Features September 1, 2000 Issue

Are Masts Getting Too Skinny, Too Fragile?

When a marine surveyor reported three boats dismasted while sailing with headsail alone, a lot of people began to wonder why.

Dear Editor:

Some time ago you published a letter from a marine surveyor who said he’d seen three boats whose masts failed when sailing under jib alone. Subsequently, there were in Mailport quite a few letters from curious readers. But you never did settle the issue of whether (or with what kind of rig) it is safe to sail with headsails only.

Leo Niemeier
Miami, Florida

 

You’re right. It all started when readers like David Q. Wark, of Clinton, Maryland; Paul Jay Walchenback, of Seattle, and Dr. Robert Gillette, of Poland, Ohio, joined in a Mailport discussion about our editorial extolling whisker poles.

Is it safe to fly your jib without the main?
Probably no problem on this Block Island 40
with double lower shrouds, but what if you
have single lowers?

That’s when a marine surveyor, David Stainton, of Cranberry Island, Maine, jumped in with his warning to “never sail under jib alone if your boat has single lower shrouds.” Stainton said he’d surveyed three such boats with broken masts.

Since then, other readers have offered comments. Among them: Stan Spitzer, of Edenton, North Carolina; Steven A. Gabovitch, of Sharon, Massachusetts; Fred Hoheisel, of Detroit, and John Tesoriero, of Florham Park, New Jersey.

Some readers said they have for years sailed often with jib only and that for downwind sailing, especially in heavy air, a headsail will tow you home like an arrow, with minimal steering required. A couple of readers said they’ve sailed spinnaker-only many times.

Several readers pointed out that it is common, of course, on ocean-going cruisers to use twin headsails only, with the main stowed.

However, the simple question on the table is: Is it safe to sail under jib alone? With what rig? On what boat?

What Evolution Produced
On most sailboats, a forestay, backstay and two upper shrouds position and hold in place the tip of the mast…but are no help in countering the compression loads working on the mast. In fact, the stays create the compression load. Any stayed mast tries to get out the bottom of the boat if it rests on the keel or through the deck if deck-mounted. Unstayed masts are different.

The forestay and backstay provide no control for the middle of the mast. The uppers provide some athwartship support via the spreaders, but very little support fore and aft.

To control the middle of the mast, most boats have two sets of lowers.

With the mast’s base and tip locked in position and the middle restrained by the lowers, the mast is well supported. It can be bent, raked or straightened…but it takes time, thought and patience.

With single lowers in the same plane as the mast, a thin bendy mast can flex fore and aft. If the shrouds (and spreaders) lead a bit aft, the middle of the mast can bow aft. It also can “pump,” which like anything uncontrollably repetitious is very bad. Keeping the mast in check (to resist or control compression bending) becomes the task of the double lower shrouds.

The geometry is all triangular, which is structurally very powerful. Witness the superb qualities of Buckminster Fuller’s geodesic dome, which is based on the triangle.

There has been a tendency in recent years toward skinny, bendy masts—for sail control, weight aloft, etc.—which suggested that the lower shrouds be singled up. Single lowers also make it possible to carry the boom further forward when running. Moving the lowers inboard also improved jib sheeting angles but detracted from the superior geometry of conventional mast engineering.

Single lowers created the need for a babystay, which is an inner forestay close to the mast. A babystay is nothing more than an attempt to replace two forward lowers with a single stay whose function is to prevent the middle of the mast from bending aft. That’s good, but a babystay provides very little athwartship support; the mast still has considerable “wiggle room.”

To counter the force of a babystay and prevent the middle of the mast from pumping or excessive bending forward, the spreaders can be raked aft and the lowers’ chainplates can be positioned further aft on the rail. But when the raked shrouds limit boom travel when running, the answer is running backstays (so the leeway runner can be slackened to permit the boom to go forward) and that surely is antediluvian.

The next step backwards from running backstays is a gaff-rigged mainsail, which can’t have a backstay, and that will get you back to using a whole tree as a mast, which means you might, as the need presents itself, send a crew ashore to cut a new one.

