A dolphin is a group of

piling A deep foundation is a type of foundation that transfers building loads to the earth farther down from the surface than a shallow foundation does to a subsurface layer or a range of depths. A pile or piling is a vertical structural eleme ...

s arrayed together to serve variously as a protective hardpoint along a dock, in a waterway, or along a shore; as a means or point of stabilization of a dock, bridge, or similar structure; as a mooring point; and as a base for

navigational aid Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navigation, ...

Structure

Dolphins typically consist of a number of

piles Hemorrhoids (or haemorrhoids), also known as piles, are vascular structures in the anal canal. In their normal state, they are cushions that help with stool control. They become a disease when swollen or inflamed; the unqualified term ''hemo ...

driven into the seabed or riverbed, and connected above the water level to provide a platform or fixing point. The piles can be untreated or pressure treated timber piles, or steel or reinforced concrete piles. Smaller dolphins can have the piles drawn together with wire rope, but larger dolphins are typically fixed using a reinforced concrete capping or a structural steel frame. Access to a dolphin may be via a pedestrian bridge, particularly in the case of mooring dolphins, but is often by boat.

Use

As mooring point

Dolphins are usually installed to provide a fixed structure when it would be impractical to extend the shore to provide a dry-access facility, for example, when the number of ships is greater than can be accommodated by the length of the berth/pier. Typical uses include extending a berth (a berthing dolphin) or providing a mooring point (a mooring dolphin).

To protect structures

Dolphins are also used to protect structures from possible impact by ships, in a similar fashion to boating fenders. A notable example of dolphins used to protect a bridge is the Sunshine Skyway Bridge across the mouth of

Tampa Bay Tampa Bay is a large natural harbor and shallow estuary connected to the Gulf of Mexico on the west-central coast of Florida, comprising Hillsborough Bay, McKay Bay, Old Tampa Bay, Middle Tampa Bay, and Lower Tampa Bay. The largest freshwater ...

. In 1980, the MV Summit Venture hit a pier on one of the bridge's two, two-lane spans causing a section of the bridge to fall into the water, resulting in 35 deaths. When a replacement span was designed, a top priority was to prevent ships from colliding with the new bridge. The new bridge is protected by 36 dolphins: four large dolphins protecting the two main pylons supporting the cable-stayed main span plus 32 smaller dolphins protecting bridge piers for 1/4 mi (1/2 km) to either side of the main span. The cost of the dolphins was $41 million (approximately $90 million in 2017 dollars).

To support navigational aids

Dolphins are also used to house navigation aids such as lights or

daybeacon A day beacon (sometimes "daybeacon") is an unlighted nautical sea mark. A signboard identifying it is called a day mark. Day beacons typically mark channels whose key points are marked by lighted buoys. They may also mark smaller navigable rout ...

s, and display regulatory information such as speed limits and other safety information, or advertising.

References

{{DEFAULTSORT:Dolphin (Structure) Nonbuilding structures Nautical terminology

Structure

Use

As mooring point

To protect structures

To support navigational aids

See also

References