Imagine a colossal iceberg made of pumice. It's long and narrow, shaped almost a little like a battleship above the water; underwater, its draft is shallower at the ends and deeper in the middle, making it wedge-shaped. At the "stern", two rocky promontories frame an underwater shelf that gives rise to a crescent of sandy beach. The forbidding uplands of the island are actually fairly fertile; crop fields and grazing for the Thousand Hands Convoy's few animals take up most of the island's area, except for one precious stand of tall, straight ironwoods near the center. The whole thing's about a mile long and a quarter-mile wide, with a draft of about six hundred feet at the deepest point.
Now add to this island a series of hundred-foot towers of solid ironwood, nearly impervious to sun, wind, and sea-spray. Crossbars on these masts are booms; from each boom hangs a great canvas sail. The island has thirty masts, each with four sails; needless to say, there's a lot of pretty serious full-time jobs to be had in keeping them repaired. Thankfully, the booms normally rest on the ground, to be hauled into place (via blocks-and-tackle at the top of each mast) when the island needs sailing, so they're more accessible than one might think. The rigging for these masts is a pretty darn impressive lot of rope.
And that's just power: they've got to be able to steer the thing, too. At each long side of the island, five huge rudders hang from shafts driven deep into the rock. Another series of pulleys and gears connects the ten rudders to a central wheel and makes it possible for just five men to steer the island.
That said, even this impressive system gives the island just enough maneuverability to keep it out of the Wyld and off the reefs. Most of the time, eight of the ten rudders are out of the water, and all the sails are folded round their booms and resting on the ground. When the island is under full sail, it's both a serious emergency and an incredible sight. Half the ships of the Thousand Hands Convoy lie aground on its aft beach or anchored in the harbor, and half the Hands work its rigging while the others sail around it -- or even cast lines around one of the rudder-shafts or masts and help tow. Even then, the island can only barely fight the current to make five or six knots, and its turning radius is something like two miles.
Stats[]
Speed: 3/6 MPH/50 miles per day
Maneuverability: Attacks always hit
Endurance: Needs at least three repairmen at all times
Crew: 30/5
Cargo: Several dozen tons
Armor: None
Health Levels: Ux1000/Mx500/Cx300/Ix100/D (or whatever the ST says)
Weapons: None normally