Mailport July 2018 Issue

Seacock Thru-Hull Caution

Regarding your DIY Inspection and Maintenance (May 2018) letter from the Beneteau Oceanis 38 owner. We, too, own an Oceanis 38, built in 2014 in Marion, South Carolina. We purchased our yacht from a Beneteau dealer in Texas in December, 2016. We were the first owners, our yacht having resided in the water two years unsold. Just before our first haul out, I noticed corrosion on the raw-water intake through-hull for our AC unit. It turns out that all six seacocks on our yacht were in imminent danger of failure.

Silicone bronze
Photos by Frank Lanier (left), Drew Frye (right and below)

Silicone bronze (left) and Marelon (right) are fit for use as marine seacocks according to the American Boat and Yacht Council. Beware of alloys containing zinc. Note the mounting flanges, and backing plates for each. The Starboard backing plate (left) is much weaker in compression than the hand-laminated fiberglass plate (right), which features a bevelled edge to dissipate point loads. We compared backing materials and designs in the August 2016 report, “How Big Does a Backing Plate Need to Be?”

We have since replaced all through hull fittings with pure brass. My question is: “Does PS or do other Beneteau owners have information on other inferior materials issues that we should look for?” My wife and I are planning on an extensive cruise on our yacht. We don’t want to experience a catastrophic failure that can be avoided.

Jim and Cathy Tyree

Corpus Christi, Texas

Romance, Beneteau Oceanis 38

We contacted Beneteau regarding the through-hull materials and have not yet heard back. Based on our research, it is clear that other Beneteau owners have had similar experiences. There is a thread “Thru-hull Replacement Experience” in the Beneteau owners group (https://groups.google.com/forum/#!forum/beneteau-owners) that describes the measures that others have taken. In some cases, you will not only need to replace the through hulls with marine grade through hulls, you will also want to add a backing plate to reinforce the area where the through hull is installed. The recent article on air conditioning featured an illustrated guide to making your own backing plate out of FRP (see “Plumbing Your AC for Longer Life,” see Practical Sailor June 2018 online). PS Contributor, Rod Collins, at Compass Marine, has also posted an illustrated guide to correcting poor through hull-installations. Capt. Frank Lanier, the marine surveyor who wrote the report in the April issue, reminded us that he has encountered similar problems with through-hull corrosion on a variety of brands of boats, and that common offenders are often owners who unwittingly use hardware-variety brass fittings instead of silicon bronze.

Comments (11)

Jin and Cathy, I will echo Paul's comment. Brass is the worst possible thing you could use, due to the high zinc content.

If you put in brass seacocks, and they subsequently fail, you can expect your insurance company to find you at fault.

So-called "DZR" (de-zincification resistant) brass mentioned above does not provide any protection from stray-current electrolysis! It is merely a (slightly) better choice for non-critical applications. It should never be used for thru-hulls.

Posted by: Electronaut | July 28, 2018 10:40 AM    Report this comment

This, or similar, problem surfaced a few years ago when a writer queried a number of yacht surveyors and it emerged that numerous through-hull/seacock devices were found close to mechanical failure, or had failed. This was raised by the writer with the MDs of several UK yacht insurance brokers and a couple of the mags.... and it was investigated.

It emerged that many European boat builders had stopped fitting expensive marine bronze through-hulls, and instead started fitting much cheaper common brass units. Why?

It emerged that the EU Recreational Craft Directive was negotiated by civil servants with limited technical knowledge, relying mostly on the larger Euro-manufacturers ( i.e French ) to keep them straight. That led to a requirement which stipulated that such items should last 'a minimum of 5 years from being put into service', if my reading is correct. Of course, marine bronze was already known to last a lifetime, so this permitted the manufacturers to change to a far cheaper material, simple brass- without telling anyone.

They could have fitted Dezincification Resistant Brass, and still saved money, but didn't.
It's NOT enough simply to trust blindly in The Standard. One needs to read it, and reading the ISO 6957 Standard referenced by Beneteau seems to relate to Stress Corrosion, not dezincification.

