Editing Electric boat (section)

===Wired electric boats===
[[Image:Strausberg Faehre Steffi.jpg|thumb|The electric ferry ''Steffi'' on the Straussee, 30&nbsp;km east of Berlin]]
[[Trolley boat]]s are a special category of electric boats are the vessels receiving their electrical power by wire. This may involve overhead wires, where one or two wires are fixed over the water and the boat can make contact with them to draw electric current, or a waterproof tether cable may be used to connect the boat to shore. In case of a single overhead wire the electrical circuit has to be closed by the water itself, giving rise to a larger resistance and corrosion of the electrodes. In case of two wires no electric current has to be sent through the water, but the twin wires, which cause a short-circuit whenever they come into contact with each other, complicate the construction.

Naturally the boat has to stay close to the wire, or its tether point, and therefore it is limited in its manoeuvrability. For ferries and on narrow canals this is no problem. The [[Straussee Ferry]] in Strausberg, Germany is an example. It crosses a lake along a 370&nbsp;m trajectory and is powered by 170&nbsp;V from a single overhead wire. The [[Kastellet ferry]] crosses a {{convert|200|m}} wide shipping channel in Sweden, using a submergible tethered supply cable which is lowered to the sea-bed when the ferry is docked at the opposite terminal to its tethering point.

In the {{Interlanguage link|Mauvages tunnel|fr|3=Tunnel de Mauvages}} on the [[Marne-Rhine Canal]] a bipolar overhead line provides 600&nbsp;V DC to an electrical tug, pulling itself and several ships through the 4877&nbsp;m tunnel along a submerged chain. This prevents the buildup of diesel exhaust fumes in the tunnel. Another example was the experimental {{Interlanguage link|electrical tug Teltow|de|3=Teltow (Schiff)}} on the Kleinmachnower See, 17&nbsp;km south-west of Berlin. It was used from 1903 until 1910 and had current collection poles based on those used by [[Trolleybus|trolley buses]].