Bone-bile constructs are well known for their reliability and customization options. They have the possibility of being a worker, fighter or steed, it all depends on their design and etchings. While most folk see them on land, such adaptability means they aren't restricted to terrestrial work. These automaton can be found upon the coast, but not in the way people think. Indeed, worker constructs are often employed on the docks, aiding in the loading of ships, but that is still dry land. There are bone-biles that are designed for a more aquatic lifestyle, though obviously they are not as common and fill a more specific niche.
The "sea steed" is one such creation, a bone-bile that has been specially built to work in a fluid environment. Meant for coastal waters, such creations can be easily identified by their blue coloration. Unlike most bone-biles, those meant for aquatic work swap out the typical ivory bone for that of fish. The Blue Blood stained fish bone is lighter and more resistant to constant fluid exposure than other bone types. Plus, it naturally comes in hydrodynamic shapes, calling for less alterations when assembling the construct. Some folks even say that fish bone, and abyssal bone, has a certain "smell" to it that helps such automaton or equipment better fit in with the local fauna. Black Bile is still used to program and power the construct, though the strains used are usually harvested from aquatic sources. Such materials are crucial for creating an automaton suited for fluid environments, which is a big reason why they are uncommon. But of course, the niches they fill do not have high demand, thus their fewer numbers rarely cause issues for the target audience.
The function of the sea steed is noted right in its name: it is a bone-bile mount that is built for carrying someone through fluid. The usual place of their employ is in coastal regions, swimming through the ocean shallows. The design has many piscine properties, forgoing usual arms and legs for fins and steering tails. More hollow spaces are built in, as well as air bladders to help reduce their weight and increase buoyancy. When at rest in fluid, their programming has their fins execute specific movements to keep them floating, idle paddling so that they do not sink or be swept away by waves. Much of their etching is dedicated towards its survival in aquatic environments, as the sea is a far more demanding place than land.
To ride a sea steed, all one needs is a saddle and fluid resistant clothing. Sit upon its back and grab hold of the pair of short appendages that jut from its spine. These give the rider something to hold onto, while also functioning like its reins. By pulling or pushing either of these limbs, you can steer the construct as it swims. Sea steeds can swim fully submerged, diving deep in the fluid, but most people ride them on the surface. Makes it much easier to breath and calls for less equipment for the rider to handle the voyage. Visiting the coast will have folks see them be used mostly for transportation and guidance, allowing individuals to ride through the shallows or meet up with boats around the docks. Many major ports have a number of these constructs on hand so that workers can help guide boats in and out, deliver messages or perform inspections. Though they are suited for aquatic environments, they rarely leave the shallows and enter the open ocean. There is only so much weather they can handle, plus there is little reason for an individual with hardly any gear to go out into the endless sea. Thus, much of their work is around the coast, even when it comes to fishing or diving down for harpooning or salvaging.
Of course, the other role they can fulfill is one of attack. Sea steeds can be deployed to attack incoming vessels, or be sent from said boats to assault the coast. Though small in size compared to warships or even trade vessels, their speed and maneuverability makes them a serious threat. Heavy weapons like cannons are not designed for such small targets, and long range weaponry may fail when the steeds move in too close. Riders will carry weapons and equipment designed for breaching hulls, crippling rudders and causing general chaos. With the right gear, they can disable the weapons of a ship, allowing their larger vessels to approach with little threat. Such tactics are a favorite of pirates, as there are bands that rely on these steeds to ambush trade ships. Rush in and take out all movement and attack options, that way it is easy pickings.
However, it should be warned for any who dream of zipping about the ocean with these steeds: there is always a bigger fish. Sea steeds are designed like aquatic fauna so that they perform well in such environment. However, the drawback is that they look and swim a lot like said creatures. In the shallows, such predatory threats are rare, but it can still happen. In fact, it is said that some trade vessels have learned to flee towards deeper waters, or even use lures to attract larger beasts to the scene. The animal may not be big enough to eat the boat, but these little darting things may fit right on their menu.