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If sacrificial anodes are disappearing very quickly this can indicate there is a galvanic or electrolytic problem caused by electrical currents, which means an electrical circuit is being made for some reason. In order to understand what could be going on, it is worth trying to get to grips with the differences between these two forms of 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). In other words, one piece of metal will be corroded, known as the anode, and the other piece of metal will be unaffected, known as the cathode. Common examples of galvanic corrosion are where an aluminium outdrive comes into contact with a stainless steel propeller, causing the aluminium to corrode, or where aluminium comes into contact with copper or bronze fittings. The first signs of galvanic corrosion is blistering of paint below the waterline and the formation of a white powdery substance on exposed metal. The exposed metal areas become deeply pitted as the metal is eaten away by the corrosion.

Electrolytic corrosion, also known as stray current corrosion, is an electrochemical process where a metallic surface is corroded by another metal it is in contact with, due to an electrolyte and the flow of an electrical current between the two metals, caused from an external source of electromotive force (EMF). In other words, electrolytic corrosion is caused by a current such as a boat’s battery or a shore supply. Metal hull boats are particularly at risk because their hulls are good conductors and stray wires or connections use the hull as a ground.

Preventing electrolytic corrosion requires good electrical installation where marine grade wiring should be insulated return with two wires rather than earth return. Metal hulls must never be used as the earth return.

Risks from electrolytic and galvanic corrosion

Aluminium boats are at risk from electrolytic and galvanic corrosion. Aluminium boat owners need to take precautions that would not be of concern to owners of GRP boats. For example, it is wise not to stay too long berthed next to a steel-hulled boat in a marina, where both vessels are connected to shore power. The reason for this is an electric circuit can form between the two vessels with the aluminium hull acting as an anode and the steel hull acting as a cathode, resulting in galvanic corrosion of the aluminium hull.

Owners also need to make sure that the shore power polarity is correctly wired in marinas as this can lead to corrosion too. They also pay particular attention to the condition of their wiring and electrical systems, to protect the boat from electrolytic corrosion.

Some aluminium boats are equipped with current leakage meters which display real time corrosion potential that warns of problems with electrolytic and galvanic corrosion.

Protecting an aluminium hull

  • Electrolytic action – all stray currents must be removed from the boat’s electrical system.
  • Anodes – zinc anodes should should be positioned on the outside of the hull and replaced when 80% consumed.
  • Stern gear – to protect the stern gear, the propeller shaft should be fitted with an electro-eliminator brush and earthed to the hull.
  • Insulation – insert plastic seals between aluminium and other metals. For example, ensure gaskets are fitted between aluminium and the flange of a stainless steel or brass valve. The same applies to lead or iron keels, where insulating washers and gaskets between the hull and keel.
  • Painting – while aluminium topsides do not need to be painted, antifouling coating beneath the waterline does need to be applied. Only use coatings that are designed for use with aluminium.

 

First aid at sea basics

At least one person on board should be trained in first aid and know how to administer the contents of the first aid kit, ensuring there are adequate supplies for the planned duration of the trip.

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.

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!

Stern gear maintenance

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.

Capsize – understanding the risks

A skipper should know how their boat will cope with rough seas. By working within known limits and understanding the risks,...

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..

Boating Rules of the Road – International ColRegs

    International ColRegs Rule 7: Risk of Collision Anyone who is responsible for a vessel at sea, from the...

Common medical emergencies at sea

A medical emergency aboard a boat at sea requires immediate attention to ensure the safety of the casualty and the crew in general. The skipper needs to know which crew members, if any, have had medical training or have a first aid qualification. All boats should carry first aid handbooks to help an untrained crew cope with a medical emergency.

Sailing at the touch of a button

Easier and more controlled sail handling can also be achieved by powering up a furling mast. I came across some interesting solutions at the Southampton Boat Show this week on the Selden Mast stand, where they were running demos of their E40i electric winch and SMF furling system.

Care of boat batteries

Boat batteries need to be kept properly charged, which means never allowing the batteries to discharge below 50 per cent of their total charge. As well as the batteries themselves, keeping a boat’s charging systems in good shape will also help to keep batteries topped up to a higher level of charge.

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.

Man Overboard Drill

How to respond to crew overboard under sail • Keep the MOB in sight • Tack into the heave-to position, do not adjust the...

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.

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?...

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.

Right boat vs Wrong boat – Over 30 Ways to Cut the Cost of Your Sailing and Cruising

Sailing and cruising offer unparalleled freedom and adventure, but they can quickly become costly. Fortunately, there are numerous strategies to help you enjoy the open water without breaking the bank. Here are over 30 practical ways to cut your sailing and cruising costs.

How to Avoid Collisions At Sea With The ColRegs

      Every Skipper Needs Accurate Knowledge of the IRPCS ColRegs As a responsible skipper it is every skipper’s duty to learn and apply the IRPCS...

Anchoring – getting it right is not always straightforward

If you can set an anchor correctly with confidence and know your boat will be safe in a secure anchorage, then you can rest...

Nautical paper charts – a reminder of the basics

The nautical chart is an indispensable tool for navigation. A chart is a graphic representation of an area of the sea which might also include coastlines, estuaries and islands. All cruising leisure boats should carry up-to-date paper charts.

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.

Marine engine oil system maintenance

The regular maintenance of a marine diesel is key to preventing engine failure at sea. This means doing regular checks of the fuel, cooling, electrical and oil systems.

Competent crew skills: arriving and leaving a berth

Skilled boat handling is needed when entering or leaving harbour. Crew tasks include preparing the mooring lines and fenders before docking and...

2023 Rolex Fastnet Race – Part 3

This is our third and final article about the 2023 Rolex Fastnet Race. It is a first hand account by Simon Jollands who was one of the crew of Lancelot II, a Beneteau First 40 skippered by John Gillard.

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.

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.