I'll check re one being linked to the house, however if that was true how am I getting 30v showing on the battery voltage meters? Could one engine/alternator/regulator feeding the pair of batteries do that?
I found the loose connection but I won't know until I run her properly tomorrow at usual cruising speed if it resolved the issue. I'd rather not run the engines at 1800 on warm. Apart from tightening the battery terminal and changing the regulator settings to P04 I have not changed anything else yet.
A question on your thoughts. Even if the regulators were set in parallel and each on one side of the battery pair, because the batteries are in series doesn't it mean that the batteries "see" both feeds in total?
Now the other thing in play is a ACR relay that was discussed on here a while back. My belief was that was there to turn off or on shore charging of the batteries as well as the house. It could be it turns off and on alternator charging of the house. I will have a look at the wiring today but not convinced it will be that clear as the wiring would probably look identical. That might be a question I would ask the yard's electrician to answer. Maybe even pay them to map out that part of the system.
https://www.trawlerforum.com/forums/s4/question-dc-experts-43933.html