April 27, 2010

Tense moments in the shrouds

CAUTIOUS BOAT BUYERS are usually suspicious about deck-stepped masts. They check to see if the deck directly beneath the mast has sagged. And the way the canny buyer does this is by feeling the tension in the mast shrouds. A soft deck simply won’t support much tension. It will just sag further.

You can just about play a tune on a properly tensioned shroud. In fact, I’m always amazed at how much tension the experts advise you to wind in via the turnbuckles.

I have in front of me the carefully preserved pamphlet that came with a pair of Loos tension gauges I bought many years ago and it says:

“Contrary to popular thought, a slack rig is more punishing on a hull than a properly adjusted tight rig. Insufficient tension will not reduce the loads transmitted to the hull. Slack rigging will punish the spar and rigging needlessly by allowing excessive movement, chafe, and shock loading.”

Now for a boat with 7/32-inch 1 x 19 stainless-steel shrouds, such as a 27-foot Cape Dory, the Loos people advise you to pre-load the tension to 700 pounds. The forestay should be tightened to 1,000 pounds.

I’ve always been scared to do this. The numbers sound too big. When I first bought my gauges I screwed up my nerve and set the shrouds at 450 pounds apiece. Years later, encouraged by the fact that the sides of the boat had not yet risen to meet each other, and the mast had not yet been driven through the deck, I raised the tension to 600 pounds. But I never got as far as 700 pounds.

The Loos pamphlet goes on to warn that “the lateral stiffness of the mast and the fore-and-aft stiffness of the spreaders is reduced by a factor of 2 when the leeward shrouds go slack. This important structural characteristic is not generally recognized.”

I presume that when they say “reduced by a factor of 2” they mean the mast stiffness is halved. That sounds quite serious. But then, one must also recall that they are in the business of selling rigging tension gauges. Not that I would suspect them for one moment of deliberately scaring people into buying their gauges. It’s just that I’m a born skeptic. And 600 pounds is just fine for me, thanks.

Today’s Thought
We're probably the opposite of the Osbournes. We run a very tight ship.
— Hulk Hogan

Boaters’ Rules of Thumb, #44
The cost of cruising. How much does long-term ocean cruising cost? The rule, according to the legendary French singlehander Bernard Moitessier, is that it costs you “just as much as you have.” But here’s another rule of thumb from two very experienced cruisers: Take your everyday onshore living expenses. Subtract all of your automobile costs, two-thirds of your clothing expenses, your home rent or mortgage payments, and your mooring costs. Add one-third to your food costs. The result is a close approximation of what it would cost you to cruise over an extended period.

Last week a local Small Claims Court judge told a nervous woman witness to make herself at ease, and talk to him as if she were talking to her husband or friends.
The case is still proceeding.


Aaron Headly said...

Unrelated - and not formally a comment on the post: A fellow in England ran out of fuel circling an island. He figured he'd just keep the shore on his right and would eventually get to his destination. Link here.FIgured it might amuse you.


John Vigor said...

Great story, Aaron. Thank you.

John V.