Composite thru hulls: good or bad idea ?

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Mambo42

Mambo42

Guru
Joined
Oct 26, 2021
Messages
974
Vessel Name
Endless Summer
Vessel Make
1979 Defever 49
By coincidence I stumbled on 2 videos this last week talking about the benefits of composite thru hulls. There is a brand called Trudesign, they are from New Zealand and they apparently specialize in these thru hulls.
Since the are composite they don't corrode and since some of my thru hulls don't look in such good condition anymore (boat is 45 years old) I am thinking of changing those into composite thru hulls. The ones that are still good I will simply keep as they are.

Does anyone have experience with composite thru hulls ? Are they really so much better ? Is there a negative side to it as well or is it just a positive innovation all around ?
 
I use the composite Marelon thru hulls pretty much everywhere above the waterline. I stick to brass below the waterline though, as I've heard mixed reviews on the composite valves (as far as issues with sticking) and I wouldn't want to put a metal seacock on a composite thru hull. Plus, properly installed and maintained bronze parts can easily last 30+ years below the waterline, so needing to replace them probably once in the boat's life isn't a big deal in my mind.
 
I had Forespar Marelon seacocks on a previous boat that was 18 years old. They looked good as new and worked fine.
 
rslifkin said:
I use the composite Marelon thru hulls pretty much everywhere above the waterline. I stick to brass below the waterline though, as I've heard mixed reviews on the composite valves (as far as issues with sticking) and I wouldn't want to put a metal seacock on a composite thru hull. Plus, properly installed and maintained bronze parts can easily last 30+ years below the waterline, so needing to replace them probably once in the boat's life isn't a big deal in my mind.
Click to expand...
Most of them are still good, but some, difficult to reach valves, don't function anymore. That means this winter I will have to get to them when the boat is out of the water and most likely I will have to take them out anyway. I can either go with brass again or go for composite.
Composite seems to be much easier to install, but I have no experience with them as underwater thru hull. I have see the composite thru hull of my old depth meter, that one was not completely intact anymore. I have changed that one for a new one, but if that will happen in a few years to new composite thru hulls, it is something to think about.
 
2 or so years ago I was required to remove all my Nylon through hulls and replace them with bronze units. Reasoning was they were to low and on the hull sides so subject to being broken by a wayward log. Hard to argue with both insurance co. and the surveyor.
I was a wee bit annoyed as it was a LOT of work and a fair bit of expense but it was done.
What really put me off is I took a couple of the original through hulls and smacked them solidly with a sledge hammer. They flew but did not break or crack .

The boat was launched in 1,977 and is now 47 years old.

Oh well, sometimes you can't win.
 
I have all Marelon thru hulls on my boat and they are original (22 years). They all operate perfectly and when I added a new one for a dedicated raw water washdown I used the same type. I'm more worried about de-zincification of bronze over that period of time than I would be any issue with the Marelon ones.
 
Some are referring to brass through hulls, never use brass below the waterline only true bronze or a quality composite. I have seen some very old bronze through hulls that were in great condition. My feeling is why mess with a proven product. I know that composites have been around a long time but I still prefer bronze. Your opinion may vary…
 
The only time I've used Marelon was for a Y-Valve in a sanitation system. Handle broke a year or so later. I'm surprised to hear they work fine as below waterline skin fittings. Are they as strong as bronze for side-loading? Tool chest sliding into it?

I'm with Comodave - Groco bronze have served me well. But keeping an open mind so curious about composite.

If memory serves, topic comes up frequently on CruisersForum as sailboats seem to have composite more often. Might want to check there too.

Peter
 
Through hull fittings are supposed to withstand 500 pounds of pressure for a period of time, forget exactly how long. That is one reason I like a quality bronze fitting.
 
Thanks for the replies, my boat was launched in 1979, still has the original through hulls, plus some additional ones which were put in later. Now that I know I have to exchange a few I was asking myself which quality should I use. But I understand the overwhelming majority says bronze and since an insurance company demanded it of C-Lectric I think I will go for bronze again. As long as they are good quality, are safe and work fine I will be happy.
Thanks.
 
