Preparation for working on 12V High Amp circuits

[j-yelroc]

Hi, my brother-in-law asked me to help him with documentating his electrical system for his 37' French made catamaran with no drawings. The boat is 25 ? years old and has had some rewiring done before he bought it a few months ago. We spent two days this week digging around in the electrical system and I didn't find any safety disconnect means other than disconnecting each battery.

Major Equipment
1 starboard engine, 4 batteries, pumps etc.
1 port engine, 2 batteries (one for refrigerator), 10A charger
1 120V generator on port.
1 12V breaker/switch panel
1 120VAC breaker/switch and shore power/generator switch
Lights, electronics, communications and navigation

I'm a retired electrical engineer and a radio/electronics/computer hobbist for 50+ years but know nothing about practical aspects of boat electrical systems. Being rather uncomfortable around the 12V high amp circuits (70 mm2 conductors) prompts the following questions.

1. Do these boats normally use disconnect switches between batteries and the rest of the 12V systems?

2. Are circuit breakers or fuses used between the batteries and the rest of the 12V systems?

3. Is removing the positive conductors from each of the batteries the usual way to de-energize the high amp circuits for maintenance?

4. We found a switch (DPDT) which apparently connects two battery systems together which had a loose connection on one terminal which had overheated.

Both POS and NEG conductors are switched as verified by measuring different 12V readings on each side of switch and a small voltage (< 0.2V) between positive terminals when it was open.

5. The switch is labeled "Servitudes", a possible definition being "to bind" ?? What would be the English label?

I will appreciate any comments and information to help keep us (and the boat) safe while trying to document the system.

Many thanks!