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FINDINGS LIBRARY · UNDERWATER GEAR

Leaking shaft seal: stuffing box drip rates, dripless seals and survey findings

UPDATED 6 NOVEMBER 2026 · 3 EXAMPLE FINDINGS · 2 SOURCES

How many drips a stuffing box should make, when it needs repacking, what a surveyor checks on the shaft log hose, clamps and dripless seals, and three example findings graded A, B and C.

AT A GLANCE
Leaking shaft seal
USUAL GRADE
A for a steady stream into the bilge or a cracked or soft shaft log hose. B for a stuffing box dripping 10 or more a minute, or dripping with the shaft still, or single clamps. C for adjustment and records
FOUND WITH
Watching the seal with the shaft turning and still, feeling the stuffing box after a run, and checking the shaft log hose and its clamps
JUDGED AGAINST
Practical Sailor puts a healthy stuffing box at 3 to 4 drips a minute underway. About 10 a minute, or drips with the shaft still, needs adjustment or maintenance
REPAIR COST
Packing is small parts and a few hours. A new shaft log hose or dripless seal bellows means a haul-out. Priced per boat

Where the propeller shaft passes through the hull there's a hole to the sea. A stuffing box or a dripless seal closes it round a turning shaft, held on by a short rubber hose, the shaft log hose, and its clamps. If the hose splits or the seal lets go, water comes in at the speed of the hole.

How a surveyor checks it

Start with the hose. Practical Sailor says to inspect it for age deterioration, a common problem, and for corroded clamps, and calls double clamping essential. Squeeze it: cracked, soft or swollen hose is replaced.

Then the seal, with the shaft turning and with it still. A traditional stuffing box should drip: Practical Sailor gives 3 to 4 a minute underway, and says about 10 a minute or drips with the shaft not turning means adjustment or maintenance. After the sea trial, feel the box. Good Old Boat's rule is warm, never hot.

A dripless seal holds a graphite collar against a stainless collar with rubber bellows. It should be dry. Practical Sailor notes these seals still have scheduled maintenance, so ask for the records and check the bellows for cracks.

What decides the grade

The rate of water coming in and the hose holding it back. A stream, or a failing hose, is an A. Too many drips, drips with the shaft still or single clamps are a B. A dry seal with no service record is a C.

Leaking shaft seal: example findings

The same defect written up at each grade, the way Axsail writes it from what the surveyor says on board. The grade follows what was found, so use these as wording, then grade what you see.

PROPULSIONA
Stuffing box, propeller shaft

Steady stream of water from the stuffing box with the shaft still. Shaft log hose cracked on the outside and soft when squeezed. Single corroded clamp at each end.

Recommendation: Monitor the bilge until hauled. Replace the shaft log hose with double stainless clamps at each end and repack the stuffing box before the vessel is next underway.

PROPULSIONB
Stuffing box, propeller shaft

Stuffing box dripping about 12 times a minute with the shaft turning and continuing to drip with it stopped. Box warm after the sea trial. Hose sound, single clamps.

Recommendation: Adjust or repack the stuffing box and fit a second clamp at each end of the shaft log hose within 12 months.

PROPULSIONC
Dripless shaft seal

Dripless seal dry on the sea trial. No record of when the bellows were last replaced.

Recommendation: Obtain the seal maker's service schedule and replace the bellows as it requires.

ASafety. Safety or compliance deficiency. Fix before the vessel is next underway.
B12 months. Deficiency that needs timely attention. Fix within about 12 months.
CRoutine. Note or observation, cosmetic or maintenance. Routine maintenance at the owner's convenience.

What the fix involves

Job Reported cost
Adjust the packing nut Owner's time
Repack the stuffing box Packing material and a few hours, in or out of the water
Replace the shaft log hose Haul-out, hose, clamps and labour
Replace dripless seal bellows Haul-out and parts to the seal maker's schedule

Practical Sailor's warning on packing: an overtightened stuffing box scores the shaft. A grooved shaft won't seal with new packing either.

Photos to take

The stuffing box or seal, the hose and both sets of clamps, and a short video of the drip with the shaft turning. With Axsail, count the drips aloud as you film and the rate goes into the finding.

Writing it up

Say what kind of seal it is, the drip rate with the shaft turning and still, the temperature after the run, and the state of the hose and clamps. With an A, tell the owner to watch the bilge until the boat is hauled.

Frequently asked

How many drips per minute should a stuffing box have?

Practical Sailor puts it at a few drips, 3 to 4 a minute, while underway. Good Old Boat suggests about one drop every 10 seconds with the shaft turning. Around 10 a minute, or drips with the shaft still, means it needs adjusting or repacking.

Why does a stuffing box need to drip?

The water lubricates and cools the packing where it rubs on the shaft. Tighten it until it's dry and Practical Sailor warns it will eventually score the propeller shaft.

How hot should a stuffing box get?

Warm, never hot. Good Old Boat's rule is that the box should feel warm after prolonged use. Hot means it's too tight.

Do dripless shaft seals need maintenance?

Yes. Practical Sailor notes they still have regularly scheduled maintenance requirements. The bellows age, so check the seal maker's schedule and the boat's records.

Why double clamp the shaft log hose?

The hose is all that stands between the sea and the boat at the shaft. Practical Sailor calls double clamping essential, and the hose itself ages and needs checking.

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