Page 164 - The Complete Rigger’s Apprentice

Inclining
Most rig scantling formulas are based on the ves- tance from the center of the vessel to their location.
sel’s righting moment at 30 degrees (see text). If Let’s say it is 4.5 feet. Note that. Now go to your
that information is not available from the vessel’s inclinometer, and see what it says. Make a note of it.
designer, the most convenient way to get that figure is Have everyone repeat the heel on the other side of
from the chart shown in Figure 5-24. the vessel. If the measurements are a bit different,
But that chart is only an approximation for many average them out. Serve the pizza. While everyone is
vessels; if you want a more precise basis for your eating, run the numbers.
calculations, you can get it by inclining the vessel First, take the total friend poundage and multiply
yourself. All you need is some form of inclinometer, it by the distance they were from the centerline. Let’s
a bathroom scale, an extra-large pizza or two, and as say that is an even ton (10 friends with an average
many of your largest friends as will fit on your side weight of 200lbs each). This times 4.5 = 9,000 foot-
deck. Here’s the procedure: pounds.
Before everyone shows up, use the inclinometer to Next take a look at how much they heeled the
see if the boat is relatively plumb athwartships. You boat. Let’s say it is 11 degrees. In other words, 9,000
can rest it on a hatch top, cabin sole, or other ostensi- foot-pounds is needed to heel your vessel 11 degrees.
bly level surface that is on the centerline of the vessel. Since resistance to heeling increases in a straight
My favorite inclinometer is the Clinometer iPhone app, line at least through 30 degrees of heel, we can calcu-
but you can also go old-school, using a plumb bob, late how much force will be required to heel the boat
square, and some rudimentary trigonometry skills (see to 30 degrees: 30/11 = 2.7273, and this times 9,000
the sidebar to this sidebar). = 24,545.7 foot-pounds. Take your result to ‘A For-
If the vessel is leaning one way or the other, move mula,’ below, to begin the process of dimensioning
things around until it isn’t. Once you are set, take the standing rigging. Most often the result will be the
the bathroom scale out to the dock, and invite your same as that derived from the chart in Figure 5-24,
friends aboard. Weigh each of them as they come but it’s always good to verify by other means. If the
aboard, jotting down the figures. Total the result, and two methods disagree, recheck everything. If they still
set it aside for the moment. disagree, the direct test is likely to be the correct one,
Let’s say you have 10 friends, and a 35-foot though consulting with a naval architect would be a
vessel. Get them to line up, in as straight a line as good idea.
practicable, along one side deck. Measure the dis-

RM 30 5 1.5
translation, we divide by the length of the lever shroud load = 1
⁄2 beam
arm of the hull, which is to say one-half the vessel’s
beam at the chainplates. My assistant, Erin Sage, and in our case that’s: or
says this is like putting foot-pounds into a colander 50,000 pounds 5 1.5 6,925 kg 5 1.5
and straining out the feet. ( )
5.5 feet 1.67 meters
A Formula which equals 13,636 pounds (6,220 kg).
To put what we have so far into numbers, the trans-
verse load on the rigging = RM 30 (righting moment At last! We now know how many actual pounds
at 30 degrees of heel) 5 1.5, where 1.5 is our extra of force will be pulling on the weather shrouds when
factor, getting us to maximum righting moment. If the boat is heeled to its maximum righting-moment
our RM 30 was 50,000 foot-pounds (6,925 meter-ki- angle.
lograms), then RM 30 5 1.5 would result in 75,000
foot-pounds (10,388 meter-kilograms). Now to Selecting Wire—or Rope
strain out the feet. If our sample boat has a one- But you don’t just go out and get a piece of wire with a
half beam of 5 feet 6 inches (1.67 m), the formula 13,636-pound (6,220-kg) breaking strength; unless
would read: the boat is very small or the mast very short you’ll

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