Stern Gland Leaking Or Overheating

The stern gland is where the propeller shaft passes through the hull. It is the fitting most likely to sink a boat at its berth, which is why a change in its behaviour deserves attention rather than a mental note.

Is it safe to keep going?

Depends on which type you have and what it is doing.

A traditional packing gland dripping a little is correct. A few drips per minute under way lubricate and cool the packing.

A dripless seal should not drip at all. Any water from one needs investigating now — the bellows that holds it in compression is a rubber component with a service life, and when it fails the ingress rate can exceed the bilge pump.

A gland that is hot is over-tightened, running dry, and scoring your shaft.

Which type do you have?

Likely causes, ranked

Propeller shaft vibration · Shaft seal and stern gland service

The maintenance almost nobody does

A dripless seal’s bellows has a service life, specified by the maker and usually measured in years. It is rubber, underwater, under compression, in a hot engine bay. Owners routinely run them well past their interval because nothing appears wrong — right up until it does.

If yours has never been replaced and the boat is not new, find out how old it is.

What you can check yourself

• Which type you have, and whether its behaviour matches the table above
• Whether the packing gland is hot after a run — it should be warm, not hot
• Whether the dripless bellows looks perished, cracked or swollen
• Whether the seal was vented after the last launch

When to call a mechanic

For any water from a dripless seal, for a gland you cannot get to stop dripping by adjustment, or if the shaft is scored. Most of this work needs a haul-out and is sensibly combined with the cutless bearing and alignment.

Propeller shaft and cutless bearing service · Slipway and haul-out engine work

What marine engine work costs in Australia

Common on these installations

Shaft-drive inboards of every brand. Saildrives use a different arrangement with its own diaphragm interval.

→ Yacht auxiliary engine service · Yanmar and Volvo saildrives

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.

My stuffing box is hot — is that normal? No. It is over-tightened and not being cooled, and it is scoring the shaft. Back it off.

How often does a dripless bellows need replacing? On the maker’s interval, in years. It is a safety item, not a suggestion.

Why does it squeal after launching? Trapped air. Many dripless seals need venting after launch or they run dry.