Dripless Shaft Seals: A Straightforward Buyer's Guide
A dripless shaft seal — also called a dripless stern gland or stern seal — closes the gap where the propeller shaft passes through the hull. Instead of compressing flax packing around the shaft the way a traditional stuffing box does, a mechanical face seal runs a stainless-steel rotor against a stationary carbon face, so no water gets past and nothing drips into the bilge. The shaft turns freely, the bilge stays dry, and there is no packing to tighten or replace.
This page covers why owners make the switch, how the PSS Type A achieves a completely dry seal, and the four things worth checking before you buy any propeller shaft seal.
Why switch from a weeping gland?
A conventional stuffing box is designed to drip. Rubber-impregnated flax packing is compressed around the shaft, and a steady drip of seawater is what keeps that packing cool. So even a correctly adjusted gland puts constant water in the bilge, needs periodic tightening and repacking, and gradually wears the shaft under the packing. None of that is a fault — it is simply how the design works.
A dripless shaft seal takes a different approach: it moves the sealing surfaces off the shaft entirely. With nothing pressed against the shaft to keep cool, there is nothing to drip, nothing to repack and no wear point on the shaft itself. If you are weighing up the options — including rubber lip seals, which run a nitrile lip directly on the shaft — our rubber shaft seal vs dripless comparison walks through all three designs, and our brand comparison puts PSS, Tides Marine, Glide and Lasdrop side by side.
What a dripless seal changes on board
Dry bilge
Completely dripless — the bilge under the engine stays dry instead of collecting a steady drip of seawater.
No repacking
No packing to tighten or renew. Routine care is a visual check of the bellows, like any underwater rubber hose.
No shaft wear
The sealing faces are a rotor and a carbon flange — not material pressed on the shaft — so the shaft doesn't wear at the seal.
Absorbs movement
Bellows compression keeps the faces mated while soaking up propeller thrust, minor misalignment and vibration.
How the PSS face seal stays dry
The PSS Type A is a mechanical face seal. A 316L stainless-steel rotor clamps to the propeller shaft — two o-rings seal it to the shaft, and two pairs of set screws at 90 degrees lock it in place — and spins against a stationary carbon flange carried on a nitrile rubber bellows clamped over the stern tube. Compression in that bellows (the pre-load) holds the two faces together, and because the carbon is lapped flat to four helium light bands, the seal stays dripless at shaft speeds of up to 10,000 RPM. The full mechanics are on our how it works page.
The best dripless shaft seal? Our pick is the PSS Type A
"Best" always depends on the boat, but our answer is straightforward: we supply the PSS Type A because it is one of the most widely fitted dripless seals worldwide, the mechanical face seal design keeps every wearing surface off the shaft, and — as the authorised Australian PSS distributor — we back it with genuine maintenance kits, o-ring kits and spares held locally. The bellows has a roughly six-year service life, so choose a seal you will still find genuine parts for when that service falls due.
Volvo Penta, Yanmar or something else? Engine brand doesn't matter
A prop shaft seal is sized to the shaft, not the engine. PSS fits any standard shaft installation — what you need is the propeller shaft diameter and the stern-tube outside diameter, and the badge on the engine makes no difference. Whether your boat runs a Volvo Penta, a Yanmar or anything else turning a standard shaft, the same two measurements pick the seal.
Choosing a dripless seal: four things to check
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1
Proven design and parts backing
Marine shaft seals stay in service for years between haul-outs, so pick a design with a long track record and genuine spares you can actually get. The PSS Type A is one of the most widely fitted dripless seals worldwide, and we hold genuine PSS parts in Australia.
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2
Correct sizing — two measurements
Every seal is picked by propeller shaft diameter (metric or imperial) and stern-tube outside diameter. The bellows seals across a small OD range — about 1/8", a few millimetres — per size. Our seal finder lists every seal for your shaft with the OD range each covers, plus live stock and prices.
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3
Water supply for your boat speed
The seal faces need water. Boats under 12 knots vent the PSS via a 3/8" hose run at least 2 ft above the waterline, with no loop that could siphon. Over 12 knots it needs a positive water feed at no more than 10 PSI, and twin-engine boats that exceed 12 knots on one engine need a crossover line.
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4
Serviceability
Inspect the bellows regularly like any underwater rubber hose and replace it about every six years with the PSS Maintenance Kit — bellows, new o-rings, set screws and hose clamps in one box. Set screws are never reused, and the seal must never see oil, grease or silicone — soapy water only during assembly. See our maintenance guide for the full schedule.
Sizes, prices and availability in Australia
The PSS Type A range covers boat prop shafts from 3/4" to 3-3/4" (20–95 mm). Prices run from $872 to $5,421 AUD including GST depending on size, and the seal finder shows the live price and stock for every seal that fits your measurements — so you are never guessing.
| PSS Type A | Details |
|---|---|
| Shaft sizes | 3/4" to 3-3/4" (20–95 mm) |
| Rotor | 316L stainless steel (Nitronic 50 available on request) |
| Operating limits | -15°C to 107°C, up to 10 PSI, up to 10,000 RPM |
| Prices | $872–$5,421 AUD inc GST — live prices in the finder |
| Availability | In stock sizes dispatch fast Australia-wide; other sizes are special order, dispatched in 2–3 weeks |
Fitting a seal usually means a haul-out, and that is the natural time to look at the rest of the shaft system: our installation guide covers what is involved, and our sister store CutlassBearings.com.au — same family business — stocks Exalto cutlass bearings if the bearing is due at the same time. For a deeper look at the seal itself, see our PSS shaft seals guide.