Seacock misconceptions busted – Yachting Monthly

After uncovering a range of popular misconceptions online, Ben Sutcliffe-Davies explains the importance of fully understanding your seacocks and whether they are fit for purpose.

How long should an outboard motor last?

That was the question recently on the Sailing monthly forum along with recommendations for when to replace them and by what.

About 90 responses followed, some of which I thought were bad advice.

Always wear softwood plugs, properly sized, fitted next to each seacock

Always carry softwood plugs, properly sized, fitted next to each seacock. Credit: Graham Snook/Yachting Monthly

Comments such as ‘the ones with green handles are the best’, ‘just change the valve’, ‘secure them on’ or ‘paint them to prevent them from corroding’ convey the perception of what some boat owners think and care about me.

It’s worth remembering that what’s shiny isn’t necessarily bronze these days! Sea cranes are vital, so it’s worth taking the time to fully understand them.

seacock myths

The handle colors are for identification in plumbing.

Just replacing the valve and gluing DZR brass seacocks are also not wise moves (I’ll discuss this later).

Painting them may make them look good externally, but it’s not part of valve maintenance.

Often when I see faulty skin fittings they have broken off from the inside as the zinc is being removed from the alloy.

The handle colors of a seacock are for identification in domestic plumbing and say nothing about the quality of the product

The handle colors of a seacock are for identification in domestic plumbing and say nothing about the quality of the product

It’s usually not the bits you can see where they fail first, but where the seacock is fed through the hull or on the shoulders where it’s connected.

From the days of the J class yachts we have British made bronze gate valves and skin fittings and various types of bronze sluice gate valves.

These were fitted to almost every British yacht I can think of built before the 1990s.

After that, the RCD (Recreational Craft Directive) came into effect and allowed craft built by bean counters to save on owners costs by fitting cheaper, inferior fittings.

A real, all-bronze seacock

A real, all-bronze seacock

Fitting mass-produced brass plumbing products or DZR brass valve assemblies would save around £300 per boat at the time.

I remember not understanding how fitting brass or DZR brass with a five year warranty was considered acceptable, especially when we were building yachts and fitting bronze taper valves that last a lifetime.

Indeed, many of those boats still have the same bronze valves fitted!

Remember, we have known for over 100 years that the use of bronze in yacht manufacturing is very reliable.

Simply put, bronze is an alloy of copper and tin, while brass is an alloy of copper and up to about 40% zinc, which is exactly what your anodes are made of!

The problems with the sea crane

If any of you attended the Southampton Boat Show 2019 I gave a daily lecture on yacht maintenance on the foredeck and highlighted many of the seacock issues and things to look out for.

The main problem with many of the mounted DZR brass valve assemblies is not always the actual valve, but the machined thickness of the skin-matching walls and hose tails.

Many of these fittings have no obvious markings and can be made from almost anything!

If the valve is not used regularly, there is a risk that the ball valve will become stiff and put a high load on the skin fitting when it is used.

Water ingress on board a yacht

A faulty seacock can be a disaster. Credit: Graham Snook/Yachting Monthly

Likewise, if hoses are not properly supported, their weight can be enough to break off at the worked shoulder.

Three other risks with seacocks that I will briefly discuss are: that can freeze just below the waterline, causing the valves themselves to split; when applying the skin fittings, the basic recommendation is that the tail should be no more than 1.5 times the diameter protruding through the fuselage opening.

When fitted and this advice is not followed, you could cause a shear problem if the valve seizes or becomes stiff.

Attaching to the vessel’s cathodic system is generally considered a bad idea.

The problem with gluing DZR copper valves into a vessel’s cathodic system is that any connection problems will cause the valves to sacrifice themselves.

When the seacocks fail, it's most likely where it goes through the hull, like this one, or at the tail to the attached hose

When the seacocks fail, it’s most likely where it goes through the hull, like this one, or at the tail to the attached hose. Credit Graham Snook/Yachting Monthly

So what to check? First, with many ball valves it is not always easy to determine what they are made of.

