Page 320 - The Complete Rigger’s Apprentice

so it needs a different standing rigging configuration Unfortunately, the compression load on the
(Figure 8-2). spreaders is trying to make the mast buckle forward
Since aft-pulling strain is localized at the mast- in the middle. The lower shrouds, which have a
head, a forward-facing “jumper stay” running over slight forward lead, stabilize the lower section of the
a strut stabilizes the upper section of the mast in this mast laterally, but exacerbate the spreader-induced
plane, preventing the head from sagging aft under forward bow. What to do? We could move those
the pull of the sail. To widen the staying angle, the lower shrouds aft, but, oops, this is a deck-stepped
upper shrouds run over spreaders, to handle lateral mast, with no springstay. It needs forward-leading
loads at the same point. To prevent the masthead’s shrouds to stay up.
whipping forward in a chop, the spreaders are swept To make things even worse, the bottom end of
aft, so the uppers pull aft as well as laterally, elimi- the jumper stay also pulls forward as well as up,
nating the need for running backstays. adding to the efforts of the upper shroud spreaders
and lower shrouds. The grand effect of all this is to
Figure 8-2. Jenny Ives’s mizzen has a long unsupported make the mizzen frighteningly mobile in any kind
length below the spreaders and is deck-stepped. The of wind or sea.
mast stiffness is adequate, except that as built the mast The lid for this particular can of worms is two-
had no aft-leading lower shrouds; aft staying was pro- fold: turning those forward-leading lowers into for-
vided by the aft-led upper shrouds. The spreaders, ward-leading intermediates; and adding aft-leading
along with the pull of the jumper strut, bowed the mast lower shrouds, going to the same (overbuilt) chain-
forward in the middle. Aft-led lowers, sharing chain- plate that the uppers lead to. The intermediates hold
plates with the uppers, solved the problem. the mast stable forward; sufficient tension is applied
to the aft legs to keep the mast stable aft. As a bonus,
the aft thrust of the jumper strut, which used to be
unopposed, causing the upper portion of the mast
to bow aft, is now balanced by those intermediates.
This is my favorite mizzen staying configuration, the
one I start with when designing for a new spar, and
the one I usually try to get the client to convert to on
an old one.

Cirrus
The N. G. Herreshoff yawl Cirrus is from an era—
the 1920s—when rigs and hulls were changing from
low-aspect designs like Cutty Sark and Jenny Ives to
the sleeker, spindlier rigs of our own era. The mast
is relatively tall and set in a skinny boat, so there
are higher compression loads on a narrow mast.
Accordingly, the mast is supported at more points—
with lower shrouds, upper shrouds, and a pair of
lateral jumper stays called “diamond stays.” The
distance between the staying points is called “panel
length”; the higher the compression loads and the
lighter the mast, the shorter the panel lengths need
to be to prevent buckling (see Chapter 5 for mast
scantling details).

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