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Marelon vs. Bronze

33K views 49 replies 22 participants last post by  colemj 
#1 ·
I am in the process of replacing all thru hulls on my Irwin 28. Would the marelon be better to use beneath the waterline? Can I use bronze valves with marelon thru hulls? I greatly appreciate any feedback.
 
#2 ·
I just did the same thing. I never got an answer I was comfortable with so I used a bronze thru hull for my raw water intake with a bronze seacock( the bronze seacock was cheaper also). That is my only hole below the waterline and I felt more comfortable with the bronze than the marelon.On all of my cockpit drains/deck drains total of 8 I used the marelon drains these are all well above the water line and the marelon are cheaper than bronze as thru-hulls.
thomas
 
#3 ·
oh yeah I probally went the extra mile ,but my exhaust thru-hull is bronze also with a sea cock on it as well, that I turn off once I am out to sea on an extended passage.For regular day sailing I leave it open all the time. I do have a nice bend in my exhaust with a proper siphon break ,but when iwas putting in my engine I met an old salty who ruined his motor from water siphoning in . I figured I would double protect myself.
thomas
 
#4 ·
I just sold a boat that had Marelon seacocks and through hulls and replaced it with a boat of virtually the same age with bronze seacocks. The Marelon still worked well and required minimal maintenance. Quite a few of the Bronze thru hulls and seacocks are shot and in need of replacement. For a 28 footer I would not hesitate to use the Marelon.

Jeff
 
#5 ·
Another consideration is what happens to the bronze thru hulls if the boat gets hit by lightning??

I''ve heard of metal thru hull fittings disintigrating from a strong lightning strike, as they provide a good path to the water.

If you weren''t on the boat if this happened, it could sink.

I suppose that and corrosion are the only real disadvantages to using bronze. Make sure the bronze is electrically connected to a sacraficial zinc and that should solve the corrocion problem.
 
#6 ·
Would you feel comfortable using a marelon sea-cock below the water? Also its probally alot easier to change down the road since they are impervious to corrsion.If you did use all bronze should you ground them all together ? I noticed when I was fighting to remove old sea-cocks thier appeared to be some sort of wire glassed in, I am assuming this was some sort of ground? I have heard very different opinons on this.
thomas
 
#8 ·
I dont know, Im asking too. Either way you go I dont think trying to save a dollar in this situation is the way to go. For me holding the bronze sea-cock and marelon in my hand i felt the bronze was more solid. A marelon sea-cock could be superior, maybe some one will let us know?
thomas
 
#10 ·
Hi Mohican,

Is your thrugh hull near the waterlin?. If you carry, marelon and get stucked on your thrugh hull, probably it couldn`t cope with your vessel´s weight. Moreover, heat melts marelon.

In any case, mu boat carried marelon for the last 8 years, and there were OK. I just changed them, because I thought there were old enough.

Mixing Marelon and bronze spherical valves is not recommende since both materials have disimilar rates of dilatation. However if you will only navigate in waters where it tempersature have a small amplitude, this will not be an issue.

Last, some guys recommend kicking your thru hull and valve after instalation with a ski boot. If it remains in place, means that it was ok.

Regards
Fernando
 
#13 ·
Marelon has a lot going for it. After all, it will not seize as readily as bronze sea-cocks, is usually cheaper, and doesn''t require grounding like bronze. If you''re not planning on doing a lot of maintenance, it may be the better option. Lastly, Marelon is not attacked by some substances like blackwater waste the same way as Bronze. Furthermore, it doesn''t interact galvanically if you were to attach it to a stainless tank.

Bronze sea-cocks are usually more solid and tougher than their marelon cousins. Reinforced plastic only goes so far. But "Marelon" is not only a brand name, it also assures some modicum of quality. The same cannot be said for a lot of "bronze" fittings which the layperson cannot distinguish from those actually fit for ocean service. Good Alloys cost money, and much of the stuff sold in discount stores is simply adapted from home use and sourced from the cheapest supplier they could find. Caveat Emptor!

Furthermore, bronze sea-cocks require monthly openenings and closings or they will seize hard and fast. Ideally, they should be taken apart and regreased yearly. That keeps corrosion to a minimum. In this sense, the bronze sea-cocks are no different from your average folding propeller which also usually needs a yearly greasing, cleaning, excercise, etc.

Having worked on the entire sanitation system in our boat, I see a role for both systems. Our stainless holding tank had no proper nipples to interface with hose - just a flat tube weldment which leaked invariably. A Marelon fitting might have been more appropriate because it has the barbs that keep the waste where it belongs. On the other hand, that presupposes access to the interior of the tank, etc.

I prefer bronze systems all around, but I''ve also had to deal with seized sea-cocks. They are no fun. One more reason to create a monthly/annual check-list for preventative maintenance. You either do it now or pay for it later. If interested, have a look at www.vonwentzel.net/Prout/ for more info on what we did to make our holding tank system work.
 
#14 ·
thinredmohican,
I for one have never been sure about using marelon through hulls below the
waterline, but here''s what I think:
I picture hitting something like a rock (or that 12''" by 12''" by about 10'' long piece of wood that was floating in the water the other night) I would imagine objects like these would seriously damage marelon so, I, personaly don''t use or recomend them below the waterline.

Dennis L.
 
#15 ·
I would imagine hitting something like that would damage your hull, much less the thru hulls. I think the marelon thruhulls are just as strong as the fiberglass surrounding them and the seacocks only weakness is the handle. If there is fire aboard, well, a lot of fiberglass is going to melt too, probably long before the thru hulls and seacocks melt.
 
#16 ·
Hi Rick,
No I don''t think it would damage my hull.
When I passed the peice of wood it was lined up longitudally(spelling?) with the boat. If I''d have hit it like that, it might have slid along the under body in that position and hit a protruding through hull, it would tend to try to shear it off, Do you know if marelon is stronger than bronze? I really don''t know.

