This posting and the next one are definitely intended for the technos and are a précis of an article I wrote recently for a New Zealand boating magazine.
Seawater constantly tries to find weaknesses in your hull integrity to gain entry. If a leak occurs, flooding can take place at extremely high rates with possible catastrophic consequences; for example a 25.4mm (one inch) hole, 610cm (two feet) below the water line will allow 106 litres (28 gal) per minute, or 6.4 tonnes per hour of water to enter the hull. Leaks and flooding often occur as a result of faulty seacocks or the hoses and fittings connected to them.
What is a seacock?
Seacocks are used where liquids are required to pass out through the hull, for example toilet waste from heads, as well as in through the hull, for example seawater used for cooling engines or flushing heads. A seacock usually consists of a skin fitting that passes through the hull and a ball valve. It performs a vital function because it can be closed when necessary, for example to clean internal seawater strainers, or to stop the flow of water during routine maintenance of below waterline components, or if a problem occurs with a downstream item of equipment, a hose or a fitting.
It is common for boats to have something like 20 seacocks, for example Envoy has 23, and sinking can easily occur if only one seacock should fail.
Highly respected boating author, Nigel Calder, writes that despite the critical importance of seacocks to a boat’s safety, marine surveyors undertaking boat inspections find that 40% to 50% of seacocks are unable to operate (mostly stuck in the open position), 25% can be reached only with difficulty, and 5% to 10% are totally inaccessible from inside the boat, making their installation a virtual waste of money.
What is the problem?
Even relatively new boats have been known to sink because of defective seacocks, and recently in Europe there has been a series of sinkings and near-sinkings caused by seacock failure, particularly with boats built by some of the mass-producers.
Largely these problems have resulted from using seacocks made from inappropriate materials, and have been in two areas. Firstly, there has been corrosion of the ball in the seacock’s ball valve, resulting in the ball being unable to rotate against the synthetic seal in the valve to stop the flow of water. Secondly, ball valve bodies have been corroding where standard brass has been used in their manufacture. Brass is an alloy of copper and zinc, and corrodes in sea water just as a sacrificial zinc anode does, leaving a porous copper residue that will fail under the slightest pressure.
While the most highly recommended materials for producing seacocks are bronze or polymer composites, some recent research has found that many European boat builders using metal seacocks don’t even know what type of metal they are produced from - most surprising considering the vital function that seacocks serve.
Traditionally seacocks have been produced in US and Europe using bronze, which offers a trusted and reliable solution, its only disadvantages being weight (although this is not an issue for all vessels) and the potential for galvanic corrosion.
Nowadays more boats are kept in marinas and connected to shorepower, increasing the incidence of galvanic corrosion, caused when two different metals are in electrical contact with each other while immersed in seawater, which acts as an electrolyte. Electrolysis can even occur if the metals are on different boats, both using shorepower and therefore connected electrically, or it can occur if there is a problem on a boat with stray-current from faulty electrical equipment or wiring.
The risks of galvanic corrosion can be minimised by using a galvanic isolator or an isolation transformer, and by connecting together all of the seacocks and other metal components of the boat with a “bonding wire” (an electrical cable that picks up stray current and sends it to the boat’s ground before it can damage metal components).
Groco produce highly respected and reliable seacocks and accessories using bronze, with a range to suit all applications. These all meet the stringent Underwriters’ Laboratory (UL) standard and have excellent features including (depending on model) a large flanged base for rugged mounting, in-situ serviceability, terminals for attaching bonding wires, drain plugs for winterising and to spray in anti-seizing lubricants, ptfe seats and seals, a patented ability to change the opening and closing handle’s position, and an additional side port for connecting a bilge pump.
In recent years some seacocks have been produced in Asia using lower quality bronze, and these have caused problems, so it is prudent to stay with proven brands such as Groco.
Some manufacturers have also produced seacocks from chrome-plated brass, and these need to be treated with caution, as standard brass is not corrosion resistant in salt water, and when the chrome plating wears off there can be considerable corrosion problems with the unprotected brass, resulting in the eventual failure of the seacock.
