I've being saying a lot lately: I'm a noob here, and I've been caught out before asking for a feature that was already there (but somehow missed) so I hope I don't annoy anyone if this can already be done.

It seems to me, the only was of adding a new ship to an existing fleet is by deleting the old fleet, then making a new one. Is it possible we can just add a new ship to an pre-existing fleet? I think these kinds of short-cuts that speed things up, and also decrease pages downloaded, just help everyone

that exists just press on the fleet name when the fleet page open you can add the ship there

The fleet and the ship have to be in the same port. The fleet route must be paused( coming soon) or terminated before you can add the ship.
Either click on fleet name or select fleet from manage fleets.

We have just added the ability to add/remove ships on a paused trade route fleet. So you can now pause the fleet, change the fleet composition and then activate it again.