Qactus
Romani ite domum
That depends on the settings. There are archipelago maps where almost all islands are connected w/o ocean in between. That's what I meant when I said it is sometimes possible to circumnavigate (and unlock the extra movement) with galleys.Thank you! How many of the island will usually be connected by sea, as opposed to ocean, tiles?
Here are some sample archipelago maps for (left to right) snaky continents, islands and tiny islands:
(This is from https://civ-wiki.de/wiki/Kartensammlung_(Civ4). It's a very useful overview to get an idea what mapscripts will look like and what their landmass settings will do, it's in German though)