November 5, 2009

Saggy spreader syndrome

OVER-ZEALOUS LEGISLATORS have made various attempts in the past to ban droopy drawers, the kind that hang below the waistline and expose one’s unmentionables to the gaze of the scandalized public. But no attempt that I know of has ever been made to rid sailboats of droopy spreaders. And that’s a pity, because spreader sag is not only unsightly, it could also be dangerous.

Spreaders normally tilt up slightly at their outer edges, giving a boat a look of happiness and confidence. But occasionally you’ll come across a boat whose spreaders are horizontal or even drooping slightly, which promotes a sordid, down-in-the mouth look.

The golden rule is that all spreaders should exactly bisect the angle formed by the shrouds at their tips.

If that doesn’t make immediate sense to you, you might want to go off in a corner for a while and think about it. Meanwhile, the rest of us will proceed backward to find out why we need spreaders in the first place.

Mast designers and riggers try to keep the angle between the shroud and the top of the mast at 10 degrees or more. If you have a tall mast and a narrow boat, that angle will likely be less than 10 degrees. But if you poke the shroud out sideways from the mast with a stick, you can make the shroud join the top of the mast at a better angle.

Why is this important? Well, it’s a question of physics. In rough terms, if you impose a 20-pound sideways load at the masthead, you will induce about 240 pounds of tension in a stay with a joining angle of just 4 degrees. But if you cleverly increase that angle to 12 degrees with a spreader, the tension is reduced to about 80 pounds. I presume you can see why that is desirable. If you can’t, you’d better join that other fellow in the corner over there.

All right, then, but why should the spreader tips be higher than their bases at the mast? It’s because most spreaders are designed as pure compression struts. In bad cases of the droops, the spreaders would tend to slide farther downward, slackening the shroud and robbing the mast of its proper support.

This is why your shrouds should always be captive at the ends of the spreaders. If your spreaders don’t already have built-in clamps, you should seize the shrouds in place with Monel wire, and cover the tips with plastic spreader boots to prevent damage to the sails.

So have a good look at your spreaders. If they’re droopy, please do something about it. And okay, yes, you two can come out of the corner now.

Today’s Thought
It basically was an art before. We’re just starting to scratch it into a science.
— Dennis Conner, on yacht racing

“This a pet shop?”
“Yeah, whatcha want?”
“Gimme 318 cockroaches.”
“Why do you want that many?”
“I just got thrown out of my apartment and they say I have to leave it exactly as I found it.”

1 comment:

Aaron Headly said...

Saggy spreaders are — to me, certainly — as much an offense to the eye as they are a danger to the boat.

It is fascinating to me how sailboat aesthetics get pulled in so many directions by so many factors. Often, though, the things that most sailors agree to be offended by are seaworthiness-related.

But at the same time, most people think that the various Meter-Class boats from the first half of the 20th century are the most beautiful ever built, in spite of the fact that they are creatures of the then-current racing rules (and barely seaworthy at that). And many sailors think that the now-current rules make for ugly boats.

I'm just as bad on the other side of aesthetics, too: I bought a 30 year old boat this spring, and it had a perfectly seaworthy paint job on it; I could have spent a week on touching it up and been in the water in June.

But it was ugly (sigh). So I repainted the whole thing and didn't get her wet until September.

And I'm glad I did, in spite of all the sailing I missed. And it sure makes the other sailers in the marina happier as well.