4-wire bow thruster. Why is it 4-wire?

[auditdata]

My side power bow thruster is giving about half the thrust. Props and gear box seem ok after diving and trying to spin by hand. The engineer is on his way but on taking the cover off it has 4 heavy duty wires and is listed as Model '99 4 Wire on the label.
What does 4 wire mean and what are the pros and cons if any?
Clive

 

[cliff]

What does 4 wire mean and what are the pros and cons if any?
Clive

Guess, 2 wires go to the commutator and 2 wires go to the field coil. Reversing either the commutator connections or the field coil connections reverses the direction of rotation of the motor.?

 

[philip_stevens]

Does this pdf throw any light on the subject?

http://www.g-o.dk/Files/Billeder/PDFer/SIDE_POWER/Paralell_switchbox.pdf

 

[William_H]

Does this pdf throw any light on the subject?

http://www.g-o.dk/Files/Billeder/PDFer/SIDE_POWER/Paralell_switchbox.pdf

I don't think that series parlleling box is anything like what OP has. It is interesting in that it parallels 2 batteriers for charging but switches them to series for running the thruster on 24v. The thruster motor has only 2 leads. This might lead one to believe that it has a permanent magnet field so reversing the power to the motor gives reverse direction.
As said OP with 4 wires to motor suggests that it has powered field coil and that is separately reversed to get reverse motor direction. (With a powered field like a starter motor reversing applied power will reverse both the field and the rotating magnetic field so direction remains the same.)
To the OP this is a mystery as electric motors tend to be reliable on power out. I would suggest he check voltage supplied to the thruster system as any voltage drop will cut power. (check also condition of brushes and commutator) You can't just check the voltage across any 2 wires of the 4. If it is a series wound motor then voltage will be divided betwween field and armature while shunt would motor voltage would be constant to both field and armature. good luck olewill

 

[auditdata]

Thanks William you seem to have it sussed. The engineer arrived and took the motor out and spotted one of the brushes held on by a copper spring lead had come array as the copper had broken. It is away at the machine shop at present but will post the details later.