question

As long as they are from the same model and type number it will work. This means its best to order them from the same year. Older ones can be slightly different which makes it impossible to combine them

One approach would be to split your AC loads between the two shore power inlets and run the Multis completely independently. You'd still be able to parallel the battery connections to a common battery bank and have both Multis charge the batteries.

Another approach would be to use separate chargers and inverters. For example two Phoenix chargers, one on each shore power inlet, a common battery bank then any number of Phoenix chargers to meet your load requirements running in parallel. The down side to this is there is no pass-thru or assist. Loads are always powered by the inverter. A big plus however is the Phoenix charger accepts 90-265 volts and 45-65 Hz so your boat would easily accommodate shore power anywhere in the world.

[moderator's note: edited to remove incorrect information - JC]

@Jonathan Contre, yes, this is absolutely possible, and quite routinely done. If possible, please provide a link to the thread you saw stating that this was not possible, as we'd like to correct that information.

For reference, please see the Parallel and 3-Phase VE.Bus Systems Manual and the several external documents referenced therein; as noted by others, there are several requirements, such as matched units (be sure to tell your authorized Victron dealer that you're planning this type of setup so they can be sure the units are matched) but, aside from a bit of added complexity in wiring and programming, it's entirely common to do what you're planning and it works perfectly!

You can to use 2 separate shore AC inputs, one for each MP, but you need 2 separate circuits on your boat.

Outputs from those 2 MP's cannot be connected together.

Both MP's can charge the same battery, but they cannot be used in the parallel setup on the AC side.

Firstly, I'm an RV guy and not a boat guy, so I'm not very familiar with shore power hookups at docks -- take the following with a grain of salt.

When you say "dual 30 amp shore inputs," are you talking about two separate receptacles that each expect 30A/120VAC input?

If so, it's going to get complicated, because if you're docked somewhere and are looking at two separate 30A/120VAC outlets there's probably no expectation that the two "line" conductors (one from each outlet) are either on the same phase or opposite phases. If you could guarantee that those two outlets' line conductors were bonded upstream and hence were on the same phase, you could set up the Multis for parallel operation. On the other hand, if you could guarantee that the two line conductors were on opposite phases, you could set them up in split-phase operation and that would also be fine. But there's no reason to expect either situation to be the case when looking at a pair of 30A/120VAC outlets; they could be in phase, 180 degrees out of phase, or 120 degrees out of phase (if each outlet was on a separate leg of a three-phase system). You'd really have no idea, and even if you determined this, you'd have to do some pretty clunky reconfiguring of the inverters (in software) to accommodate the input phase configuration. Not a great idea.

Also, a cautionary note about putting Multis in parallel (same phase input) and supplying independent circuits or bus bars. In parallel operation, the Multis expect their output line conductors to be bonded together downstream; i.e., they have continuity. If you have power assist enabled in such a scenario, then when the load exceeds the input current limit, both inverters will briefly step up their voltage to overcome the instantaneous demand. But if their outputs are supplying separate circuits or bus bars that do not have continuity, what will happen when the load exceeds the input current limit is that the circuit or bus bar without the increased demand (imagine an air conditioner overcoming its locked-rotor amperage) will actually experience an overvoltage fault and the inverter on that phase will likely shut off completely.

I spent around $15k on my RV's power system and used all Victron components and connected everything by-the-book, and even some of the very basic claimed functionality is not currently working (for example, my Multis are only drawing 23A despite the input current limit being set to 30A, and thus unnecessarily draining my batteries to power a 29A load), so before you do anything that does not reflect a completely standard implementation I suggest you actually see the same configuration working as you expect on someone else's rig before you invest in any components.

Good luck and let me know if you have any questions.

Edit: If you set up the inverters for split-phase input and they wind up on single-phase input (i.e. the two 30A outlets you're plugged into are not 180 degrees out of phase), what will happen is that only the primary inverter will accept grid input. The second inverter will reject it and invert from the batteries. This may be okay for your application, because the first inverter will charge the 12VDC side as the second inverts, so continuous operation without battery discharge is possible -- but only up to the charging capacity of the primary inverter, which is 120A VDC. That's around 1500 watts, but after conversion losses, you'll really only get ~1200 watts of continuously usable power on L2. Any draw in excess of that will result in battery discharge. If your continuous loads on L2 are significantly below that threshold you should be fine.