With that kind of draw you should be able to run the thrusters on a 270Ah AGM for about 30 minutes to 50% DOD (technically empty for an AGM) and then need to recharge again, if not charging the battery at all while using it. If accounting for the 50A from the DC to DC you will be able to run 45 mins continuously before the battery needs to rest and recharge, although discharging the battery 1C constantly is not always good
>The estimated current draw of the thrusters is 270A (Fused at 325A). Its a 6.5kw motor
Blimey. I would have thought 3 phase motors with AC drives supplied by the generator and cut out all the battery stuff.
I have a 5.5kw 3 phase motor for the BT and the Fischer Panda generator, ex BBC outside transmission van, is dual wound 1 and 3 phase. I did consider a DC BT but concluded it was too much hassle and phaff, with much DC larger wiring. I also considered hydraulic, but again concluded that a 3 phase cable pen thickness was easier to do.
But, I could probably now use a 5.5kw 1 to 3 phase AC drive, but I don’t recall seeing those in 2006. (I’ve recently added a 1.5kw 1 to 3 phase AC drive to use the anchor winch 3 phase motor off the inverter rather than starting the generator).
I’m 22m and 70 tons.
@BruceBaby A couple of thoughts if your 60 ft vessel/systems are still at a design stage.
I’d definitely be tending towards 3 phase AC BT.
With careful design of steering gear and rudder, eg articulated hinging rudder or 90 - 0 - 90 rudder arc, then I reckon the rudder can be used as a stern thruster instead of installing a conventional system.
@CRuMbS WOW that’s a serious setup - thank you for the ideas but definitely passed the design phase, just purchased the boat, all is complete but in a different environment which requires a little more thruster work and the current system just doesnt keep up. Probably going overboard but I guess it’s easier just to do it once.
@JakesNell Thank you for the calculation, definitely more thruster time than I need 
As far as viewing information once installed, is the App and BMV’s enough or connecting the entire system to a display/monitoring system recommended?
Have you thought about using a Automatic Charging Relay?
https://www.bluesea.com/products/category/35/91/Automatic_Charging_Relays/ML-ACRs
The bigger ML-ACR’s are a lot better at handling the loads you are looking at. I’ve installed a lot of these in the exact system/battery bank layout your describing.
And they also work as emergency paralleling switches in a pinch to get dead engine start batteries going.
Hi @Captian thank you for the recommendation.
These are instead of the DC-DC?
Yes, they are meant to replace the DC-DC converters.