Going the other way might lead to rigs based on carbon fiber technology, such as Carbo Spars’ AeroRig®, which has a stayless rotating mast with a fixed one-piece boom for both main and jib (it’s marketed in the US by Forespar) or a B&R rig (invented by the late Lars Bergstrom and Sven Ridder), which, in order to get rid of the backstay and carry a big roach in a fully battened main, has a skinny mast made rigid by deck struts, many swept spreaders and a lot of wire.

The Moving Parties
The move to thin bendy masts generally has been attributed to those who race sailboats. They have been said to be fanatical about weight saving, sail shape and tight sheeting angles. And there is no doubt that what they do produces speed on the race course, be it round the buoys or ocean racing.

However, blaming racing sailors for delicate, demanding rigs may be only part of the answer to the question of rig integrity.

Practical Sailor has been told that both sailboat builders and sailmakers have been instrumental in the trend toward slender, complicated masts and that sailboat manufacturers in search of ever-lower costs sometimes go to spar makers and demand cheap, light masts. Naturally, to make them seem desirable, these masts were christened “high-tech.” Perhaps they should be dubbed “high risk.”

Sailmakers, constrained by racing rules that limit the versatility of a single mainsail or limit the number of sails that can be carried aboard, have encouraged bendy masts as a means to make one mainsail perform like several—by making quick, relatively easy adjustments to the luff and foot tension.

Although not as true as it was a decade or two ago, sailmakers’ reputations still are based too much on getting their sails aboard boats that win widely known races.

Mast Makers Speak
Jim Kulibert, the veteran sales manager for Charleston Spars (R.D.M. Sparcraft) in Charlotte, North Carolina, said:

“My problem is with that marine surveyor who said three masts with single lowers failed while running with headsails only. That shouldn’t happen. You should be able to fly anything off the mast head…until the headsail blows out. Of course, on a racing boat that means setting up the backs and the baby stay. On an Island Packet, nothing special is required.”

Robert Quates, technical manager for Charleston Spars, which is a supplier to Beneteau, Cabo Rico, Caliber, Catalina, Freedom, Gemini, Hunter and Island Packet, explained more fully.

“We like rig proposals. They can be very exciting. However, the thin spars require very precise tuning. If anything gets the least bit out of tune, the mast pumps and everything goes.”

He said builders often demand that sparmakers make the lightest and cheapest possible rigs, even specify the weight and the cost. He said that for builders, single lowers permit the elimination of some hardware and a set of chainplates.

“Saves some money. That’s good. But it can make,” Quates said, “for some borderline applications.

“Running backstays? They’re an unfortunate reality. Personally, I like fore and aft lowers.”

(Quates is in good company. The book, Desirable and Undesirable Characteristics of Offshore Yachts, by the Technical Committee of the Cruising Club of America and edited by John Rousmaniere, states in a chapter by Rod Stephens and Mitch Gibbons-Neff, “…the babystay…provides fore-and-aft support for the mast when there are no forward lower shrouds, as is often the case in modern boats… We prefer forward lowers…”)

Another mast maker, Chuck Simmons, the US distributor of England’s Proctor Masts, said that unless you have a robustly sectioned mast, you should not sail jib only on a boat with “in-line” single lowers. Because Proctor makes masts for both small one-design racing boats and larger boats (both racing and cruising), Simmons seems well-positioned to comment on this subject.

“If a mast fails while sailing headsail only, with or without a whisker pole, on a boat with in-line single lowers (plus the standard forestay, backstay and uppers), it must be considered ‘operator error,’” he said. “That means you’re supposed to know enough not to do it.”

Simmons said that most mast sections don’t mind being bowed forward, but that they are notoriously weak when inverted—meaning bowed aft. He said that on all boats, but especially smaller boats, the mainsail provides considerable support for the mast.

“When sailing headsail only,” he explained, “the mast can suffer inversion and snap like a matchstick.”

