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Presenting an original unpublished article on problems with sailboat rigging

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Sailboat Rig Problems: A Surveyor's View

By J. C. Stormer, Jr., SAMS-AMS(Retired), NAMS-CMS(Retired).

We rarely see problems with the wire of the standing rigging itself. More often it is with the terminals, chainplates and other fittings. Many of the problems with sailboat rigs originate near or below deck level where anyone can see them if they are looking. A few examples from our recent surveys are shown below.

Swaged Terminals Cracking

These swaged terminal fittings, are cracking due to stress corrosion. "Swaging" is a process where the tubular stainless steel fitting is squeezed, under high pressure, until it cold "flows" around the wire and grips it.
Cracked Swage on PEA26
Cracked Swage on PacSea25
Incipient cracking like this will continue over time until the swage fails and the wire pulls out unexpectedly. Generally swage cracking is more prevalent at the lower terminals because of the salt and pollutant laden water running down the wire. If we do see problems with the wire it is also often at the point where it enters the fitting. (Stress Corrosion Cracking at the "Corrosion Doctors" web site gives technical details on this type of failure.)

Norseman Terminal Sta-Lok Terminal

Some boats have NorsemanTM or StayLocTM rather than swaged terminals. These are mechanical fittings which grip the wire strands between a conical wedge inserted in the center of the wire and the body which covers the end of the wire. More rarely we see fittings where the ends of the wire are cast into a lead alloy or polymer inside the body of the fitting. Rigs with any of these mechanical or cast fittings do not have the problem of swage cracking. The fittings apparently last at least as long as the wire.
Evidence of Repairs?

Clues to probable repair of cracked swage
The clues to what has actually happened with a rig are sometimes subtle. The features seen to the left suggest to us that this shroud probably had a cracked lower swaged terminal like those seen above. The terminal was apparently cut off, which would shorten the wire a few inches. A new terminal was then swaged on to the old wire.

We see this sort of thing on a surprizing number of 10-15 year old boats. Some riggers feel that this is an acceptable repair. To us it is at best a temporary fix until the gang can be replaced. We feel it is certainly something a buyer should know.

Note also the close fitting white plastic cover on the wire. These give poor chafe protection, but are great for trapping dirt, grease, and chlorides - a recipe for corrosion. Get rid of them!
Chainplate Crevice Corrosion I

Chainplates, such as those shown here, are also a common source of rig failure.

The chainplates shown below were removed from a Taiwanese built cruising yacht with decks overlaid with teak. As you can see the lower plate has developed a serious crack. However this was hidden within the deck (below the top surface of the teak and above the lower surface of the deck). The caulking on the upper chain plate shows the position of the deck surface. The only clues to impending failure are minor "rust" stains from leaking water running down the chainplate. Only after it is actually cracked and beginning to fail will the chainplate may show some deformation above the deck surface.

Chainplates with cracking due to crevice corrosion

Some boats have fittings bolted through the deck rather than chainplates. Once the bedding of these fittings begins to leak even slightly, the bolts are subject to the same sort of crevice corrosion.

Stainless steels are particularly susceptible to corrosion in oxygen deficient, chloride rich, elevated temperature environments. The salt water soaked wood decks heated by hot sun fit that recipe.

("Stainless Steel at Risk from Corrosion" By Dewey Ives, another SAMS surveyor, was published in the National Marine Underwriters Winter 2001 "Water Log". A copy may be downloaded in PDF format at www.nmu.com (Pull down the menu there to "Water Log"). The Intercor International site also has information on crevice corrosion and stress corrosion cracking in stainless steel.

Chainplate Crevice Corrosion II Here is a second example of an impending rig failure due to stress corrosion cracking in a chainplate.




Chainplate1
Chainplate2
Chainplate3
Chainplate4
Shown to the left is a lower shroud chainplate removed from a Bristol 29. It shows no sign of deterioration above decks, but has extensive stress corrosion cracking around all the bolt holes where it was secured to the interior of the hull. (View close up photographs of the above deck portion, A, B, or C. by clicking on the image.)
Clevis Pins and Holes

Small Clevis pin Clevis pin hole It appears that there is also some deformation of the clevis pin holes in the chain plates discussed above (see right). This would probably be impossible to see without disassembling the connection which is not normally done in a standard pre-purchase or insurance survey.

Clevis pins that are not matched to the holes in the chainplate can be a cause of deformation of the holes or bending and cracking of the clevis pin. The size of the clevis pin should exactly match the hole or there will be a concentration of stress at the point where the pin is tangent to the hole. The pin shown to the right is almost certainly smaller than the hole in the chainplate allowing it to tilt.

Turnbuckles I (crevice corrosion) Vagabond 42 Bowsprit shroud

This is a picture of a bowsprit shroud on a Vagabond 42. Note the closed type turnbuckle (left arrow) with threaded stainless steel T-toggle screw. The port side shroud was found to be to be loose so this shroud was pushed lightly to test its tension. The T-toggle parted suddenly and completely (see below) . The right arrow is the bobstay fitting also shown in close-up below.

