Thru-Hull Replacement Experience

[jwshukis]

I  recently decided to replace all of the thru-hulls on my 2007 Beneteau 40. None of them were leaking, and in fact they mostly looked brand new at six and a half years old, but I have heard so much about the sub-standard metals used on Beneteau thru-hulls that I decided to just take care of it. I'm glad that I did.

 

 

 

Beneteau OEM Thru-hulls: Looking Good but Deeply Flawed

The photo shows one of my original thru-hulls. It looks pretty good, doesn't it? Unfortunately, it wasn't. Beneteau, like most if not all production boat builders, uses mushroom style thru-hulls with straight (NPS) threads. These are bolted to the hull with a threaded backing ring, and then attached to ball valves that have tapered (NPT) threads. There are, however, a number of serious problems with this installation:

• Straight-thread thru-hulls should never be mated with tapered-thread valves. You end up with surprisingly little contact between the two components, which makes for a weak connection and a great potential for leaks. Of course you can't buy tapered thru-hulls nor straight threaded ball valves, which is why the production builders get away with doing it incorrectly.
• That tiny threaded backing ring is no substitute for a real backing plate. When you grab the thru-hull and give it a good shake, it actually moves, flexing the hull. This is made worse by the round well or recess into which Beneteau installs their thru-hulls - see the photo again. The Beneteau hull consists of an outer shell plus an inner shell, both of roughly equal thickness, strongly bonded together. Where there are such recesses, however, you get only the outer hull, which is perhaps a bit more than 1/4" thick. In other words, the hull is thinnest where you'd want it to be the thickest. The diagram shows a cut-away view of the situation.
• Beneteau does not appear to use bronze thru-hulls. Some parts on my boat, such as the hose barb adapters, were almost certainly plain brass, and were tinged with pink when I removed them - a clear sign of dezincification. Others may have been DZR brass or something similar.
• The thru-hulls are surprisingly thin - far too thin. One Beneteau dealer told me that my particular generation of boats - from 2008-2010 or so - used thinner metal than usual, and that they switched to thicker materials after receiving many complaints.
• For some reason, some of the components attached to the ball valves were firmly glued or epoxied in place. In the photo, for example, this shows up as a thin red line of glue at the top of the ball valve between components. Upon inspection, I suspect that they were using some metric threaded components that didn't mate properly without the glue.
• You can't see it in the photo, but the thru-hull in the photo terminated in a 1.25" hose barb onto which was attached a 1.5" hose. Beneteau used hose clamps to crush the 1.5" hose down to 1.25". This connection never leaked, but I was really disappointed to see such sloppy work in a bit of plumbing that spent all of its life below the waterline.

 

Removing the Existing Thru-hulls

There are a number of different ways to remove an old thru-hull. My boatyard usually chisels or grinds off the mushroom head from outside the boat, which is easy for them to do but has the potential to gouge the hull and/or compromise the epoxy barrier coat. I chose instead to use a multi-tool from inside the boat to cut through the threads just above the backing ring, and then to use a very large socket and an impact driver to quickly "spin" off the threaded backing ring.  The cutting might have been a challenge except for the very thin metal and, I suspect, its partially de-zincified and weakened condition. For me, it cut like butter in a few seconds and the impact driver spun off the threaded backing rings instantly with no drama.

 

New Hardware - Backing Plates This Time

I could have replaced the old thru-hulls with identical hardware made of top quality silicon bronze and, very likely, had no problems for ten years or more. I instead chose to "do it right", by which I mean that I used the Compass Marine method here: http://www.pbase.com/mainecruising/backing_blocks. The right half of the diagram shows the setup in cut-away view. Like the excellent Compass Marine how-to article, I used 5/8" thick G10 board (from eBay) for my backer plates, Groco flanged adapter plates, and replaceable bronze studs threaded into the backer plates. I deviated slightly from his method by adhering the backer plates with epoxy thickened by long-strand "kitty hair" additive for even more strength. Also, I found that a cheap Harbor Freight tap and die set worked perfectly - no need to buy something more expensive.

 

Other Thoughts To Share

• Using the Groco adapter plates will make future replacement - if needed - a breeze. I can remove and replace a mushroom fitting without touching the inside of the boat, and I can replace a corroded ball valve without breaking the seal on the mushroom.
• With the hull, the backing plate, and the layer of reinforced epoxy between them, the new thru-hull  openings are almost 2" thick - much better than the 1/4" original depth, and deep enough that I didn't have to trim the mushrooms for length.
• It is absolutely critical that your new backing plates are aligned properly so that your new thru-hulls seat flush against the hull - and they won't be unless you work at it. The Compass Marine article glosses over this topic somewhat. I ended up test-fitting everything dry and then using temporary wooden shims to get the alignment just right before applying epoxy. It worked perfectly.
• Because the new thru-hulls are taller than the originals, I needed to re-run quite a bit of plumbing. This was not an easy task. If you embark on the same project, allow time for this.
• Disenchanted with the Beneteau hardware, I decided to replace every metal fitting attached to any thru-hull, and to switch from the OEM hose clamps to a top quality clamp with a rolled edge. Overkill, but I like it.
• G10 board is extremely difficult to cut and drill. Your table saw will work, but the blade will dull quickly. A drill press works very well to drill the holes, but you need something quite powerful - I ended up using a friend's when my 0.75 HP press just wasn't up to the task.