He said the mainsail boom and gooseneck pressing forward even a bit helps to prevent mast “inversion.”

Simmons said that, in his opinion, it is not cost that has led to single-lower rigs.

“There’s not much saving involved,” he said, “in getting rid of some wire and a couple of chainplates and tangs, because you have to go to a heavier mast section. Now, if you don’t go up on the mast section, you’re flirting with…well, I wouldn’t do it.”

A Naval Architect Explains
Eric Sponberg, a naval architect in Newport, Rhode Island, commented:

“I hate to think that the survivability of a mast depends on the mainsail. In the cases cited, something else happened. Some eccentric load developed and something broke.”

He pointed out that spars and rigging once had built-in redundancy because, he said, “The mast was stiff. The stays and hardware were robust. The staying was rugged.

“You could look at the rig and say, ‘I can lose that and nothing bad will happen; that can break and I can still save the rig.’ Too often now, that’s no longer true. The mast is minimum and the wire and hardware are taken down so far that if any one thing fails, the whole rig is overboard.

“It’s the nail in the horseshoe all over again.”

In addition, Sponberg said that, with sailboats, it is unfortunate but true that advanced performance on the race course always has converted to cruising boats.

“What’s wrong with that,” he said, “is that the cruising sailor may have neither the time nor the manpower to keep the rig in the precise configuration that it demands.”

Sponberg said that although sailboat builders, who are always cost-conscious, may be responsible for the trend toward “minimalized” rigs, it was his opinion that racers and sailmakers bore an even heavier responsibility.

Sponberg has done considerable work on the development of unstayed masts, which he said, “Provides another answer to your question. Engineer the mast to do whatever is required, without any wire and bits of hardware to hold it up.”

The original question still is: On what boat and under what circumstances is it unsafe to fly a headsail only?

Back To Those Broken Masts
Let’s go back to David Stainton, the 65-year-old marine surveyor who started all this. Stainton runs a 60-boat yard on Cranberry Island, Maine. He said the three boats whose masts (all with single lower shrouds and no babystay or inner forestay) failed while sailing jib only included a Pearson 26 (a popular model; 2,039 were built) and a 27' O’Day. He cannot retrieve from his files the name of the third boat. None of them are high-tech racing boats.

It’s not possible to list here all boats with single lowers. Among them are C&Cs, the San Juan 24, the Santana 2023, the O’Day 22, J-Boats, some Catalinas, the MacGregor 26, some Cal boats, the Olson 30, some Pearsons, some Irwins, some Beneteaus, some S2s, etc., but that doesn’t mean that the masts will break if any of these boats are sailed with a headsail only.

On the other hand, you’re unlikely to find single lowers on boats like Grampians, Com-Pacs, Cabo Ricos, Luders, Island Packets, Nicholsons, Shannons, Gozzards, Westsails, Masons, Cape Dorys, any Allied boats, etc.

On boats whose standing rigging consists of a forestay, backstay, two uppers and single lowers, how many masts have broken? That’s not known.

A Simple Test
As it stands, the only advice that emerges for owners of such boats (or any boat, for that matter) is that if your boat has a sturdy mast, not too bendy, “in-line” lowers are okay, and it’s safe to sail headsail only.

What is “sturdy” and what is “not too bendy?”

A practical answer came from Eric Sponberg. Here’s what he said: “It gets scary if the mast pumps fore-and-aft one quarter to one half of its overall dimension. In other words, if the mast measures eight inches from the front edge to the rear edge and it moves two to four inches, watch out!”

Conversely, he said that if the mast is steady and doesn’t pump, there is no cause for worry.

So, the answer to the question, “On what boat should you be able to sail headsail only?” the answer is, “Any boat,” but if it has single lowers give it the Sponberg test.

 

Contact- Sponberg Yacht Design, PO Box 661, Newport, RI 02840; 401/849-7730; email: ewsponberg@cs.com; www.boatbuilding.com/sponberg.

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