Page 319 - Brion Toss - The Complete Rigger’s Apprentice

Cutty Sark only staysail on this mast—the mizzen staysail—is
A gaff ketch looks archaic to modern eyes, and it is an off-the-wind sail, and, unlike the main staysails,
the least weatherly rig around, but it’s also simple, is never sheeted in so far that the shrouds might be
strong, low-cost, and very powerful when reaching. in the way. And because the staysail here is never
The mizzen on Cutty Sark, a 44-foot Angleman sheeted in tight, it never puts huge compression
design, has a bulletproof simplicity. Because it is so loads on the mast (see “Mainmasts”), so the mast
simple, it is easier to see principles that are buried in and its rigging can be lighter than a comparable-size
more complex, latter-day mizzens. main. Lessened compression load also means that
The standing rigging here consists of four Cutty Sark’s mizzen can have a long, unsupported
shrouds (Figure 8-1), all going to the masthead. section of mast between tangs and deck. The stick
Because the mast is relatively short and the ves- will flex some, but never to the point where lower
sel relatively beamy aft, the shrouds have a wide shrouds are necessary.
staying angle, so there’s no need for spreaders (see
“Angles”). The shrouds lead well forward and well Jenny Ives
aft, staying the mast fore-and-aft as well as later- If Cutty Sark’s mizzen were taller, or thinner, or had
ally. When the mizzen staysail is set, particularly if a narrower staying angle, the compression loads rel-
the breeze or chop is up, there is also a pair of run- ative to the mast’s stiffness would be greater, and
ning backstays to reinforce the aft-leading shrouds. that ultra-simple standing rigging wouldn’t work;
There’s enough space between the runners so that, the stick would be inclined to “pump” in its midsec-
on the wind, they can both be left set up and still tion. The Bermudian mizzen on the ketch Jenny Ives
have room to tack the mizzen back and forth. is taller and lighter, with a narrower staying angle,
Note that the chainplates are all the way out-
board; there’s no need to move them in, since the Mizzenmast Scantlings

Because mizzen sails are much smaller in area
Figure 8-1. The mizzen of the ketch Cutty Sark. than mainsails, and because mizzen staysails, set
off the wind, do not impose genoa-grade tension
or compression loads, and because mizzens are
usually furled when the wind picks up to prevent
weather helm, mizzenmasts aren’t exposed to the
level of forces that mains are. Accordingly, the
standard formula for mizzenmast scantlings, while
still based on RM 30 (see “Mast Strength” in Chap-
ter 5), uses a much lower constant. The formula is:
RM 30 5 0.5
1 ⁄2 beam (at chainplate)
Because the mizzen staysail is low-load, the
same formula is used for both mast and rigging.
A recommended safety factor of only 1.5 to 2
further reflects most mizzens’ easy life.
The formula works well for most boats. Even if
you lower the main in a storm and sail under for-
estaysail and reefed mizzen, the latter sail, maybe
20 to 30 percent the size of the main, just isn’t big
enough to generate a maximum righting moment
load. An exception would be vessels like Sundeer
(see page 303), in which mizzensail area is uncom-
monly large (around 40 percent of the size of the
main).

298