Page 174 - The Complete Rigger’s Apprentice

Figure 5-29. A chronology of materials. All the exam- Figure 5-30. Weight per foot for four stainless steel
ples shown are of equal strength, rated for loads of stay constructions. All are rated for 12,000- to
about 12,000 pounds. Over the decades, diameter 12,500-pound loads.
has shown a downward trend due to better materials
and constructions. to rig elasticity can impair it. It’s odd to think of
wire rope as something that stretches, and it’s true
advent of improved alloys and cold-drawing tech- that we’re dealing with tiny increments here, even in
niques, rod rigging is now at home in the cruising the most elastic wire, but this is a situation in which
and charter market. tiny increments can make a difference. To the extent
that wire stretches more than we want it to, the mast
Weight Another trend has been the reduction of will bend or “go out of column.” Stayed masts are
rig weight. One extra pound of weight 30 feet up designed to function as nearly pure compression
adds 30 foot-pounds to a vessel’s heeling moment, members, so it is important that they stay relatively
making the vessel that much less stable and putting straight. In cases where fore-and-aft bend is induced,
that much more strain on the mast and rig. Light- in the interests of resistance to flexing, or improved
ness is a virtue. But again, recent developments have mainsail shape, the mast must be engineered to han-
produced a diminishing-returns catch: Increasing dle the deflection. Even then, bend must be kept
the cross-sectional area of metal in wire of a given within design parameters. Consult with a rigger or
diameter in order to increase wire strength means sparbuilder about appropriate bend for your mast.
increasing weight relative to diameter. Faced with There are two forms of stretch at rated loads
this, designers often resort to making the rig lighter that are of interest to sailors: constructional and
by reducing scantlings. According to C. A. Marchaj, elastic. Constructional stretch is a permanent elon-
rig weights have dropped by an average of 30 per- gation that results from the strands in a new piece
cent since the 1960s. (For more on this, see the of rigging settling into place when it is put to use.
“Effects of Engineering” section later in this chap- This does not affect sailing efficiency unless it is not
ter and “Blocks” in Chapter 2.) Figure 5-30 shows allowed for when the piece is cut for rig fabrication;
in graph form the relationships between weight per with long pieces of the more elastic constructions,
foot, diameter, and strength for 7 x 19, 7x 7, 1 x 19, one can use up a lot of turnbuckle thread taking out
and rod rigging of comparable materials. this stretch, and thus have too little adjustment left
for tuning.
Elasticity Induced mast bend can alter sail shape Although HSR and other standing-
to improve performance; unwanted mast bend due rigging-grade forms of Spectra are fabulously

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