Since we're mangling units a little bit, let's take a moment to clarify Power vs Energy as apply here.
Fundamentally, the MKS (meter/kilogram/second) units:
For Power, it's Watts ( and 1 Watt = 1 Kg*m^2 / sec^3)
For Energy, it's Joules ( and 1 Joule = 1 Watt-second)
For Speed, it's Meters/sec
Typical Unit of POWER for EV's: KW (Kilowatt = 1000watts)
Typical Unit of ENERGY for EV's: KWH (Kilowatt-Hour = 3.6Million Watt-Secs = 3.6MJoules)
Typical Unit of SPEED for boats: Knots (n-mile/hr ~ 0.514m/sec)
A moving boat retains momentum and kinetic ENERGY at speed, but due to hull friction and other factors, it requires steady POWER to maintain a given speed. So, if you said that 'for 3knots, my boat required 1kwh', you'd be saying that you put in 1kwh of ENERGY and got 3knots of SPEED…while average energy (in KWH) and power (in KW) would be equal after 1 hour, the right thing to have said was 'for 3knots, my boat required 1kwatt' since POWER is what is what goes up with the cube of the speed. Yes, energy usage also is going up with the cube of the speed, so it's hardly worth all this diatribe, but anyway, what we should see then are statements like this:
'My boat does 5knots with 2.5kw of battery power (or motor power if you prefer) and its energy storage of 21kwh (lithium battery pack) gives it a range of approx. 40n-miles.'
Your mileage may vary-
-Myles Twete, Portland
Posted by: "Myles Twete" <matwete@comcast.net>
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