An example:
http://www.torqeedo.com/us/hn/products/cruise-r/technical-data-measures.html
Given technical data for Cruise 4.0 R:
Input power: 4 kW
Comparable gas outboard (propulsive power): 8 hp
Comparable gas outboard (thrust): 9.9 hp
Let's see:
1 hp = 0.735 kW (8 hp = 5.88 kW, and 9.9 hp = 7.28 kW)
Now technical data above can be written:
Input power: 4 kW
Comparable gas outboard (propulsive power): 5.88 kW
Comparable gas outboard (thrust): 7.28 kW
Weird specs!
Instead they should write:
>Cruise 4.0 R propulsive power is comparable with 8 hp gas outboard
propulsive power.<
This is really possible as gas motor prop efficiency is typically less
than 30% (!), and Cuise prop efficiency may well be (5.88kW/4kW) * 30% =
44%. Less rpm, larger prop diameter.
They should say:
>Cruise 4.0 R thrust is comparable with 9,9 hp gas outboard thrust at
boat speed of 0 m/s.<
This is possible, as propeller is better, and el-motor thrust is good
at low rpm.
redu
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