Vagabond 42 Bowsprit shroud turnbuckle

On the left above is a close-up of the port side T-toggle which is identical in appearance to the starboard side T-toggle before it failed. Note the rusty stain on the stainless steel parts. On the right is a close-up of the failed T-toggle. Note the advanced crevice corrosion. There is no bright metal to indicate fracture of any uncorroded metal. Only interlocking boundaries of corrosion products were holding this fitting together. Yet, it didn't look too bad, just a little stained. The boat had not been sailed for some time. What might have happened on starboard tack with a good breeze?

Threaded stainless steel fittings like this must be regularly disassembled and inspected for crevice corrosion. We prefer open bronze turnbuckles with forged forks and toggles.

Below is a close-up of the stem fitting for the bobstay on this Vagabond pictured above. Note the rust staining around this fitting in the picture two above.
Vagabond 42 Bowsprit bobstay fitting
This needs to be removed for inspection of the bolts and backing plates as well as the threaded stainless steel rod bobstay.
Turnbuckles II

One of the most common problems we see is turnbuckles with no cotter pins, as this one in the picture to the left. This boat was about to leave on a 300 mi. offshore passage! Turnbuckles can and do loosen with alternating strains and vibration.

Less commonly we see problems like the deformed turnbuckle body seen below. Someone applied a wrench or bar a little too zealously and twisted the body in the direction of the arrows.

Mast Fittings and Terminals

Even when we don't climb aloft, we do take a careful LOOK up. The photo below shows a mast on which the lower shrouds have a bad misalignment with the terminal fittings. This put a sharp bending strain on the wire as well as the terminal and the mast fitting. It suggested to us that these fittings and wire needed to be more carefully inspected.


In the particular case shown above, the rig has survived for a long time and even at this time did not show any obvious signs of failure. However, the photo below (credit) shows a similar situation where misalignment, as well as use of a miss-matched fitting has put an excessive strain on a mast socket, which has cracked the fitting and the mast. (The socket fitting is a metal piece inside the mast with only a small portion of it showing. It is secured by rivets, three above and three below the socket.)


(Photo is of a Kemp/Selden deck stepped mast on a 1985 Sadler 34 used by permission of the photographer, Chris Kessell, SAMS-AMS ) This boat has had the wrong terminal fitting installed on the wire shroud, compounding the misalignment problem.

Scott Alexander (OEM Sales Manager, Selden Mast, Inc.) recently sent us the following: "Although this is a Selden Mast the terminal that is attached to the rig is a Gibb and should not be used with Selden backing plates. Selden backing plates require Selden (a.k.a. Hasselfors) rig fittings. The Gibb terminal does not allow for enough articulation or proper transfer of loading to the designed area."

The damage demonstrates the necessity of carefully matching the correct components to insure proper load transfer. It has certainly progressed to the point where a repair (not just drilling holes to stop the cracks) is necessary.

Curved terminal fittings such as the one just above also sometimes develop cracks on the underside, or inside of the curved section which cannot be seen without disassembly. This is another example of the situations which lead us (and many other surveyors) to recommend that a mast should be taken down and fittings disassembled for inspection every five years.

Time to Replace?

What is the expected "life span" of a rig before it should be replaced? Some authorities suggest 10 years for replacement. All of the problems above were with rigs that were more than 10 years old. But, we see some rigs at 15 years or more with no apparent problems.

There are too many variables for a simple answer. One of the most important variables is the type of stainless steel alloy used. Type 304 is often used because it is initially somewhat stronger. But, Type 316 stainless, which has 2% molybdenum in the alloy, is much more corrosion resistant.*

Where the boat has been makes a difference. Stainless deteriorates faster in hot salty tropical waters (TX summers and pollution). Usage makes a difference. Again, one authority suggests replacement after one hard leg of a round the world race, or a couple of seasons of serious offshore racing. Rarely do we as surveyors, or you as buyers, know for sure where the boat has been or how hard it has been used.

Without more definite information, the position we take is conservative. If problems such cracked swages, broken or pitted wire, etc. appear, we feel it is time to replace the entire gang. If a rig is more than 10 years old, it should be carefully monitored for such problems, and consideration made for the likelihood that replacement will be necessary in the near future. Even in the absence of problems, replacement of a rig more than 10 years old should be considered before embarking on major offshore passages or extended cruises.

J. Stormer, Marine Surveyor

* Although both 304 and 316 stainless steels are basically non-magnetic, type 304 can become slightly magnetic when cold worked. Type 304 wire and swages generally show some attraction when tested with a strong magnet; 316 does not. However this test may not be definitive for all fittings..






All the photos above were taken by J. Stormer except the photo of a cracked mast at the stem-T socket which is by Chris Kessell, SAMS-AMS, Kessell Marine Survey & Engineering, Co., POB 1723, St. Lucia, West Indies.
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Revised 02 Feb 2005