Chainplate hell

BCC Forum
1

I have needed to replace the 1/4" 316 SS chainplates on my boat. They appear to have stress cracks as opposed to crevice corrosion. These plates are 25 years old. They are coming off a 28’ 15,000lb Bristol Channel Cutter.

My first shot at doing this was buying flat bar from online metals. They carry aluminum bronze. After drilling and shaping the plates they needed bent to shape. I took them to a local machine shop that does mostly marine work. They broke 3 before giving up. So at that point I either bought more and had the stock Anneled or looked elsewhere. This would have been very expensive.

I contacted Port Townsend founders, as they were known to cast plates and hardware for the Bristol Channel Cutter. I had in my possession the factory construction manual with detail drawings of the chain plates. I asked if the plates were made to factory specs… “Yes, they were”.

After 2 months the beautifully made chain plates arrived. They were the proper shape. The holes were in all the right places ect. Just like the drawings except…

The plates were 1/2 inch thick at the top area where the rigging would attach. Now this would not be much of a problem if I was using 1/2 turnbuckles. But I have a 4 year old Dynex Dux rig. The hardware (aluminum deadeyes) are sized for 1/4" chain plates.

So now I am stuck again.

I seem to have a few options:

  1. Buy 8 new bronze turnbuckles and fittings for the Dyneema. Cost ~300 each=2400

  2. Buy new aluminum deadeyes of a larger size that would fit over the 1/2 inch bronze. I would use some .02" nylon washers for insulation between the bronze and aluminum. Cost~100 each=800

Or, have the plates at the attachment point for the rigging machined down to 1/4". Cost, probably a whole lot cheaper than my other options.

Now my understanding is that manganese bronze is very comparable in strength to SS 316, if not stronger. But the bronze doesn’t work harden and fatigue like SS. Or have the problem with crevice corrosion.

So would I be in just about the same or better position with the bronze cut down to 1/4 as I would have been if I was using 1/4" SS?

Thanks in advance for any imput or advise. This really has me bummed for a number of reasons.

Gary

2

Manganese Bronze
Manganese Bronze is a high-strength bronze alloy primarily used in heavy-duty applications.

Manganese Bronze (C863)

Minimum Properties Ultimate Tensile Strength, psi 119,000
Yield Strength, psi 66,700
Hardness, Brinell 225
Elongation at break 18%
Machinability 8%
Chemistry Copper (Cu) 60.0 - 68.0%
Aluminum (Al) 3 - 7.5%
Iron (Fe) 2.0 - 4.0%
Manganese (Mn) 2.50 - 5.0%
Zinc (Zn) 25.0%

I am surprised the zinc content is 25%.

IDUNA

3

Manganese Bronze
Manganese Bronze is a high-strength bronze alloy primarily used in heavy-duty applications.

Manganese Bronze (C863)

Minimum Properties Ultimate Tensile Strength, psi 119,000
Yield Strength, psi 66,700
Hardness, Brinell 225
Elongation at break 18%
Machinability 8%
Chemistry Copper (Cu) 60.0 - 68.0%
Aluminum (Al) 3 - 7.5%
Iron (Fe) 2.0 - 4.0%
Manganese (Mn) 2.50 - 5.0%
Zinc (Zn) 25.0%

I am surprised the zinc content is 25%.

IDUNA

4

Good Morning Gary , You Know , there is always a fix of some sort on boats .

I too have a set of P T Foundry manganese .C / P 's , yes they are 1/2" thick .

I was fortunate to be able to use toggles on those over thick C / P 's , so that solved my problem with them .

I might also mention that Brion Toss , recommends using “Link Plates” to solve connection problems , like this . Maybe you could use your Aluminum Ni bronze as link plate material ?

I am as surprised as you and your machine shop are about the Al Ni brnz being soo brittle as to break upon bending pressure , as the curvature is not that much .

It is a very good thing that you warn us all , about that !

Gee , isn’t it easy to anneal bronze and copper ? Don’t you just heat the metal to cherry red , and quench immediately in cold water , that shouldn’t be expensive .

What ever , try not to connect Aluminum to bronze at any time , especially with structural fittings , it has been tried many times and failed each time .

It sounds like you have heard of anneling the brnz plate , would you try and let us know the result ?

Being in the remote location that you are , it is hard to get answers and information redilly , and experimentation seems the only way , sometimes .

Gee , do all your photos come out perfect each time ? Remember how many rolls of 35 mm film have gone to the dump ?

Who was it that said , " If it was easy , our wives and girl friends would do it for us " .

So hang in there , we all are still learning ,

BTW , Pete’s castings are way over size , he seems to think if it is strong enough it won’t fail , he has reason for this thought , as his parents lost their sailboat ( when he was onboard ) , on a lee shore in a S Pac storm , due to rudder failure .

6

Hi Gary,
The 1/2 inch chain plate distributer that Colligo makes fits PT’s 1/2 inch thick chain plates. They sell for $53 each. I think you might be able to keep your deadeyes as long as the lashing line fits and runs fair through Colligo’s 1/2 chain plate distributor and your dead eyes. Here is a photo of mine…the Dyneema shrouds are both 9mm.

