Leonardo designed a range of water craft, from floating dredgers, to paddle boats, to semi-submersibles intended for use in times of war. He started his studies by drawing the shapes of fishes rationalising that nature had designed these to move smoothly through the water.

Sludge and silt needed removing from canals, rivers and harbours. In one design for a dredger Leonardo mounted large toothed wheel between two barges, along similar lines to a catamaran. A crank or winch turned the wheel, and four attached scoops rotated collecting the sludge, then discharging it into another barge. This barge was only suitable for depths of a few feet.

For deep dredging, of the type required in a harbour, Leonardo considered a completely different option. A dozen anchors would secure this barge to the bottom; such a large number would be needed to hold the barge against the drag of large boxlike bucket beneath it. The bucket had spikes at the open end and perforations to allow for the free flow of water. This 'plough' (Leonardo's term) was then to be dragged out to the required spot and the bucket moved along the seabed, lifted out using a windlass, and discharged into another barge.

The crank-operated paddle boat shown here is just one of many similar designs to be found in Codex Atlanticus. It had shovel-shaped paddles which were turned by a crank system. To assist the operator Leonardo planned a gearing system which caused the paddle wheel to turn at a faster rate than the crank. But the lack of our modern power systems severely hampered Leonardo in this area. He only had wind, water, or muscle power to work with so was forced to try and design ways they could be made to work more efficiently.

One solution he tried was treadle power. As the treadles are raised and lowered they operate a belt around a central drum. This, in turn, is geared to toothed wheels which drive the paddles. This is a very practical design really only required the addition of a steering device to be useful. It is considered that this is about as far as Leonardo could go with the technology available to him at the time.