Underwater Systems



Anodes are fitted to a boat's hull's underwater section, including propellor, shaft and rudder. The material the anode is made from is dependent on the type of water and cruising area the boat is in.

Salt Water - Aluminium anodes are the more active protect better and last longer.Traditionally zinc anodes have been used in salt water, but it doesn’t provide as much protection or last as long.

Brackish Water - Aluminium anodes give the best protection in brackish waters.

Fresh Water - Magnesium anodes give the best protection in fresh water.

It is generally accepted to change anodes if 50% degraded.

Anodes are also found on some main engine cooling water systems, where it flows around the top end of the engine.



Keels come in three main types Fin, Encapsulated and Lifting Keels.

A Fin Keel or Bolt on Keel is a heavy steel plate with a steel bulb welded to the bottom and a heavy steel mounting plate welded to the top. The mounting at the top of the keel bolted through the bottom of the boat. This area of the boat is strengthened to take the weight of the keel and stresses caused by a fully rigged yacht on a windy beat.

In the event of grounding, the yacht may need immediate attention. If it is a gentle grounding on a soft bottom, ok, but if it is a collision with a rock, the keel could be pushed up and back into the boat, causing significant damage. The boat will need to be lifted out of the water asap, and a survey of the damaged area carried out.

Maintenance requires frequent checking of the keel securing bolts and an inspection of the hull area around the bolts inside and the hull area around the keel plate outside.

Encapsulated Keels are a one-piece mould, i.e. integral with the whole hull moulding, and later, ballast is placed into the keel area and sealed in. There is very little maintenance required on these keels.

Lifting Keels include daggerboards and swing keels; they both need a lifting arrangement to reduce the boat's draft, and subsequently to drop the keel or daggerboard to prevent leeway whilst under sail. Various mechanical lifting devices have been designed over the years resulting in their particular maintenance tasks.


Rudder Systems

There are three rudder systems for boating people, each with its variants.

Transom hung on the transom with pintles, easily removed and used on dinghies and small craft.

The next is a skeg-hung rudder immersed with the leading edge secured to the skeg. This system is a strong and secure arrangement favoured by most cruising boaters.

The last one is the spade rudder hanging from the bottom of the boat. The spade rudder is vulnerable to underwater damage.

Check your handbook or investigate for the type of maintenance.  Plastic bearings are excellent and require very little maintenance, 'O' rings, stuffing boxes and roller bearings need some degree of care.


Sea Cocks

A sea cock is one of the most critical valves on a boat. Constructed of either bronze or stainless steel. Do not use plastic through hull connections on steel boats.

Sea cocks should be regularly checked to see if they easily open and shut. The location and access to the sea cock are to be kept clear.

Wooden bungs, the diameter of the internal bore of the sea cock, should be readily available beside the sea cock.

All pipe work connected to the sea cock must have two stainless steel clips securing the pipe to the sea cock. Keep a register of the sea cocks on your boat, their location and opening and closing dates.


"A" Bracket

Is a metal bracket designed to support the propeller shaft outside of the boat between the hull and the propeller. It has a water lubricated bearing called a 'Cutless Bearing'.  This bearing is generally brass with a fluted insert of rubber/nitrile. The fluted insert allows sand to be washed down and away from the flutes of the bearing.



The boat's main engine supplies the rotational force to turn the propeller, which in turn creates thrust by pushing the water backwards to propel the boat forwards.

Propellers can be 2,3,4, or 5-bladed. Some boats now have the duo prop system, two contra-rotating propellers, the same as torpedoes; there is a slight difference here as with a torpedo, fitted to stop the torpedo spinning on its axis, as it would with a single prop.

A severely covered prop with barnacles, seaweed etc., can considerably reduce the prop's efficiency. Folding props can fail to open fully, and feathering props can seize up if heavily covered in weed.

When out of the water, clean with a wire brush and polish. Deal with any dents using a grinder.

Folding and feathering props out of the water should be stripped down and regreased at least once a year.

Always best when cruising to have a spare prop aboard.

Finally, it is your responsibility to check the securing arrangement of your propeller around the boss nut, being a tab washer or split pin etc., after the propeller has been removed and replaced.



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