Select Page

As their name implies, dripless shaft seals are designed to completely stop water from entering a boat’s hull via the stern tube. There are two main types of dripless seals known as face seals and lip seals which many boat manufacturers now fit to production boats. They can also be fitted as replacements to boats with traditional stuffing boxes.

Face seals

A face seal has a flexible bellows attached to the stern tube that presses a carbon or graphite flange against a stainless steel rotor, or sealing ring, which is attached to the spinning propeller shaft, making a seal between the spinning rotor and the flange. Once installed correctly they should not need adjustment or maintenance, aside from a check every now and again of the hoses, clamps and sealing faces.

These are popular as they are considered maintenance free and keep the water out even if the shaft is slightly out of alignment. However, while they are known to last for more than five years with no problems, if either the setscrews that hold the rotor in place or the bellows fail, then water can quickly flow into the bilge and serious problems will arise. This might occur because of fatigue of the bellows material or improper installation. If your boat is fitted with a face seal, you need to be aware that it is definitely not maintenance free.

Here are some maintenance checks:

  • The bellows should be inspected every six months and checked for signs of cracks, splits, tears or brittleness.
  • If leaks are noticed where the bellows attach to the shaft log or flange, check the hose clamps for looseness or damage.
  • Be aware that if the seal or bellows are attached incorrectly the seal faces will be subjected to uneven pressure which will cause uneven wear.
  • A common cause of minor leaking is where foreign material gets between the rotor and flange – a grain of sand can cause the seal to be broken. The remedy for this is to clean the two surfaces, which is easier said than done with the boat in the water but more easily done in the boatyard.
  • The bellows can lose tension over time due to slippage, which can result in leaks as the pressure on the face seal reduces. A remedy that can prevent this from happening is to clamp a propeller shaft anode right alongside the face seal as a backup to prevent the bellows from slipping along the shaft.
  • A further action to be aware of is that face seals are lubricated by water and that if air is trapped in the bellows, for example after the boat has been out of the water, then the seal will no longer be lubricated. Some systems have a water injection tube to deal with this but others need to be manually squeezed or “burped” once back in the water so that the air can escape. If in doubt your yard should be able to assist with this.

Some manufacturers advise the bellows should be replaced every six years or less, even if they appear to be in good condition. As always, it is advisable to check through your manufacturer’s instructions and include the seal inspection as part of your winter maintenance schedule.

Lip seals

Lip seals also use a flexible rubber type sleeve to keep the water out but unlike face seals which use a stainless steel rotor, the seal is made from nitrile rubber and bears directly against the propeller shaft. The shaft rotates inside the seal and no water escapes into the boat. Most lip seals are lubricated by water that comes from the engine’s raw water system, while some are oil lubricated. There is no dripping of water and the seal does not need to be tightened.

boat engine lip seal

Things to be aware of about lip seals include:

  • Lip seals need a smooth, pristine shaft surface. If the shaft is not in an unblemished and polished condition it will leak.
  • They rely on a water supply for lubrication which should be checked periodically.
  • Oil lubricated lip seals are supplied by a small header tank of oil which needs to be kept topped up. If this runs dry the seal will heat up and fail.
  • Correct installation is vital so it would be advisable to have this done professionally to avoid any leakage.

The only maintenance required is as follows:

  • Lip seals should be greased with manufacturer’s recommended waterproof grease every 200 hours of operation or once a year.
  • Replacement of the seals is usually advised every 5 years or after 500 hours of operation.
  • As with face seals, lip seals need to have any trapped air removed from them after launching. This is done by squeezing the sleeve and pushing it back towards the stern.

Know your Navlights & Shapes – essential for all skippers

Know your Navlights & Shapes International Regulations for Preventing Collisions at Sea (ColRegs) Anyone who is...

Sterndrive maintenance

Sterndrives are a popular form of propulsion in the powerboat market, but require a fair amount of care and maintenance. The main factors to be aware of are salt water corrosion, lubrication and regular inspection of the bellows, the condition of which is vital to prevent water from entering into the hull.

Essential Boat Buying Tips for First-Time Boat Owners

The first question that comes to mind when thinking about buying a boat is: what type of boat? There are more than 20 different kinds, of different sizes, for different purposes, and different pockets. So, your first step is to decide your boat type.

Anchoring – getting it right

If you can set an anchor correctly with confidence and know your boat will be safe in a secure anchorage, then you can rest in comfort and will not...

How to cope with an emergency at sea

A safe skipper will be mentally prepared for all kinds of potential emergencies happening at sea, including medical emergencies, engine failure, fire, a holed hull, capsize and dismasting.

Boat plumbing maintenance & troubleshooting

A boat’s fresh water system needs annual maintenance to keep it in good condition. Some boats have far more complex systems than others, with pressurised hot and cold water, associated pumps, an accumulator, calorifier and pressure valves, all to keep a boat owner busy.

