As we come into autumn and boats begin to be used less frequently- or are laid up for the winter- the subject of through-hull fittings become an especially relevant subject. Ed looks into it in greater detail in this article.
South Pier Marine offers a full program of winterization services including through-hull fittings maintenance and replacement, and we will be delighted to visit your boat and provide tailored advice.
At our Chandlery on South Pier, we stock a range of anodes, through-hull fitting valves, components and maintenance materials. We’ll be happy to advise you on all aspects of this.
Seacocks- your first line of defence!
Seacocks are small valves fitted through the hull both above and below the water line. They allow water to pass through for various purposes, for example to supply water to an engine’s cooling system or to allow flushing of the heads or drainage for the sinks.
The seacock valve is there primarily in case a pipe should fail, as the valve can then be closed to stop the flow of water. It is your first line of defence, and as such, the condition of your seacocks is of paramount importance. Many boats have sunk due to faulty or neglected seacocks. To be prepared in case of a sudden pipe failure aboard your boat, I recommend having a bag of various sized soft wood bungs aboard and readily available. We supply these at our chandlery on South Pier.
Seacocks are generally always left open by most owners. However, if you intend on leaving a boat for extended periods such as during the winter layup, I recommend shutting the valve off during the period of inactivity.
The seacock valve should be opened and closed on a regular basis to make sure it moves freely and to clean off any growth which may have accumulated inside the valve.
There are three types of valve commonly used in seacocks.
1- Ball valve
A ball valve has a ball within the valve’s body which has a hole through the middle allowing water to pass through. Rotating the handle through 90 degrees will shut the valve. The fact that you need to turn the handle fully 90 degrees makes it very easy to see if a valve is open or closed based on the position of the handle. If the handle cannot be turned completely through the required 90 degree motion, it is likely the valve is partially blocked or getting too stiff to close fully.
We would suggest an annual thorough inspection of all valves be carried out when the boat is ashore. This allows for inspection from below looking up into the ball valve, at which time you will be able to see during its operation that the valve is closing fully and there is no obstruction. It also gives an opportunity to lubricate the valve.
Frequent operation during the year will help keep the valve moving freely.
2. Gate Valve
The gate valve has a wheel-type handle. When rotated, it moves a disc up and down to close the aperture which allows water through.
It is difficult to know if the valve is fully closed due to the typical 20 or so quarter turns it can take to close the valve fully. Often with age the opening for the gate to slide in gets blocked with marine growth or corrosion and therefore restricts the ability for the valve to be shut completely.
These valves are difficult to lubricate and clean.
3. Cone-Shaped Valve
The cone-shaped valve was typically used in older boats, As the name would suggest, a cone sits within the body of the valve. The handle- when operated through 90 degrees- shuts the valve off.
This type of valve is very easy to service due to its design. Generally, this type will last the longest due to the ease of maintenance.
Materials Used For Through-Hull Fittings
Skin fittings, Seacocks and hose tails are primarily constructed from the following materials, which we’ll look at in a little more detail.
Brass
Brass fittings have been used on many production boats in the past and generally have a short life span, typically five years or less. They should be replaced regularly as they generally corrode from the inside out, with little external sign of damage.
Brass loses its zinc content through electrolytic corrosion and as a result, gradually becomes brittle. It is not suitable for underwater use.
DZR (Dezincification resistant brass)
DZR fittings (in accordance with the recreational craft directive) need to be changed every five years. They contain zinc at a percentage of about 32%, however, when the zinc corrodes away you are then left with brass, which is very soft.
DZR fittings were produced primarily for the domestic plumbing market.
Bronze
Bronze skin fittings are the most reliable. Their lifespan is much better than Brass or DZR.
Composite
Composite skin fittings, valves and hose tails can be made from carbon fibre or injection moulded polymers.
Composite fittings contain no metal and therefore are not subject to electrolytic or galvanic corrosion and do not need to be bonded.
FREQUENTLY ASKED QUESTIONS
How often do skin fittings and seacocks need replacing?
As mentioned above, Brass and DZR skin fittings, valves and hose tails typically can last for about five years, with Bronze lasting up to ten years. Composite can last the lifetime of the boat.
The longevity of the fittings can be greatly reduced by stray currents which need not always originate from your boat but can be generated by boats nearby.
What do I replace my sea cocks with?
I recommend replacing the skin fittings, valves and hose tails with either Bronze or composite components.
What is a skin fitting?
A skin fitting fits in a hole passing through the hull with a securing nut on the inside. It is installed using plenty of mastic to ensure a watertight seal between the fitting and hull.
What is a Seacock?
A seacock is the valve which is attached to the skin fitting and can be closed to stop the flow of water. It screws onto the skin fitting and is sealed in place using a thread sealant.
What is a hose tail?
The hose tail is what hoses connect to, and they are screwed onto the seacock and sealed with thread sealant. The hose needs to be heated before pushing over the fitting and while still soft, secured with two stainless steel jubilee clips. It is a critical part of the skin fitting assembly.
Why do my through-hull fittings fail?
The issue is not simply that boats have some metal components underwater, but rather that they have different types of metal under the water (which is an electrolyte) in the presence of an external electrical current. The less noble metal acts as an anode and corrodes and dissolves while the more noble metals acts as the cathode and is protected!
To help combat this corrosion, we fit anodes and ensure that corroded anodes are replaced before they stop providing sacrificial protection. With anodes being a softer metal, consequently they get eaten away first.