Sailboat Rig Problems: A Surveyor's View

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.

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.


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.)

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.

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.

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.

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.

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.

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.

* 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..