Looking at the sailing ships (non coastal)
Man O'War (Warship) - Perhaps slow it a little Max move 3, 4 with navigating the world, (no longshore available). Remove its cargo capacity completely. Bombardment of 8%.
Queen of the Line - Should have the same movement as the Man O'War. But increase its cargo to offset the loss of the Man O'War
Frigate - This was created to counter piracy, convoy protection. Should be faster than the Man O'War - cargo of 1 max. Allow it a promotion specifically against pirates, and Lanun versions can capture other vessels, without the boarding party. It should also be fast at least move 5 or 6 with a strength of 6, No Bombardment function. They were too small and light to be anything more than an irritant.
Galleon - This is a rather unhappy cross between the caravel, the Queen of the line and the frigate, famous for carrying gold and getting sunk by hurricanes and pirates. It was after all an early version of the Man O'War with cargo. Which if implemented in game would probably result in lots of Galleons at the expense of everything else.
So same speed as the Man O'War, with 3 cargo. But there are down sides. They should be especially vulnerable to weather events. Weather was a far greater threat than anything else in the age of sail (a wee stat - Between 1745 and 1815 the RN lost 238 frigates, of which 16 were to enemy action. Some were badly built but most foundered in bad weather)
Caravel early explorer ships. They should be faster but with a low combat factor and perhaps a greater visibility. STR 3, Mov 6. Id leave the cargo at one which gives them a variety of options. See below I think the Amurites should get a fireball equipped version of this as well.
Pirate everybodys favourite Its combat factor and move should stay the same. It should get a promotion against any cargo ship and a further one against galleons. All pirates get gold from galleons, but Lanun should get extra again.
Arcane Barge I think its actually fine as is. But instead of giving an extended one to the Amurites, give them a caravel version as well.
Id also like to see the Dirge come back, possibly as a UU for the Sheaim or Hyborem in addition to the arcane barge.
Weather events
Squall at sea, a ship is lost. If on the ocean, with all hands. If on a coast then a warrior or scout is created from the survivors. If the ship is Lanun it creates a boarding party. The nationality of any of any of the above units is hidden, as they are lost far from home, it also avoids problems with border control. Of course survivors probably wont last long.
Storm at sea. As above except that the ship is lost with all hands regardless of location. There is plenty of precedent for this.
Hurricane - If this happens it kills all ships in a stack or hits a coastal town and destroys any ships in port with a chance that it may destroy improvements in the town too (biased towards harbours, walls and other port improvements).
On the less bad side
Navigator one of your ships captains has developed a knack for interpreting the weather.
+1 Movement or
Avoid storms and squalls events or
+1 Visibility
If these arnt already available for the Lanun -
Pirate captain
+10 value on any ships captured or
+1 STR or
+10% chance or withdrawal from combat
Hero of the seas
Gives the ship the Hero promotion.
Finally a building, Lanun or all?
Coastal Fort fires back at ships that try to bombard. (Can this be done?) STR 0/10. Make bombarding soo much more dangerous.
I also think Lanun ships should be able to attack and capture ships in cities. It was called Cutting out and involved sending small boats into the harbour and boarding and nicking ships in the harbour, again plenty of precedent.
