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).

Always have an emergency grab bag to hand when at sea…

  Grab bag: In the event of having to abandon ship, it is recommended to have a designated waterproof bag to carry...

Feeling anxious at sea

  Some people feel anxious at sea. Will they be seasick? What if they get caught in a violent storm? Could the boat...

How to operate a winch

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

Seasickness – how can you prevent it?

Seasickness is a common problem at sea and affects both seasoned sailors and novices. What are the causes and symptoms of seasickness?...

Sailing & Motoring in Fog

Sailing & Motoring in Fog You can only measure the visibility accurately if sailing & motoring in fog when you have...

Wooden Hull Repairs

While wooden boat hull maintenance is mostly straightforward, it is always a good idea to take expert advice on any repair job needed doing to a wooden boat, unless you have done the job before and know what you are doing.

Antifouling for leisure boats – Part 4

Applying antifouling. Antifouling is best applied on a dry, calm day. It is best to apply the antifouling in the middle of the day to ensure the hull is dry and as warm as possible.

Tools and spares for your boat

It is wise to have a comprehensive and well-organised tool kit and a supply of spares for your boat. This is both for routine...

Repairing chips and dings in gelcoat

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.

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:

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...

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...

First Aid Afloat – jellyfish stings

  Wherever you are boating in the world I am sure you will be using a pilot guide to aid your navigation. Often in the...

Essential Knots: Clove hitch

Essential Knots: Clove hitch Use: Tying a rope to posts, bollards, rings or a guardrail. Step 1. Make a turn around the object and lay...

Essential boat engine checklist

Boat engine checklist Engine oil level check Even if you have checked it previously, confirming the engine oil level is up...

Winch Servicing

It is not essential to service the winches when a boat is ashore, but if time allows I prefer to do this maintenance job when the boat...

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,...

Boat Engine Safety Checks

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

How diesel engines work

The basic principle of a diesel engine is less complex than that of a petrol engine. No spark plug or ignition system is needed, making the basic diesel engine a comparatively straightforward system that results in fewer faults and has lower maintenance costs than a petrol engine.

Tacking a sailing boat

Tacking is the sailing manoeuvre used to change a boat's direction through an oncoming wind. Tacking a sailing boat calls...

First Aid Afloat – fish spine injury

First Aid Afloat - Here is what to do if somebody stands on a fish spine: • Check for dangers. Is it safe for you to enter...

Sail boat rig checks – Part 2

In part two of Sail boat rig checks we run through some useful rig maintenance tips and then finish with a brief look at what a professional rig check involves.

A simple guide to understanding tides when passage planning

Understanding tides when passage planning When planning a trip in tidal waters, check the tides before going afloat. Use...

Learn ColRegs: Traffic Separation Schemes

Learn ColRegs Rule 10: Traffic Separation Schemes. (c) A vessel shall, so far as practicable, avoid crossing traffic lanes...

Antifouling for leisure boats – Part 1

Boats that are kept afloat can very quickly become a home for small marine organisms such as barnacles, weed and slime. Applying an antifouling paint to your hull is necessary to protect it from these micro-organisms, as a fouled hull can cause problems and will slow down a boat’s maximum speed considerably if left unchecked.