caltexflanc
Guru
Can I say that Deep Cycle and dual purpose batterys have no place driving DC Bow thrusters. The issues are simple, deep cycle batteries do not deliver cranking amps for anything like the duty cycle required and although some quote outstanding CCA numbers the duty cycle is in some cases less than a second. The other problem with dual purpose batteries including deep cycle is in their in ability to recover - they dont absorb current well and need trickle charging.
In my experience thrusters will fail when the boat owner is returning home after being away and the batteries are down, there is a thought that simply running home is enough to re-charge the banks but that isnt always true.
In a series wound DC motor cranking capacity of your battery and its duty cycle is the only thing that matters.
Sometimes the cheap batterys are the good ones - good old lead acid for me.
Funny thing, Vetus specifies what size battery to use for their thrusters by giving an amp hour (not a cranking amp) specification and range. They also note that if the capacity exceeds the top end of that range, and the cables are larger (or much shorter) than that specified in their table, the usage time must be reduced to avoid motor damage.