well they wear them because their cheap, easy to launder, and do the job on a industrial site. Seems like that applies to the working environment of a naval ship. What’s the advantage of two pieces? Surely that creates gaps in flash protection?
For the bolded part, I highlighted who already uses coveralls on ship, the Marine Systems Engineering(MSE) Department, they work in the parts of the ship that would be like an industrial site. The Combat Systems Engineering Depart sometimes work in industrial conditions (mostly armaments, though I suppose all do to some extent or another), but often also work in essentially office spaces and server rooms afloat.
All work uniforms on the CPFs are laundered in the ships laundry already, so apart from slightly less folding for the people working laundry, there is no benefit to coveralls.
There are no real gaps in your protection wearing either coveralls or NCDs that don't exist in the other option. Coveralls are slightly quicker to put on, but then become cumbersome while working on the upper decks in the tropics, and are annoying in the heads(washrooms). The new NCDs that have a zippered vs. buttoned shirt essentially eliminate the advantage coveralls had over the old buttoned NCDs, and also remove the negatives of having your top attached to your bottom.
What’s preferred vs what’s better. My pint is about cost, practicality, and usability in what is, from my view, a floating set of workshops, machine stations, and industrial sites.
As I pointed out in the above reply, the people who work in the "industrial" part of the ship already have coveralls. The rest of us work in essentially office type spaces like the bridge, operations room, server rooms, stores spaces, and literal offices.
I’d argue that a ship has a lot more in common with an industrial work site that anything that the new combats were designed for. While I never claimed to be an expert I the navy’s combat operations, this is less like you talking about the tac vest than it is if you argued we should only wear OTW shirts.
Our new Naval Combat Dress was designed for use specifically at sea, in warships. It's flame retardant, can be layered with a FR fleece jacket for cold weather, and comes in multiple sizing options so that it actually fits the individual. It is essentially, apart from the lack of reflective piping, the ideal uniform for the task.
The biggest issue with it kind of goes back to the OTW shirt thing though, in that we don't have a lightweight version for use in warm climates, so we bake in the sun wearing double layer black shirts over black t-shirts when working in tropics.
My intent isn't to attack, rather to point out as someone that has sailed while wearing the new NCDs, that they are great uniforms for use at sea, and the benefits of them outweigh the slight downside of them(speed) compared to coveralls.