Tackles and Purchases mean one and same thing.
A block and tackle is a system of two or more pulleys with a rope or cable(Wire rope) threaded between them, usually used to lift heavy loads.
The pulleys are assembled together to form blocks and then blocks are paired so that one is fixed and one moves (Floating) with the load. The rope is threaded through the pulleys to provide mechanical advantage that amplifies the force applied to the rope.
Please go through www.shipofficer.com for understanding different types of tackles and calculations.
Also read relevant chapter from
1. Cargo Work for Ships Officers– Capt. Errol Fernandes
Since the rope bends over a pulley, there are some rules to prevent over-bending that can damage the rope. Refer to
1. Cargo Work for Ships Officers– Capt. Errol Fernandes
Marking of safe working load.–
(1) Every lifting appliance and every item of loose gear shall be clearly marked with its safe working load and identification mark by stamping or where this is impracticable, by other suitable means.
(2) (a) Every ship’s derrick (other than derrick crane) shall be clearly marked with its safe working load when the derrick is used,-
(i) in single purchase,
(ii) with a lower cargo block and
(iii) in union purchases in all possible block positions;
(b) The lowest angle to the horizontal, that the derrick may be used, shall also be legibly marked.
Marking
Cargo-handling appliances and gear shall be permanently marked (by means of chiselling, punching, steel stamping) with their S.W.L. (Safe working load, sometimes term WLL Working Load Limit is used) and certificate/registration number.
Wire rope shall be accompanied by a certificate stating for which derrick/crane and for what purpose (cargo runner, masthead rope, guy, etc.) the rope is intended. If the entire length of rope is not used for the stated purpose, the amount used and any remnant shall be specified in the certificate. This entry shall be dated and signed by a competent person at the initial examination and subsequently by the chief officer, alternatively the master where the latter is the only deck officer on board.
Slings shall be marked with S.W.L. in easily legible figures or letters, either on the sling itself or on a plate or ring of durable material securely fixed to the sling, or the S.W.L. shall be posted on notices easily legible by all concerned. Wire rope fitted with ferrules (talurit) shall have its S.W.L. stamped into the ferrule.
Senhouse slip: A hinged hook, fitted with a securing ring which can conveniently be released when under strain. It is used for holding chain for quick release.
Swivel: a device joining two parts so that one or both can pivot freely (as on a bolt or pin).
Mooring arrangements: A mooring refers to any permanent structure to which a vessel is secured. Examples include quays, wharfs, jetties, piers, anchor buoys and mooring buoys. A ship is secured to a mooring to STOP free movement of the ship on the water. Just like parking of a car.
Mixed moorings: it means ship is moored using wire ropes as well as Synthetic fibre Ropes.
Rat Guards: Means an arrangement to prevent Rats from boarding ship via mooring ropes.
Bights: Loose part of a rope likely to cause an accident.
Mooring shackle: Very large shackle used for connecting anchor chain to a mooring buoy.
Tonsberg Shackle (Link): used for connecting wire rope to rope. Link can pass over fairleads easily.
Mandel Shackle (Link): Similar like Tonsberg. Mandel link has a sheave whereas Tonsberg link has Pin.
Synthetic rope tails: Piece of synthetic rope connected to a wire rope for purpose of moorings. Synthetic rope absorbs shocks (Acts as spring for sudden jerks).
Sledge hammer: It is a BIG hammer needing both hands for hammering.
Stockless anchor: Standard anchor used on ships.
Pilot ladder: A rope and wooden ladder specially made for boarding of Pilots.
Scuppers: A pipe arrangement to drain water from the deck. Pipe opening is in level with deck.
Scupper plug: Plug to blank off drain hole.
Hand lead line: Device used for measuring depth of water. Also used for taking samples of sea bottom. Look for base of the Hand Lead where you will find a cavity. This is filled with White lead paste. When lead hits the Bottom, sediments stick to white lead. On recovery of lead, we get sample of the bottom.
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