Page 151 - The Complete Rigger’s Apprentice

is like a sling-and-load turned on its side. I know make the spreader stronger, and thus fatter and
that’s not how Herreshoff might have put it, but heavier, to compensate.
forces don’t care what they’re doing. Explore unfa- A longer spreader is more inclined to buckle
miliar forces, and you’ll get a clearer understanding than a shorter one under the same load. That’s
of familiar ones. because the stiffness of any compression member is
relative to its “unsupported length”—the length of
the section not braced by shrouds, brackets, or other
SPREADER LOADS deflection-preventing devices.
To demonstrate the relationship between
On a sailboat, the width of the hull limits the shroud unsupported length and stiffness, get out a piece
angle at the base. Put a tall rig in a narrow boat, and of uncooked spaghetti and brace it between your
it becomes impossible to get that crucial 12-degree fingertips. (Figure 5-12). It is very easy to deflect
angle, unless we add spreaders. Spreaders widen and then break the spaghetti by moving your hands
the angle of the shrouds to the mast, interjecting together. Now take one of the resulting shorter
themselves as compression struts in the process. pieces and repeat the procedure. This time it takes
As Figure 5-11 shows, the longer the spreader, the more force to deflect and break the spaghetti.
lower the load on mast and rigging. Long spreaders Finally, have a friend hold the middle of a short
would seem to be desirable. But there are, as usual, piece between thumb and forefinger. This shortens
complications. the unsupported length, not the overall length. Push
As the load on the mast and rigging goes down, on the ends. Now you’re in danger of poking a hole
the load on the spreader goes up. So you have to in your hands before the noodle will break.
A mast, by comparison, is usually a
Figure 5-11. The longer the spreader, the lower the moderately stiff item with a long overall
load on mast and rigging. length, but it is broken into two or more rela-

20° 35°
12°

shroud

mast

spreader

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