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Solved problems · Propulsion · Crew answer

How much should my stuffing box or dripless shaft seal leak?

A packed stuffing box should drip a few drops a minute underway and little or none at rest. A face-type dripless seal should be dry at rest. Here's how to adjust or service each one safely.

Symptom

Water collects in the bilge from the propeller shaft area, the bilge pump runs more than usual, or the shaft seal sprays or drips steadily.

Likely cause

Packing in a traditional stuffing box hardens and wears, letting in more water. On a face-type dripless seal, dirt between the carbon and stainless faces, lost bellows compression, or an aging bellows causes drips or spray. Corroded clamps or a deteriorated shaft-log hose can also leak.

Stop now if

Water is coming in faster than a few drops, or the seal or hose has moved or split. Keep the bilge pump running, stop the shaft, and arrange a haul-out or a diver. Never adjust a stuffing box with the shaft turning, and keep hands, sleeves and hair clear of the shaft.

The fix, in short

  1. Know what normal looks like. Practical Sailor puts a healthy packed stuffing box at about 3 to 4 drops a minute underway and little or none at rest; around 10 drops a minute, or drips at rest, means it needs attention. A face-type dripless seal should not leak at rest and should only mist briefly while it beds in.

  2. Adjust packing in small steps with the engine off. With the engine off and the shaft still, hold the gland and tighten the packing nut a little at a time, then lock it. Run the shaft in gear only at the dock with lines doubled, the prop area clear, and hands, sleeves and hair away from the turning shaft. Check gland temperature after shutting down; a hot gland is too tight. If tightening no longer slows the drip, repack it rather than overtightening, which can score the shaft.

  3. Clean the faces of a dripless seal. Engine off, shaft stopped. If a face-type seal drips at rest, debris is usually caught between the faces. The maker's fix is to work a clean rag carefully between them so incoming water flushes it out; some water will enter while you do it.

  4. Burp a face-type dripless seal after every launch. With the engine off, briefly squeeze the bellows to part the carbon from the rotor until water flows, then release. Trapped air lets the faces run dry and overheat. Seals with a vent hose above the waterline purge themselves; check the hose is clear.

  5. Restore bellows compression and keep the vent high. If the seal sprays underway after break-in, the bellows may need more compression; follow the maker's chart and set-screw procedure exactly. If the seal has a vent hose, keep its top end secured above the waterline even when heeled, with no loop that could start a siphon.

  6. Inspect hoses, clamps and bellows age. Check the shaft-log hose and its double clamps for cracking and corrosion. PSS calls for replacing the Type A bellows at least every 6 years regardless of how it looks.

Written by Sailor Cruiser crew. General guidance, not an inspection of your boat.

Equipment involved

  • Shaft seal: Traditional packed stuffing box or face-type dripless seal (for example PSS)
  • Drivetrain: Inboard engine and propeller shaft

Related guides

Sources

Background reading we checked while writing this answer. The wording above is our own.

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