Select Page

The term “stern gear” encompasses propellers, propeller shafts, shaft couplings, rudder tubes, rudder assemblies, propeller shaft brackets, propeller shaft seals, stern tube assemblies, bearings and more.

The stern gear of a boat needs to be checked carefully when the boat is ashore as this is something that can only be done when it is out of the water. The same applies for any maintenance and repairs that may need doing, so it is best to check it all over as soon after an end of season lift out as possible.

There are a number of ways that inboard boat engines can be connected to their propellers. The conventional system has a straight line of components leading back from the engine including a gearbox, engine coupling, propeller shaft, stern tube (or shaft log) then through the hull to the propeller. Other arrangements include saildrives, sterndrives, hydraulic transmission and water jet propulsion.

Stern tube

The stern tube can be made of metal and built into the deadwood at the stern of a hull, or embedded in a resin glass moulding through which the propeller shaft passes. The forward end of the stern tube has a watertight stern gland and a bearing for the shaft may also be incorporated.

Stern glands

The stern gland, or stuffing box, is the clever part of the stern gear that prevents water from entering the hull while at the same time allows the propeller shaft to rotate at high speed – it is an ingenious type of seal in other words. The gland is packed with three or four rings of compressible material around the shaft (traditionally greased flax) that enables the shaft to turn without abrading the metal and prevents water from getting into the hull. More modern materials used include graphite, acrylonite and Kevlar. The packing material is compressed by a large nut which encompasses the shaft and this can be tightened as the packing material slowly wears away. In time the packing gets worn away to the point that it needs to be replaced with new packing material.

It should be noted that while this is a clever and well proven system, the traditional stern gland arrangement is not 100% watertight and is designed to allow a tiny bit of water to drip into the bilges – in the region of 1 drop every minute or so when the engine is running. The gland needs to be adjusted just tight enough to prevent the shaft from overheating, enabling it to turn. If the packing is over-tightened then the friction on the shaft is increased and it will heat up as a result, which is not at all desirable. Worse still, the shaft will struggle to turn and may fail completely, which is not pleasant to contemplate.

     

There are many variations of stern glands and it is worth have a good study of your boat’s particular arrangement, taking expert advice if in any doubt about how it works. Most stern glands incorporate a greaser that allows grease to be injected into the gland through a tube. The grease is applied every few hours of engine running time by turning a small handle on the stern tube greaser reservoir. Here are some stern gland maintenance tasks and tips:

  • If your boat has a traditional type of stern gland then it needs to be checked and tightened if necessary, when the boat is ashore.
  • Remember not to over tighten the packing.
  • Care should be taken not to over lubricate as this can cause packing to run hot.
  • Check and re-fill the stern greaser with waterproof grease.
  • It is recommended to change the packing in most stern glands every two or three years.
  • Many arrangements include a section of heavy duty rubber hose in the stern gland which is held in place by stainless steel jubilee clips. If your boat’s system has this, check the condition of the hose as this can perish. If it is in bad condition, it will need to be replaced ,which is probably best done by a professional as it is a tricky job which involves disconnecting the prop shaft which puts everything out of alignment.

Aside from the traditional stuffing box type stern gland there are two other groups of seals which are more recent developments and are collectively referred to as dripless shaft seals (DSS).

Getting a tow for your sail or power boat at sea or on inland waterways

FREE tips from the Safe Skipper App for iPhone/iPad/Android: Getting a tow for your sail or power boat Plan how to secure a...

Light characteristics – how do navigators identify lights at night?

How do navigators identify the different types of light around our coasts at night and what are their characteristics?Navigating at...

Engine failure at sea – common causes and how to avoid them

Many engine failures are caused by lack of maintenance, resulting in fuel filter blockages, water pump failures, overheating and other breakdowns. Indeed, one of the most common reasons for marine rescue service call outs is for one of the most basic reasons possible – boats that have run out of fuel.

Sending distress signals

In an emergency situation at sea, it is a top priority is to know how to send and receive emergency radio calls and alert others of your predicament. Likewise, if you receive a distress signal, you must be ready to go to the help of others.

Boat electrics inspection checklist

With the boat ashore, here are some recommendations for carrying out a boat owner electrics inspection. Safety is always paramount so remember to do the checks with the batteries off. Wearing a head torch helps, make notes as you go and only tackle a repair if you are 100% sure you know what you are doing:

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...

The Boatyard Book – a boat owner’s guide to yacht maintenance, repair and refitting

The Boatyard Book is a fully illustrated 224 page practical reference manual that provides advice for boat owners on planning and carrying out annual maintenance, repairs, upgrades and refits of sailing yachts and motorboats, up to 20 metres in length.

Sailboat rig checks – Part 1

Sailing boat rigs need to be checked regularly to reduce the risk of rig failure at sea. In part one of Sail boat rig checks we run through a series of useful checks that owners and skippers can carry out.

Dag Pike’s Boat Survey

We're really pleased to be working with Dag Pike on some great new apps for iPhone & Android. Here'a a bit more about the first app: Dag Pike's...

Essential yacht tender safety for skippers and crew

Essential yacht tender safety - the dangers inherent in using a dinghy to get ashore from a moored or anchored yacht are all too easily...

Rudders and steering systems – Part 2

One thing all rudders have in common is that they have three main parts that need to be checked: the rudder, or a steerable drive leg in the case of many power boats; the system that joins the rudder to the steering; the steering control itself.

Seized fixings and fastenings

Maintaining a boat can be a rewarding experience but at times it can also be frustrating. A prime example of this is when you come across a seized fixing or fastening that refuses to budge. Read our tips on how to release and fix them:

Boat Handling – anchoring

Anchoring your yacht or motorboat Anchoring is one of the most important boat handling skills. If you can set an anchor...

Rudders and steering systems – Part 1

Rudders and steering systems. A rudder is one of the most critical parts of a boat. Rudder failure is a common occurrence on neglected or overworked boats and a very unpleasant and potentially dangerous thing to happen when you are out at sea.

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.

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.

Safe Skipper – crew management tips

Effective crew briefings are a vital part of the good on-board communication that helps everything to run smoothly on a sailing vessel at sea, whether it is cruising or racing.

How to trim a genoa sail

I recently had two new sails made by Sanders Sails, based in Lymington UK. The first to arrive was the new genoa and it took me a little while to get to know it and learn how to adjust it correctly. Here is an aide memoire for getting to know how to trim a genoa so that it will deliver the best performance.

Jester Challenge 2022 – Sailing single handed from Plymouth UK to the Azores: Part 3 – Preparations

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

Boat Engine Safety Checks

  Boat Engine Safety Checks Every skipper needs to make regular essential boat engine safety checks. Below you will...

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...

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.

Peer to Peer yacht charter – How can you monetize your boat?

There is a growing trend in peer to peer yacht charter. How does it work? People already rent rooms, cars and bikes from one...

Boat gas system maintenance

There are correct types of hose for marine plumbing, sewerage, exhaust, cooling and gas and all hoses should be checked regularly for wear and deterioration.

Fire prevention on boats

  Fire prevention on boats - common causes of fire: • Smoking below decks • Galley cookers • Build-up of butane or...