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 silicone bronze.

Comments (5)

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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