Why not bronze chainplates?

[zachduckworth]

Great answers. I’m going to be looking for some bronze chainplates now. I really need to get the rig redone before anything becomes a problem. It’s been 13 years since she was re-rigged, definitely time…

[Dockhead]

Originally Posted by SailingHarmonie

This is 100% Wrong.

If you ACTUALLY look up an appropriate bronze alloy used for chain plates and compare tensile strengths you will find it very similar to any of the otherwise appropriate stainless steel alloys. Although I will grant you that there are OTHER types of bronze and OTHER types of steel where your general statement would be true.

An example: Bonze alloy 954 has a tensile strength of 85KSI, and 304 Stainless has a tensile strength specification of 75KSI.

Bronze and stainless chainplates can be interchanged size for size, almost exactly. There are only three reasons that bronze is not used by commercial boat builders for chainplates:

#1 Reason: Cost
#2 Reason: Cost
#3 Reason: It doesn't stay shiny without polishing.

You owe me a cup of coffee, as I was just going to write this exact post, and you spoiled it.

Some grades of bronze well exceed common grades of SS in UTS and yield strength, and don't suffer from crevice corrosion. Even if you wanted to use a somewhat weaker grade of bronze this is easily compensated for in the design.

SS is actually a crappy material for chainplates, which is used only for the reasons you state, and not because of strength, or reliability. Why boat builders use stainless -- and not just stainless, but thin plates of it, and even worse, thin SS plates encapsulated in glass -- I have no idea. Seems like a design defect to me, and I speak from experience, having broken a chainplate like that on my previous boat (only a miracle kept the mast up).

Bronze is much better than SS for chainplates. Titanium is better still, but even more costly. High strength alloy steel -- not stainless -- is probably the best bang for the buck. That's what my present boat has -- massive 15mm thick steel plates, one on either side of a stringer on each side, through-bolted with 20 or 30 17mm bolts each.

Whatever they are made of, massive overbuilding is a good approach to something like chainplates, which are highly stressed, and the failure of which can bring the rig down. Our boats are not airplanes where every gram of weight counts and design has to be pushed to the limits of strength. The chainplates on my previous boat were accidents waiting to happen.

[Benz]

Originally Posted by dlj

With all due respect, these kinds of answers are not particularly useful as you are not stating what copper alloy you use. Are you using cast or wrought copper alloys? From the CDA website:

"Broadly speaking, bronzes are copper alloys in which the major alloying element is not zinc or nickel. Originally "bronze" described alloys with tin as the only or principal alloying element. Today, the term is generally used not by itself but with a modifying adjective. For wrought alloys, there are four main families of bronzes: copper-tin-phosphorus alloys (phosphor bronzes); copper-tin- lead-phosphorus alloys (leaded phosphor bronzes); copper-aluminum alloys (aluminum bronzes); and copper-silicon alloys (silicon bronzes)

The cast alloys have four main families of bronzes: copper-tin alloys (tin bronzes); copper-tin-lead alloys (leaded and high leaded tin bronzes); copper-tin-nickel alloys (nickel-tin bronzes); and copper- aluminum alloys (aluminum bronzes).

The family of alloys known as "manganese bronzes," in which zinc is the major alloying element, is included in the brasses, above."

The above are the very broad brush alloy families. Within each of the above mentioned groups, there are many specific alloys.

It would be really useful if folks that are using these alloys actually said what alloy they are using. Simply saying "I use bronze" is barely a step above saying "I use metal"....

This post is meant with the best of intentions....

dj

With apologies: I used Silicon Bronze, I believe it's "Alloy 651"
You're right that there is wide variety and not all is suitable. I always specify the above, and other than some plain copper for rivets, use almost exclusively that.
All external bolts are also silicon bronze; I use a great deal of bronze screws from West Marine and Jamestown of unknown alloy, but not in critical places.

[zachduckworth]

Would this bronze bar be an appropriate blank to start with?

[Cheechako]

Originally Posted by SailingHarmonie

This is 100% Wrong.

If you ACTUALLY look up an appropriate bronze alloy used for chain plates and compare tensile strengths you will find it very similar to any of the otherwise appropriate stainless steel alloys. Although I will grant you that there are OTHER types of bronze and OTHER types of steel where your general statement would be true.

