The previous owner of my sailboat installed an electric DC motor and batteries. I cannot find any specifications on this motor besides what is on the plate on the motor housing.

The plate says:

Advanced DC Motors Inc.

  • Part No. AC4-4002

  • Volts DC- 72

  • Serial No. 138

  • Rating 2.940

  • 57B loT

I would like to know horsepower, rpm range, and anything else about the motor. I have searched the internet for hours and once in a while find the motor part number but no other information is provided.

  • 5
    \$\begingroup\$ 72 volts does not remotely imply 72 Horsepower. Realistically speaking,what do do you hope to learn? Does it move the boat usefully or not? \$\endgroup\$ Mar 27, 2016 at 2:08
  • \$\begingroup\$ Measure the length and diameter of the motor. Now google for the same type of motor, with similar volume. The power should be broadly similar. \$\endgroup\$
    – Neil_UK
    Mar 27, 2016 at 15:27

2 Answers 2


This is the only approximation i was able to find:


Advanced DC AC4-4002 6.7" 72 volt

  • 10"x 6.7"

  • Series wound

  • 47 Lbs

  • 20 HP (Nom 6.5, peak 27)

  • should be kept below 5700-5800 RPM

Other "findings", for you to check the motor driver details if you require -between 300 and 400A on these pages. One of these projects even uses batteries too...



http://www.formula-hybrid.org/pdf/program-2008.pdf (page 6, right paragraph)



I am saying that your yacht does not have a 72 HP DC motor. Yachts, unlike, say, jetboats and outboards, have what's called a displacement hull. This means that it's good in choppy water and it needs very little power to go slowly. In fact, more power won't help speed much. If you look at the wiring and ballpark the current at your known voltage of 72 V then the kW will be apparent. You can ballpark the efficiency of the DC motor at, say, 90%. Remember that 1 HP is 735 watts (horsepower according to DIN 66036) and then you are done. I would also study the size and hence kWh of the heavy onboard battery pack and use this to support a much lower answer.

  • \$\begingroup\$ One HP equals to 746 watts... Not 735. \$\endgroup\$ Mar 27, 2016 at 4:21
  • \$\begingroup\$ @soosaisteven A metric horsepower is 735 watts. \$\endgroup\$ Mar 27, 2016 at 13:19
  • \$\begingroup\$ Horsepower has always being imperial.... No such thing as metric horsepower. \$\endgroup\$ Mar 27, 2016 at 13:56
  • \$\begingroup\$ @soosaisteven See DIN 66036. \$\endgroup\$ Mar 27, 2016 at 14:11
  • \$\begingroup\$ "kWh " for kilowatt-hours. KWH = kelvin watt henries = nonsense. \$\endgroup\$
    – Transistor
    Mar 27, 2016 at 14:16

Not the answer you're looking for? Browse other questions tagged or ask your own question.