Shaft Seal and Stern Gland Service in Australia

The stern gland is where the propeller shaft passes through the hull. Its job is to let the shaft turn while keeping the sea out — and it is the fitting most likely to sink a boat at its berth.

The two types

Traditional packing gland (stuffing box). Rings of packing material compressed around the shaft by a threaded nut. It is designed to drip — the water lubricates and cools the packing. A few drips per minute under way is correct; no drips at all means it is over-tightened, which overheats the packing and scores the shaft.

Dripless / mechanical seal. A carbon face running against a stainless rotor, held in compression by a rubber bellows. It does not drip in normal operation. The bellows is a rubber component with a finite life, and when it fails the water comes in fast.

Both work well. Both need maintenance. The dripless type gives less warning.

Symptoms and what they mean

A packing gland dripping heavily — packing worn, needs adjustment or repacking
A packing gland running hot — over-tightened; back it off before it scores the shaft
Any water from a dripless seal — investigate now, not later
Salt crystals or rust staining around the fitting
Squealing on start-up — a dry seal face
A perished, cracked or swollen bellows on a dripless unit

→ Stern gland leaking or overheating

The maintenance nobody does

The bellows on a dripless seal has a service life — commonly measured in years, specified by the maker. It is rubber, underwater, under compression, in an engine bay that gets hot. Owners routinely run them well past their interval because nothing appears wrong.

When a dripless bellows fails, the ingress rate can exceed the bilge pump. This is a genuine sinking risk, not a theoretical one.

Packing has a life too, and modern packing materials are considerably better than traditional flax. Repacking is a straightforward job.

Vent the seal. Many dripless seals need burping after launch to expel trapped air, or they run dry and overheat.

Stern gland service is usually combined with a haul-out and with shaft and cutless bearing inspection, since the same access is needed.

→ Propeller shaft and cutless bearing service · Engine alignment and coupling · Slipway and haul-out engine work

Alignment matters here: a misaligned shaft wears the seal and the cutless bearing unevenly and causes vibration.

What it costs

→ Shaft seal and stern gland cost

Find stern gland service in your city

Gold Coast · Sydney · Brisbane · Sunshine Coast · Melbourne · Perth · Whitsundays · Cairns · Port Stephens & Newcastle · Adelaide

Frequently asked questions

Should my stern gland drip? A traditional packing gland should — a few drips per minute under way. A dripless seal should not, and any water from one needs investigating.

How often should a dripless seal bellows be replaced? On the manufacturer’s interval, typically measured in years. It is rubber under compression below the waterline, and a failure can sink a boat.

My stuffing box is hot — is that normal? No. It means it is over-tightened and the packing is not being cooled. Back it off; a scored shaft is an expensive consequence.

Can I repack a stuffing box myself? Many owners do, at haul-out. Doing it afloat is possible on some installations but is not a beginner’s job.

Why does my seal squeal after launching? Usually trapped air. Many dripless seals need venting after launch, or they run dry.