C lectric said:
2 or so years ago I was required to remove all my Nylon through hulls and replace them with bronze units. Reasoning was they were to low and on the hull sides so subject to being broken by a wayward log. Hard to argue with both insurance co. and the surveyor.
I was a wee bit annoyed as it was a LOT of work and a fair bit of expense but it was done.
What really put me off is I took a couple of the original through hulls and smacked them solidly with a sledge hammer. They flew but did not break or crack .

The boat was launched in 1,977 and is now 47 years old.

Oh well, sometimes you can't win.
Click to expand...
Insurance companies don't know anything about boats, that's why they require surveys. If you get a surveyor with a personal bias for or against anything, the ins company will make you go with whatever the surveyor said, right or wrong. I'm sure there are just as many surveyors out there who would be perfectly happy with composite through hulls. The last boat I sold had all Marelon seacocks and through hulls below the water line. Buyer shared the survey defects page with me, the though hulls were not mentioned.
 
Mambo42 said:
Thanks for the replies, my boat was launched in 1979, still has the original through hulls, plus some additional ones which were put in later. Now that I know I have to exchange a few I was asking myself which quality should I use. But I understand the overwhelming majority says bronze and since an insurance company demanded it of C-Lectric I think I will go for bronze again. As long as they are good quality, are safe and work fine I will be happy.
Thanks.
Click to expand...

Question. Are Groco bronze fittings available in Europe? What are your options? I've seen chatter on the sail forums that some of the builders use brass (Beneteau) and I wonder if it's cost or availability driving the decision ---- assuming it's true.

Peter
 
mvweebles said:
Question. Are Groco bronze fittings available in Europe? What are your options? I've seen chatter on the sail forums that some of the builders use brass (Beneteau) and I wonder if it's cost or availability driving the decision ---- assuming it's true.

Peter
Click to expand...
I have not started the search yet, we are still on the boat. Haul out is in November, lots of sailing to do. Then I will also know how many thru hulls I need to change. At the moment I know of 2 and 1 is a bit doubtful.
It is true that you cannot find all spareparts and equipment in Europe. During the summer I had to replace the MPPT controller and that has turned out to be an impossible job.
On top of that, the required ferrules (prescribed by Victron) are not available in Greece, not in Montenegro, not in Croatia, not in Slovenia and also not in Italy. So yes, we can say we do have a supply problem in Europe.
 
mvweebles said:
Question. Are Groco bronze fittings available in Europe? What are your options? I've seen chatter on the sail forums that some of the builders use brass (Beneteau) and I wonder if it's cost or availability driving the decision ---- assuming it's true.

Peter
Click to expand...
Bronze fittings are easy available from the italian manufacturer Maestrini in Europe.
 
On my last boat, ( steel hull) I changed all my skin fittings and valves to marelon. I don’t know if the design has been changed over the years, but the ones I bought were well made, heavy duty, and inspired confidence. My surveyor was very happy with them. Used gpo3 for backers, completely happy with them.
 
I have always been a no composite under the water line person. Imagine my shock to find a composite transducer hidden out of sight in my engine room. It’s so old that it was decommissioned by the PO. I will be replacing it with a new NMEA 2000 transducer which is made by Airmar. Naturally, it only comes in composite.
 
Mambo42 said:
By coincidence I stumbled on 2 videos this last week talking about the benefits of composite thru hulls. There is a brand called Trudesign, they are from New Zealand and they apparently specialize in these thru hulls.
Since the are composite they don't corrode and since some of my thru hulls don't look in such good condition anymore (boat is 45 years old) I am thinking of changing those into composite thru hulls. The ones that are still good I will simply keep as they are.

