Welcome! What kind of boat? 
. (I used to spend a lot of time on the water, mostly sailboats but also deep-sea fishing, but that’s no longer practical for me. )
for right now, the classic app is much more powerful than the new app, if only because you can’t use any custom smart apps with the new app. But they’ve also told us that the classic app will be going away eventually, although no timeline has been given. You can use both at the same time, and some people are, so that’s another option for now. Just be aware that the “smart home manager” in the new app is a completely different features than the one in the classic app even though they have the same name. So if you set up something with SHM in the new app you won’t be able to disarm it in the classic app, and vice a versa. ( that confuses a lot of people.)
See the following FAQ (the topic title is a clickable link)
I’m tagging @johnconstantelo and @twack on the mimolite questions. @ogiewon might also know of some similar use cases as he’s one of the major maker contributors to the community.