I don't think it's as simple as we'd like it to be. A boat doesn't necessarily resonate with all of us. I have never had in my 40 years of living any kind of connection to a boat or known anyone else that does.
Not all psychics have all of the gifts. A clairvoyant might ONLY be clairvoyant and not clairaudient or even clairsentient. It takes a lot of time and practice to be able to interpret those things. Most clairvoyants are able to do so, and some still have a lot of learning to do with it.
Like, say a clairvoyant sees something happening near water. Well, that could be a pool, a shower, an ocean, a river, basically anything near water or that includes water. Hell it could even be drinking water. If they don't know how to interpret it properly, they just need practice. I"d say, if they share that information with you but can't interpret what it is at the time of the reading, perhaps just be on the lookout for said thing and you will then know what it was to mean.
Spiritual things are not as clear cut to us as things here in this dimension. there's maybe also a possibly that we aren't meant to know what it means until it happens. I don't know. I'm just speculating.