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Seacocks are among the most critical components on a modern yacht or sailboat. They play a vital role in preventing water ingress, ensuring the safety and integrity of your vessel. Boats with any amenities will have seacocks, making it essential to understand their proper maintenance. The American Boat and Yacht Council (ABYC) H-27.5 standard clearly mandates the use of seacocks:
"All thru-hull fittings or hull penetrations designed to accept pipes, hoses, or valves, with any part of the opening below the maximum heeled waterline when inclined from the static floating position, shall be equipped with a seacock to stop the admission of water in the event of failure."
What is a Seacock?
According to ABYC H-27.4.5, a seacock is defined as:
"A type of valve used to control intake or discharge of water through the hull. It is operated by a lever-type handle, usually operating through a 90° arc, clearly marked whether it is open or shut, and is typically of the two following types:
27.4.5.1 Flanged Sea Valve - A seacock with an integral flange used to securely mount the device directly to the boat hull structure.
27.4.5.2 In-Line Ball Valve - A seacock designed to be supported entirely by the thru-hull fitting."
Common Types of Seacocks
Unfortunately, in-line ball valves are more commonly found on production boats today. However, flanged sea valves are generally preferred for their strength and durability. Consider the potential damage from a heavy object, such as a dive weight or a foot slipping in the bilge. An in-line ball valve's shear point, located between the thru-hull backing nut and the ball valve will be threads, which is a pre-made weak spot prone to failure. Think of the thread minor, it's an angular crevice that goes all the way around the fitting. You can almost think of them like the perforations on a paper towel!
Experienced mariners often distinguish between ball valves and seacocks, reserving the term "seacocks" for flanged sea valves.
Materials Used in Thru-Hulls and Seacocks
Seacocks and thru-hulls can be made from various materials, including metals, plastics, and polymers:
Metals: Marine-grade bronze, an alloy containing copper, tin, and silicon, is resistant to corrosion and durable in saltwater. DZR (dezincification-resistant) brass is another option comparable to bronze.
Plastics: Acetyl nylon is often used for thru-hull fittings above the waterline but should not be used in raw water applications.
Polymers: Glass-reinforced polymers, such as Forespar's Marelon, are non-metallic options designed to prevent corrosion.
ABYC Strength Requirements
ABYC H-27.6.1 specifies the strength requirements for seacocks:
"A seacock assembly, including the thru-hull and tailpiece, shall be securely mounted so that the assembly will withstand a 500 lb (227 kg) static force applied for 30 sec to the inboard end of the assembly, without the assembly failing to stop the ingress of water."
Many modern production boats do not meet ABYC compliance. Manufacturers often use in-line ball valves instead of flanged sea valves to save on costs. However, a 1/2" plastic thru-hull with an in-line ball valve seacock is highly unlikely to withstand a 500 lb side load. Obviously this is a test that marine surveyors would not perform, even though it is required by the standard. The best we can do is recommend that the owner replace the ball valves with flanged sea valves.
Maintenance Tips for Seacocks
Corrosion can significantly weaken metals. A slight patina on bronze is typically healthy, but many boaters cannot distinguish it from detrimental corrosion. Galvanic corrosion from the vessel's own stray current issues, or even a nearby improperly maintained boat can quickly compromise below waterline fittings.
The valve's tight tolerances ensure it is watertight, but surface corrosion can bind the valve, making it difficult to operate. Combined with a corroded thru-hull, this can easily lead to a broken valve and a flooding boat.
Do Not Use Drano!
It's worth mentioning here to never use drain unclogging products in your boat's plumbing! These products can chemically react with metals, leading to severe damage. Many drain unclogging products contain highly corrosive chemicals like sodium hydroxide (lye) or sulfuric acid. These chemicals, while effective at breaking down organic blockages, can cause rapid chemical corrosion when they come into contact with metals like bronze, brass, or stainless steel. This corrosion weakens the metal, or can completely dissolve it!
Personal Anecdote
I was once working at a boatyard where a new boat owner, who had just bought a 40 something foot sailboat that week, decided to use a Drano-like product to unclog their sink before they went home for the day on a Friday. When they returned on Monday morning, they were greeted by a devastating sight: only the mast was visible above the water. The corrosive chemicals had dissolved the thru-hull, causing a catastrophic leak.
Alright, on to the more normal sorts of seacock issues. Here are some pictures from a recent survey of a newer production boat that had been otherwise very well maintained:
This is a very common sight on surveys. Hidden away down in the bilge, they can be easy to forget. Modern boats have so many systems most boat owners have a very long checklist of things to do when they visit their boat for maintenance day. Out of sight, out of mind. But a good marine surveyor will always check the seacocks on a marine survey and you will see them in your report if they have been neglected.
While these particular valves were still serviceable, corroded valves with corroded thru-hull threads are a recipe for disaster. But, a little prevention can go a long way!
Preventing Corrosion
Bonding System: Metallic seacocks should be electrically connected to your boat's anodes via the bonding system to prevent galvanic corrosion.
Corrosion Inhibitors: Coating exposed metallic surfaces in your bilge with a corrosion inhibitor like "Corrosion Block" can prevent corrosion. This simple and inexpensive step is far cheaper than replacing components or salvaging a sunken boat.
Addressing Existing Corrosion
If your metallic seacocks are already corroded:
Haul the Boat: Have a professional thoroughly inspect the seacocks.
Diagnosis:
Replace: If compromised, replace the seacocks.
Clean and Protect: If still good, clean them with a wire brush and apply a corrosion inhibitor.
Conclusion
Proper maintenance of seacocks is crucial for the safety and longevity of your boat. Inspecting your seacocks on a quarterly basis can save you from costly repairs and potential disasters.
If you are considering purchasing a boat or if you have noticed questionable corrosion on your current boat, don't hesitate to reach out to Clayton Marine Surveys. Our skilled marine surveyor is ready to identify maintenance and compliance concerns and provide guidance on preparing your boat for your specific needs, whether that involves leisurely dockside activities or adventurous voyages. Get in touch with us now to schedule a marine survey and ensure peace of mind.
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