April 10, 2011

Where do they get 11 percent?

SAFETY EXPERTS say their rule of thumb for the working load of three-strand laid line is that it should not exceed 11 percent of its tensile strength.

Those experts! Where do they get 11 percent from? It’s one of those statistics that gnaws at the mind. Why not a nice round figure such as 10 percent, or 25 percent?

Eleven percent, besides being a very odd figure, also seems awfully low. That’s using only about one-tenth of the line’s ultimate strength — surely a wasteful and expensive way to go about things.

The fact is that ropes have become so strong in recent years that we choose our sheets for their handling qualities more than their strength. A properly sized sheet would most often be too thin for comfort if you’re using bare hands.

Braided rope, on the other hand, may be pressed into use at 20 percent of its breaking strength. They claim that the core of braided rope is better protected as the rope ages.

I have to say that 25 percent seems to be a perfectly reasonable figure for the three-strand rope, though — with the possible exception of the anchor rode, and the halyard that’s hauling me up the mast in the bosun’s chair.

Today’s Thought
Who can hope to be safe? who sufficiently cautious?
Guard himself as he may, every moment’s an ambush.
— Horace, Odes.

Boaters’ Rules of Thumb, #183
Are your crew or passengers going to be seasick or not? The symptoms of mal de mer often occur in the following order, thus giving the observant skipper a chance to find calmer water or return home before the inevitable happens:
► Frequent yawning
► Slight headache
► Dry mouth
► Wan pallor
► Cold sweat
► Nausea
► Vomiting

Teacher halted the class in front of the deer enclosure at the zoo.
“Tommy,” she said, “do you know the name of that creature over there?”
“No, teacher.”
“Come on now, Tommy, I’ll give you a clue. It’s what your mother often calls your father.”
Tommy’s eyes opened wide in amazement. “Gee, Miss,” he said, “I never realized a louse was so big.”

(Drop by every Monday, Wednesday, Friday, for a new Mainly about Boats column.)

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