Unexplained electrical behavior when engaging Bowthruster.

[Oceanride007]

Hi
Helping out some friends departing on a voyage soon. My job for the day was finally installation of a Fridge system. My job compleated and while monitoring voltages and currents, while they were moving the vessel to Fuel dock. I happened to put my Amp clamp meter on the Perkins, Leece Neville Alternator to check if it was working, 40Amps at idle, not bad, then they engaged the bow thruster and the Alternator amps dropped to zero, this happened several times on both alternator cables. The thing is that the bow thruster is hydraulic, its engaged by a electric clutch, at least 15 amps I saw the Amp meter move on the main panel.

You got to understand on this vessel, a 65' Swan, Heath Robinson has been at work and no electrical drawings remain.

The problem is not a voyage stopper as it probably has been like it since Bow thruster installation about 5 years ago.

So why did the alternator amps drop to nothing?. I'm thinking the Clutch takes power from the Ignition circuit and although enough to kill alternator output, no other consequence.
Any other thoughts and would you bother with a repair.?

[Neptune's Gear]

Check the voltage on the exciter circuit when the bow thruster is operating. If it is taking so much power from an ignition switched circuit that it stops the alternator, I'd want to fix it before it causes another failure. A relay for the thruster circuit might fix it. But confirm the issue first. IMO.