[jwshukis]

This shows the Beneteau OEM thru-hull installation and the Compass Marine method that I used:

[Captain Guy]

Lies... that is not a 2007 installation... WOW, I don’t recall ever seeing a cleaner piece at 6 days, much less 6 years.

 

Guy

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[Mohammad Bayegan]

Mine on my B 49 2007 looks pretty much like that. I do spray them with WD40 on regular intervals.

Sent from my Verizon Wireless 4G LTE DROID

[ume...@comcast.net]

Great report. Well done. I'm on the same mission. I choose to install adapter flanges because it allows me to use "Street elbows" to get stuff out of the way rather than having plumbing with goes straight up and waste's valuable space. Used "West Systems" "SixTen" for installing the G-10 backing plates. Great stuff!   

What did you use to seal the threads with? Teflon tape or 3M4200? I'm planning on using 4200. My thinking is, the straight threads will leaf spaces which must be filled up.

           Uwe Mewes

                 45f5

      Heaven Can Wait

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From: "jwshukis" <jwsh...@yahoo.com>
To: benetea...@googlegroups.com
Sent: Friday, March 7, 2014 6:34:43 PM

Subject: {Beneteau Owners} Thru-Hull Replacement Experience

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[jwshukis]

I used pipe thread sealant - Rectorseal #5 to be specific.

[jwshukis]

Ha ha!   It must be the weather in San Francisco - not that hot, not that cold, and not that humid. Around here, most modern boats with dry bilges look like that.

[dcreno]

Great report, thanks for the details. I'm replacing a couple now and found a great four part video on Youtube which covers most of this in great detail. Here's a link to part 1: http://youtu.be/a9ZBrBWnNAs

My concern with the video is that he doesn't thread the FR4 sheet; seems like a good idea to thread it.

Regards,
David Reno
B361

[Bligh]

I do not think Bene actually chose an inferior material intentionally if that is the case.  We did learn that the thru hulls on at least the early 411 units had a high zinc content. Those things happen. I purchased my one and only luxury car a couple of decades ago and after only a year, the entire engine wiring harness failed due to some new glitzy environmentally friendly insulation on that wire. I am guessing the manufacturer was as surprised as I. 

Sent from Coopers' galactic communicator

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[jwshukis]

I'm quite sure that Beneteau knew they were putting in lower quality metal. The ball valves had the standard mark "CR" stamped on them, which indicates that they are "corrosion resistant" brass and not bronze. CR brass was invented to be a lower-cost alternative to bronze in the marine environment, with "good enough" resistance to meet the five-year lifespan specified in the guidelines.

That's the ball valves. The smaller hose barb ends were smooth and shiny like brass, with a brass color, instead of dimpled and dull like cast bronze.

[jwshukis]

I agree with you. His method will be plenty strong, but it permanently embeds the bolts into the backing plate, which will be a nightmare if any of them ever get damaged or corroded. The Compass Marine threaded method, or even the original method of drilling completely through the hull, would be much better. 

[Sailing]

I  am in need for a C-Map card quickly for raymarine RL80 plus for the Gulf of Mexico specifically Corpus Christi

Joe Sircely

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[BDoyle]

How did you deal with the increased thickness of the hull from the hull liner? Did you cut away parts of the liner to let the flanged adapter sit directly on the hull? A picture of the finished product would be really, really helpful as others embark on this task.

[Howard]

This brings back memories.. ALL BAD.  YES... my 411 hull #10 came close to total submerge.  If it hadn't been for liveaboards in the next slip it would have sunk.  Yes, it was brass that failed from the inside. Also, I was disappointed how worthless the sumpump was. 

Always be sure that new fittings are not counterfeit. That's the reason why I have the local yard install the thru-hull fittings. They accept 100% liability. 

Still sailing ENCORE in its 19th year. 

411 is fun sailer, even as I reach #80. 

Howard 

Marina del Rey 

Los Angeles 

...sent by my average intelligence cellphone  :~》

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[Wout gmail]

Consider installing Maretron fittings to avoid any future worries about dezincing, electrolysis, etc. http://www.forespar.com/boat-marine-plumbing-thru-hull.shtml

 

Cheers, Wout

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