Bow thruster / Battery issues - Winter project

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Hi all,
After lots of searching on the internet I thought i'd ask the collective on here for advice. This is my first season boating, the boat is new to us June this year.

It's a Maxum 2600 SE, current battery set up is 2 x 85 AH deep cycle batteries connected to a 1/2/Both switch. They are about 18 months old. Thruster a side power SE 40/125

I start the engine on 1, switch to 2 on the anchor then 1 to start again at the end of the day. Both charged on shore power when back at the marina.

When using the bow thruster frugally (pain in the backside home berth and it's installed so why not use it!) , the voltage drops quite significantly on the dash display and the other day cut out the nav display.

This is my plan :-
Parallel the 2 x 85 AH deep cycle batteries and use as the house bank (Switch position 2), buy and fit a proper starting battery with some serious CCA to use for starting and also to help deliver some decent power to the bow thruster as I don't think the deep cycle batteries can deliver the power in quick short bursts.
I figure this is the easiest and cheapest way to do it.

Questions are....
1. If the thruster is connected directly to the battery already should switching to the both switch help? It doesn't seem to at the moment . I also need to check which battery the thruster is currently attached to.
2. Will the two AGM's in parallel charge together on shore power and by the alternator? (If not I have a third slot on the shore power charger)
3. Will my described set up work or improve things?

I'm aware of voltage drop through cables and have included a picture of the existing cables at the thruster, they seem thick enough, I would estimate the run at about 5 metres from batteries to thruster.

I don't really want to add dedicated batteries up front for the bow thruster due to expense/complexity/room and it really is only used for 2 - 3 short bursts.
I also don't really want to change my whole battery/switching process to VSR charging and also hoping to avoid the apparent life long depate about the 1/2/both switch !

Really appreciate your time and thoughts, if my plan wouldn't work then i'll have to re-think the battery up front.
Cheers.

 

[Keith-i]

Voltage drop could be as much to do with dirty or corroded connections as anything else. I’d certainly consider pairing up two batteries as the house set and a new high CCA for the start and thruster. To finish it off nicely I would as a VSR or 2 way Mosfet switch to automatically deal with charging the two banks and avoid the need for all the 1,2 and both switching.

 

[GaryJeffery]

Yes, check and clean up the connections first before spending out. I was a victim of this couple of years ago, thruster worked fine when leaving berth, then two hours later manoeuvring into a lock it just popped the breakers and shut down both my engines, not fun! No fuses blew, no apparent cause you could see, after much musing and checking everything, the very last thing I checked was the battery terminals. They were a bit corroded but not terribly, quick clean up with some wet n dry and reassembly did the trick, back to perfect. I’ll check the terminals first next time!

 

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Cheers for both replies. Heading down to the boat tomorrow so will check all connections.