Replacing thru hulls-- bronze or marelon?

[Frank Langer]

Hi,
I discovered that the bronze raw water intake thru hull is degrading badly, and will replace it, along with six other thru hulls as they are all about 20 years old. I'm guessing that the raw water thru hull is worst due to the faster sea water flow compared with the other thru hulls, but I'm not sure.
I'm leaning to replacing them all with bronze, but am wondering if anyone thinks marelon would be a better choice, especially for the raw water thru hull to avoid the deterioration I'm seeing now.
Any and all thoughts are welcome, as well as any advice on tips to replace thru hulls.
Thanks,
Frank

 

[Rocinante33]

I like the Marelon through hulls, especially the cool version which Loren has written about. Check his blogs, IIRC. No galvanic corrosion issues at all.

others will possibly bash them because, “they are made of plastic.” Yes they are, but it is fiberglass reinforced plastic (FRP), just like the rest of the entire boat.

 

[Loren Beach]

FWIW, all of our sea-cocks have worked out well, for about 20+ years, but the most useful one is the engine water intake with its three-way valve.
Picture here: https://ericsonyachts.org/ie/threads/new-strainer-thruhull.551/

And here: https://ericsonyachts.org/ie/ubs/coupler-shaft-seal-and-antifreeze.140/

 

[gabriel]

They’re both excellent materials cant go wrong with either.

I went with bronze because they were about the same price as plastic and thought the bronze just looked better in my hand.

If my boat was moored in a busy marina I would have been more inclined to go with plastic though.

 

[Loren Beach]

They’re both excellent materials cant go wrong with either.

I went with bronze because they were about the same price as plastic and thought the bronze just looked better in my hand.

If my boat was moored in a busy marina I would have been more inclined to go with plastic though.

As the saying goes, "can we get an A-men?!"
And, if Frank's marina is 'hot' enough to degrade bronze, I would recommend that he change to Marelon. (and make sure that his anodes are changed often.)
Further, given that actual cast plastic valves are very common and cheap, remember that the Forespar Marelon and their similar competitors are reinforced /composite material, same principal as your hull construction. I would never use a (cast) 'plastic' valve below the waterline.

 

[G Kiba]

My boat came with all Marelon thru hulls and valves. Only broke the handle off one so far. Forespar recommends lubricating them periodically with their special Marelube.
Not that I am interested in changing what I already have, there is also the choice of titanium. Which will not corrode and is not plastic.

Titanium Thru Hulls, Items 1 to 4 of 4 - Allied Titanium

I have no experience with them but they do make nuclear submarine hulls out of titanium as well as the SR71 Blackbird.

 

[Rocinante33]

My boat came with all Marelon thru hulls and valves. Only broke the handle off one so far. Forespar recommends lubricating them periodically with their special Marelube.
Not that I am interested in changing what I already have, there is also the choice of titanium. Which will not corrode and is not plastic.

Titanium Thru Hulls, Items 1 to 4 of 4 - Allied Titanium

I have no experience with them but they do make nuclear submarine hulls out of titanium as well as the SR71 Blackbird.

Those seem like neat options, too.

not likely to impart any of the Blackbird’s speed to our Ericsons, though;

Record set was Washington DC to California coast in 58 minutes!

 

[Frank Langer]

Thanks for all your helpful replies! I am leaning strongly towards avoiding bronze, because my existing bronze thru hulls seem to be corroding faster than I like. I don't know if it's a "hot" marina, larger power boats nearby, or some other issue with galvanic corrosion on my boat, but I'm likely to go with the fibreglass reinforced plastic. Forespar has a good reputation, but the local boatyard has persuaded me to consider True Design seacocks and thru hulls, made in New Zealand, which seem stronger than Forespar and are also less expensive. Has anyone used these, any comments or experience?
Thanks,
Frank

 

[markvone]

Hi Frank,

My first consideration would be how much work is it going to take to convert from bronze to Marelon or vice-versa.
Both materials have issues. Bronze has galvanic corrosion which may be harder to monitor. The Marelon thru-hull/valve combo is weaker and the handles can break off the ball valves leaving the valve stuck in one position or another. The newer Marelon seacocks that Loren has referenced are stronger. Not sure if the valve handles are stronger too.
I've got Marelon thru-hulls with screwed on ball valves from the factory. My thru-hulls are flush which is nice. (Not sure if you can get bronze thru-hulls in flush.) I think even the older Marelon thru-hull/valve combo is strong enough IF you protect them from damage by isolating them from other stored gear. The E36RH has six thru-hulls located in four isolated areas, the base of a cabinet box, with no other gear in that isolated space.
I've broken one valve handle in ten years, the galley sink drain which I leave OPEN all season. Since I have new, best quality hoses on all my thru-hulls, I'm OK leaving a broken valve OPEN until I haul out every three years. I replaced the engine seawater intake thru-hull because it was leaking. It was sitting in a puddlle of water it's entire life due to a quirk in the E36RH bilge/TAFG design. The plywood backer eventually rotted causing the thru-hull to leak slightly. The 40 year old thru-hull looked fine when I replaced it. I used a G10 backer on the replacement and have diverted bilge drains to avoid a puddle in the future. My other 5 thru-hulls are still original.

If I were designed a boat from scratch I would use the newer Marelon seacock style valve with the flush thru-hull. I'd build an isolated space for all the thru-hulls.

Before you make the switch, I would investigate a galvanic isolator or bonding all the thru-hull fittings. I used to go through two shaft zincs in 5 months before I added a galvanic isolator. Now my two shaft zincs will last three years between haul outs.

