How to Dye-Test Swage Fittings, Chainplates and Toggles for Cracks

Make a list: lower shroud and stay terminals, turnbuckles, toggles, clevis pins and the chainplates above deck. The best time is when the mast is unstepped for the season, when every swage, tang and toggle can be laid on a bench. Cox did exactly that, spraying fittings on a sheet of cardboard. With the mast up, test only what you can reach from the deck, one fitting at a time.

The dye is thin, very red and stains gelcoat, teak, sails and lines. Tape plastic sheet or cardboard around and under each fitting. Cover the deck below the turnbuckle and the wire just above the swage so drips don't wick into the wire strands or onto the boat.

Remove any old tape, boots or covers. Wash off salt, then polish lightly with a non-metallic pad and mild metal polish to remove grime and staining (Practical Sailor stresses that even a slight film of growth, grease or corrosion hides cracks). Avoid grinding, heavy sanding or wire-brushing on the area you're testing: aggressive abrasion can smear metal over the mouth of a fine crack. Then spray the kit's cleaner/remover on, let it work for a moment, and wipe dry with a clean, lint-free cloth. Magnaflux says to let the surface dry completely before applying penetrant, and to clean on the same day you test.

Before any dye, inspect each fitting with a 10x loupe and a flashlight held at a low angle across the surface. Practical Sailor notes low-angle light shows cracks and pits better than bright overhead light. Note anything suspicious; the dye will help confirm it.

Shake the can and spray (or brush) the penetrant over the whole area so it's completely wet. Magnaflux says that if the penetrant pulls back into droplets, the surface isn't clean enough: stop and clean again. Cox noticed the dye formed small globules on polished stainless but still went into the cracks; your kit's instructions decide.

Leave the penetrant on for the time your kit specifies. Magnaflux's general guide is 10 to 30 minutes, longer for very fine cracks; Cox's cans said 15 minutes and he preferred about 20. In cool weather, err toward the longer end. Don't let it dry out in hot sun; work in the shade.

This is the step that makes or breaks the test. Wipe off the bulk of the dye with a dry clean cloth. Then wipe with a fresh cloth moistened (not dripping) with cleaner/remover, and repeat with clean cloths until no pink shows on the cloth. Magnaflux warns not to spray cleaner directly onto the part or flood it, because that washes the dye out of the cracks you're looking for.

Shake the developer can until the ball rattles freely, then spray from about 8 to 12 inches away in light passes over short sections, just enough to leave an even, thin white film. Magnaflux notes that too much developer hides small indications and too little doesn't draw them out. Let it dry.

Large cracks show up as red lines almost immediately; fine cracks can take several more minutes. Cox suggests giving fine cracks 10 to 15 minutes to develop. Look with your magnifier and photograph each fitting next to a label.

• A sharp, continuous red line in the metal of a swage barrel, toggle, tang, chainplate or around a pin hole is a crack. A crack running along the length of a swage barrel is a typical stress-corrosion crack in stainless.
• Red bleeding out of joints and gaps where the wire enters a swage, between threads, around a pin or where two parts touch is usually just dye trapped in the gap, not a crack. It can make the mouth of the swage hard to judge; look closely at the barrel next to it.
• Faint, fuzzy pink or scattered dots usually mean excess dye wasn't fully removed or the surface is pitted. Clean and retest that spot.
• A line that matches a visible scratch you already noted is probably the scratch. If you can't tell, retest after cleaning, or ask a rigger.

If an indication is unclear, clean the fitting completely and repeat steps 3 to 9. Practical Sailor suggests practicing on a part with a known small crack (for example, an old bolt bent back and forth until a crack just starts) so you know what a real crack looks like with your kit.

Above-deck chainplate surfaces and pin holes can be tested in place. The part that runs through the deck is where crevice corrosion usually hides, and the dye can't reach it. The sailboat chainplates guide covers when plates should come out for a full look, including a surveyor's preference for pulling them on older boats and checking them under magnification with dye. Removing a chainplate means supporting the mast first; plan it as a rigger job or a mast-down job.

Wipe off the developer with a damp cloth or wash with soap and water (Magnaflux lists both). Clean any stray dye from gelcoat right away. Refit boots, covers and fresh tape only after inspection, and don't seal over a fitting you're unsure about. Dispose of used rags and cans as the labels say; solvent-soaked rags are a fire risk if piled up.

Photograph and log every fitting, pass or fail, in BoatMend, so you can compare next time. Any confirmed crack means replacing that part before sailing, and a rigger should look at the matching fittings: rigs tend to age together. Practical Sailor's old axiom for ocean sailors applies: if one shroud needs replacing because of wear, replace all shrouds of the same age.