cast bronze chainplates

[Thad Van Gilder]

OK, so I want to cast new chainplates for my ketch.

The main is 40 feet from the deck and the mizzen 30.

I plan to cast the main chainplates in the range of 3/8 by 3 by 18 inches and the mizzen 5/16 by 2 1/2 by 14.

I'm planning on using silicon bronze. What do ou guys think? strong enough?

I'm casting because I want them to be diamond shaped.

-Thad

[mmd]

Not intending any insult to your casting prowess, Thad, but can't you buy silicon bronze flat bar and cut & file it to form? I'd be worried about porosity, inclusions, and crystalization in home-cast fittings, especially ones so vital to the ship's well-being.

[Jim Ledger]

The big ones might cost $150 each, probably less, at Mystic River Foundry, where they'll be able to advise you on the correct alloy, probably not SB. Make a pattern and let them do it. You'll save money.

[paladin]

What size is the rigging wire? and what do the plans call for in dimensions? If I were to have them cast, I would have an experienced foundry do it, in the required shape, and have the metal at the top shackle/rigging screw hole doubled in thickness for wear. The hole should be a bit more than the wire/pin diameters length from the edge. I can work up the dimensions if I know the wire size.

[Thad Van Gilder]

I hate to admit you guys may be right...

I figured I could cast them for the big boat because I casted chainplates for three smaller boats... much smaller.

of course a mast is much easier to replace on an 18 footer...

-Thad

[Michael D. Storey]

Used to have a cast bronze lawn ornament. Broke my shin in the dark one night.

[Russ Manheimer]

Chuck,

You continue to amaze me.

Russ

[Robert L.]

Chuck,

You continue to amaze me.

Russ

Russ, as long as you have an uncompleted task you have something to look forward to and a reason to stick around. My last trip to the E.R. being a 'real-man' I refused pain meds and was working via their "closed" internal wireless network until I saw what they were going to do next. "Your going to put that where?" Shut down and let them dope me up.

Keep at it Chuck, just remember to save often and hit 'Submit Reply' ;=)

[Gold Rock]

Manganese bronze is more typical for chainplates. Appx. 85K psi tensile v.s. 60K for silicon bronze and being harder, it also wears better. Best yet would be aluminum nickel bronze. Even better wear and 90-95K psi tensile.

[PeterSibley]

I plan to cast the main chainplates in the range of 3/8 by 3 by 18 inches and the mizzen 5/16 by 2 1/2 by 14.


-Thad

At 85000psi,manganese bronze 3/8" x 3"gives 95625 lb or 42.6 ton ,with a 5 to 1 safety factor thats 8.5 ton .Frankly it seems to exceed the strength of the hull locally .

[Canoeyawl]

Marks' engineering handbook shows most cast bronze derated from billet specs.
The exception being manganese Bronze. There is a "high strength" cast manganese bronze listed at 100K.

[Gold Rock]

Canoeyawl's right. We, myself included, toss around performance figures as though they were all pervasive fact. Data gleaned from labratory tests using strictly controlled conditions and materials frequently differ from "actual" performance parameters realized in field performance of manufactured parts. Standard compiled data does offer largely accurate assessments of relative performance amongst various alloys.

[Feazer]

Just a quick note to do a bit more research on manganese bronze. This is one of the heavily marketed alloys that most of the time is nothing more than a brass due to high percentages of zinc. Most of your over the counter props are manganese bronze and how they get away with calling it bronze I can't fathom since this alloy may contain 30% or more zinc. This is also used in cheaper seacocks and other budget underwater fittings. Today's marketing lawyers have been able to make the bronze label stick but be careful. These are the same legal buzzards that have been able to call plastic veneered particle board furniture "solid wood " based on a clever scheme of percentages. Anyway when commercial 'manganese bronze' finally de-zincs, and it will, you can carve it like Ivory soap. Please understand this is not something that is unusual or rare by any stretch but a natural metallurgical cycle of zinc being beaten to death by big brother copper.

If you want to consider manganese bronze for chainplates then consider whether chainplates get wet ? do they live in an environment where a lesser alloy could succumb ? Is there a chance where they may be in contact with wetted surfaces or materials where general inspection access and visibility is limited ? If you do your homework you may find this is an alloy that may be a bit risky for chainplates. Play with the yield numbers all you want but in the final analysis there may be a reason most of the good builders of yesteryear stuck with silicon bronze.

Oversize, shape to please, bolt forever and sleep well

[PeterSibley]

Canoeyawl's right. We, myself included, toss around performance figures as though they were all pervasive fact. Data gleaned from labratory tests using strictly controlled conditions and materials frequently differ from "actual" performance parameters realized in field performance of manufactured parts. Standard compiled data does offer largely accurate assessments of relative performance amongst various alloys.

That's what the "safety factor " is for :D,select one depending on your confidence in the calculations and the expected quality of the casting .

[Canoeyawl]

Feasers comments are correct, There is a consideration for chainplates and other stressed fittings above the waterline (not submerged) to be constructed of a Tin-Copper bronze.

Because of evaporation there can be a higher concentration of electrolyte. The water will continually evaporate away leaving a salt rich envronment and when wetted again the solution will be more concentrated and conductive than plain seawater. This is an important reason to select a non-corrosive alloy and to pay close attention to deck and rigging fittings. My choice is to use the more noble alloy and engineer the fitting to that spec. (Cast as opposed to wrought silicon bronze is rated about 40K )

[rregge]

All these tensile strength numbers have major assumptions around them.

