Biggest bugbear I've had with the first two Tropicos is stopping the indefatigable drain on happiness levels for all my citizens..... nothing seems to stem the happiness haemorrage! Any tips guys?

Try putting down entertainment buildings, (Cabarets, an the little food places in the beginning) and eventually when you get power, casinos and stadiums

In Tropico 2 you have to manage happiness both of your pirates and your captives.. they have different needs.

Anyway.. first 6 months the happiness level remains quite stable...

For pirates:

Start building as soon as possibile some Wench houses and set up the production of beer ..then build a Smuggler's Dive where they can drink .. and an Animal Pit for gambling...

When you start cruising and making some money .. continue to provide more and more advanced entertainement to the Pirates ..kidnap specialist to set up fruit farms.. and all the chain of food production .. 'cause having tastier foods and more choice.. makes pirates happier.

Create some pirate housing plots .. pirates are glad if they have a place where to store their booty!

Keep "Big spender" policy while cruising .. Pirates get happier this way (and richer too!)

There are some edicts to improve happiness, too..

For captives:

Don't make them starve! Keep an eye on having enough chuck tents .. and provide them with enough corn to produce the slop to feed every worker/prisoner on the island ( it's the only thing they eat). Starving makes captives very unhappy!

Build some Bunkhouse where they can sleep and rest.. they're happier to have a place to rest than having to rest outside under a tree!

Satisfy their needs for religion (kidnap a priest - build a church) ..and build the advanced structures to keep them safe and sound.

One trick I use in Tropico 1 is to look at the unhappiest person in the journal and see what he is complaining about. It is certain that other citizens also want what that person wants. If he complains about the island being boring, I build entertainment; if he is short on food, I provide more markets near residential buildings; if the island is getting polluted, I issues some decrees to clean it up; etc.

It's counterintuitive, but you don't need more of entertainment buildings in Tropico 2. Just build each type of buildings once.
Keep big plunder share for seamen, their share even with that option is too low!