Replacing thru hulls-- bronze or marelon?

[Frank Langer]

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

The Tru Design thru hulls are made with a thick collar around them to withstand a blow up to 500 lbs. so they meet the ABYC standard. I haven't tested it myself.
Frank

 

[Pete the Cat]

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

I am sure the sellers of bronze would suggest that only that should be used below the water line. And I would believe that, except when I discovered a pinhole leak in a recently installed, supposedly silicon bronze seacock---I was never sure exactly how this came to be--a hot spot in my marina, stray current in my electrical system, or a defect in the metal? My point is that there is always opportunity for failure in any human creation. There is no such thing as an anchor that will not drag or other boat related device that will not, under some condition, fail. Manufacturers sell products. Practical Sailor sells feigned objectivity--often with an appallling lack of real world context. I suggest those of us trusting our boats and lives to their recommendations maintain a healthy skepticism about universal assessments.

 

[Loren Beach]

I might prefer fittings made of "Unobtanium" but it's difficult to come by............

 

[Frank Langer]

For those who haven't read the complete thread, a caution:
My bronze thru hulls looked good and worked normally, after 20 years. However, while diving the boat to clean the hull I noticed a small spot where the bottom paint had flaked off, on the water side mushroom piece of the raw water intake. I flicked it with my finger, and some of the bronze flicked away, so I returned home, hauled the boat and replaced all of the thru hulls. If the entire mushroom piece had corroded, the seacock would be unstable, a possible sinking hazard.
I subsequently learned that corrosion in salt water occurrs faster when the flow speed is greater, which is the case in our boats as the raw water pump draws water into the engine at some fast rate. So keep an eye on your raw water seacock and thru hull fitting as it may be the first to fail, as mine did.
I also learned that the quality of bronze varies alot more now than in the past, yet it all looks shiny in the store. That persuaded me to buy Tru Design fibreglass reinforced marelon instead (no affiliation with them).
Frank

 

[gareth harris]

This is the kind of real world feedback that no book can provide.

Technology has clearly moved on during my wilderness years, and since a number of my new and waiting to be installed bronze through hulls and sea cocks got stolen, I may reconsider what I replace them with.

Gareth
Freyja E35 #2411972