Page 407 - Brion Toss - The Complete Rigger’s Apprentice

LOADING FORMULAS Genoa System Loading
Here are some additional tables, graphs, and for- Because wind speed is squared, it is the most import-
mulas, courtesy of Harken and Lewmar, that I use ant variable and can greatly influence loading. Wind
when calculating loads. is the apparent wind and should be calculated for
Harken’s require calculations, but are an excel- the specific sail being analyzed. For example, the
lent follow-up, for sheet loads at least, because they #1 genoa on a 25-foot (7-meter) boat might only be
take apparent wind speed into account. carried in 15 knots of wind, while the #4 blade on a
Lewmar’s are easier to access, being entirely maxi boat could well be carried in 40 knots.
visual, and are useful for any ocean-going yacht, To calculate loading on a genoa lead car, multi-
not just racers. ply sheet load by the load factor of the sheet. Most
#1 genoas will deflect about 45 degree, while a Kev-
lar #3 might deflect 75 degree or more.
HARKEN’S FORMULAS Lead car adjuster tackle load depends on the
angle of deflection of the sheet in the lead car, but is
The following charts and formulas have been generally assumed to be 0.3 of lead car load when
compiled by Harken from many catalogs, marine deflection is 45 degree, and 0.5 of lead car load
publications, and related resources. Because of the when deflection is 60 degree.
constant developments in hull and rig design, and
new materials for sails, lines, and rigging, this infor-
mation might become dated and is offered only as
a general guideline. Consult your rigger or naval
architect for your specific requirements.

Boat Type
Most load formulas assume a medium displacement
monohull, but you can easily correct for other boat
types. Multihulls have great form stability and speed
and will often carry sails very high in the apparent
wind speed, so calculations must be done with this
wind speed in mind. Ultralight Displacement Boats
(ULDBs) are typically tender and often change sails Mainsheet System Loading
or reef quite early, so loading may be done at rela- The formula for mainsheet loading is not as widely
tively low wind speeds. For example, a modern tri- accepted as that for genoa sheet loads, and should
maran may carry its blade jib in 25 knots of wind at be used only as a rough guide for offshore boats
speeds over 15 knots for an apparent wind of nearly from 30 to 60 feet.
40 knots, where a ULDB will probably remove its Travel car adjuster load is generally considered
#1 genoa at about 15 knots of apparent wind. to be 0.2 times car load.

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