While carrying out my monthly checks this winter the bowthruster burst into life as usual but then quickly faded away, stopped. First thoughts were that there must be debris stuck in the propellers so I took the top off the weed box at low tide and checked it out. No debris, just some barnacles which I cleaned off. The thruster ran fine with no water to slow it down (see below) so I put that all back together. We tried it again at high tide and there was a loud bang and the top blew off one of our 4 batteries. They were maintenance free Gel batteries in series making 48v so I guess they had slowly failed and one had built up gas and blew its top off.
We replaced the batteries with Gel again with the main requirement being 800 CCA (Cold Cranking Amps) as the bow thruster draws hundreds of amps when it runs.
After resetting the electrical relays it all worked fine and Waterdog is fully mobile again.
It is a SIDEPOWER 285 Kg Thruster Twin counter rotating 4bl props., IPC, 48V / 24V. It starts with 24v and after a second a relay closes to make it 48v and it speeds up. It has given great service since 2007 so far and seems clean and efficient. It will run continuously for up to 4 minutes before shutting down to stop it over heating, but we generally use it for less than 10 seconds at a time as this is all we have needed. When doing a 180 turn in a river we occasionally need a longer burst but never more than 30 seconds so we would recommend these to most barge owners.