Hi,
Scott asked about the ratings which he said he was confused by, so I replied in another post to him.
Regardless Torqeedo are thorough about their ratings ref:
And their respective product pages. They along with James Lambden of Electroprop are the few that go into them in detail.
They do compare, calling propulsive force effectively as bollard pull. If you read the page you'll get it.
I did all the measurements for my own system so understand that their figures are pretty good. You don't get 56% overall efficiency by having poor efficiency elsewhere. Efficiency though is a map but for the purpose of tests we must assume normal salinity of seawater, ambient temperature of say 25C and efficiency measured at cruise speed. Single component efficiency whilst important is only a part, the full propulsion efficiency as Torqeedo give in terms of thrust in relation to that taken from the battery is the most complete picture and theirs is good.
What do you consider a bad efficiency figure at cruise speed for a sailing yacht auxiliary drive? Anything above 90% for the motor is pretty good. For instance I'm 92% at cruise for the motor. I could be 94% but I use direct drive so what I lose from a higher amp/torque lower volt/rpm combination, I gain from no gearing. I use a high kt, low kv motor, and those constants are directly related.
The bottom line is overall system efficiency is what counts and Torqeedo have good numbers.
John R
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