There is a mixture of numbers applied to some valves that are actually meant for the thread diameter or water pressure in plumbing.

CR was cast on some DZR brass valves for “corrosion resistance,” but it was not required to include it.

When we talk about sea cranes, we also have to pay tribute to the good old Blake Valve.

Until about 30 years ago they were all made in cast bronze and I have seen many that are still very usable at over 50 years old!

However, with the cost of production and competition from inferior competition, they began to cast the main components in DZR brass.

I accept that the main casting has a much thicker wall than most DZR brass ball valves which is an advantage but I wish there was enough demand from owners who understand you only get what you pay for so they can offer bronze again body casts.

A softwood stopper is an essential safety kit that is sufficient to prevent a boat from sinking

A softwood stopper is an essential safety kit that is sufficient to prevent a boat from sinking. Credit: Graham Snook/Yachting Monthly

In my opinion they were the best you could buy.

If you have old Blake valves fitted, don’t unless you have a really good reason to replace them!

Some bronze valves have small markings confirming that they are bronze, but it is never always obvious and can be misleading.

One brass to steer clear of is Tonval Brass – this is not suitable for ever being used below the waterline.

Casting marks on an outboard crane

Casting marks give the clues: a well-marked bronze body, but no mention is made of what the ball is made of. Be sure to check

There are several reports of craft sinking with these in just a few years.

Over the years I’ve come to the conclusion that the best way to look at marine cranes is to photograph them and look at the wires.

If there is obvious corrosion, water leakage, or pinkness of the skin fittings or tails, it’s time to change.

The biggest problem with many seacocks is that it’s not clear until the valves are removed and the threads slide off or the hose barb collapses how bad they really were.

Realistically for what they cost, I would treat them like a consumable and replace them every five years.

Alternatives to consider

There are a number of alternatives on the market.

First, getting a good bronze valve assembly is a good way to go, but it’s important to confirm what the valve ball is made of; some use a chrome brass ball.

A few new bronze valves have been launched in recent years, including the Alex valve, a bronze valve with a composite valve action.

One of the things I regularly pick up online and when measuring is that owners simply replace the valve body and ignore the condition of the skin fitting and hose tails.

They are equally likely to be faulty and should always be replaced.

An Alex valve: one of the latest solutions with a bronze housing and a composite valve

An Alex valve: one of the latest solutions with a bronze housing and a composite valve

Some older yachts have fabulous quality bronze skin fittings, but were initially for gate valves which in most cases had tapered threads; most modern valves are cut as square threads and therefore are actually not compatible to connect to.

I’ve had an owner yank one off the tail when shutting it off as they stick with about three wires if you’re lucky.

It must have been at least five years since I wrote about using composite seacocks in Sailing monthly, I’ve noticed that since then there has been a growing interest in buying them when replacing the old DZR brass.

Some dealers call them plastic valves in their descriptions, but they are definitely not!

Continue below…

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At the time, I mainly covered Forespar’s Marelon valves which are US based and imported through UK importer Aquafax.


Ben Sutcliffe-Davies has been in the marine industry for over 40 years as a long-time boat builder, surveying for over 20 years and a full member of the YDSA.

I have a large number of clients who have fitted them over the past 10 years and still look exactly the same as when fitted.

In my own yacht where I replaced some old DZR brass valves, I mounted the Marelon valves without any trauma.

It is also worth knowing that Trudesign in New Zealand has been producing a range of high quality composite plastic valves that are also ISO compliant for over 30 years.

Some of the modern production yachts have been using composite valves for the holding tanks etc for a number of years.

Whatever you have fitted to the yacht, regular operation and lubrication of each valve is important for reliability.

With brass or DZR brass, for what they cost, it’s not worth the risk of letting them go for the past five years.

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