Page 201 - The Complete Rigger’s Apprentice

ference. We need to know how much extra wire to
Elasticity Deductions
add for a given thimble length. Second, as you’ll see
When dimensioning standing rigging, deduct for in the “Comforts of Service” section of this chapter,
constructional and for working elasticity. For some thimble eyes are oversize to allow for replac-
example, a 60-foot upper shroud of 1 x 19 stain-
less will gain .021 percent of its length, or ⁄32 inch ing damaged thimbles. With this configuration, one
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from constructional stretch. 7 x 7 stainless will must allow for thimble circumference minus the
1
gain .07 percent, or about ⁄2 inch. Galvanized length from the throat of the splice to the bearing
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7 x 7 will gain .06 percent, or about ⁄16 inch.
Constructional elasticity for Spectra varies widely, point of the thimble. Third, since the clevis pin that
but can be two percent or more. Therefore it is attaches to the wire will affect length, we deduct for
extremely important to remove all constructional one-half its diameter.
stretch from this material before measuring it. The easiest way to solve these problems is to
The other form of elasticity we need to deal
with is working stretch. If our 60-foot shroud is set up a sample eye using the same size wire and
tuned to 20 percent of its strength, it will gain thimble that will be used in the actual rig. With the
1
almost another 1 ⁄2 inches or so from working eye clamped in place, measure the distance from
elasticity, in 1 x 19 stainless. Therefore, deduct
about 1 ⁄8 inches inch from the measured length thimble head to splice crotch. Then mark this latter
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of the wire before cutting. The deductions for the point on both sides, remove the wire from the vise,
7 x 7 wires will be a bit higher. For the Spectra, if it straighten it, and measure the distance between the
is properly sized, stretch will be much less than for
1 x 19. This is because we size Spectra to reduce two points. This gives you the thimble-eye circum-
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creep in the material, so it will be much stronger, ference. In our case, the thimble length is 1 ⁄4 inches
and therefore will stretch less, relative to a given and the circumference is 4 ⁄2 inches. (When precise
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load. For working elasticity information, see thimble-eye length is not important, as when mak-
page 153.
ing slings or pendants, use the technique in Figure
6-4 to find thimble circumference.)
length from the original length for the new piece. To put this information to work, start again
Moving to the jib- and forestays, subtract 3 /2 with the starboard after lower shroud (Figure 6-5).
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inches from the former and add 5 inches to the lat- Subtracting a thimble length (1 ⁄4 inches) from each
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ter, as per notes, to obtain finished lengths. end leaves 11 feet 7 inches. Proper length is restored
by adding a thimble circumference (4 ⁄2 inches) to
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Thimble Length and Circumference It is one thing each end. Finally, add enough length to splice with,
to measure thimble-head-to-thimble-head for a in this case 12 inches to each end (see “The Liver-
finished length, quite another to cut a piece of wire pool Eyesplice Made Difficult,” later in this chap-
that, when spliced, will have the required length. ter). After these assorted additions and subtractions
There are several complications. First, in order to
reach the thimble head the wire must detour around Figure 6-4. Rolling a thimble along the wire is one
the thimble’s contours; there is thus a considerable way to determine approximate thimble circumference.
difference between thimble length and eye circum- Add a bit extra for an oversized eye.

180