Some boats sank. IMHO, lives were put at risk by this sharp practice. This problem is continuing.

We need some expert comment here and Practical Sailor, with its many technical editors, is ideally positioned to commission it.

Posted by: oldbilbo | July 28, 2018 9:36 AM    Report this comment

I replaced all original thru-hulls, both metal and plastic, with brand new Marelon. The design of Marelon thru-hulls has been improved due to improving ABYC standards, so the new ones are stronger than the old. Easier to sleep!

Posted by: David Smyth | July 24, 2018 3:14 PM    Report this comment

"American bronze is kinda snobby and of no use" ...really? After scores of years being sold on Swedish or German steel now the objection to American as a standard smacks of a phoney cultural issue. "Kinda" like resistance to our superior industrial system copied by the rest of the world. Suggest you look up ASTM origins.

Posted by: WM Richardson | July 22, 2018 3:13 PM    Report this comment

I think the term American Bronze is kinda snobby and of no use. Most countries can make any quality level of bronze you request. If you are going to reference a rust resistant impact resistant level of bronze you should use the proper names. Its like calling 316 stainless American stainless.

Posted by: Robert Legate | July 22, 2018 9:25 AM    Report this comment

I think the term American Bronze is kinda snobby and of no use. Most countries can make any quality level of bronze you request. If you are going to reference a rust resistant impact resistant level of bronze you should use the proper names. Its like calling 316 stainless American stainless.

Posted by: Robert Legate | July 22, 2018 9:25 AM    Report this comment

HopCar, would you please provide more information about DZR not being fit for underwater throughull, valves and fittings? All I have been reading is that DZR was close to be as good as Bronze for this application. Do you have scientific proof for this statement? Thanks

Posted by: Frederic.mora | July 16, 2018 5:28 AM    Report this comment

HopCar, would you please provide more information about DZR not being fit for underwater throughull, valves and fittings? All I have been reading is that DZR was close to be as good as Bronze for this application. Do you have scientific proof for this statement? Thanks

Posted by: Frederic.mora | July 16, 2018 5:28 AM    Report this comment

Any surveyor worth his mettle ought be able to identify whether the seacocks are standard US bronze issue. Or something else. Generally US boatbuilders of voyaging sailaboats and larger powerboats use conventional US bronze seacocks and other critical equipment such as steering quadrants. The problems come evaluating foreign built boats claiming "bronze seacocks". High school chemistry students often learn the difference between bronze and brass. And why real bronze (ASME specs) can last virtually forever under water.

We recently looked at a 1998 Beneteau 46 Oceanus. Every single underwater thru-hull seacock shows signs of incident failure. And need to be replaced. It's a major job. They all looked like brass. Moreover the Beneteaus usually do not employ heavy backup plates.
Relying on the hull thickness to provide support.

In the "old days" it was not uncommon for a surveyor to wack each seacock to make sure it was installed solidly and worked easily. There's a good reason why the USCG requires routine replacement/inspection of seacocks. When they fail the results are often quite serious if not deadly.

The long and short of it is that if the offshore cruiser doesn't have seacocks that are readily identified as meeting US bronze standards then change them out. And don't hesitate to change house the hoses and clamps. There are other ways to economize.
But with the underwater gear.

Posted by: Piberman | July 15, 2018 9:15 PM    Report this comment

I think you'll find that Beneteau uses DZR Brass thru-hulls and valves. DZR Brass is somewhat better than regular brass, but not much.

Posted by: HopCar | July 15, 2018 9:42 AM    Report this comment

Hi Jim
You mentioned that you replaced the original through hull fittings with ones made of "pure brass". Unfortunately brass is a copper based alloy containing zinc and therefore you should expect continued corrosion. I hope you meant bronze, rather than zinc.

Posted by: Paul Turje | July 5, 2018 5:34 PM    Report this comment

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