Does anyone have experience with composite thru hulls ? Are they really so much better ? Is there a negative side to it as well or is it just a positive innovation all around ?
Click to expand...
Hi to all,
I have been sailing for 70 years (far too bloody long!). Cruised for most of that time including circumnavigating Australia and Tasmania some years back. I have found composite fittings to be excellent; but for a cruising boat I would not use them below the waterline as thru hulls. With some of the composites the material appears to 'grow' after a few years and threaded pieces bind up. So, you have to only buy the best quality.
With the last yacht we built and circumnavigated in, I went all out and chose 2205 Stainless for the keel bolts, the ridder shaft and the propellor shaft. Now this quality is now available in marine fittings. A company called Dixon manufacture a range of Artic Steel in duplex 2205 stainless steel, which is designed for submerged application and is significantly stronger and more corrosion resistant than 316 stainless. These are unique in the marine market, providing much higher resistance to corrosion than regular 316; they are significantly stronger than 316 and bronze, making them ideal for a critical hull penetration fitting.
These are expensive BUT well worth it and would be my choice. They are made in South Australia. They make incredible steel strainers for main saltwater intakes, scoop strainers to cover thru hulls, thru hulls and other marine gear. Have a look at their catalogue on dixonvalve.com.au.
All the best with it. RonT
 
RonT said:
Hi to all,
I have been sailing for 70 years (far too bloody long!). Cruised for most of that time including circumnavigating Australia and Tasmania some years back. I have found composite fittings to be excellent; but for a cruising boat I would not use them below the waterline as thru hulls. With some of the composites the material appears to 'grow' after a few years and threaded pieces bind up. So, you have to only buy the best quality.
With the last yacht we built and circumnavigated in, I went all out and chose 2205 Stainless for the keel bolts, the ridder shaft and the propellor shaft. Now this quality is now available in marine fittings. A company called Dixon manufacture a range of Artic Steel in duplex 2205 stainless steel, which is designed for submerged application and is significantly stronger and more corrosion resistant than 316 stainless. These are unique in the marine market, providing much higher resistance to corrosion than regular 316; they are significantly stronger than 316 and bronze, making them ideal for a critical hull penetration fitting.
These are expensive BUT well worth it and would be my choice. They are made in South Australia. They make incredible steel strainers for main saltwater intakes, scoop strainers to cover thru hulls, thru hulls and other marine gear. Have a look at their catalogue on dixonvalve.com.au.
All the best with it. RonT
Click to expand...
I should have added; The thru hulls should be reasonably inexpensive for you guys with the exchange rate etc. I regularly import items from the USA and the UK and with the free trade agreements it has become incredibly simple. I ordered a minimum/maximum reading weather thermometer from England (over the internet) two or three weeks ago. It arrived in just under a week. And there was no mention of VAT or Sales Tax or the like. It just arrived in my mailbox at the original purchase price. Regards RonT
 
The TruDesign and the Forespar (from which they are essentially copied) are both UL and USCG listed. They pass the same tests as bronze ones. The TruDesign is relatively new, Forespar (and RC before them) have been making them at least 50 years with hundreds of thousands installed. If installed with a mushroom thru hull there is a small risk of scraping the mushroom off on a rock. The flush thru hulls eliminate even that small possibility. On my custom built boat I specified Forespar Marelon seacocks and thru hulls as I thought on balance it was a better compromise than bronze, and still do.
 
mvweebles said:
I've seen chatter on the sail forums that some of the builders use brass (Beneteau) and I wonder if it's cost or availability driving the decision ---- assuming it's true.
Click to expand...
The time I saw simple brass through-hull fittings was on a very simple, cheap day cruiser. I would think that any legitimate builder would know not to use them. Do you know if RCD CE allows brass?

tiltrider1 said:
I have always been a no composite under the water line person. Imagine my shock to find a composite transducer hidden out of sight in my engine room.
Click to expand...
I was wondering how composite thru-hulls do in freezing temps, ice in the water, if they become brittle and more prone to breaking. Quick search on Marlon's website yielded:

TEMPERATURE RANGE
Marelon® has an excellent operating temperature range from -40o to +176o Fahrenheit.
 
The time I saw simple brass through-hull fittings was on a very simple, cheap day cruiser. I would think that any legitimate builder would know not to use them. Do you know if RCD CE allows brass?

With the exception of a bell, brass has no place anywhere on a boat.

--Peggie
 
Unfortunately many people use brass/bronze interchangeably. Hopefully no one is actually using brass through hulls or seacocks. I think that some people don’t really understand the difference.
 
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