Lubricating Aluminum Boat Fittings: The Essential Maintenance Guide

Aluminium boats are a popular choice for fishing and other water-based activities. However, they require careful maintenance to prevent corrosion and deterioration. Owners of aluminium boats need to pay particular attention to the fittings, which can be made of plastic, stainless steel, or other metals. When lubricating aluminium boat fittings, it is important to consider the type of material used in the fittings as well as the environment in which the boat will be used, such as saltwater or freshwater.

Grease and anti-seize compounds

Anti-seize compounds are typically made from petroleum grease with added graphite, aluminum, copper, or other metals. They are designed to prevent threads from corroding and sticking, especially in stainless steel fasteners. One such compound is the Star brite Anti-Seize Thread Lubricant, which contains molybdenum. This product can be applied to trailer lug nuts, spark plugs, and any stainless-steel fasteners to make removal easier.

Another example of an anti-seize compound is the ANTI-SEIZE SPECIAL™, a superior-grade assembly compound and high-pressure lubricant. This formula contains aluminum, copper, and graphite, protecting metal parts under extreme heat, pressure, and contaminating conditions up to 2000°F (1095°C). It is designed to resist washout and burn-off, providing a long-lasting protective film. It is compatible with all types of metals and most plastics, making it a versatile option.

It is important to note that anti-seize compounds should not be used underwater, especially in saltwater. This is because they can induce galvanic corrosion when dissimilar metals come into contact with an electrolyte, such as saltwater. Instead, a waterproof grease should be used for underwater applications to prevent corrosion and seizing.

Seacocks

Lubricating seacocks is a straightforward process. First, close all the seacocks. Then, paint the balls from outside the boat with a grease that lasts underwater, such as Lubriplate 130-AA grease, using an acid brush. Work the seacock through its entire travel a few times and repeat as necessary.

It is important to note that you should avoid using any grease containing graphite when lubricating seacocks. Graphite is at the top end of the galvanic scale and will lead to swift galvanic corrosion of bronze and stainless parts. Instead, use a high-viscosity, water-resistant grease. Some seacock manufacturers offer their own proprietary grease, such as Groco's, which includes a marine growth inhibitor.

If your seacock has a zerk fitting, you can use a grease gun for lubrication. Ball and cone or taper plug seacocks must be greased in the open position. If greased while closed, the grease will be pumped into the bore of the ball or plug, where it will not be effective.

For dormant seacocks, pack the top of the valve with grease and cap it with a bronze pipe cap or plug. This will prevent the valve from being a source of flooding, even if it is inadvertently opened, and the grease will reduce the likelihood of seizure and corrosion.

Through-hull fittings

Plastic through-hull fittings are prone to becoming brittle and snapping off over time, which can be a serious safety issue. To prevent this, it is recommended to use high-quality plastic, such as Marelon, and to replace plastic fittings regularly, especially those made of cheaper materials.

Metal through-hull fittings are more durable but require proper lubrication to function effectively and avoid seizing up. It is recommended to lubricate metal through-hull fittings with a waterproof grease or a non-petroleum-based lubricant, such as Marelube, and to exercise the valves regularly by opening and closing them to ensure they remain operable.

When lubricating through-hull fittings, it is important to note that some products, such as WD-40, are not suitable as they are ineffective as long-term lubricants and can be harmful to the environment. It is also important to consider the type of material used in the fittings, as some plastics may be damaged by certain lubricants.

In addition to regular lubrication, proper installation and maintenance of through-hull fittings are crucial. This includes ensuring that the fittings are securely attached and that there are no signs of deterioration or damage. It is also recommended to have backup solutions, such as rubber bung plugs, in case of emergencies.

Sacrificial anodes

A sacrificial anode is a metal rod or electrode that is designed to attract corrosion away from the boat by being more easily corroded than the metal it is protecting. When the anode is connected to the metal object, the oxidation reactions are transferred from the metal surface to the galvanic anode, which is then sacrificed in favour of preserving the original metal. This process occurs via "galvanic corrosion", which happens when two metals with different electrical activity levels are immersed in the same conductive liquid, such as seawater.

There are three main types of sacrificial anodes: zinc, aluminium, and magnesium. Zinc has been the traditional anode material due to its effectiveness in saltwater and ease of access in the past. However, it is the heaviest option and more toxic to the environment. Aluminium is lightweight, works in both saltwater and brackish waters, and can last up to 50% longer in saltwater than zinc. Magnesium is the best option for freshwater environments due to its low electrical potential, but it does not perform well in saltwater.

It is important to choose the right type and size of anode for your boat to ensure optimal protection and prevent damage. Marine anodes need to be replaced regularly, with the frequency depending on factors such as the type of anode and the size of the boat. As a general rule, anodes should be replaced when they have visibly reduced in size to about two-thirds of their original size, or annually.

Galvanic corrosion

To prevent galvanic corrosion, it is crucial to isolate dissimilar metals and use appropriate fasteners. Stainless-steel through-hull fittings, for example, may require special precautions to reduce the potential for galvanic corrosion. Sacrificial anodes, such as zinc or aluminum, can also be installed on the hull to protect against corrosion. Additionally, it is important to regularly inspect the boat for any signs of corrosion and to clean and dry the boat after use in saltwater.

Boat owners should also be cautious when choosing lubricants, as some, such as those containing graphite, can contribute to galvanic corrosion. Instead, anti-seize compounds, which are designed to prevent threads from corroding and sticking, are recommended.

Frequently asked questions