The design of watercraft requires a tradeoff among internal capacity (
tonnage), speed and
seaworthiness. Tonnage is important for transport of goods, speed is important for
warships and racing vessels, and the degree of seaworthiness varies according to the bodies of water on which a watercraft is used. Regulations apply to larger watercraft, to avoid
foundering at sea and other problems. Design technologies include the use of
computer modeling and
ship model basin testing before construction.
Watercraft propulsion can be divided into five categories.
Water power is used by drifting with a river current or a tidal stream. An anchor or weight may be lowered to provide enough
steerage way to keep in the best part of the current (as in
drudging) or paddles or poles might be used to keep position.
Human effort is used through a
pole pushing against the bottom of shallow water, or
oars operating in the surface of the water.
Towing is used, either from the land, such as the bank of a
canal, with the motive power provided by
draught animals, humans or machinery, or one watercraft may tow another.
Mechanical propulsion uses a
motor whose power is derived from burning a fuel or stored energy such as batteries. This power is commonly converted into propulsion by
propellers or by
water jets, with
paddle wheels being a largely historical method.: 33
Any one watercraft might use more than one of these methods at different times or in conjunction with each other. For instance, early steamships often set sails to work alongside the engine power. Before steam tugs became common, sailing vessels would
back and fill their sails to maintain a good position in a tidal stream while drifting with the tide in or out of a river. In a modern
yacht, motor-sailing – travelling under the power of both sails and engine – is a common method of making progress, if only in and out of harbour.: 33–34 : 199–202 
^Tupper, Eric (1996). Introduction to Naval Architecture. Oxford, England: Butterworth-Heinemann.
abMcGrail, Sean (2014). Early ships and seafaring : European water transport. South Yorkshire, England: Pen and Sword Archaeology.
^Harland, John (1984). Seamanship in the Age of Sail: an account of the shiphandling of the sailing man-of-war 1600-1860, based on contemporary sources. London: Conway Maritime Press.