Dripless shaft seals

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.

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.

Jester Challenge 2022 – Sailing single handed from Plymouth UK to the Azores: Part 9 – Around the Azores

Jester Challenge – A modern experiment in old-fashioned self-reliance, self sufficiency, and personal responsibility. This is the ninth 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.

Rewiring a boat – overcoming the challenges involved

Skippers need to have a basic knowledge of boat electrics, to avoid potential problems and to be able to solve them when they happen.

Rudders and steering systems – Part 3

In the third of our three blog articles on rudders and steering systems, we look at how to replace rudder bearings and repair a water-saturated core.

Seacock maintenance

If seacocks are always left open and neglected they can eventually seize which will prove a serious threat to boat safety should a connecting hose fail and the seacock refuses to close. There are three main types of seacock – ball valves, cone valves and gate valves.

Rig check – how to prevent failure at sea

Regular rig checks prevent the risk of mast and rigging failure at sea. This includes regular rig inspections of the spars, rigging and fittings,...

Boat maintenance log

Keeping a boat maintenance log is an ideal way of reminding owners what needs to be done to a boat and when. Read on for some tips,...

Boat maintenance – what does it involve?

The maintenance of a boat involves things like cleaning, varnishing, painting, polishing, antifouling, servicing the engine, servicing the seacocks, and maintaining the gas and plumbing systems. It all amounts to a fairly considerable amount of work that can’t be ignored if you are to keep your boat in a safe and good condition.

Tips and advice for staying safe on a sailboat at sea

Here we focus on how to stay safe on a sailboat at sea. We cover key things to ensure you have on board before you set sail as well as covering the most common cause of incidents on sailboats and how to deal with them.

The Round The Island Race 2023

This year’s Round the Island Race turned out to be a really thrilling and competitive event. 1100 boats entered the race, which took place on Saturday 1st July. The race started from the world famous Royal Yacht Squadron line in Cowes UK, with the largest and fastest boats starting first, leaving the rest of us to wait our turn.

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!

Sailing Boat Rig Care

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 carried out at regular intervals.

Repairing a leaking hull-to-deck joint

If you suspect a hull-to-deck joint has failed, then being absolutely sure where the actual leak is occurring is of prime...

Essential Yachting + Power Boat Safety Briefing

Yachting Safety Briefing Down below Lifejackets and harnesses - fitting, when to wear, clipping on Gas - risks, precautions, gas bottles and...

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.

2023 Rolex Fastnet Race

Safe Skipper’s Simon Jollands took part in the 2023 Rolex Fastnet Race – a classic offshore sailing event. This is the first of several articles on the race and focuses on the start.

How to tackle osmosis

Many owners of old GRP boats live in fear of osmosis, but what exactly is osmosis and what can be done about it? Osmosis comes about...

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.

Tidal terms and definitions

Getting to grips with tidal terms and definitions can seem a little daunting, even to the most experienced sailors! Here we look at some of the key terms and definitions associated with the language of tides.

First Aid Afloat – Jellyfish Stings

Jellyfish stings are a common occurrence when boating or swimming in many parts of the world. While most stings are not serious, some can cause...

Points of Sailing

The course on which a boat is sailing can be described by its angle to the wind, not to be confused with its compass heading. The different angles...

Galvanic and electrolytic corrosion

Galvanic corrosion is an electrochemical reaction between two or more different metals, in the presence of an electrolyte (note salt water is a good electrolyte).

Jester Challenge 2022 – Sailing single handed from Plymouth UK to the Azores: Part 5 – Boat Management

Jester Challenge – A modern experiment in old-fashioned self-reliance, self sufficiency, and personal responsibility. This is the fifth 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.

Fire safety advice at sea from the Marine & Coastguard Agency

Fire safety advice for boaters Top fire safety advice at sea: 1. Fit smoke alarms, carbon monoxide and gas detectors 2. Turn...

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.

Keeping boat records and doing checks

A boat’s records should provide information about maintenance schedules, when major work was done and when equipment was replaced or added to the boat. Without this information you are left guessing when things are likely to need replacing in the future and also what the costs are likely to be.