To be continued …
Seawater constantly tries to find weaknesses in your hull integrity to gain entry. If a leak occurs, flooding can take place at extremely high rates with possible catastrophic consequences; for example a 25.4mm (one inch) hole, 610cm (two feet) below the water line will allow 106 litres (28 gal) per minute, or 6.4 tonnes per hour of water to enter the hull. Leaks and flooding often occur as a result of faulty seacocks or the hoses and fittings connected to them.
What is a seacock?
Seacocks are used where liquids are required to pass out through the hull, for example toilet waste from heads, as well as in through the hull, for example seawater used for cooling engines or flushing heads. A seacock usually consists of a skin fitting that passes through the hull and a ball valve. It performs a vital function because it can be closed when necessary, for example to clean internal seawater strainers, or to stop the flow of water during routine maintenance of below waterline components, or if a problem occurs with a downstream item of equipment, a hose or a fitting.
It is common for boats to have something like 20 seacocks, for example Envoy has 23, and sinking can easily occur if only one seacock should fail.
Highly respected boating author, Nigel Calder, writes that despite the critical importance of seacocks to a boat’s safety, marine surveyors undertaking boat inspections find that 40% to 50% of seacocks are unable to operate (mostly stuck in the open position), 25% can be reached only with difficulty, and 5% to 10% are totally inaccessible from inside the boat, making their installation a virtual waste of money.
What is the problem?
Even relatively new boats have been known to sink because of defective seacocks, and recently in Europe there has been a series of sinkings and near-sinkings caused by seacock failure, particularly with boats built by some of the mass-producers.
Largely these problems have resulted from using seacocks made from inappropriate materials, and have been in two areas. Firstly, there has been corrosion of the ball in the seacock’s ball valve, resulting in the ball being unable to rotate against the synthetic seal in the valve to stop the flow of water. Secondly, ball valve bodies have been corroding where standard brass has been used in their manufacture. Brass is an alloy of copper and zinc, and corrodes in sea water just as a sacrificial zinc anode does, leaving a porous copper residue that will fail under the slightest pressure.
While the most highly recommended materials for producing seacocks are bronze or polymer composites, some recent research has found that many European boat builders using metal seacocks don’t even know what type of metal they are produced from - most surprising considering the vital function that seacocks serve.
Traditionally seacocks have been produced in US and Europe using bronze, which offers a trusted and reliable solution, its only disadvantages being weight (although this is not an issue for all vessels) and the potential for galvanic corrosion.
Nowadays more boats are kept in marinas and connected to shorepower, increasing the incidence of galvanic corrosion, caused when two different metals are in electrical contact with each other while immersed in seawater, which acts as an electrolyte. Electrolysis can even occur if the metals are on different boats, both using shorepower and therefore connected electrically, or it can occur if there is a problem on a boat with stray-current from faulty electrical equipment or wiring.
The risks of galvanic corrosion can be minimised by using a galvanic isolator or an isolation transformer, and by connecting together all of the seacocks and other metal components of the boat with a “bonding wire” (an electrical cable that picks up stray current and sends it to the boat’s ground before it can damage metal components).
Groco produce highly respected and reliable seacocks and accessories using bronze, with a range to suit all applications. These all meet the stringent Underwriters’ Laboratory (UL) standard and have excellent features including (depending on model) a large flanged base for rugged mounting, in-situ serviceability, terminals for attaching bonding wires, drain plugs for winterising and to spray in anti-seizing lubricants, ptfe seats and seals, a patented ability to change the opening and closing handle’s position, and an additional side port for connecting a bilge pump.
In recent years some seacocks have been produced in Asia using lower quality bronze, and these have caused problems, so it is prudent to stay with proven brands such as Groco.
Some manufacturers have also produced seacocks from chrome-plated brass, and these need to be treated with caution, as standard brass is not corrosion resistant in salt water, and when the chrome plating wears off there can be considerable corrosion problems with the unprotected brass, resulting in the eventual failure of the seacock.
To be continued …
1 comment:
PTFE seals are generally used in conjunction with rubber elastic material or metal spring, which provide the necessary contact pressure and preload with the sliding surface.
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