How to Know It’s Time to Replace Your Shaft Seal
A shaft seal is not the place to ignore “small” symptoms. The stern tube is a below-waterline path into your boat, so you want early detection and planned replacement, not a surprise.
A shaft seal is not the place to ignore “small” symptoms. The stern tube is a below-waterline path into your boat, so you want early detection and planned replacement, not a surprise.
First, know what “normal” looks like
Traditional packed stern glands (stuffing boxes) are older and forgiving, and they can be set up to drip slightly to lubricate the packing. Mechanical seal types are designed to be dripless.
So, what is normal depends on what you have fitted
Common signs it is time to service or replace
1) Drips, weeping, or salt crust around the seal
If a dripless seal starts to leak consistently, investigate immediately.
2) Heat at the seal body after running
Overheating often points to lubrication or cooling issues. Lip seals in particular require water for cooling and lubrication, and faster boats may need dedicated injection water.
3) Water feed problems (blocked line or poor source)
Lasdrop guidance for higher speed hulls stresses injecting water from a clean source after the raw water pick-up and avoiding debris-prone sources.
4) Shaft wear where the seal runs
Shaft scoring or damage can affect sealing choices and can quickly destroy a new lip seal if the lip runs on a worn track.
5) Misalignment symptoms
If the shaft is not centred to the stern tube, it can reduce seal life. Lasdrop installation tips explicitly reference verifying concentric alignment before continuing.
6) Infrequent use
Lasdrop’s Gen2 guidance notes that if the vessel is not used regularly, rotating the shaft every two weeks helps avoid oxygen deprivation issues.