Best
David Kent

7

Gary,

Forgot to mention that Hayn makes a double jaw toggle if you need to switch from a fork to eye connection.

8

Doug, I have to check with PTF as to the type bronze they used. Toss says to NOT use manganese bronze. It’s actually not a bronze, but a brass. Rod was slightly perplexed when he saw the 25% zinc content. Zinc and copper is brass, not bronze. Brion Toss thinks that cutting down the bronze (whatever it is) would be fine. After all specs call for only 1/4 inch wire.

David, here is a link to the colligo distributors. Which one did you get? I don’t see a 1/2 incher that would fit. If I could get some deadeyes for 53 I would go that route.

Thanks guys!

9

Gary
link to the 1/2 inch chain plate distributor. Call John Franta at Colligo tomorrow He will email you dimensional drawings.

http://www.colligomarine.com/products/colligo-value/chainplate-distributors/product/111-chainplate-distributor-1-2-black-css61blk

10

Wow - David she’s looking truly beautiful. Tremendous job !

11

Hi All,

I’ve got a 1983 Falmouth Cutter that needs new chainplates… can I get confirmation that the originals were 316? I was wanting to use 316L for my new ones, but want to make sure I don’t make them weaker than they need to be, as 316 is weaker than 304. Thanks!

Jason

12

Ahoy Hypo , you can get a chemical test kit, which the results will tell if your SS is 304 or 316 , see : http://sfiaust.com.au/search_results/display/1549-avesta-classic-moly-drop-960

13

Ahoy Gary , Yes , indeed , Manganese Brnz is a Brass , as far as I have read.

Pete told me that he gets his casting ingots from Atlas metals , and showed me their specification sheet . At that time I just assumed Pete would cast a metal that would perform well for the life of the boat .

If I was to do it over again I would ask Pete to cast my C / P’s out of Al Ni Brnz .

If I am not mistaken , my bronze propeller is also Manganese Brnz , and BTW , Alameda Prop shop was able to re-pitch that prop without it breaking, but I didn’t know to ask how they do it .

It was a seminar lead by L & L where Larry said that Seraffyn’s C / P 's were cast of Al Ni Brnz . I didn’t know to ask him why he used casting instead of flat plate , drats ! He did go on to say that his C / P 's were extra long and went below the water line , thus giving a “passive” lightning ground .

I also would trust most things Brion Toss recommends , like if he says it is Ok to thin down your C / P’s from 1/2" to less , it would be Ok , by me , so why not thin down the full length of the C / P too ? Who needs all that, extra weight and reserve of neglect , but confirm that with Pete first , and I too am very interested in the answer that Pete gives you , as to the brnz composition .

Oh , forgot to ask , would you post pics of the SS stress cracking on your original C / P’s , either here on this forum or Shanti’s forum ?

14

Hypo, if they are original SLM CP’s they are 316. Don’t remember any talk or specs re: 316L

David,
Had to go with the next size up. Still 73 each…ouch. The link you sent, the throat was only 5/16. Did PTF know you were going to use the plates with aluminum rigging parts? Pete was very concerned that I was going to put aluminum parts on his parts. I didn’t understand the concern at the time but I do now. From what I have learned you will need to keep a close watch for de-zincification. Here is a quote from a reply to my dilemma from Brion Toss

Hello,
And ouch, a series of nasty problems. I am, first, amazed that a shop that allegedly works primarily on marine projects can’t bend bronze without destroying it, and further shocked that they didn’t pay you for the damage. But what is done is done.
The P.T. Foundry plates might be made to factory spec, but are definitely thicker than they need to be for this boat; 1/2" is the thickness you might see for 7/16" or 1/2" wire. So they can definitely be milled down some.
What wire size is specified for your boat? If 1/4" is the biggest, then 1/4" thick is fine. I realize you are using Dux, but the loads will be the same. If larger diameter is called for, re-check the clearance inside those deadeyes; I have some here in the shop with a gap of about 5/16". It might make for a tight fit on a similarly-sized chainplate, but occasional treatment with Tef-Gel should prevent any corrosion.
The short form is to thin the chainplates as little as possible, to preserve maximum strength. Also, be sure that the transition to the thinner dimension is gradual, so you don’t create a stress riser.
Bronze specs are indeed the same as for stainless, according to most sources. Some bronzes, like aluminum bronze, are a good deal stronger than 316 stainless. But note that manganese bronze isn’t a bronze at all, but a brass, and therefore vulnerable to de-zycifying. Avoid it, along with the similarly misnamed naval bronze.
Fair leads,
Brion Toss

As you can see I have decided to get new rigging pieces instead of milling down to 1/4. The milling would have been expensive because of the convuluted shape of the CP. plus I don’t trust the shop that broke the first ones or the other shop here. But I have also purchased some nylon washers used for insulating dissimilar metal parts, and I will also slather on some Tef-gel.

Doug, this manganese situation is very disappointing. I spent good money on “bronze” so I could basically neglect them. But that doesn’t seem to be the case now. No doubt they are strong, just reference what Rod posted earlier. But the zinc component is troubling.

