Dripless shaft seals offer a dry bilge without the drip-per minute of the traditional stern gland. PBO checks out what’s available
The once-ubiquitous stuffing-box stern gland still has much in its favour – it’s simple, tried-and-tested and easy to repair and service. But even a well-adjusted stuffing box should drip into the bilge around once per minute. That was fine back in the day when boats were built with deep bilges and tended to leak at the seams anyway – but modern, leak-free boats with shallow bilges are different. Many boat owners want their bilge to be as dry as the rest of the boat. Nowadays there’s a much wider choice when it comes to stopping the water coming in via the stern tube. There are five main makes available in Britain – Tides Marine, Volvo, PSS, ManeCraft/Deep Sea Seals and Vetus – offering what are known as ‘dripless’ shaft seals, claimed to be completely waterproof for leisure craft. Other types and makes can be found in use – some, like the Halyard oil-filled seal, are no longer manufactured but are still giving sterling service.
Types of seal
Seals can be divided into two main groups – face seals and lip seals. Both types use an articulated rubber sleeve to keep the water out, but face seals use a collar, clamped to the shaft, that bears upon a surface on the end of the articulated hose.
Lip seals are similar in appearance but seal via a lip, or sometimes two, which bear upon the shaft itself. Most require a pressurised water feed to keep the seal lubricated and cool.
Some seals must be ordered for your exact shaft size and stern tube size, while others have some adjustment and fit a range of sizes.
Sizing your seal
Before you order a new dripless stern gland, you’ll need to know the following:
- Propshaft diameter A vernier gauge is useful here. Don’t make simple inch/millimetre conversions – 25mm is not exactly the same as 1in.
- Outside diameter of your stern tube You’ll need this in order to determine the size of hose and seal you’ll need.
- Space available Check the distance between the stern tube and the coupling, and that there will be enough space available. Exploded and detailed diagrams are available on the manufacturers’ websites.
- Damage: Check the shaft for scoring, nicks and other damage as this may affect your decision on which seal to go for.
- Speed range This is unlikely to be a problem on a sailing boat, but faster boats may not be suitable for some shaft seals or they may need extra water lubrication. Check the manufacturer’s specifications.
- Bearings: Most shaft seals are not designed to act as a bearing, so check that the propshaft’s alignment is correct.
Tides Marine seriesOne
PRICE FROM £170.40
The seriesOne is Tides Marine’s lower-cost seal designed for smaller boats and small engines. It has no serviceable parts and is designed to be replaced at the end of its life.
Models are available to fit shafts from 3⁄4in to 11⁄4in Imperial and 22mm to 30mm metric. It comprises an articulated rubber hose and a moulded lip seal housing, to which a pressurised water supply must be fed. The seriesOne comes with a one- year/1,250-engine hour warranty.
(A) Hose cuff length: 48mm (B) Overall length: 156mm (C) Shaft sizes: 22mm, 25mm, 30mm, 3⁄4in, 7⁄8in, 1in 11⁄8in, 11⁄4in (D) Stern tube sizes: 38mm, 41mm, 45mm, 51mm, 57mm, 63mm, 70mm, 76mm, 11⁄2in, 15⁄8in, 13⁄4in, 2in, 21⁄4in, 21⁄2in, 23⁄4in, 3in
Volvo Rubber Stuffing Box
PRICE FROM £79.60 (1in shaft)
Volvo Penta’s solution is what they call a ‘rubber stuffing box’. It’s simpler than its competitors, combining the rubber hose with a lip seal in one assembly, with no moving parts. It has an internal,
water-lubricated bearing and lip seals which must be greased
every 200 hours/once a year. It comes with a single, wide hose clip, secured with machine screws, to clamp on to the stern tube.
After launch it must be ‘burped’ to remove air, as it does not have a pressurised water feed. Volvo Penta recommend it is not used for installations where flexible couplings are used.
(A) Hose cuff length: 36mm
(B) Overall length: 102mm (25mm shaft)
(C) Shaft diameters: 25mm, 30mm, 35mm, 40mm, 45mm, 50mm, 1in, 11⁄4in, 11⁄2in, 13⁄4in, 2in
(D) Sleeve diameter: 42mm, 48mm, 54mm, 60mm, 64mm, 70mm, 13⁄4in, 2in, 21⁄4in, 21⁄2in, 23⁄4in (all +0.5/-0.3)
Tides Marine SureSeal
PRICE FROM £345.60
Manufactured for shaft diameters of 13⁄8in to 8in (35mm to 200mm) and suitable for a wide range of shaft speeds and ambient operating temperatures, Tides Marine’s SureSeal is made from non-corrosive materials and there are no moving parts. A pressurised cooling water supply is required to lubricate the lip seal and alignment bearing in the seal head.
The Sureseal comes with a two-year/2,500 engine hours warranty, and spares kits are available so that its lip seal can be replaced with the boat afloat.
