1 Blocks, Tackles, Cordage, Sailcloth Toronto Brigantine Grade III 2 Parts of a Block Piloting, Seamanship and Small boat handling: Chapman 1972 Oxford Companion to Ships and the Sea 3 Types of Blocks • Single block • Double block • Triple block • Fiddle block • Snatch block The complete Rigger’s Apprentice, Brion Toss 1998 The Young Sea Officer’s Sheet Anchor: Lever 1858 4 Types of Sheaves The complete Rigger’s Apprentice, Brion Toss 1998
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Blocks, Tackles, Cordage, Sailcloth
Toronto BrigantineGrade III
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Parts of a Block
Piloting, Seamanship and Small boat handling: Chapman 1972
Oxford Companion to Ships and the Sea
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Types of Blocks• Single block• Double block• Triple block• Fiddle block• Snatch block
The complete Rigger’s Apprentice, Brion Toss 1998 The Young Sea Officer’s Sheet Anchor: Lever 1858
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Types of Sheaves
The complete Rigger’s Apprentice, Brion Toss 1998
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How do Blocks and Tackles Work?
• To lift this 100 lb weight 100 ft you will need to pull 100ft of line
• There is no mechanical advantage to this
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• We have added a pulley
• But we are still lifting 100lbs and pulling 100 ft of line
• No mechanical advantage and we have only changed the direction
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• We have now added another pulley• The ring in the ceiling is holding 50lbs, and
the pulley in the ceiling is holding 50lbs• So now the weight we are lifting is half, but
we have to pull twice as much line to raise it the same amount
• This a 2:1 advantage
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• We have now added another pulley• The person pulling is now only has to pull
25 lbs, but they must pull 400 ft of line to raise the object 100 ft
• This a 4:1 advantage
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How do you calculate your mechanical advantage?
• In a block and tackle there will be a stationary block that is attached to part of the vessel, and a block attached to a moving object (sail, dory, yard, boom etc).
• When calculating mechanical advantage focus on the moving block
• Count the number of lines entering or exiting a sheave, or attached to a becket
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Mechanical Advantage• Notice A and B are the same block and line
arrangement just reversed, but B has a 2:1 advantage and A only has a 1:1. This is the same for C and D with a 3:1 vs 2:1
• When the line you are pulling on is leading from the moving block it is rove to advantage, when it leads from the stationary block it is rove to disadvantage
Friction• Friction increases as the number of sheaves
increases• There is roughly a 10% increase in the “weight”
of an object per sheave• If you are lifting the 250lb AP with a double
purchase (two double blocks) you would have 4 sheaves, and the extra 10% due to friction would be 25lb per sheave = 100lbs, for a rough total “weight” of 250lb + 100lb = 350lb
• With a 4:1 purchase the weight that the person would have to pull would be roughly 350/4 = 87.5lb
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Reeving methods• Lacing: when blocks are facing
the same direction and line is passed from one sheave to the next. Lots of friction produced when chock-a-block, wear on cheeks and line.
• Right-angle reeving: blocks are at right angles, less friction when chock-a-block
• Triple blocks should always have the fall leading from the middle sheave, this prevents the block from tipping with the force of hauling
The complete Rigger’s Apprentice, Brion Toss 1998
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Types of Rope Fibres
• Traditionally made from manila, hemp, linen, cotton, coir, jute, and sisal.
• Most rope is now made from synthetic fibers such as polypropylene, nylon and dacron.
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Types of Rope fibres• Polypropylene:
– Stiff, hard to work with, hard on the hands, very little stretch, easily damaged by UV and heat, Floats
• Nylon:– Easy to work with, looses shape, easy on the hands,
doesn’t float, can stretch up to 40% of its length, weak when wet
• Dacron:– Easy to work with, maintains shape, easy on hands,
doesn’t float, not as stretchy as nylon• Roblon:
– Synthetic material (from Denmark) that looks like natural fiber, used on replica vessels
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Rope Making• Many fibres (A) are twisted together to form yarn (B)• Many yarns are twisted together to form strands (C)• Strands are twisted together to form rope (D)• Rope is twisted together to form cable (E)
Knots, Splices and Ropework. A. Hyatt Verrill http://www.gutenberg.org/files/13510/13510-h/13510-h.htm
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Traditional Rope Making
• Rope was made in a rope walk or ropery• A traditional operational ropery remains in
Chatham England. It is 346m (1135 ft) long, and when constructed was the longest brick built building in Europe capable of laying a 1,000 ft (300 m) rope