James, you asked about electric power ratios on larger boats (ships?).
My wife and I enjoyed our cruise on Royal Caribbean Voyager of the Seas.'
I am sure its propellers, motor fairings and hull shape are optimized for efficiency at 22 knots.
Using info available on line, the 1020 ft ship has a hull speed of 42 knots, is designed to cruise at 22 knots and we have been aboard when it was making 26 knots in 26 ft seas. It is rated at 142000 gross tons. Depending on how you accommodate the 3 bow thrusters of 3,000 kW each, and its 3 pods of 14,000 kW each, its power to displacement ratio is between 0.3 and 0.36 kW/ton.
It looks like 1 kW/ton is a reasonable number when care is taken in hull and prop ... probably need more than either of those are less than optimum.
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See My sources and simple calculations for Voyager of the Seas below:
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http://www.marinelog.com/DOCS/cen7a.html
ABB electric propulsion system comprises three ABB 14,000 kW Azipod units (two azimuthing and one fixed). Maneuverability is enhanced by three 3,000 kW thrusters supplied by Sweden's KaMeWa.
http://www.ship-technology.com/projects/voyager/
142,000 gross tons.
http://www.cruisedeckplans.com/DP/Main/decks.php?ship=Voyager%20of%20the%20Seas
Built 1999, Years old 15, Passengers 3110- 3732, Crew 1180, so Souls on Board < 5000
Cabins 1555, Space Ratio 37 sq ft/pax, Tons 137276,
Speed 22.0 knots, Length 1020 ft, Beam 161 ft
Refurbished: 2009
Hull Speed = 1.34 Sqrt[1020 ft] = 42 knots.
Power Ratio = (3*14000 kW)/(142000 tons) = 0.3 kW/ton
or (3*14000 kW+9000 kW)/(142000 tons) = 0.36 kW/ton
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