Page 181 - The Complete Rigger’s Apprentice

vessels. On tall modern rigs, however, the slight shift- formance. Then there is the matter of modern turn-
ing of the eyes around the mast from tack to tack can buckles: very nice, very strong. But if you splice your
result in appreciable mast bend that could endan- 7 x 7 shrouds around heavy-duty thimbles, you will
ger the mast and will certainly impair sailing per- find that the thimbles will not fit into turnbuckles of

Chainplates
For long-term fatigue resistance chainplates need minum bronze is of comparable strength, and is far
to be at least 1.5 times stronger than the wires they more fatigue- and corrosion-resistant. Grade 5 tita-
hold. Chainplates are also as sensitive as tangs to nium is even stronger than either bronze or stainless,
things like hole size, lead, and hole angles. and sneers at fatigue and corrosion. It is also more
Chainplates differ from tangs in that they are noble, so is not susceptible to galvanic action.
attached to the hull. They don’t need to pivot because If you’re designing chainplates, the accompany-
the hull doesn’t move much. Instead chainplates are ing chart from Skene’s Elements of Yacht Design is
locked in place, usually with multiple fasteners, to a quick way to the right size. Notice that the offset
spread the load to the hull. But this means they must gives you more “meat” on the load side of the hole.
line up precisely with the shrouds, laterally as well as This prevents the hole from deforming into an egg
fore and aft. Because chainplates and their fasteners shape over time. You’ll find a slightly different chart
are near the water, crevice corrosion becomes a prob- in Larsson and Eliasson’s Principles of Yacht Design.
lem: Poorly-bedded stainless can get wet, and waste Either source will give reassuringly stout chainplate
away to nothing. Like all corrosion, this problem is dimensions
worse the farther south you go, but it’s a good idea in If you’re designing or checking tangs, each of the
any climate to pull some chainplates and their fasten- two parts should be at least half the strength of the
ers once in a while. If you find water, or any signs of corresponding chainplate.
corrosion, rebed, replace, or both. Note: This table can be used for titanium. Grade
Highly-polished type 316 stainless has long been 5 is much stronger than the other materials, but
the preferred material for chainplates; it is relatively making it thinner will put excess load-per-square-
strong, and relatively corrosion-resistant. But alu- inch on clevis pins.

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