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References
The following publication supports the content in this lesson:
Boatswain’s Mate Nonresident Training Course, NAVEDTRA 14343
Seaman Nonresident Training Course, NAVEDTRA 14067
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Description
Canvas is an extremely heavy-duty fabric used for making sails, covers, tents, marquees, paulins, backpacks, and other functions where sturdiness is required. Modern canvas is usually made of cotton. It differs from other heavy cotton fabrics, such as twill, in the way it is woven.
Canvas is often called duck. Numbered duck is the canvas encountered most often, but occasionally you see the terms ounce duck or army duck.
Numbered duck runs from No. 1, the heaviest to No. 12, the lightest. Numbers 7, 9, and 11 are no longer issued.
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Classification of Canvas
Each number means a certain weight in ounces per square yard of cloth. For example, No. 1 is 28.71 ounces per square yard, No. 6 is 20.74 ounces per square yard, and No. 12 is 11.16 ounces per square yard.
Canvas is usually made up in bolts from 85 to 100 yards, but is issued by the linear yard, in widths from 22 to 72 inches.
The following items are a sample of articles made from different weights of canvas
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What numbered duck is the heaviest cloth?
- 1
- 7
- 12
- 15
1
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Round Stitch
The round stitch is the most common stitch you will use to join two pieces of canvas.
1. Turn back the edges of the two pieces of canvas.
2. Hold the pieces together.
3. Send the needle through both pieces at right angles to the seem.
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Flat Stitch
Use the flat stitch when you need an especially strong seam.
1. Pencil a guideline 1 1/2 to 2 inches from the edge of each strip of canvas.
2. Crease each piece on a line slightly less than halfway to the guideline.
3. Make the folds away from the guidelines and interlock the folds.
4. Insert the needle at the guideline, and stitch diagonally so the stitches appear at right angles to the seam on top but run at an angle on the reverse side.
5. Complete one edge, then turn the canvas over and sew the other edge of the seam.
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Baseball Stitch
Use the baseball stitch to mend tears in medium and light canvas:
1. Keep enough tension on the thread to remove all loops and slack thread.
2. Do not apply too much tension, as this tends to pucker or draw the seam out of line.
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Herringbone Stitch
Use the herringbone stitch to mend tears in heavy or painted canvas.
Each stitch locks itself as it begins the next one, making it a very strong stitch.
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Cutting Punches
A cutting punch is a hand tool designed to cut holes in canvas and other materials. To punch neat, clean holes in canvas, lay the canvas on a piece of heavy sheet lead.
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References
The following publications support the content in this lesson:
Wire and Fiber Rope and Rigging, Naval Ships' Technical Manual, Chapter 613
Seaman Nonresident Training Course, NAVEDTRA 14067
Boatswain’s Mate Nonresident Training Course, NAVEDTRA 14343
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Construction
The design arrangement of the components of a wire rope is called the construction.
Wire ropes are made up of three parts:
Wires
Strands
Core
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 Wires and Strands
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A fiber core contributes flexibility, cushions the strands as the wire rope contracts under strain, and holds a portion of lubricant for continuous lubrication.
A wire core is stronger than a fiber core and can be used where conditions such as high temperatures would damage the fiber.
An independent wire rope core is a separate wire rope over which the main strands of the row are laid. This core strengthens the rope more, provides support against crushing, and supplies maximum resistance to heat.
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Inspection
Wire rope should be inspected frequently. Check for fishhooks, kinks, and worn and corroded spots.
To inspect a wire rope, you need to know the:
- Original diameter
- Present diameter at the worn spot
- Diameter of a single wire in one of the strands
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Short splice – used for joining two wire ropes end-to-end under ordinary conditions
Long splice – used for joining two wire ropes end-to-end for haulages, inclines, or where no increase in the wire diameter is allowed
Eye splice – used for installing thimbles or eyes permanently into the ends of the wire rope
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Eye Splices
An eye splice is used to terminate the loose ends of a wire rope when forming an eye. The splice develops up to about 95% of the strength of the rope, but the efficiency decreases to 70% as the diameter of the rope increases.
The only reason it will not carry up to the full breaking strength is that the wires nick each other under heavy stress where the strands cross inside the tuck and are weakened slightly.
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Types of Eye Splices
There are three types of eye splices:
Liverpool – easiest splice to make. Do not use it in a rope that is free to spin when loaded because it may pull out
Lock and tuck – preferred splice because it can be made as quickly as a Liverpool splice, but it will not pull out or spin out when a load is applied.
Flemish eye (Molly Hogan) – an alternate method of forming a temporary soft eye in the end of a wire rope without permanent splicing. The eye is simple to form, requires a minimum amount of tools, and does not require use of a splicing vise. The breaking strength of a Flemish eye approaches 90% of the breaking strength of the rope. In choosing wire rope for this purpose, use rope with an even number of strands.
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Where is the weakest part of a splice?
a. One rope diameter from the seizing
b. In the vicinity of the first set of tucks
c. Six rope diameters from the seizing
d. In the vicinity of the last set of tucks
d. In the vicinity of the last set of tucks
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Safety Precautions
Working with wire rope can be hazardous, or at least painful, if the proper safety precautions are not followed.
Here are some precautions to remember when working with wire rope:
It is best to tape or seize the ends of wire rope when cutting, no matter how much experience you have.
Always wear safety goggles to protect your eyes.
Do not place any objects on the wire rope while splicing.
Heavy leather gloves may be worn while splicing, but often make splicing difficult.
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The spur type grommet has the following characteristics:
Sizes 0 to 6
Inner diameters range from one-fourth to three-fourths of an inch
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The eyelet and ring type grommet has the following characteristics:
Sizes 6 to 15
Inner diameters range from three-fourths to two inches
Great for use on awnings and sails
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