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The ring constitutes the rotor of an electric motor and sits within a surrounding stator, which is also ring-shaped and creates the necessary torque. Rotor and stator are water tight and the whole unit operates submerged. Similar to an azipod, a rim-driven thruster can be designed to be fixed, retractable and/or azimuthing.
A daggerboard is a retractable centreboard used by various sailing craft. While other types of centreboard may pivot to retract, a daggerboard slides in a casing. The shape of the daggerboard converts the forward motion into a windward lift, countering the leeward push of the sail. The theoretical centre of lateral resistance is on the trailing ...
Other types feature a casing under the boat, which does not take up space but instead has the problem of increased drag. For this reason, it is not uncommon to find boats with a combination of shallow keel and centreboard (e.g. Randmeer). The keel provides the housing for the centreboard, moving it out of the hull, but adds only a small amount ...
If the ladder is parallel to the ship, it has to have an upper platform. Upper platforms are mostly turnable. The lower platform (or the ladder itself) hangs on a bail and can be lifted as required. [citation needed] To prevent damage to boats going under the ladder as the water level rises and falls, a boat fender is fitted to the end of the ...
It is the use of spreaders (long treads that extend well past the vertical ropes) in a pilot ladder that distinguishes it from a Jacob's ladder. When not being used, the ladder is stowed away, usually rolled up, rather than left hanging. On late 19th-century warships, this kind of ladder would replace the normal fixed ladders on deck during battle.
English inventor Francis Ronalds described what he called a propelling rudder in 1859 that combined the propulsion and steering mechanisms of a boat in a single apparatus. . The propeller was placed in a frame having an outer profile similar to a rudder and attached to a vertical shaft that allowed the device to rotate in plane while spin was transmitted to the propell
Diagram of retractable fin stabilizers on a ship. Ship stabilizers: a fixed fin stabilizer (foreground centre) and bilge keels (left background). Ship stabilizers (or stabilisers) are fins or rotors mounted beneath the waterline and emerging laterally from the hull to reduce a ship's roll due to wind or waves.
A retractable bridge is a type of moveable bridge in which the deck can be rolled or slid backwards to open a gap while traffic crosses, usually a ship on a waterway. This type is sometimes referred to as a thrust bridge. The bridge is retracted to the right. Borden Avenue Bridge, Long Island City. Retractable bridges date back to medieval times.