An example: Bonze alloy 954 has a tensile strength of 85KSI, and 304 Stainless has a tensile strength specification of 75KSI.

Bronze and stainless chainplates can be interchanged size for size, almost exactly. There are only three reasons that bronze is not used by commercial boat builders for chainplates:

#1 Reason: Cost
#2 Reason: Cost
#3 Reason: It doesn't stay shiny without polishing.

Yep, I'm a little shy of using CAST bronze for some things though. I just don't trust 'marine industry casting' like I would cast products for aircraft etc. And chain plates would be one thing I would avoid in castings.
There used to be many types of wrought Bronze alloy flat bar etc available from Alaska Copper and Brass. I don't know if there is much selection anymore or not though.

[fourlyons]

Originally Posted by zachduckworth

Would this bronze bar be an appropriate blank to start with?

Yes, but you will have to finish the surface, it comes fairly rough, I have used it. It is also about 1/16-1/8" thicker than listed, hence "over sized", to allow for finishing. Look up the yield strength, it's a little weaker than stainless steel, and adjust to match your stainless steel.

[Bowdrie]

Originally Posted by zachduckworth

Would this bronze bar be an appropriate blank to start with?

The material is ok, but I would make sure that the dimensions of the stock referenced in your pic are suitable.
A piece of stock that's 1" wide by 1/2" thick might not work as well as something a little wider and not so thick.
Will your turnbuckles fit over a piece of stock that's a 1/2" thick?
Will you have to do any bending?
There are dimensional criteria for how much stock should be above the pin hole and how much stock on each side of the pin hole as well as recommended thickness of stock.
"Skenes Elements of Yacht Design" gives the criteria/sizes broken down by the pin sizes of the toggles/turnbuckles.

[Duurzaam Jacht]

Bronze is used when you use carbon. If you have a carbon 'chain plate' (just an eye of carbon weaving coming out of the deck), often a bronze connection is used and from there it can be stainless steel. There is always some carbon in SS, so to prevent corrosion you need bronze in between.

[thinwater]

Originally Posted by SailingHarmonie

This is 100% Wrong.

If you ACTUALLY look up an appropriate bronze alloy used for chain plates and compare tensile strengths you will find it very similar to any of the otherwise appropriate stainless steel alloys. Although I will grant you that there are OTHER types of bronze and OTHER types of steel where your general statement would be true.

An example: Bonze alloy 954 has a tensile strength of 85KSI, and 304 Stainless has a tensile strength specification of 75KSI.

Bronze and stainless chainplates can be interchanged size for size, almost exactly. There are only three reasons that bronze is not used by commercial boat builders for chainplates:

#1 Reason: Cost
#2 Reason: Cost
#3 Reason: It doesn't stay shiny without polishing.

^^. Number 3 is, oddly, probably more important to new boat buyers than we think.

[scherzoja]

Zach,

You might find this table useful.

[Benz]

Originally Posted by zachduckworth

Would this bronze bar be an appropriate blank to start with?

That isn't silicon bronze. I would keep looking--it's not that hard to find. Sequoia Brass and Copper has treated me well in the past. Surely there are many others.

[zachduckworth]

Ok, I can get a 12” x 12” sheet of 1/4” thick 655 silica bronze for about $550 with tax. Would that be sufficient for fabricating some chainplates? The 6 I have now could fit into the sheet. It’s pricey but never having to worry about crevice corrosion would more than make up for the extra cost.

[scherzoja]

Here's a CF thread that might be helpful.
https://www.cruisersforum.com/forums...es-254157.html

Have you calculated the strength needed for your chain plates? That's the first thing you should do before buying chain plate material.

What is the breaking strength of your shrouds? If your shrouds are 1/4", they might have a breaking strength of 7500 lbs (or is it 8200lbs?). If your turnbuckles are 1/2" pins and chain plates made from your 1/4" plate, then they might not be strong enough. Consider using 3/8" thick instead of 1/4" thick to give a broader bearing surface for the turnbuckle pin.

Attached is a quick spread sheet I made so you can calculate the breaking or yield strength of your chain plate. You can adjust the metal thickness and width to get a pretty good idea of the chain plate design you need.

