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Old 08-10-2012, 17:27   #31
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Re: Is this enlongation acceptable?

Is that the bobstay attachment point? If so, I'd recommend you have a fabricator look at it. Why risk losing the whole rig when a bit of metalwork can make things new?
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Old 08-10-2012, 17:44   #32
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Re: Is this enlongation acceptable?

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Originally Posted by delmarrey View Post
And attach that to SS rigging?

Being 3/8" thick it's probably OK but w/o actually seeing in ones own hands it's hard to know for sure. As a Machinist (45 yrs.) I make a lot of my own gear, but I wouldn't commit myself of a picture over the internet.
of course, most turnbuckles are a combination of Bronze and SS.
The fitting should be fine, but as long as most the rig is going to be renewed... "make it whole again" and test it for cracks! Being a Westail, that fitting is likely US SS. May be better than what you could replace it with!
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Old 08-10-2012, 17:46   #33
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Re: Is this enlongation acceptable?

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Originally Posted by delmarrey View Post
And attach that to SS rigging?

Being 3/8" thick it's probably OK but w/o actually seeing in ones own hands it's hard to know for sure. As a Machinist (45 yrs.) I make a lot of my own gear, but I wouldn't commit myself of a picture over the internet.

I prefer a bronze solid rod bobstay, but yes, the whisker stays on a bronze cranse iron are usually rigged with ss rigging to bronze turnbuckles. It's quite common. It's not like it's a problem for the turnbuckles, why would it be for the iron?
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Old 08-10-2012, 18:04   #34
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Re: Is this enlongation acceptable?

I am not trying to convince anyone one way or the other but...

If you think about it any time you put a pin in a hole you will get point loading when the load is in one direction as in this case. The contact area is tiny. In a few short months the point load wears on pin and hole and in fact you get more contact area. Improving the situation?

3/8 inch thick on a 32 foot boat. My concern is the pitting which are stress risers and good origination points for cracks.

I still vote clean it up and put it back together. Check it next haulout...
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Old 08-10-2012, 18:27   #35
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Re: Is this enlongation acceptable?

Yeah, I've thought of that before too.... unless the pin is a press fit, it's point loaded when new.... gradually conforming to the loaded area.
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Old 08-10-2012, 18:40   #36
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Re: Is this enlongation acceptable?

Quote:
Originally Posted by minaret View Post
I prefer a bronze solid rod bobstay, but yes, the whisker stays on a bronze cranse iron are usually rigged with ss rigging to bronze turnbuckles. It's quite common. It's not like it's a problem for the turnbuckles, why would it be for the iron?
Would you put a SS valve on a bronze thruhull. A bobstay sees a lot of saltwater, where a turn buckle should be lubricated, separating the materials a bit. Even at that silicon bronze (turn buckles) is a different substance then cast bronze and a lot closer to SS on the galvanic charts. IMPO I don't think it is a good idea mixing metals. Just saying..........



Galvanic Corrosion Chart*
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Old 08-10-2012, 18:58   #37
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Re: Is this enlongation acceptable?

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Originally Posted by delmarrey View Post
Would you put a SS valve on a bronze thruhull. A bobstay sees a lot of saltwater, where a turn buckle should be lubricated, separating the materials a bit....


All I know is, this has been done this way for a great many years with no problems. I have owned boats rigged like this, and worked on a great many boats rigged like this. Never seen a problem in a cast bronze cranse iron, that's why you see so many used ones for sale, they are one of the pieces of hardware that is always salvaged from a wrecked vessel. They are much better than a welded steel iron. I prefer a bronze rod bobstay because the SS rigging gets eaten up, not the cranse iron. I just dont think there's enough contact there to create a problem. I've seen bronze cranse irons over a hundred years old still in great shape...
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Old 08-10-2012, 19:19   #38
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Re: Is this enlongation acceptable?

@ delmarrey:

If mixing metals was a No-No in all marine cases, it seems to me that we would be stuck with not using metals.

Some metals co-exist relatively happily, and stainless & bronze, provided the grades are suitable, have done so happily since stainless was first put to marine service.

To answer your specific question, I would not hesitate to fit a stainless valve to a bronze thru-hull.

In relation to which grades to choose, the distance apart on the galvanic series does not tell the whole story, at least in some specific cases.

For instance, pairing 316 stainless with Nickel Alu Bronze does not produce measurably different results, in terms of material lost to galvanic corrosion, from pairing it with Alu Bronze.

The surface activity does not remain at the instantaneous levels shown by the chart, which list the potential differences as measured between shiny new coupons.

Apologies for deviating from the thread topic.
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Old 08-10-2012, 20:47   #39
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Re: Is this enlongation acceptable?

It appears that most if not all experienced machinists have said it should be okay but needs to be tested for internal pitting and cracks. They are the people I would listen to.
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Old 09-10-2012, 10:13   #40
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Re: Is this enlongation acceptable?

