Tuned Ships are the most ancient and valuable vessels to sail on the Thousand Tides. Millennia ago, Elves learnt how to attune something to the Tide they’re attuned themselves and applied this knowledge to shipbuilding. For this reason most non elves simply call them “Elven Ships”. Building an elven vessel may require decades, which explains the rarity of this kind of Ships. When a Ship, or at least the Ship’s hull, is completely attuned to any one Tide, it can sail on that Tide as if it was water. So, an elven ship attuned to the Tide of Sand (which some sailors may call “a Sand Ship”) can sail on every sandy terrain as if sand was a fluid (which means sandy beaches and desert dunes alike), while a ship attuned to the Green Tide could navigate every terrain with enough vegetation. That applies only to the ship itself, so a sailor falling from the deck or the masthead while sailing on the Tide of Stone, will impact on solid ground, no matter how close to the hull he falls. Of course the perils of navigation still apply: where a small amount of sand covers a stony terrain, a Sandy Ship could get stuck (while a ship attuned to the Tide of Stone could sail easily) and a wide prairie could be suitable for a small Green Ship, while a greater vessel would require a more luxurious vegetation (and both regions could not be navigable in winter on a boat attuned to the Tide of Green, due to the lack of vegetation).
Also, attunement to a Tide does not confer to the ship any kind of propulsion, so the usual means are necessary to make the vessel move: wind and oars (which must also be attuned) are the most obvious, but pulling is also widely employed and various forms of magic (such as binded elementals or magical wings) are not unheard of.
A Tuned Ship’s hull is submerged in its tuned Tide roughly as much as a Mundane Ship’s is submerged in water, so she sails more or less horizontally, according to the shape and currents of the medium. As a Mundane can be submerged in water, a Tuned Ship can filled by the Tide she’s sailing on, should the hull be compromised. But an Eleven Ship can also sail through her tuned Tide unharmed, should the crew find a way to have the Ship move up or down. This is extremely useful to reach submerged kingdoms and Vaultlands. All the sailors speak in awe of the Elves of the Winds shifting airstreams with their vessels, while many songs have been written about Blue Elves’ warships rising from the depth of the seas to sink the ships of their enemies on the surface. Note that this property is not extended to the crew members, who can’t automatically pass through stone or breath underwater only because they’re on a properly attuned Ship (though below deck they may be protected).
To Elves, navigation is the highest form of art. Elven navigation techniques are so refined that members of other races find it difficult to operate their Ships properly (though Sophians are rumored to have achieved impressive results), but Elven Ships seldom fall in non elven hands anyway.
An Elf can only attune something to the same Tide she is attuned to (and changing attunement is an important and intimate matter for any elf), so, a ship that can sail on the Tide of Winds, the Tide of Green and the Tide of Sand, will need three different teams of elves from different Kingdoms to work together (which is harder than it sounds). Of course you can take your Green Ship built from Forest Elves to the Elves of the Sands for another attunement, but that would probably require them to disassemble the ship, attune every single piece of the hall and then put it together once again, which will probably require years of work (not to mention the costs).
Paradoxically, elven ships, sometimes, don’t float in water, since they don’t need to be made of wood to float in the Tide they are attuned to: the attunement itself makes them lighter then the Tide (which explains why the expression «lighter than the Tide» means “able” “fit” “capable” in the sailors’ cant). For example, the White Marmaid is made of white marble, sailing the Tide of Stone all the way to the sea, where she doesn’t sink just because she’s also attuned to the Tide of Blue.
Tuned Ships were once, back in the Elven Age, the only means to Sail the Tides, but now they are increasingly rare, due to the fact that elven kingdoms are not populous as they used to be, that the times and costs of construction are extreme, and that a great number of vessels went lost through the centuries because of wars, shipwrecks, monsters and pirates.