A davit (pronounced "dayvit"[1] or see Wiktionary) is any of various crane-like devices used on a ship for supporting, raising, and lowering equipment such as boats and anchors.[2]
Boat suspended from radial davits; the boat is mechanically lowered
HMS Victory in the 19th century, showing her boats suspended from wooden davits
Gravity multi-pivot davit holding rescue vessel on North Sea ferry
Freefall lifeboat on the Spring Aeolian
Frapping line
Labeled Tricing
Gripe
Steps to launch davit
Roller Gravity Davit
Look up davit in Wiktionary, the free dictionary.
Davit systems are most often used to lower an emergency lifeboat to the embarkation level to be boarded. The lifeboat davit has falls (now made of wire, historically of manila rope) that are used to lower the lifeboat into the water.[3] Davits can also be used as man-overboard safety devices to retrieve personnel from the water.
Davits were first devised in the 17th century for use by whaling ships in the Greenland whaling grounds. They began to be introduced into Royal Navy warships in the late 18th-century and originally took the form of squared baulks of timber. Curved iron davits began to be introduced later in the 19th century.[4]
Development of the davit has also been in terms of material. Traditionally davits have been made in aluminium or steel but recent advances in composite material have led to the manufacture of davits in carbon fibre which has an excellent strength-to-weight ratio. This means davits can be stowed away when not in use and the same davit used in multiple deck sockets fitted permanently on deck.[5]
Lifeboat 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 lifeboats of the RMS Lusitania. Each arm must be rotated out manually; uses manila rope falls. Goose-neck shape to the arm that is swung out.[6]
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. An example is the Welin Quadrant davit type used on RMS Titanic.[6]
Gravity (industry standard) – There are multiple forms; one man can operate; uses wire falls.[6]
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 where space is limited.
Free fall – Lifeboat slides right off vessel. Lifeboat must be an enclosed type. Main type of Davit on merchant ships now. This type does not use falls.
Fixed – Common on oil rigs. Lifeboat is hung above the water (at embarkation level) and lowered into the water. [7]
Components
Liferaft
These can be enclosed, partially enclosed, or open. (There are pictures of these on the page already so no description is added)
Frapping lines
These lines are used on all davits except the fixed and freefall davits. The frapping lines are used to pull the lifeboat over to the embarkation deck along with the tricing pendant to be loaded.
Gripes
Ropes used to hold the lifeboat in the stored position while underway.
Tricing pendants
Lines used to initially pull the lifeboat over to the embarkation deck so that the frapping lines can be connected.[7]
Falls
The wires which lift or lower the lifeboat are known as falls.
Release mechanisms
There are three basic systems used to release the lifeboat from the davit. (Coast Guard Questions are for the Rottmer, On-Load releasing gear)[8]
On-load
For this style of release mechanism, the lifeboat can be released at any point from the davit. This type of system allows a lifeboat to be released when it is not in the water, whether this is because of the emergency or an accident. Because of this, during an evacuation the release mechanism must be watched to make sure there is not an accidental activation.[9]
Off-load
This release mechanism requires the weight (load) of the lifeboat to not be on the hook when it is released. This includes the Titanic-era Monomony hook design that requires someone to remove the hook from the lifeboat by hand. But this type also includes the hydrostatic system many lifeboats use now. For this, a float is raised up and engages the release once the craft is in the water to the right depth.[9]
Free-fall
This type of release mechanism is very basic. The (enclosed) lifeboat is on a ramp and slides down and off of the ship when engaged. This is done by pumping a lever that is inside the lifeboat by the pilot.[9] If there is not enough hydraulic pressure to release the stop fall, a pump on the inside must be rotated to build up the hydraulic pressure to release the lifeboats stopfall hook. Once the stopfall hook (hook attaching the lifeboat to the davit that holds it to the ship) is released the lifeboat will slide off the ramp and into the water. This type of lifeboat is more common due to its quick deployment and ease of operation.[10]
Procedure
For all lifeboats using a roller gravity davit and Rottmer releasing gear, this is the procedure:
Make sure the davit tracks are clear of debris
Remove the lifeboat cover if applicable
Put in the lifeboat plugs
At this time the Rottmer releasing gear is checked to be secure.