Bronze and SS have been proven to be the best case scenario for threaded pieces in a salt water environment. Threads are probably one of the most difficult tests. Some things just are what they are. I probably wouldnt put a SS valve with Bronze underwater... simply because SS is such a poor metal underwater with any enclosed portions in the first place.
SS rudder shafts have often been set in a bronze shoe on skeg or full keel boats with little problems that I've seen, although it sure wouldnt surprise me to see deterioration on the bottom end of the shaft....
An interesting thing about the galvanic chart above... they show 400 series stainless very near to bronze on the scale.... but I can tell you that if you put a piece of 400 series SS in salt water (with or without bronze next to it) it's going to become a pile of rust very quickly! One has to be careful with the chart... it doesnt mean just because two alloys are near each other, that they will work well in a salt environment. (i guess that's probably obvious... sorry!)
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Old 09-10-2012, 17:53   #41
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Re: Is this enlongation acceptable?

Another thing the above linked chart doesn't show is that many stainless alloys, including the 3xx series, can occupy two different places in the hierarchy, depending on whether they're active or passive.

This is why (as Cheechako implies) it's not a great idea to use the 3xx SS alloys in quiescent permanently immersed seawater service: the lack of oxygen can mean that certain localities can become active, meaning that they occupy a lower rung on the pecking order WITH RESPECT TO other regions on the same piece of metal. Effectively the piece attacks itself. (Google pitting+stainless)

The reason stainless and bronze work so well in turnbuckle service will be well known to most but in case future people reading this are puzzled, it's because stainless is notorious for "galling" under load, particularly when both loaded surfaces are similar in composition (Stainless is particularly prone, in my opinion, mainly because of poor thermal conductivity, but I don't think this is universally accepted - Google galling+stainless for further investigation)
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Old 09-10-2012, 18:10   #42
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Re: Is this enlongation acceptable?

I haven't addressed the OP's question:

My feeling is this: whether or not the pin is too small (and if it is I would improve the fit - either bush the fitting or go for a bigger pin):

the pattern of corrosion is symptomatic of stress corrosion: when stress is applied to a material, any corrosion will happen preferentially in the zone of highest stress. If you drew a stress map of the fitting under load, it would closely match the corrosion shown in the photo. This is normal behaviour for a stressed fitting in a marine environment, but it has to be watched.

If the pin is too small, the stress will be more concentrated than if close-fitting.
This is undesirable, because the next stage is that the pin rubs away increasing amounts of the corrosion product, exposing fresh new substrate which in turn corrodes, and gradually the hole elongates. The greater the size difference, the quicker this can happen.

However it has a long way to go in this case, and I don't for a moment think you'll need to scrap the item. As others have said, at worst it could do to have the hole carefully bored or reamed to clean, and a close-fitting bush of a similar grade of SS TIG welded in, by someone who knows all about welding highly stressed parts for low corrosion in a marine environment.
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Old 09-10-2012, 19:09   #43
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Re: Is this enlongation acceptable?

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Originally Posted by Andrew Troup View Post
Another thing the above linked chart doesn't show is that many stainless alloys, including the 3xx series, can occupy two different places in the hierarchy, depending on whether they're active or passive.

This is why (as Cheechako implies) it's not a great idea to use the 3xx SS alloys in quiescent permanently immersed seawater service: the lack of oxygen can mean that certain localities can become active, meaning that they occupy a lower rung on the pecking order WITH RESPECT TO other regions on the same piece of metal. Effectively the piece attacks itself. (Google pitting+stainless)

The reason stainless and bronze work so well in turnbuckle service will be well known to most but in case future people reading this are puzzled, it's because stainless is notorious for "galling" under load, particularly when both loaded surfaces are similar in composition (Stainless is particularly prone, in my opinion, mainly because of poor thermal conductivity, but I don't think this is universally accepted - Google galling+stainless for further investigation)
YEP! and bronze is just the opposite; self lubricating and is essentially a bearing material.
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Old 09-10-2012, 20:02   #44
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Re: Is this enlongation acceptable?

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I'm sending it to a fabricator that is making up the rest of the rigging for testing and I suppose I'll go with what he says.

If everyone had said, "Nope no good." or if someone had said, "No that is manifestly unsafe, I'm a metallurgist and I know." I would have probably just said fabricate another one. As it stands I might be throwing money away having it tested, but its worth a shot. The thing is 3/8" thick. Hopefully it passes muster.

As with many matters nautical, it seems there are many opinions and variables to consider. Sometimes it seems difficult to navigate this web of confusion. I have only so much money. Do I replace this piece and not buy extra charts? Do I leave this piece and replace a different worrisome part? etc.

This piece is one of the few pieces of rigging I was hoping to preserve since it is sort of a specialty piece and its so stoutly built.
I have a couple of opinions from a machinist point of view as well as a cost estimator.

First, as a machinist I am not qualified to form an opinion regarding the failure potential of the shown part. I can say that the hole is no longer round. Beyond that, a structural engineer should be consulted.

Alternatively, as a cost estimator I would say to cut it off and weld a new piece on. The raw material will be less than $20, add another $10 to put the hole in and about $50 to cut the old off and weld the new on.

Problem solved with a $100 bill and enough left over for a decent lunch.

If you are looking for everyone to say "Nope, no good", you should post the question and picture on a pilots forum.
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Old 10-10-2012, 10:09   #45
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Re: Is this enlongation acceptable?

That piece looks pretty good; a fabricator cant tell you if it will fail or not, neither can an engineer or a machinist. Only someone with Dye penetrant inspection facility can tell you if it's as good as it was all these years. If the Fabricator has that ability... bravo! If that passes and you are worried about the hole, have it TIG welded on the edge and then electropolish the whole thing like new.
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