Marine toilets – care and maintenance

There are a number of different types of marine toilet, or heads. They fall into one of three categories – manual, electric and vacuum, the most common being the manual, hand pumped type. These have double acting piston-pumps which both discharge the waste and flush the toilet with sea water.

Gybing a sailing boat

Gybing is the sailing manoeuvre used to change a boat's direction through a following wind. As with the tacking manoeuvre, gybing a sailing boat...

Understanding your mast and rigging

The rig of a sailing boat is put under huge stresses and strains so it is important for inspections of a yacht's spars and rigging to be...

Jester Challenge 2022 – Sailing single handed from Plymouth UK to the Azores: Part 10 – The Return Trip

Jester Challenge – A modern experiment in old-fashioned self-reliance, self sufficiency, and personal responsibility. This is the final instalment of a 10-part post where solo sailor, Bernie Branfield, shares his first-hand account of his single-handed, 2022 Jester Challenge, from Plymouth, UK to the Azores, in his 26′ Invicta Mk2, Louisa.

Jester Challenge 2022 – Sailing single handed from Plymouth UK to the Azores: Part 7 – Motivation

Jester Challenge – A modern experiment in old-fashioned self-reliance, self sufficiency, and personal responsibility. This is the seventh of a 10-part post where solo sailor, Bernie Branfield, shares his first-hand account of his single-handed, 2022 Jester Challenge, from Plymouth, UK to the Azores, in his 26′ Invicta Mk2, Louisa.

Cleaning & polishing gelcoat topsides

The gelcoat topsides of a GRP boat can be pampered and restored to their former glory relatively easily when it is ashore. Gelcoat is only a very thin outer layer of the hull, often less than 1mm thick, so you should avoid cleaning it with highly abrasive cleaners, or an-ything that could potentially damage its surface.

2023 Rolex Fastnet Race – Part 2

Simon Jollands took part in the 2023 Rolex Fastnet Race. This is the second of his articles on the race aboard Lancelot II, a Beneteau First 40.

Fixing position at sea using traditional methods

This post looks at some traditional methods used for fixing a vessel’s position at sea, within sight of land. Electronic fixes using chart plotters are very straightforward to record, but if for some reason a vessel’s electronics are faulty it is essential that a skipper knows how to use traditional methods.

How to operate a winch

Winches are drum shaped mechanical devices used to handle halyards, sheets and control lines. One of the important crew...

Safety at sea principles

Safety at sea is not as simple as just spending money adding shiny new emergency equipment such as liferafts, danbuoys, distress flares, EPIRBs and so on.

Boat electrics

All boat owners should have a basic knowledge of electrics, both to avoid encountering electrical problems at sea and to stand a chance of solving them should they occur.

Essential Knots: Bowline

Essential Knots: Bowline Use: Making a secure eye or loop in the end of a rope. Bowlines have many uses on a boat, for example to make a...

Navigating Through Rough Waters: Tips for Handling Adverse Weather Conditions in a Sailboat

Navigating through rough waters in a sailboat requires skill, preparation, and a good understanding of both your vessel and the environment. Here are some tips for handling adverse weather conditions including Preparation, Techniques, Safety and much more..

Understanding marine sealants & adhesives

Sealants, adhesives and adhesive sealantsThere is a bewildering variety of sealants, adhesives and even adhesive sealants available for...

Marine engine electrical system

The typical basic electrical system associated with a marine engine includes a dedicated engine starting battery, a starter motor, a charger in the form of an alternator, a solenoid and some engine sensors and instruments.

The dangers of running aground in a motor boat

The peril of grounding a motor boat is not only an inconvenience; it can lead to substantial risks for both the vessel and its passengers. . In this article, we’ll explore the potential dangers of running aground and highlight the importance of proper navigation and preparedness to avoid these hazards!

Jester Challenge 2022 – Sailing single handed from Plymouth UK to the Azores: Part 8 – Arriving at the Azores

Jester Challenge – A modern experiment in old-fashioned self-reliance, self sufficiency, and personal responsibility. This is the eighth of a 10-part post where solo sailor, Bernie Branfield, shares his first-hand account of his single-handed, 2022 Jester Challenge, from Plymouth, UK to the Azores, in his 26′ Invicta Mk2, Louisa.

Understanding tides

If you are used to sailing in tidal waters, you will know that tides can be both a benefit and a hindrance to the sailor. In many ways,...

Saildrive maintenance

There are less maintenance tasks to carry out on a saildrive transmission than on a traditional inboard shaft drive system with its associated stern gear. However, there are a few critical things that require maintenance, as recommended in detail by the engine manufacturers, and should be adhered to.