Page 165 - The Complete Rigger’s Apprentice

Old-School Inclinometer

Start by setting a bucketful of water on the cabin 45
sole, amidships, under the companionway hatch.
Suspend a plumb bob from the hatch, into the
water (the water will damp the swing of the
plumb bob).
Level the vessel laterally, as nearly as you can,
and clamp a two-foot batten in place parallel to 55 single
the string, so the string is just touching one edge shroud (60
of the batten. This will give you a vertical refer- when abaft 32.5 apiece
ence point later on. Mark the string at the end of mast CL) for doubles
the batten.
Get your friends aboard, on the side that will
make the string move away from the batten. Mea-
sure the distance from the end of the batten to the
mark on the string. Move the string over to the
other side of the batten, and repeat the process on
the other side.
Average out the results, then divide the average
by 24 (the length of the batten in inches). Con-
gratulations, you have just found the tangent of
your angle. Let’s say the distance from batten to
3
string was 4 ⁄4". That number, divided by 24 =
1979. The arc tangent or inverse tangent function
on any scientific calculator will tell you that your
angle of heel was 11.195 degrees. And again you
can calculate the force needed to get to 30 degrees,
and plug the result into the accompanying text. 30

want at least two wires, attached at different heights,
to spread the load on the mast. And it is prudent
to make these wires stronger than they absolutely 30
have to be—two or three times stronger—as a
safety factor.
The safety factor is where our careful calcu-
lations meet the real world. It’s how we take into
account the shock loads that could exceed the cal- 40 single 25 apiece
for doubles
culated maximum RM, how we compensate for (45 when
the eventual degradation of the wire, or loss of abaft mast
CL)
efficiency of terminals, and how we deal with that
nagging voice that wonders if we really, really did
those calculations right. It also assures us that the
wire is strong enough that the load on the wire never
exceeds the Elastic Limit (see sidebar).
In theory, you can share the load among any Figure 5-25. Percentages of the maximum shroud
number of wires. In practice, you’d probably choose load allotted to each shroud in a single-spreader and
among a few tried-and-true configurations, depend- a double-spreader rig. (From Sea Sense, 3rd Edition,
ing on the hull, the type of sailing intended, and by Richard Henderson. International Marine, 1991)
your own pet theories. Figure 5-25 shows two of

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