Why your stern gland is a job that never ends
Whether yours is a traditional packed stuffing box or a lip-type seal, the problems follow the same script — and every boat owner on Port Phillip knows at least one act of it:
A stuffing box is designed to drip
A traditional stern gland needs a steady drip — a few drops a minute underway — to cool and lubricate the packing. That drip is your wet bilge, and it never stops being your job to manage.
The adjustment trap
As packing hardens, owners crank the gland down to chase the drip. Over-tightened packing overheats, burns out its lubricant, scores the shaft — and a badly scored shaft won’t seal again without machining or replacement.
The stagnant-gland corrosion trap
A stainless shaft starved of oxygen inside a packed gland invites crevice corrosion — whether from an over-tightened box or stagnant water on a boat left idle. It pits shafts from inside the one place you can’t inspect.
Lip seals groove the shaft
Lip-type seals wear a groove where the lip rides. Once grooved, the seal can’t seat — and the fix means disturbing the shaft: a sleeve, a reposition, or a new shaft.
Neglect sinks boats at the berth
Boats sink at the dock far more often than at sea, and leaking underwater fittings — stern glands prominent among them — are a leading cause. A gland hidden under the companionway steps is easy to forget until the bilge pump can’t keep up.
How a PSS Seal ends it
The PSS is a mechanical face seal: a carbon stator, lapped optically flat, rides against a polished stainless steel rotor, held together by a compressed bellows on your stern tube. The seal happens between those two faces — not against your shaft — so there’s no packing to drip, nothing to adjust, and nothing wearing a groove into the shaft. It’s the biggest-selling marine mechanical seal in the world — the standard Type A alone has over 200,000 in service — and it rated in the top tier of Practical Sailor’s independent dripless-seal test.
A genuinely dry bilge
100% watertight in operation — no designed drip, no oily bilge water to deal with, no musty smell, no corrosion mist over your engine.
No adjusting, no repacking
A stuffing box is a maintenance loop: adjust, harden, repack, repeat. A PSS face seal has nothing to tighten and no packing to replace.
Kind to your shaft
The rotor seals to the shaft with static O-rings that rotate with it — no packing grinding a groove, no lip wearing a track. It can even rescue a shaft grooved by old packing or a lip seal: the faces do the sealing, so the O-rings just need one clean, smooth section of shaft to sit on.
Proven engineering
A carbon stator lapped flat against a 316 stainless rotor — the same face-seal principle used in commercial service, where these seals routinely run tens of thousands of hours.
Spares on hand in Melbourne
The national PSS distributor is headquartered right here in Melbourne — the same supply network behind our Yanmar engines — so seals, bellows and O-ring kits are stocked locally, not a freight order from overseas.
3-year manufacturer warranty
PSS seals carry a 3-year limited manufacturer warranty, and classification recognition from Bureau Veritas, ABS and RINA.
The honest bit — what a PSS asks of you
- A PSS is low-maintenance, not no-maintenance: glance at the bellows when you check the engine (formally, every six months), and replace the bellows as preventive maintenance — every 6 years on the standard Type A, 8–10 years on the PSS PRO. We do it as part of a normal haul-out.
- Boats capable of more than 12 knots — or with a bearing in the shaft log — need a positive water feed plumbed to the seal; slower boats can usually run a simple vent line. That’s the manufacturer’s rule, we confirm which applies to your boat, and we plumb it as part of the installation.
- After every relaunch the seal must be “burped” of trapped air so the faces run wet — your yard or we do it at the lift, and we’ll show you how.
- The skeptic’s argument is that a face seal fails suddenly while packing fails gradually. It’s worth taking seriously — and reported failures typically involve installation or maintenance shortcuts: wrong bellows compression, reused set screws, missing venting, bellows left in past their replacement date. That is precisely the case for having it fitted properly, with new hardware, to the specified compression.
- A well-kept modern stuffing box with PTFE packing is a legitimate choice — we’ll tell you honestly if yours is fine as it is. This page exists because most of the ones we see aren’t.
