Another repair screw up.

[ronobrien]

Good grief! Thanks for the update and warning. This is why even though I’m not an expert at fixing most things on my boat, I always just try to do it myself.

I am refitting my 1973 GB36 and I am doing the work myself. I have decided that if am not an expert on something I will study and become one.

 

[Steve DAntonio]

Steve I concur with your statement regarding silicon bronzes and zinc percentages should be around 3% + - . Actually I don’t think it’s possible to dissolve much more than 4% silicon in copper. Of course there are several good bronzes suitable for various marine applications all of which are alloyed differently with copper, metals such as lead, aluminum tin etc. my statement above where I noted 9-13% zinc is technically incorrect. What I should have said in my statement above regarding allowable zinc percentages was copper with 3-4% silicon, 2-3% tin and 3-5% zinc or between 9-13% total alloying agents. By attempting to simplify my remarks I made it worse at least for you, not sure anybody else caught it.

However there is no shortage of silicon bronze, in name anyway, that doesn’t have close to 7-10% zinc and almost always for its machinability. Above the waterline these alloys serve a purpose and generally hold up well enough but like manganese bronze which is 60/40 copper and zinc it’s all about marketing. Try to find a true bronze propeller or rudder these days.

Below are two “ silicon bronze “ bolts certified by the USN for wooden Minesweeper construction. Both badly dezincified in fact I broke that big fin headed bolt in a vice with a pipe. Followup lab testing revealed apprx 8% zinc.

Rick

Rick, understood and agreed. Indeed, metallurgy and corrosion is a field not well understood by most folks in this industry, and frustratingly they too often don't learn from their mistakes. In fact, corrosion is the area where there is by far, in my experience, the greatest degree of misunderstanding among professionals, it isn't intuitive, it requires education to understand and diagnose. But, most simply guess.

Hard to find is an understatement, there really is no such thing as a bronze propeller in the true sense of the word, nearly all are "manganese bronze" (as are "bronze" prop nuts) which is, because of its zinc content, actually brass. Nickle-Aluminum-Bronze or NiBrAl, is an option that has greater corrosion resistance and tensile strength, however, it more costly, less common. Because most props are manganese bronze/brass, they absolutely require cathodic protection, i.e., zinc protection.


Interestingly, that broken minesweeper (or was it a YP?) bolt doesn't look dezincified, were there signs of pink?

 

[twistedtree]

Rick, understood and agreed. Indeed, metallurgy and corrosion is a field not well understood by most folks in this industry, and frustratingly they too often don't learn from their mistakes. In fact, corrosion is the area where there is by far, in my experience, the greatest degree of misunderstanding among professionals, it isn't intuitive, it requires education to understand and diagnose. But, most simply guess.

Hard to find is an understatement, there really is no such thing as a bronze propeller in the true sense of the word, nearly all are "manganese bronze" (as are "bronze" prop nuts) which is, because of its zinc content, actually brass. Nickle-Aluminum-Bronze or NiBrAl, is an option that has greater corrosion resistance and tensile strength, however, it more costly, less common. Because most props are manganese bronze/brass, they absolutely require cathodic protection, i.e., zinc protection.


Interestingly, that broken minesweeper (or was it a YP?) bolt doesn't look dezincified, were there signs of pink?

To me the practical problem is when I go to buy a part, I really don't know what I'm getting. I can tell if it's plain old brass. But visually it's hard to tell the difference between between red brass and bronze, let alone what composition of bronze. You can ask an attendant at the store, but do you really think they know the lineage of the parts in the bins? For bigger or specialized parts, Groco is a safe bet, but many smaller or more common parts aren't marked, and could really be anything.

 

[garbler]

Rick, understood and agreed. Indeed, metallurgy and corrosion is a field not well understood by most folks in this industry, and frustratingly they too often don't learn from their mistakes. In fact, corrosion is the area where there is by far, in my experience, the greatest degree of misunderstanding among professionals, it isn't intuitive, it requires education to understand and diagnose. But, most simply guess.