Mark

 

[nquigley]

Another option is to replace just the seacock and leave the thru-hull in place if it's not leaking and the backing plate is not rotted. I did this with two seacocks last fall - you just have to get the right size seacock body to match the OD of the threaded part of the thru-hull. I replaced OEM Forspar seacocks with TruDesign ones.

 

[G Kiba]

Mark, I replaced my broken handle galley valve while in the water. Had the diver who cleans the bottom plug the thru hull while I replaced the valve. It was a bit nerve racking but all worked out really well. The diver waited for me to finish and stuck around a while just to make sure there were no leaks. I sure understand why you would want to wait till you haul out. My valve was broken in the closed position so I was really frustrated to be without a sink for so long. Took 2 months of "no sink drain" to build up the nerve to replace the valve.

 

[Rocinante33]

Mark, I replaced my broken handle galley valve while in the water. Had the diver who cleans the bottom plug the thru hull while I replaced the valve. It was a bit nerve racking but all worked out really well. The diver waited for me to finish and stuck around a while just to make sure there were no leaks. I sure understand why you would want to wait till you haul out. My valve was broken in the closed position so I was really frustrated to be without a sink for so long. Took 2 months of "no sink drain" to build up the nerve to replace the valve.

I did the same with my raw water engine intake after the handle broke off the shaft. I dove myself and put a toilet plunger over the opening. Back inside I had soft wood plugs standing by, as well as my Boat U.S. card handy! I changed the valve using teflon tape and thread sealant and it worked out well, I'm happy to say. Make sure you have the right "tailpipes" on hand, as Marelon calls them. I added a Marelon seawater strainer at the same time.

 

[Shannon & Doran Jones]

@Frank Langer curious what you ended up doing?

 

[Nick J]

I know you asked frank, but I thought I'd throw my experience in for some additional data. I ended up going the true design route and I'm not disappointed. I've only had them in for a few months, so I don't have any experience with how they perform over time. The only downside is the load collar can be tricky to install. If the old Marlon thru hulls are any indication of how these will perform over time, I don't see a reason to go with bronze. My wife loves how easy they are to operate.

 

[Shannon & Doran Jones]

I know you asked frank, but I thought I'd through my experience in for some additional data. I ended up going the true design route and I'm not disappointed. I've only had them in for a few months, so I don't have any experience with how they perform over time. The only downside is the load collar can be tricky to install. If the old Marlon thru hulls are any indication of how these will perform over time, I don't see a reason to go with bronze. My wife loves how easy they are to operate.

Thanks for responding. We are just digging into thru hulls.

 

[Frank Langer]

@Frank Langer curious what you ended up doing?
[/QUOTE

Hi,
I chose the Tru Design thru hulls made in New Zealand, and have been very happy with them. Two of the seven were initially a bit stiff to operate, but when I applied some grease, that solved it, though the factory reps said they don't need grease as the ball is made from Teflon.
I am pleased that they will not corrode. No regrets so far, and they were a bit less expensive than bronze.
Frank

 

[Pete the Cat]

I am curious. I have Marlon through hull valves. I was replacing a hose in the head and when I put a channel lock on the hose end to loosen it (admittedly a dubious technique) the 90 degree fitting shattered into hundreds of shards--I was going to remove it anyway, so no loss. Doing a post mortem on the pieces it appears this factory installed nipple was some sort of poor quality PVC and not Marlon at all. Really scared the hell out of me and caused me to look at all the rest of the through hulls for this fitting---I found a better quality nylon fittings elsewhere. I am reasonably certain this was a factory installed part. Seemed dangerous as this was, obviously, below the waterline. Marlon is strong, this nipple was junk PVC. Anyone have a similar experience?

 

[Prairie Schooner]

I am curious. I have Marlon through hull valves. I was replacing a hose in the head and when I put a channel lock on the hose end to loosen it (admittedly a dubious technique) the 90 degree fitting shattered into hundreds of shards--I was going to remove it anyway, so no loss. Doing a post mortem on the pieces it appears this factory installed nipple was some sort of poor quality PVC and not Marlon at all. Really scared the hell out of me and caused me to look at all the rest of the through hulls for this fitting---I found a better quality nylon fittings elsewhere. I am reasonably certain this was a factory installed part. Seemed dangerous as this was, obviously, below the waterline. Marlon is strong, this nipple was junk PVC. Anyone have a similar experience?

When we bought our boat the surveyor called out several white PVC elbows between thru-hulls and valves as unsafe and against ABYC standards. I replaced those with Marelon for now, however, will be going through the systems and converting them to seacocks.

 

[Loren Beach]

My experience with the OEM thru hulls, albeit all were well above the DWL in our model. They should have used Marelon rather than the Celcon (or whatever cast resin that they used).

Transom Thru Hull Replacement

Yesterday I removed all the above-water factory thru hulls on our transom. It's been over 20 years and from the outside I had observed for some time that the exterior part of each was getting attacked by UV. One of the 1 1/2" ones had been replaced a few years ago by the yard when a workman...

ericsonyachts.org

 

[gareth harris]

I have heard it said that bronze should always be used below the waterline since it has the strength to survive something heavy falling on it underway, and I am inclined to go with that although no doubt modern composites are a lot stronger than their predecessors.

Bronze should last for decades in sea water so if fittings are deteriorating in just a matter of years it is a sure sign of stray electrical current in the marina.

When replacing a sea cock in the water I have always had someone (who had to be a keen sailor who could be rewarded with time under sail) stay in the water holding the plug in place while I did the job.

Gareth
Freyja E35 #241 1972