differences in performance and efficiency. When purely comparing thrust and power consumption, it is true that a trolling motor will be more efficient than our thrusters. This is due to a number of reasons.

  1. A trolling motor has a much larger electric motor, which can run much more efficiently than a smaller one at the same level of thrust. The less a motor is pushed to the edge of its operating envelope, the more efficiently it can run.

  2. A trolling motor also has a much larger prop size, which again boots efficiency. A larger swept area at a lower RPM requires less power to achieve the same thrust as a smaller swept area at a higher RPM.

  3. Most trolling motors also have a large internal gear reduction between the motor itself and the propeller. Thus by fining tuning the torque load on the motor, the motor can run it its “sweet spot” point of maximum efficiency more easily and more often.

  4. Our thruster are optimized for efficiency and static thrust over high speed running (A T200 will only move water a theoretical maximum of ~10mph) but trolling motors often take this to an even further extreme, moving water at only a few miles an hour at most. Since mechanical power is the product of both thrust and speed (torque and RPM), a T200 and a trolling motor can have similar mechanical power due to their differences in speeds despite the T200 having lower thrust. This is made up for by the higher water flow speed in the T200.

  5. Many trolling motors often run at higher voltage (32V+) than a T200 (12-20V), which results in less power loss due to heating of wiring and other power transmission components.

If a trolling motor uses a brushless electric motor, it is also possible it may be using a sine wave ESC, which would be more efficient than the square wave BasicESC.

The fully flooded design and small size of the T200 is great for decreasing expense and alleviating pressure concerns (I’m sure most of not all trolling motors are only rated for surface use), as well as allowing it to be mounted to smaller vehicles, but its’s not quite comparable efficiency-wise. At the end of the day, trolling motors are a better option for large heavy, and slow moving surface vessels, while our thruster are best for ROVs and smaller lighter faster moving surface vessels.

I hope this is the answer you were looking for!

-Adam


(Bret Howe) #3

Thank you so much for your detailed reply. There’s so much to consider I will have to give this a lot of thought. Thanks again.