I was going to post a similar topic to this but from a different angle (I probably will at some point), but Archipelago generally in Civ 3 is appallingly bad and even selecting Archipelago with 80% Water still leaves you basically playing a Continents Map, so it might well be that you've actually been randomly selected an Archipelago Map but it just doesn't feel like that because the world is designed so badly it feels like a Continents game.
I played a Huge Archipelago 80% recently, started on a smallish island, boomed to be first to Seafaring and The Great Lighthouse, set out to be the first to any 'spare' islands and... I had three land masses to my north, one mega-mass with three Civs already on it, so big it would take me all game to conquer (it took me 1000s of years to circumnavigate it alone), one pretty darn big land mass with two Civs on it and one just plain massive 'island' already completely dominated a Civ.
There was nothing at all to the south of my island that could be found prior to Navigation, even with very long distance suicide runs.
So I was basically playing Japan if Japan was where Indonesia is - a choice of 'expanding' to either China, India or Australia (all of which were already fully covered with a dominating Civ).
I was, like, "so where's my 'Archipelago' feels game? Are you, like... ripping me off or something?"
When I select 'Archipelago' I'm wanting the idea of competing to settle similarly sized tiny to small sized islands, many connected by easy Sea and Coast squares, but some really neat rewards for risking Ocean squares and prioritising naval Techs and production. I'm not selecting Archipelago to get Continents + some islands thrown in.
The game designers really dropped the ball here in my opinion. It's like no-one at head office had any love or interest in the concept of making Archipelago actually feel like an Archipelago, they just tweaked some parameters and thought "Oh well, that'll do" and, no, it most certainly does NOT do.
It's not like there's a lack of source material to guide what an Archipelago should 'feel' like:
And, basically, you want nothing bigger than maybe a 5-10 size twelve city island and, if it it's going to be bigger than that then it should have a large central Volcanic area that's pretty much uninhabitable. There should be very few immediately easily habitable areas, with Forests, Jungles, Marshland and Tundra covering practically every square inch and there should be very few to almost zero Plains and grasslands are mainly for animals rather than growing root vegetables (Hills with Cows on).
When selecting Archipelago, it shouldn't just be about selecting to have 5 or 6 Continents instead of 2, it should be about the whole map 'feeling' like you have chosen a completely different landscape, there should be code to limit the size of Islands, limit what they can have on them, what they look like and, most importantly, be more relevant to Seafaring Civs than simply having the opportunity to 'discover' more than just one 4by4 landmass when you've produced the Great Lighthouse.
The only way to have a 'realish' Archipelago game is to reduce the Opponents to one, which is just absurdly too far in the opposite direction. Even with 16 Civs playing, the map should be capable of allowing for all 16 to start on independent land masses with plenty left to 'discover' (maybe the largest three islands always starting with 2 Civs max).
Rant over!