First, you need to know the Yield Tensile Strength and Ultimate Tensile Strength. Just knowing that it's Silicon Bronze (655) isn't enough because, depending on the temper, those values could vary 15000 or 20000 psi.

Once you now the YTS and UTS of your metal, input that into the spreadsheet. Next, decide if your calculations will use YTS or UTS. If UTS, enter a Y in line 5, "Use UTS (y/n)"

Input the breaking strength of your shroud. This is a reference, not used in any calculations.

Pin dia: is the diameter of the turnbuckle pin, probably 1/2"

Chain plate Thickness: This is the thickness of the metal you intend to use.
Chain plate width: This is the planned width of the finished chain plate.

Now compare the Calculated Chain Plate Strength (the last line) with the breaking strength of the shroud that you entered in line 7, it should be larger. If not, adjust the width and/or the thickness

Note that chain plate length is not factored into this, but consider making the upper shroud chain plates a bit longer than the fwd and after lower shroud chain plates if you will put them on the exterior. This is just for appearance.

The spreadsheet has a 2nd tab, SkeneTable, which has Skene's table in spreadsheet form with the added row named "Vertical Distance to Center". This incorporates the Offset with the Radius to give you the vertical distance from the center of the pin hole to the top edge of the chain plate. Note that the metal to the sides of the pin hole is narrower than the metal above the pin hole by the "offset" value.

[zachduckworth]

Originally Posted by scherzoja

Here's a CF thread that might be helpful.
https://www.cruisersforum.com/forums...es-254157.html

Have you calculated the strength needed for your chain plates? That's the first thing you should do before buying chain plate material.

What is the breaking strength of your shrouds? If your shrouds are 1/4", they might have a breaking strength of 7500 lbs (or is it 8200lbs?). If your turnbuckles are 1/2" pins and chain plates made from your 1/4" plate, then they might not be strong enough. Consider using 3/8" thick instead of 1/4" thick to give a broader bearing surface for the turnbuckle pin.

Attached is a quick spread sheet I made so you can calculate the breaking or yield strength of your chain plate. You can adjust the metal thickness and width to get a pretty good idea of the chain plate design you need.

First, you need to know the Yield Tensile Strength and Ultimate Tensile Strength. Just knowing that it's Silicon Bronze (655) isn't enough because, depending on the temper, those values could vary 15000 or 20000 psi.

Once you now the YTS and UTS of your metal, input that into the spreadsheet. Next, decide if your calculations will use YTS or UTS. If UTS, enter a Y in line 5, "Use UTS (y/n)"

Input the breaking strength of your shroud. This is a reference, not used in any calculations.

Pin dia: is the diameter of the turnbuckle pin, probably 1/2"

Chain plate Thickness: This is the thickness of the metal you intend to use.
Chain plate width: This is the planned width of the finished chain plate.

Now compare the Calculated Chain Plate Strength (the last line) with the breaking strength of the shroud that you entered in line 7, it should be larger. If not, adjust the width and/or the thickness

Note that chain plate length is not factored into this, but consider making the upper shroud chain plates a bit longer than the fwd and after lower shroud chain plates if you will put them on the exterior. This is just for appearance.

The spreadsheet has a 2nd tab, SkeneTable, which has Skene's table in spreadsheet form with the added row named "Vertical Distance to Center". This incorporates the Offset with the Radius to give you the vertical distance from the center of the pin hole to the top edge of the chain plate. Note that the metal to the sides of the pin hole is narrower than the metal above the pin hole by the "offset" value.

Thanks for that link. I have 7/32 shrouds on my Islander Bahama 30. That other guy's experience is very helpful to read. I live in South Bay Los Angeles near Wilmington where there are probably a hundred metal working shops doing different things. I'll check out Atlas and run the numbers through that spreadsheet. Looks like it will run about $1000. For the lack of crevice corrosion issues I think it's reasonable. I need to do a full re-rig anyway, it's been 13 years now and no matter what I will need to have the chainplates custom made since Islander is no more. I'm doing it myself with mechanical fittings at the bottom and having the tops swaged locally, so that will save me a lot of money on labor. I'm going to be busy over the winter for sure.

[zachduckworth]

Ok,

I got a a quote of ~$520 for 6 x CDA 655 chainplates water cut to the basic shape. Includes shipping. Then I’ll have a shop out here drill the holes for me using the old ones as models.