Davit
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A davit is a system that is used to lower an emergency lifeboat to the embarkation level to be boarded. The davit has falls (now made of wire, used to be made of manilla) that are used to lower the lifeboat into the water.[1] Davits can also refer to single mechanical arms with a winch for lowering and raising spare parts onto a vessel.
Development
The development of the davit from its original "goose neck form" to the current devices advanced greatly when A.P. Schat patented a number of systems in 1926 that allowed the lifeboat to glide over obstructions on a ship's hull, known as the "Schat Skate". This was followed by a self-braking winch system that allowed the lifeboat to be lowered evenly. The standard became so common that shipyard specifications call for Schat-type davits which are available from various sources. Similar systems developed by Schat companies are used on offshore oil or gas rigs, being placed around the structure.
Types
Davits are designed to fit into deck spaces that the naval architects deemed necessary:
- Radial (obsolete) — Hand powered davit. This type was used on the RMS Titanic. Each arm must be rotated out manually; uses manila rope falls.
- Mechanical (obsolete) — This type is like the radial davit, but both arms are moved out at the same time using a screw system; uses manila rope falls.
- Gravity (industry standard) — There are multiple forms; one man can operate, and uses wire rope falls.
- -Roller: Davit slides down a track, bringing the davit to the embarkation deck.
- -Single pivot: One pivot point where the lifeboat is moved over the side of the craft.
- -Multi pivot: Common on Promenade decks of cruise ships. Useful were space is limited.
- -Free Fall: Lifeboat slides right off of vessel. Lifeboat must be an enclosed type.
- -Fixed: Common on Oil Rigs. Lifeboat is hung above the water (at embarkation level) and lowered into the water.
Procedure
For all lifeboats using a roller gravity davit and Rottmer releasing gear, this is the procedure:
1. Make sure the Davit tracks are clear of debris
2. Remove the lifeboat cover if applicable
3. Put in the lifeboat plugs
4. At this time the Rottmer releasing gear is checked to be secure.
5. Attach the sea painter to the bow of the ship.
6. Remove the gripes from the lifeboat.
7. Make sure the gripes preventing bar is free from the track.
8. Have the assigned brake man life the braking bar and lower the lifeboat to the embarkation deck.
9. Now that the Tricing pendants have pulled the lifeboat in close, attach the Frapping lines to the wire falls by passing them to a worker who is on the lifeboat.
10. Load the lifeboat. Load one person at a time and seat them so there weight is distributed between the two sides.
11. Have the brake man raise the lifeboat slightly so the workers can release the Tricing pendants.
12. Brake man lifts bar and lowers the vessel into the water.
13. Operate the Rottmer releasing gear and release the davit on the crest of a wave.
14. If ship is sinking, pull toggle pin to release the sea painter from the ship.
[2]
During this procedure, if the lifeboat has air-cooled engines start it at the beginning. If it has a water cooled engine start the engine after the lifeboat is in the water.
Gallery
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Gravity multi-pivot on cruiseferry Scandinavia -
Gravity Roller Davit -
Gravity multi pivot davit holding rescue vessel on North Sea ferry -
Freefall lifeboat on the Spring Aeolian
References
- ^ "Davit Systems | Applied Technical Services". Atslab.com. Retrieved 2014-02-21.
- ^ Suny Maritime College. (2011, 30 03). Lifeboat rotation . Retrieved from http://www.sunymaritime.edu/media/documents/2011/3/30/Lifeboats - Work Equipment.pdf