Attach the sea painter to the bow of the ship.
Remove the gripes from the lifeboat.
Make sure the gripes preventing bar is free from the track.
Have the assigned brake man life the braking bar and lower the lifeboat to the embarkation deck.
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.
Load the lifeboat. Load one person at a time and seat them so their weight is distributed between the two sides.
Have the brake man raise the lifeboat slightly so the workers can release the tricing pendants.
Brake man lifts bar and lowers the vessel into the water.
Operate the Rottmer releasing gear and release the davit on the crest of a wave.
If ship is sinking, pull toggle pin to release the sea painter from the ship.[11]
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.
References
Wikimedia Commons has media related to Davits.
^Moore, Sir Alan Hilary; Nance, R. Morton (1925). Last days of mast & sail : An Essay in Nautical Comparative Anatomy. Clarendon Press, Oxford. p. 247. OL 26571876M.
^. Atslab.com. Archived from the original on 2014-01-16. Retrieved 2014-02-21.
^Hartland, John H (1984). Seamanship in the Age of Sail: An Account of the Shiphandling of the Sailing Man-Of-War 1600-1860, Based on Contemporary Sources. Annapolis MD: US Naval Institute Press. p. 284. ISBN9780851771793.
davit, this, article, needs, additional, citations, verification, please, help, improve, this, article, adding, citations, reliable, sources, unsourced, material, challenged, removed, find, sources, news, newspapers, books, scholar, jstor, june, 2013, learn, w. This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Davit news newspapers books scholar JSTOR June 2013 Learn how and when to remove this template message A davit pronounced dayvit 1 or see Wiktionary is any of various crane like devices used on a ship for supporting raising and lowering equipment such as boats and anchors 2 Boat suspended from radial davits the boat is mechanically lowered HMS Victory in the 19th century showing her boats suspended from wooden davits 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 Frapping line Labeled Tricing Gripe Steps to launch davit Roller Gravity Davit Look up davit in Wiktionary the free dictionary Davit systems are most often used to lower an emergency lifeboat to the embarkation level to be boarded The lifeboat davit has falls now made of wire historically of manila rope that are used to lower the lifeboat into the water 3 Davits can also be used as man overboard safety devices to retrieve personnel from the water The maintaining and operation of davits is all under jurisdiction of the International Maritime Organization The regulations are enforced by the country s own coast guard Contents 1 Development 2 Lifeboat types 3 Components 4 Release mechanisms 5 Procedure 6 ReferencesDevelopment EditDavits were first devised in the 17th century for use by whaling ships in the Greenland whaling grounds They began to be introduced into Royal Navy warships in the late 18th century and originally took the form of squared baulks of timber Curved iron davits began to be introduced later in the 19th century 4 Development of the davit has also been in terms of material Traditionally davits have been made in aluminium or steel but recent advances in composite material have led to the manufacture of davits in carbon fibre which has an excellent strength to weight ratio This means davits can be stowed away when not in use and the same davit used in multiple deck sockets fitted permanently on deck 5 Lifeboat types EditDavits are designed to fit into deck spaces that the naval architects deemed necessary Radial obsolete Hand powered davit This type was used on the lifeboats of the RMS Lusitania Each arm must be rotated out manually uses manila rope falls Goose neck shape to the arm that is swung out 6 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 An example is the Welin Quadrant davit type used on RMS Titanic 6 Gravity industry standard There are multiple forms one man can operate uses wire falls 6 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 where space is limited Free fall Lifeboat slides right off vessel Lifeboat must be an enclosed type Main type of Davit on merchant ships now This type does not use falls Fixed Common on oil rigs Lifeboat is hung above the water at embarkation level and lowered into the water 7 Components EditLiferaft These can be enclosed partially enclosed or open There are pictures of these on the page already so no description is added Frapping lines These lines are used on all davits except the fixed and freefall davits The frapping lines are used to pull the lifeboat over to the embarkation deck along with the tricing pendant to be loaded Gripes Ropes used to hold the lifeboat in the stored position while