Emergency generator??

Worst case is you need to start your emergency bilge pump and all that happens is the genset grinds to an immediate halt. The inrush current on that inductive load is many times the FLA rating.

You're left with a dead ship whilst potentially sinking.

His system is set up to be USCG Subchapter T compliant. This is required for commercial operation but also used when a builder/operator is looking for best practice guidance.

For personal/recreational use there are no required standards in the US, not even something like the European RCD. If this is the case, he's free to change what he has but should understand his existing system before making modifications imho.

None of these boats are operated as small passenger vessels so that’s irrelevant. For private use pretty much nobody is going to follow them either, way to restrictive in many aspects.

Many systems will run on batteries for a while incl bilge pumps and lights giving you plenty of time to restart an overloaded gen or switch to the main gen.

OP's questions were why his system was set up the way it is and were there potential down sides to changing it. I'd say those questions were answered.

Relevance to a particular spec is for him to decide, based on how he operates now and any plans for the future, potential resale value, or any other metric that may be relevant to him.

The 240 Vac emergency bilge pump will not be running off batteries and the whole concept of two independent power sources is to account for possible failure of the main genset.

On these boats there are multiple 24 VDC bilge pumps. The 240v pump is an emergency pump which can be started after switching to the primary gen or restarting the back up gen with fewer load

these emergency pumps on Lazzaras need to be primed and the manifold valves open to pump whatever compartment needs dewatering.

Which is precisely what the cheap and easy solution in my post #13 avoids.
Not that I'm pretending it's the best way to skin this particular cat, mind.
That's for the OP to decide - he might find it annoying to go down the e/r (or the lazarette, wherever the genset are installed) just to select which genset to use, for instance.
But other than that, the interlock and all the rest of the wiring would be unaffected.
And also reversing the wiring to the original configuration would be dead easy, if required for any reason.
Imho, boatbuilders often manage to complicate installations that they should instead try to simplify as much as possible.

When running two generators at the same time, which I have had to do on some boats I could lazzara 80 and 84s, you run one leg of the panel on one gen and the other leg on the other. Sometimes we did that with crappy shore power in the Bahamas… one leg on shore and the other one on a gen at peak time.

but for that you need the panel to be split, I don’t know if that’s the case on yours.

Yes, of course. There's a centralised pump in the main mach'y space with rigid piping routed to each WT compartment led back to the pump through a valved manifold. If a raw water pickup is included and pump sized appropriately this can also be used for the fire main (Lazzara likely does not have this). Number of pumps and minimum flow rates are typically spec'd per size and category of vessel.

Submersible DC pumps are generally not considered part of this system by most regulatory bodies, although may be used for convenience nevertheless.

I m not aware of any regulatory requirements for bilge pumps beyond the basic dc pumps. Our 110 also has an hydraulic bilge pump connected to the same manifold so you can dewater the boat if you loose both gens but the mains still run.

The 110 also has a separate 240 vac fire pump with hoses forward and aft.

Yes he can, there are (2) DPDT switches with shore power and main genset inputs with loads split into groups A and B. These should be shown on sheets 3 and 4, respectively.

Sounds like a solid set up. My own yacht has a small belt-driven pump off the single engine in addition to the main electric-driven pump, probably routed a similar way. We don't have a fire pump though

Not related.

When I looked into this, the easiest solution we found was running the generator output wiring all of the way up to the main panel, I think it was in the salon, and running it to where the main generator wiring was switched over from shore, and adding another breaker/slider and switching it there, that way you could run everything from the boat on it. I think the panel in the engine room where you switch over to the emergency gen now, is stuff you would always leave on anyways so didn't have to go to the engine room if you switched it up in the salon. You would have to shut some systems off to run it, but could get 50 amps out of the small generator or so.......the owner backed out of the purchase due to the excessive cavitation getting on plane and some other issues found on the survey so we never pursued it, and this is going back about 6 years now.

I thought all Lazzaras of that era had an ISIS system which included high water and bilge pump alarms.

These multi generator set-ups can be simple or complex. My boat is certainly not as big or complex as the Laz but I have two gens with a simple rotary selector switch. The main gen is a 20k and the day gen is a 9k. The boat came factory with just a single 20k so the 9k and selector switch is an add on. 90% of the time the 9k is more than adequate. Yes, I have to mind my load demand but it’s pretty easy to do. And if for some reason the 9k were to get overloaded (never has) it is breaker protected.

It doesn’t have to be complex. This emergency gen set up is just useless. The 110 lazzara I run has a simple pair of rotaries to choose either gen or shore power.

what is unnecessarily complex on my opinion is how interior lights are powered thru AC with various small transformers to 24 VAC. A number of circuits thru out the have relays to switch to 24VDC from the batteries.

I guess 15 years it made sense since every thing was halogen so lights could be a bit of load and would have required heavier wiring due to length. Nowadays with LEDs it overly complex When I got onboard, I replaced over 300 halogens bulbs for LEDs…

Trending to staying out of this discussion as to not enough information for a clear response, and now spooked by the concept that one might remove the safety slide.

But it would seem easy enough to simply run both legs of the service side of the supply switches to the same terminal, where they are protected from each other by the slide switch, and let both dual legs feed the main panel. Yes, you'd have to manage the loads via breakers, but at least you could power the devices that you must have up to the limits of the supply...

Mine is set up this way with multiple incoming shore and generators, all managed by slide safety switches, all feeding the same terminal bars. But the photo of the backside of the slide switch suggests to me that one incoming leg is not used to feed anything at this time? Are all items it powers presently single leg 120v? Is there power to the leg without a service line leg? Confused a bit...

Mine is complex at first glance. But then once you understand what you're looking at, it's pretty simple. Each incoming supply from shore or generator (2 each) pass through their own primary breaker, then at the panel they enter their own supply breaker amongst a slide switch and parallel to spread the load, not much unlike the single slide switch posted above. Mine has two slides, each with a shore and a generator breaker as well as a parallel breaker. You choose the incoming power you want on one slide, and then engage the parallel on the other slide to power both buses of the main panel. Again, complex perhaps at first glance, but then it's really straight forward and logical.

In theory one could run each bus off one generator by not using a parallel breaker. The theory works, but I haven't tested the circuits to rule out any AC contamination across the buses....scared to find out the bad outcome occurs...