Bow Battery

22 June 2021 – Bow Battery

During yet another COVID-19 lockdown period, another improvement job was to look at the bow battery – that drives the bow thruster and windlass. This battery is physically separate from the house bank, and gets charged from the house bank or the Volvo while running. The Wesmar bow thruster uses a very powerful motor, and draws over 300A at 12V DC. It’s not unusual for this kind of current to produce a voltage drop. I last replaced the battery when in India two years ago with the best one I could find, an Exide dual purpose wet cell maintenance free lead acid battery. It didn’t quite “fill the space” in the battery box, and always left me wondering whether it was up to the task.

Unfortunately, that Indian battery was still not “big enough”. When operating the bow thruster, the battery voltage falls down to only 10.5 volts (at the battery monitor) and I’m sure it’s even less at the motor terminals. I needed something that “fills the box” more, just gets more lead in. Finding a replacement in Turkey, or anywhere for that matter is a challenge. This meant finding the biggest, heaviest battery – the size of the 8D standard in North America. The local chandlery was able to offer a Mastervolt 8D AGM battery with 225 Ahr storage, at a weight of 63.5 kg, but I wanted the next size up, the Super 8D model with 270 Ahr coming in at 73 kg. After 3 months of waiting, and still no prospect of delivery, I sought out other batteries in stock anywhere in Turkey. I came across a vendor in Istanbul who had an Exide 8D battery with 240 Ahr and weighing 72 kg – a winner. Kemal at the local chandlery brought it in for me at the same price. This 72kg battery came with its own “challenges” to lift up and put in place, and thankfully Mesut and Ennis (two of the marina Marineroes) carried it in for me.

I felt that another incremental improvement could be gained by replacing the existing “copper welding cables” with larger diameter proper tin-plated copper marine cables. These old cables were given away to a “new home”.

While replacing all these cables, I need to remove this switch, and of course – had to fabricate a new trim ring.

After installation tests confirmed that the 300A current draw pulled this new battery down to 11.4V, a slight but worthwhile improvement over 10.5V. Another COVID-19 lockdown project finished.

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