underway Tricing pendants Lines used to initially pull the lifeboat over to the embarkation deck so that the frapping lines can be connected 7 Falls The wires which lift or lower the lifeboat are known as falls Release mechanisms EditThere are three basic systems used to release the lifeboat from the davit Coast Guard Questions are for the Rottmer On Load releasing gear 8 On load For this style of release mechanism the lifeboat can be released at any point from the davit This type of system allows a lifeboat to be released when it is not in the water whether this is because of the emergency or an accident Because of this during an evacuation the release mechanism must be watched to make sure there is not an accidental activation 9 Off load This release mechanism requires the weight load of the lifeboat to not be on the hook when it is released This includes the Titanic era Monomony hook design that requires someone to remove the hook from the lifeboat by hand But this type also includes the hydrostatic system many lifeboats use now For this a float is raised up and engages the release once the craft is in the water to the right depth 9 Free fall This type of release mechanism is very basic The enclosed lifeboat is on a ramp and slides down and off of the ship when engaged This is done by pumping a lever that is inside the lifeboat by the pilot 9 If there is not enough hydraulic pressure to release the stop fall a pump on the inside must be rotated to build up the hydraulic pressure to release the lifeboats stopfall hook Once the stopfall hook hook attaching the lifeboat to the davit that holds it to the ship is released the lifeboat will slide off the ramp and into the water This type of lifeboat is more common due to its quick deployment and ease of operation 10 Procedure EditFor all lifeboats using a roller gravity davit and Rottmer releasing gear this is the procedure Make sure the davit tracks are clear of debris Remove the lifeboat cover if applicable Put in the lifeboat plugs At this time the Rottmer releasing gear is checked to be secure Attach the sea painter to the bow of the ship Remove the gripes from the lifeboat Make sure the gripes preventing bar is free from the track Have the assigned brake man life the braking bar and lower the lifeboat to the embarkation deck 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 Load the lifeboat Load one person at a time and seat them so their weight is distributed between the two sides Have the brake man raise the lifeboat slightly so the workers can release the tricing pendants Brake man lifts bar and lowers the vessel into the water Operate the Rottmer releasing gear and release the davit on the crest of a wave If ship is sinking pull toggle pin to release the sea painter from the ship 11 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 References Edit Wikimedia Commons has media related to Davits Moore Sir Alan Hilary Nance R Morton 1925 Last days of mast amp sail An Essay in Nautical Comparative Anatomy Clarendon Press Oxford p 247 OL 26571876M Random House Kernerman Webster s College Dictionary c 2010 K Dictionaries Ltd Copyright 2005 1997 1991 by Random House Davit Systems Applied Technical Services Atslab com Archived from the original on 2014 01 16 Retrieved 2014 02 21 Hartland John H 1984 Seamanship in the Age of Sail An Account of the Shiphandling of the Sailing Man Of War 1600 1860 Based on Contemporary Sources Annapolis MD US Naval Institute Press p 284 ISBN 9780851771793 Lifting Davits for Boats Dinghies amp Yachts Atlas Carbon Fibre Davits a b c Hayler William B 2003 American Merchant Seaman s Manual CMP Cornell Maritime Press pp 10 15 10 17 ISBN 978 0 87033 549 5 a b SIU AFL CIO 1991 Water survival manual p 37 Piney Point Maryland Seafarers Harry Lundeberg School of Seamanship Murphy J 2009 U S Coast Guard license examination preparation for the professional mariner Wareham Massachusetts Academy Publishing Company Retrieved from http mdnautical com murphy s deck officers guides 7 murphy s deck officer study guide 7 lifeboatmen 2009 html a b c Wankhede A 2010 december 22 Types of lifeboat release mechanisms amp solas requirements for lifeboats Retrieved from http www marineinsight com misc maritime law types of lifeboat release mechanisms solas requirements for lifeboats Maritime Training Services n d Launching and recovery system of free fall life boats Retrieved from http www maritimetraining com Product Launching and Recovery System of Free Fall Life Boats Suny Maritime College 2011 30 03 Lifeboat rotation Retrieved from http www sunymaritime edu media documents 2011 3 30 Lifeboats permanent dead link Work Equipment pdf dead link Retrieved from https en wikipedia org w index php title Davit amp oldid 1152036231, wikipedia, wiki, book, books, library,