Dennis
 
#17 ·
Goood question! I really don''t know. I wonder of any tests have been done regarding how much each would give before cracking. I would assume that the bronze, being a soft metal, would be less affected by cold water where the marlon would (I expect) be more susceptable to cracking if struck by a hard object. In warmer waters I don''t think it would make much difference.....just my feeling on the subject...an easy test would be to take a discarded bronze thru-hull and marlon thru-hull and squeeze both in a vise....waddaya think....Rick
 
#18 ·
Fundamentally, the bronze units should be stronger and tougher than the Marelon ones. furthermore, they are usually more tapered (don''t need as much thickness for the same strength), so stuff is much less likely to catch on a protuding lip. However, once again it depends on the configuration, the type of impact, and the alloy used. Some are tougher than others.

If the bronze thru-hull is not properly bedded, the first thing to go is probably the hull around it. Any cantilevering action will exploit the 3x lower strength of the hull around the hole. Marelon would probably fail first. Either way, you have a leak to tend to.

Such a failure modes seems somewhat remote. I''d worry more about large logs hitting the bow/keel sections and causing damage the old fashioned way than shearing at the thru-hulls.

However, it hasn''t reduced my interest in common-box systems where one thru-hull/strainer feeds raw water for the whole boat much like a busbar feeds circuits on the electrical side. This minimizes thru-hulls, the associated maintenance, etc. but requires longer hose runs inside the boat.
 
#19 ·
I am not sure that the Bronze thru hulls really are all that much stronger than Marelon. While the properties of bronze are superior as a material [most bronze through hulls are cast Bronze, (Tensile strength 40-48 KSI)compared to Marelon which is glass reinforced nylon (27-33KSI)] Marelon Fittings are supposed to have heavier wall thicknesses so that they have the equivelient strength in bending and sheer. Marelon is however more flexible and so ''feels'' weaker.

I think the real choice is maintainability. Traditional bronze seacocks take more work to maintain, but no matter where in the world you happen to be, they can be maintained. It is relatively easy to plug the outside of the thru-hull and remove the tapered plug for maintenance. Most Marelon fittings are either not designed for disassembly or count on proprietary parts. Which is why I generally recommend marelon for coastal stuff and bronze if you going distance voyaging. While true marine bronze ball valves are a real favorite of mine and are really best in terms of operation, they lack the easily rebuildable qualities of a traditional tapered plug seacock. There are some neat (compact and easy to operate without freezing up) SS ball valves out there that are used in Europe but I have mixed feelings about those as I have one that is not sealing when closed and which I will replace at next haul out with a bronze ball valve.
 
#20 ·
The one thing to consider with cast Bronze versus glass-fiber reinforced plastic is that cast Bronze has isotropic material strength while reinforced plastic does not.

That is, a cube of Bronze has the same strength in all directions, while a cube of Marelon should have higher tensile strength in the direction of fiber flow (while approximately having the tensile strength of the underlying resin in directions perpendicular to the flow of fibers).

Marelons compression strength is probably not enhanced that much by having glassfibers in the mix. The fiber flow profile would mimic the grain flow inside a forged part. The only difference is that fibers flow from where the injection occurs - this may or may not be in line with needs. I assume that the makers of Marelon fittings have this part figured out.

With proper design, Marelon is every bit as strong as Bronze - just add some thickness to make up for the lower strength and toughness. However, like any material that has unequal material qualities, reinforced plastics require careful engineering.
 
#21 ·
From the Forespar Web site: http://www.forespar.com/resources/tips/MarelonGen.htm
Marelon® - Marine Grade Plumbing Systems
Non-Corrosive
Non-Conductive
Fire Resistant
Impact Resistant
Temp. Range -40° to +250° F
U.V. Resistant

Critical Marelon® plumbing components are U.L. marine listed (MQ1151R) and exceed A.B.Y.C. (H-27) (American Boat & Yacht Council) standards.

For what its worth --
 
#24 ·
The plastics of yesteryear were rarely fiber re-enforced and often inferior. Now they are all over the place in reliability but I feel Marelon is great stuff.
Lightening is not predictable and makes for a nervous voyage.
Bronze seacockadoodle-doos (playing with the spell check here)... Will melt from lightening and it most certainly does happen.
When it does there's no way to say what and if, but if the electronics are down and you are going down as well....
I think you see the point. In an instant the heat may open a huge hole where you once had some valuable scrap.
it would be wise to think of Marelon in the boatyard rather than including it in your epitaph....
Of course "there's not a horse that can't be rode or a cowboy that can't be throwed" so we should leave this up to opinion.
If I could afford it I want all thru hulls in plastic. Metal on a boat should be avoided when possible.
Bronzes have galvanic action and of course the weight are contributing factors but mostly it's because "lightening is frightening."
 
#25 ·
As for mixing plastic and metal fittings, I was always taught not to do that on any kind of plumbing. Either metal or plastic all the way. Seems the metal threads can cut the plastic ones if they're screwed together.
One thing I noticed with the Marelon fittings in my boat: The tail piece where the hose attaches is thicker and has a smaller inside diameter than a bronze one would be. That reduces the flow a little, and on the galley sink drain causes more of a step for debris to get caught on. The Marelon drain clogs up more than the bronze one did.
 
#26 ·
I know this thread is from 2002...
But why would anyone spend such a huge amount of money on an old 28 footer?
Marelon is 4 or 5 times more expensive than regular fittings.
I just did 14 through hills and if they were Marelon the value would be about 2 Irwin 28s a Bavaria plus half a Ford truck tossed in.
Don't over capatilise a boat!
 
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