As per your request I am attaching a photo of my cracked CP’s. I believe these are stress cracks because of there location.

A quick comparison between M bronze
Minimum Properties Ultimate Tensile Strength, psi 119,000
Yield Strength, psi 66,700

And SS 316
Minimum Properties Ultimate Tensile Strength, psi 89,900
Yield Strength, psi 60,200
So at twice the size needed I guess I have a very large error of neglect, as you prefer Douglas. :sunglasses:

Cheers,
Gary

image.jpg
image.jpg963×1411 312 KB

15

Ahoy Gary , T Y , for that follow-up info . I already know that Pete will be a bit resistant to provide the ingot content, as he didn’t like to show me the Atlas Metal spec sheet .

I may be wrong , but when he has to cast a difficult piece , he may choose an alloy , that gives the most reliable results . He really doesn’t have the time and money it takes to cast then re-cast a flawed piece . Maybe one of the reasons he enlarges the piece, is that, there will be less chance of having to re-melt and cast again .

All it takes is one bubble in the cast piece in the wrong location , to deem it flawed .

What I really like about Pete is that he is a seaman , and knows what we face out there , and a failure, can be catastrophic , where most Foundry men don’t have that sensitivity .

Also , many thanks for the SS C / P cracking photo , Please continue to keep us informed ,

16

Douglass, I sure Pete has good reasons for using the manganese. If you look you will also see aluminum and nickel which is a good thing. And they are strong.
And yours are still in good shape.

The worry is the interaction with the aluminum. But then there are no perfect solutions on boats just compromises.

Just found this on Atlas Metal’s site.

High-strength Manganese brasses. also called manganese bronzes and high-tensile brasses,(C86100-C86800) are among the strongest (as-cast) copper-base materials. The high-strength yellow brasses are mainly used for gears, bolts, valve stems, bridge trunnions and other mechanical products requiring high-strength, good wear resistance and reasonably good corrosion resistance.

17

Aluminum and bronze form a galvanic couple. Over a period of time,
the aluminum will look similar to flakey French pastry crusty - based
on observation.

On Thu, Aug 8, 2013 at 12:13 AM, BCC Forums bccforums@samlmorse.com wrote:

18

Gary:

I have found two reference alloy numbers for Manganese Bronze C86300 and C86500. C86500 is used to cast ship’s propellers. C86300 is “ideal for high load, low speed applications that require a combination of outstanding wear characteristics and high bearing strength. Despite its strength characteristics, however, this manganese bronze alloy is not heat-treatable, needs reliable lubrication and should be used in conjunction with hardened shafts. The lead in the alloy’s makeup improves machinability without materially affecting its mechanical properties.”

http://www.dura-barms.com/bronze/manganese-bronze/c86300.cfm

Chemical Compositions:

C86300 - http://www.dura-barms.com/bronze/manganese-bronze/c86300.cfm

C86500 - http://www.anchorbronze.com/c86500.htm

C86300 has a 22-28% zinc content and C86500 has a 36-42% by weight zinc content.

Although both alloys are reported to have good corrosion resistant properties in a salt water environment, the high zinc content bothers me.

Look at the Davey & Co. Ltd. fittings offered at RW Rope - http://rwrope.com/davey/information.html. Davey & Co fittings are made from gunmetal C86555 - copper 86%, tin 5%, lead 5%, zinc 5%.

Rod
BCC IDUNA

19

Gary:

I have found two reference alloy numbers for Manganese Bronze C86300 and C86500. C86500 is used to cast ship’s propellers. C86300 is “ideal for high load, low speed applications that require a combination of outstanding wear characteristics and high bearing strength. Despite its strength characteristics, however, this manganese bronze alloy is not heat-treatable, needs reliable lubrication and should be used in conjunction with hardened shafts. The lead in the alloy’s makeup improves machinability without materially affecting its mechanical properties.”

http://www.dura-barms.com/bronze/manganese-bronze/c86300.cfm

Chemical Compositions:

C86300 - http://www.dura-barms.com/bronze/manganese-bronze/c86300.cfm

C86500 - http://www.anchorbronze.com/c86500.htm

C86300 has a 22-28% zinc content and C86500 has a 36-42% by weight zinc content.

Although both alloys are reported to have good corrosion resistant properties in a salt water environment, the high zinc content bothers me.

Look at the Davey & Co. Ltd. fittings offered at RW Rope - http://rwrope.com/davey/information.html. Davey & Co fittings are made from gunmetal C86555 - copper 86%, tin 5%, lead 5%, zinc 5%.

Rod
BCC IDUNA

20

Just received a comment from Brion Toss.

In my last post on his Spartalk forum I posed a theoretical question.
“What would happen to my starboard boomkin chainplate on a 22 day trip to Tahiti” which would mostly likely be in the water the whole trip.

Brions answer was, I would have a copper chainplate. Then on the other hand I keep seeing references to manganese bronze as being used for props and other marine hardware. They are obviously in the water all the time.

I am researching an alternative source for fabricated chainplates out real bronze.