Why have Mariner install it
It’s a driveline job, not a plumbing job
Fitting a PSS means splitting the shaft coupling, setting bellows compression to the millimetre, locking new set screws, and deciding venting versus water feed for your boat’s speed. That’s propulsion work — our trade — and while the coupling is off we check shaft, coupling face and alignment.
Supplied through the national distributor
We source PSS seals and spares through the official Australian distributor — headquartered in Melbourne, the same network that supplies our Yanmar engines. Right seal, right size, genuine parts, fast.
Done at your haul-out, with the rest
The boat must be out of the water, so the smart time is your next slip: we’ll do the seal alongside cutless bearing, anodes or any driveline work — one lift, one bill. Preferred yards: Royals and Savages Wharf at Williamstown.
The natural repower companion
Every repower has the shaft decoupled anyway — fitting a PSS at the same time costs a fraction of a standalone job. If your engine is on the way out too, start with our repower pages.
Hauling out this season?
That’s the moment. One lift covers antifouling, anodes, cutless bearing and your PSS conversion — tell us your haul-out date and we’ll quote the seal fitted.
PSS shaft seals — your questions answered
Can a PSS seal be fitted with the boat in the water?
No — the manufacturer is explicit that installation requires the boat out of the water with the shaft coupling split. That makes your next haul-out the natural moment: we fit the seal while the boat is slipped for antifouling, cutless bearing or other work, at Royals or Savages Wharf at Williamstown (Wyndham Harbour and Sandringham possible with some travel cost).
Is it really 100% dripless?
In operation, yes — the seal is 100% watertight and your bilge stays dry. Two honest footnotes: during the first hour of running the new faces bed in, and a fine mist with a little black carbon dust is normal until they polish; and a weep at rest usually means a salt crystal or grit between the faces, which is cleanable in the water without hauling.
What maintenance does a PSS seal need?
Inspect the bellows regularly (the manufacturer says at least every six months — a ten-second look when you’re at the engine), burp the seal after every relaunch, keep petroleum products away from the rubber, and replace the bellows preventively — every 6 years for the standard Type A, 8–10 years for the PSS PRO — which we do at a scheduled haul-out.
My boat does well over 12 knots — does that rule out a PSS?
Not at all, but it changes the installation: above 12 knots the manufacturer requires a positive water supply plumbed to the seal faces rather than a simple vent line. We plumb the water feed as part of the job — it’s one of the details that separates a proper installation from a problem one.
I’ve read stories about dripless seals failing suddenly. Should I worry?
It’s the fair question to ask. A face seal’s failure mode is more sudden than packing’s slow drip, which is why we take the installation details seriously: correct bellows compression, brand-new set screws (never reused), correct venting or water feed, and preventive bellows replacement on schedule. Practical Sailor’s independent test rated the PSS design in the top tier of dripless seals, and reported failures typically involve installation or maintenance shortcuts — the exact things a professional installation removes.
Which PSS seal fits my boat?
The Type A covers shafts from 20 mm to 95 mm and is the standard choice for most yachts and launches — it’s the biggest-selling marine mechanical seal in the world, with over 200,000 in service. The PSS PRO adds reinforced silicone bellows and upgraded hardware for demanding or commercial use, and the Type B covers commercial shafts from 100 mm. We’ll confirm the right seal and size when we measure up.
Can you replace the bellows on my existing PSS seal?
Yes — bellows replacement is the same out-of-water, coupling-split job as a new installation, with a full kit of new O-rings, set screws and clamps. If your PSS is at or past six years old, book it in for your next haul-out.
Request a PSS shaft seal quote
Tell us your boat, what seal or gland it has now, shaft size if you know it, and when you're next hauling out — we'll come back with the right seal and a fixed installed price.
PSS is a trademark of PSS Seal LLC (formerly a PYI Inc. product). Mariner Engineering supplies and installs PSS shaft seals as an independent installer and is not affiliated with the manufacturer.