Electronics/Emergency Power Supply

[Dockhead]

One design brief point for my hypothetical new boat which I'm struggling with is power supply for radios.

GMDSS requires an independent backup power supply for radios. Seems like following this standard would be sensible for a boat designed to be used far from civilization and rescue services.

However, unnecessary complexity and weight is also not desirable. I've never had a blackout in decades of cruising, but that doesn't prove that it's not a risk (unlike those who reason -- I've had non-ABYC gas installation for years and never blown up my boat; ergo gas is perfectly safe and there's no need to follow ABYC). I presume that the new boat will have LiFePo batts, and I guess there will be a greater risk of a blackout, since I'll be using less developed technology.

So if I do it, how to configure it? Seems to me:

1. Should be lead acid, since FLA batts like to be kept at 100% state of charge, whereas Lithium Ion batts do not. Also easier to manage.

2. Batteries, chargers, and all electronic parts of this system should be mounted in a position which will make the system resistant to flooding in case of a flooding emergency.

3. Perhaps should be echo charged from the main engine start bank. This violates the total purity and independence of this bank, with its separate alternator, no consumers, etc., but I think this is a good enough cause for that.

4. But when using the SSB for data, I will need lots of power. Can I echo charge from the main bank also? Or maybe have the engine start bank echo charger just as a backup, manually switched? Or is this getting too complicated?

5. In any case, the emergency radio bank should have an AC powered charger, powered by the regular AC system. So power can go into this bank from any part of the boat's electrical systems.

6. Now what to power with it? Just the radios as per GMDSS? Or also the navigation electronics? And maybe nav lights and emergency lighting? Bilge pumps? Does this start to get too complicated?


Besides complexity I worry about weight, but maybe a couple of extra lead acid batteries and some wiring is not such a problem on a 20 ton boat, compared to the extra margin of safety provided.