Features May 2017 Issue

DIY Rig Check

The signs of corrosion and metal fatigue are often well-hidden

 

Here are two good examples showing the problems associated with the lower or deck level use of swage terminals for your standing rigging. “Swaging” is a process where tubular stainless steel fittings are essentially crimped onto rigging wire under high pressure.

Swage fittings are popular for a number of reasons. They’re cost effective (i.e. cheaper) and in northern latitudes they can last a good long time (15 to 20 plus years is not uncommon). They don’t do as well in southern latitudes however, where they tend to fail faster due to temperature and increased salinity.

Vertical cracks
Vertical cracks (1) can be caused by the expansion when water enters the swaged terminal and rust begins; horizontal cracks (2) are generally caused by metal fatigue.

Salt water and other corrosive elements run down the wire and migrate into the fitting. This initiates rust, which expands and eventually causes the shank of the swage to rupture (as shown in image 1) allowing the wire to unexpectedly pull free. While vertical cracks in swaged fittings are bad enough, the horizontal crack shown in image 2 is worse.

Horizontal cracks are generally caused by metal fatigue, rather than internal corrosion. Such fittings have no safety margin and must be replaced immediately. If you find either type of swage terminal failure, you’ll not only want to address it immediately, but also inspect the rest of your standing rigging prior to vessel use. The remainder of your fittings are likely the same age and prone to similar failure.

An excellent alternative to swage terminals are mechanical fittings, such as Sta-Loc, Norseman or Hi-Mod. Mechanical fittings grip the wire via a conical wedge inserted into the center of the wire and fitting body that covers it. This type of connection results in reduced corrosion and less chance of failure. Mechanical fittings are more expensive than swage fittings, but have the added benefit of being reusable.

If you crave the reliability of mechanical fittings for your standing rigging, but baulk at spending the extra money to use them exclusively, an acceptable compromise is to use swaged fittings for the upper terminals and mechanical fittings for the lower ends. Since most problems with swaged fittings occur at the deck fittings, this strategy gives you the best of both worlds. See the online version of this article features for links to PS articles on swage inspection and installation, plus results from our most recent test of mechanical fittings.

Capt. Frank Lanier is an accredited marine surveyor with over 30 years of experience in the marine industry. He is the author of Jack Tar and the Baboon Watch: A Guide to Curious Nautical Knowledge for Landlubbers and Sea Lawyers Alike. His website is http://www.captfklanier.com.

Comments (2)

"Loosing a rig makes for a bad day." We recently had a bad day on a return trip from Culebra to St. Thomas. Being upwind, the sails and rigging were close-in and tight. Then pow, the whole boat jerked and rolled as if we had struck a whale, but nothing could be seen in the water. Then we noticed that the jib was bellied low. Only then did we see the main upper and intermediate shroud chainplate swinging around. The top of the mast was swinging 3-5 feet away from the damaged stays. On each swell the mast would spring upright, stopped hard by the good stays. We backwinded the sails to hold the mast upright; then tied the spare halyard to the cap rail to hold the mast slightly fore. Next we lowered the mainsail into our Schaffer boom furl and used that halyard to connect the mast top to the sail track slightly aft. No matter how hard we tensioned the halyards, the top of the mast bent to one side about a foot and sprung-back stayed-hard at every swell. We would never be able to motor to safe harbor heading just into the swells in order to prevent the mast from bending. We needed to quarter the swells more. So finally we swung the main boom to the damaged stay side and prevented the boom down hard. Even though we had installed a solid boom vang, we decided to keep the topping lift attached. The topping lift finally stabilized the rig, by acting as a stay, and allowed us to quarter the swells to safe harbor.

We were negligent, there was old rust where the chainplate cracked and only threads of stainless left at the time of the break. The chainplate and the region of the crack was easily visible, if only we looked when opening a medicine cabinet door. While on a mooring the days before, we could feel the boat jerk as if hitting bottom, but bottom was 14 feet down. It is possible that a break had occurred then and the upper portion of the chainplate was only held wedged in the core decking, but with enough sliding play to let the mast bend a little and then straighten hard, shaking the boat with a light jerk.

When checking the rigging, take the time to check the chainplates. You'll never see damage within the deck core, unless you clear the core and bottom fiberglass away to provide the view.

Posted by: Locquatious | April 30, 2017 12:21 PM    Report this comment

Swaging deterioration typically occurs from within proceeding outward. Absent corrosion/crevice analyses in a laboratory its difficult to assess swaging from visual inspection. Which is why swaging is typically replaced after 5 years in the tropics with mechanical fittings with extended life spans and easily replaced. Through the use of "extenders" the wire can typically be reused. The only "advantage" of swaging is that its less expensive than mechanical fittings. Given the crucial importance of the rig periodic replacing of swaged fittings is essential. Taking a file and working through a seemingly fine swage will be instructive. Loosing a rig makes for a bad day. The mark of a well fit cruiser is mechanical fittings. Failures are most uncommon and its easy to inspect.

Posted by: Piberman | April 30, 2017 10:19 AM    Report this comment

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