Frigate

Notes Travels on water, can Fire cannons
Frigates are your only sea transporation, and are required to reach a number of Locations. Most notably, you need a Frigate to find Ambrosia or the Exotic Arms and Armour.

You can't buy or find a Frigate, but rather must claim them from Pirates. After defeating the Pirates in combat, the Frigate is yours to command.

There are a few points to note about Frigates. First, while Firing cannons is an effective way to remove enemies, you won't gain any treasure or experience by doing so. Second, you can only sail with the wind, so if the wind is calm or contrary to where you're going, you'll be stuck. Given how quickly the wind changes, this can get annoying fast. Finally, while touching the whirlpool while on a Frigate brings you to Ambrosia, if the whirlpool hits a Frigate you aren't riding, it will destroy it.
Compare Frigate to other Vehicles
Horse

Related

Frigate

Key d
Actions/Food 5
Weapon Cannons (range 3, 32–70 damage)
Traverses Water
Blocked By Grass, Woods, Mountains
Price 320–608 pence
Sold After Game start
The Frigate is the first Vehicle you can get with a weapon. Its cannon has a three-square range and does pretty good damage. Its maximum damage isn't as high as your Weapons by a long shot, but it is much more consistent because its minimum damage is so high. On the overworld, the cannons are often a safer choice against all but the highest-HP Creatures.

Frigate

Food/14 Actions 3
Weapon Cannons
Traverses Water
Blocked By Grass, Woods, Mountains
Price 323–608 gold
Sold At Level 1
The Frigate is the first Vehicle you can get with a weapon. Its cannon Fires at range, which is very useful at sea where all Creatures have ranged attacks. The cannons are pretty powerful, too, and well worth using.

Frigate

Food per Tile 0.00
Notes Travels on water, can Fire cannons
Frigates are the best overall mode of transportation in Ultima II, but you don't initially have access to them. You'll need a Blue Tassle to Board a Frigate. These are dropped by Thieves, but Thieves can also steal them. Frigates are so useful that many consider getting (and keeping) a Blue Tassle the key to the entire game. (Despite that, you don't actually need to ever use a Frigate to complete the game.)

There are three basic advantages to Frigates. First, they travel on water, which means you can head to other continents. Second, you use no Food while sailing, which can be a huge money saver. Finally, you can Fire the Frigate's cannons at enemies, which acts like a super-powered Attack. The damage is random, but its maximum is quite a bit higher than your own, so in the long run cannons are always the best Weapon to use if they're available.