Hard to find is an understatement, there really is no such thing as a bronze propeller in the true sense of the word, nearly all are "manganese bronze" (as are "bronze" prop nuts) which is, because of its zinc content, actually brass. Nickle-Aluminum-Bronze or NiBrAl, is an option that has greater corrosion resistance and tensile strength, however, it more costly, less common. Because most props are manganese bronze/brass, they absolutely require cathodic protection, i.e., zinc protection.


Interestingly, that broken minesweeper (or was it a YP?) bolt doesn't look dezincified, were there signs of pink?

Re. The bronze bolts in the attached photo. Yes they came from MSO’s there are no 2” diameter fin head bolts like this on a YP. I was one of four civilian principal hull surveyors working for the USN. We surveyed mostly MSO’s some MSB’s , one or two YP’s then the newer larger class MCM’s. Those bolts went to the lab and of the thirty some bolts submitted all were basically found dezincified. Had I provided you with a good macro of the fracture face and surfaces you’d be able to see the spongy type surface where the zinc has leached out. These were remarkable failures that were discovered during the time I was doing a lot of UT inspection with specially made focused probes for the USN, Lloyds, Salvage Assoc etc. Same equipment I used on keel bolts and shafts.

I’ve worked quite a bit with a couple of metallurgists including my wife who was a metallographer years ago. Seems that not all Silicon, alum or phosphor bronzes turn pink on the surface as it can depend somewhat on the environment, application and material it’s in contact with. This bolt was a thru-deck fastener for large bitts but almost complete body bound in white oak and an old style white lead based bedding compound.

Rick

 

[Steve DAntonio]

When I managed a boat yard I had customers who felt they needed to be present for all work, and thankfully in most cases it was based on previous experience at other yards. After hearing their stories I understood why they felt the way they did. As the yard manager, I worked very hard to make all of my customers feel as if they didn't need to be there to supervise, if they did feel that way it meant I wasn't doing my job.

While you shouldn't need to be present, or check up on all work, the reality is, if you can't be there while work is being performed, you should at least be prepared to thoroughly check all work before paying the bill and departing (I'm actually doing that for a client over the next two days). A former employer of mine used to say, "Inspect what you expect".

Also, keep in mind, if it's a quoted job, and I am partial to those, you should make an effort to not interrupt those doing the work except with pertinent questions and observations. Idle chit chat should be avoided.

 

[Steve DAntonio]

Re. The bronze bolts in the attached photo. Yes they came from MSO’s there are no 2” diameter fin head bolts like this on a YP. I was one of four civilian principal hull surveyors working for the USN. We surveyed mostly MSO’s some MSB’s , one or two YP’s then the newer larger class MCM’s. Those bolts went to the lab and of the thirty some bolts submitted all were basically found dezincified. Had I provided you with a good macro of the fracture face and surfaces you’d be able to see the spongy type surface where the zinc has leached out. These were remarkable failures that were discovered during the time I was doing a lot of UT inspection with specially made focused probes for the USN, Lloyds, Salvage Assoc etc. Same equipment I used on keel bolts and shafts.

I’ve worked quite a bit with a couple of metallurgists including my wife who was a metallographer years ago. Seems that not all Silicon, alum or phosphor bronzes turn pink on the surface as it can depend somewhat on the environment, application and material it’s in contact with. This bolt was a thru-deck fastener for large bitts but almost complete body bound in white oak and an old style white lead based bedding compound.

Rick

Rick:
Thanks for the detailed response, fascinating. A surveyor with a metallographer for your wife, what are the chances;-)

 

[DDW]

I learned early on ALL yard work has to be supervised by owner. No exceptions. Some yards may need a little bit less supervision than others but in the end if you are not "eyes on the job" you're going to be screwed.

I have to agree with this. Unless you know the yard - and also the actual worker doing the work - from past experience, you have to assume they need supervision. Some need so much supervision that you might as well do it yourself, you will spend less time. Even a good experience at a yard doesn't guarantee a repeat, unless the same workers are involved. In the end, I just do most of the work myself.

Regarding bronze, it really should have little or no zinc. There is no way to tell unless you carry around an X-Ray spectrometer. That is kind of an expensive instrument to buy and maintain for the average boat owner, but if I was running a boatbuilding or big repair yard, I'd have one. It would be very amusing to walk through West Marine and shoot all the stuff labelled "bronze".