(A) Hose cuff length: 51-76mm
(B) Overall length: 200-258mm
(C) Shaft sizes: 35mm, 40mm, 45mm, 50mm, 55mm, 60mm, 65mm, 70mm, 75mm, 80mm, 85mm, 90mm (13⁄8in, 11⁄2in, 15⁄8in, 13⁄4in, 2in, 21⁄2in, 23⁄4in, 3in, 31⁄4in, 31⁄2in, 4in)
(D) Stern tube sizes: 51mm, 54mm, 57mm, 60mm, 64mm, 67mm, 70mm, 76mm, 79mm, 83mm, 89mm, 102mm, 108mm, 114mm, 127mm, 140mm, 152mm, 2in, 21⁄8in, 21⁄4in, 23⁄8in, 21⁄2in, 25⁄8in, 23⁄4in, 3in, 31⁄8in, 31⁄4in, 31⁄2in, 4in, 41⁄4in, 41⁄2in, 5in, 51⁄2in, 6in
Vetus ZWB Dual Lip Shaft Seal
PRICE FROM £172
Vetus makes a dual lip shaft seal, designed for use with its bronze, GRP or steel stern tubes. Each shaft size is only available for a stern tube that matches Vetus’ corresponding stern tube size. A flexible hose is connected to a bronze housing, containing the sealing lips. The front seal chamber is packed with silicone grease, whilst raw water from either a dedicated water scoop or a branch supply from the engine exhaust cooling circuit is supplied via the water inlet fitting on the top of the seal.
PRICE FROM £180.36
The PSS (Packless Sealing System) shaft seal is a mechanical face seal, which uses the seal created between the flat surfaces of the rotating stainless steel rotor and the stationary carbon flange. The carbon flange is attached to the stern tube via an articulated rubber bellows. The carbon flange contacts a stainless steel rotor that fits snugly around the shaft, is secured with grub screws and seals via two O-rings recessed into its bore. The bellows is installed on the stern tube and is then compressed a set distance by the stainless collar, which ensures a good and even seal between the carbon flange and the stainless rotor. Two models are available –Type 1, for shafts up from 20-95mm (3⁄4in to 33⁄4in), and Type 2, for shafts 100-150mm (4in to 6in). Rudder seals, working on the same principle, are also available.
(A) Cuff length: 38mm
(B) Total length (compressed) 158mm
(C) Shaft diameters: 3⁄4in, 7⁄8in, 1in, 11⁄8in, 11⁄4in, 13⁄8in, 11⁄2in, 13⁄4in, 2in, 21⁄4in, 21⁄2in, 23⁄4in, 3in, 31⁄4in, 31⁄2in, 35⁄8in, 33⁄4in
(D) Stern tube diameters: 32mm-35mm, 38mm-41mm, 45mm-48mm, 50mm, 57mm- 60mm, 64-67mm, 70-73mm, 76mm, 83-86mm, 89-92mm, 95-98mm, 102mm, 108-111mm, 114/117mm, 120-124mm, 127mm
(A) Cuff length: 63mm
(B) Total length (compressed) 349mm to 372mm (C) Shaft diameters: 100mm, 110mm, 115mm, 120mm, 130mm, 140mm, 150mm, 4in, 41⁄4in, 41⁄2in, 43⁄4in, 5in, 51⁄2in, 6in
(D) Stern tube diameters: 140-143mm, 146-149mm, 152mm, 158-162mm, 165- 168mm, 171-175mm, 178mm, 184-187mm, 190-194mm, 196-200mm, 203mm, 220mm
Made in the UK by ManeCraft, the Deep Sea Seal comprises two components: a stationary ‘seat’ fits onto the inner end of the stern tube and a rotating seal attaches to the propeller shaft. The rotating seal runs against the stationary seat to give a watertight ‘drip-free’ seal. Both are moulded from chloroprene. The Deep Sea Seal, with a life expectancy of five years, requires water lubrication from the pressure side of the engine’s exhaust. There is an emergency sealing clip, fitted with an anti-tamper marker, which when tightened will constrict the seal and stop water ingress in case of failure of the seal. Two models are available, and the design allows some adjustment for stern tube sizes.
Cuff length: 32mm (min)
Total length: 131mm
Shaft sizes: 25-30mm, 30-35mm, 35-41mm, 43-36mm, 46-51mm Stern tube sizes: 35-43mm, 43-51mm, 51-60mm, 60-70mm, 70-80mm
Cuff length: 32mm (min)
Total length: 137.5mm
Shaft sizes: 55mm, 60mm, 65mm, 21⁄4in, 21⁄2in, 23⁄4in. Stern tube sizes: 70-80mm, 80-90mm, 90-100mm, 31⁄2in, 4in
Happy with your traditional stuffing-box stern gland? Learn how to repack it with our step by step guide.