1. They assume the material is hot rolled, not backyard cast "as cast"

2. They likley include a specific heat treatment procedure.

3. They assume you have the correct chemical composition for the specific alloy specified (could be an issue in the back yard)

Also look at yield stregth not tensile strength.

Make the non critical stuff, buy the critical stuff.

Russell

[paladin]

If you use the wire size as a gauge, and then you know the size of the shackle or fork that will attach the fitting, you can make the doubler 1/16th to 3/32nds less thick at the doubler, reducing wear and stress at that pount and getting more pin on the chainplate. I will recommend toggles top and bottom on the wire, even though some will say only one is needed, I noticed the difference in the wire rigging between my last two boats when I went the heavier route. It depends on what you use the boat, and how often you expect to be out in rough weather. I wanted everything built like a Sherman tank.

[PeterSibley]

Feasers comments are correct, There is a consideration for chainplates and other stressed fittings above the waterline (not submerged) to be constructed of a Tin-Copper bronze.

Because of evaporation there can be a higher concentration of electrolyte. The water will continually evaporate away leaving a salt rich envronment and when wetted again the solution will be more concentrated and conductive than plain seawater. This is an important reason to select a non-corrosive alloy and to pay close attention to deck and rigging fittings. My choice is to use the more noble alloy and engineer the fitting to that spec. (Cast as opposed to wrought silicon bronze is rated about 40K )

Feazer is correct and I certainly wouldn't use mang br underwater , a chainplate however is rarely wet let alone submerged ...if you consider how many days you actually sail versus moored .If seems a point worthy of discussion .

In response to rregge, I use purchased ingot , junk bronze goes as ornaments .

[Wilson Fitt]

http://i359.photobucket.com/albums/oo39/wfitt/Daybeforelaunch.jpg?t=1263775251

[Feazer]

Peter,

You may be missing my point but what I was trying to convey was that chainplates are often subject to and fail for many of the same reasons that underwater metals do. Without giving names I can tell you more than one large production sailboat manufacturer has had recalls on stainless CP's and bolts that let go from corrosive attack in way of the deck penetrations where inspection access was impossible. This has also occured with some pretty well known wooden boats that had bronze CP's also. Just because the fitting resides above the waterline don't think for a minute that it is immune from corrosive attack associated with a wet marine environment.

Good luck

[Canoeyawl]

Perhaps I was not clear in my post but -
above waterline locations make the electrolysis problems worse...

[PeterSibley]

Perhaps I was not clear in my post but -
above waterline locations make the electrolysis problems worse...


Firstly to state I'm not arguing but I don't know how that could be ? Can you explain a little of the process ,I had always understood that immersion in liquid was necessary for electrolytic removal of zinc ...which I had thought the main cause of weakening in high zinc alloys .

[Thad Van Gilder]

Knowing that manganese bronze was what props are often made of, I melted a couple down this weekend and cast a pair of bronze anchor pulpits...

Not they are pretty cool... I guess they will corrode eventually though.

Where else on earth can you find bronze anchor pulpits? All the ones I see are made of S.S. plate.

-Thad

[Bark]

Thad:

Sorry if this is a dumb question, but is the anchor pulpit you're describing the same as a bow roller/anchor roller? I ordered a bronze bow roller from Port Townsend Foundry a few years ago (haven't installed it yet) and I'm 99% sure it's manganese bronze ...

Ben

[Canoeyawl]

Firstly to state I'm not arguing but I don't know how that could be ? Can you explain a little of the process ,I had always understood that immersion in liquid was necessary for electrolytic removal of zinc ...which I had thought the main cause of weakening in high zinc alloys .
It does not have to be a liquid, it has to be an electrolyte. Concentrated salt spray is that. In fact salt spray is a test procedure to determine corrosion resistance.
"Because of evaporation there can be a higher concentration of electrolyte. The water will continually evaporate away leaving a salt rich envronment and when wetted again the solution will be more concentrated and conductive than plain seawater. This is an important reason to select a non-corrosive alloy and to pay close attention to deck and rigging fittings."

[Wilson Fitt]

I posted the pic of my cast bronze chainplates without comment. However if asked (and I have not been) I would say that they were cast by Lunenburg Foundry from simple wooden patterns that I made, are more shapely than anything that can be pounded out of flat bar and have not shown the slightest sign of deterioration let alone failure after ten years and ten thousand miles of salt water sailing. Relax guys. This is not that complicated.

[PeterSibley]

It does not have to be a liquid, it has to be an electrolyte. Concentrated salt spray is that. In fact salt spray is a test procedure to determine corrosion resistance.
"Because of evaporation there can be a higher concentration of electrolyte. The water will continually evaporate away leaving a salt rich envronment and when wetted again the solution will be more concentrated and conductive than plain seawater. This is an important reason to select a non-corrosive alloy and to pay close attention to deck and rigging fittings."

Can you give a reference for the section in quotes please ...I'd be interested to read more .

[Thad Van Gilder]

Ben,
yes an anchor pulpit is a U shaped thing with an anchor roller mounted in it.

I turned the anchor rollers on my crappy machinist lathe out of some random bronze 3" round bar I had laying around.

I don't know how to post pics, but if you email me I send you pictures.

-Thad

sailorguy26f2 at hotmail dot com