Bronze or Stainless
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Hi Greg, if it were my boat I would want to know..
the strength rating of each device before I decide which is better. Both can withstand long periods of salt water exposure, but more depends upon what stresses the device will be subject to. I would want to know that before I decide. Terry
the strength rating of each device before I decide which is better. Both can withstand long periods of salt water exposure, but more depends upon what stresses the device will be subject to. I would want to know that before I decide. Terry
crevice corrosion
Some types of stainless underwater can be attacked by crevice corrosion do to the lack of oxygen. What is the fitting and what type of stainless is it made from. Bronze doesn’t have this problem and it is considered the best metal for underwater use. All the best, Robert Gainer
Some types of stainless underwater can be attacked by crevice corrosion do to the lack of oxygen. What is the fitting and what type of stainless is it made from. Bronze doesn’t have this problem and it is considered the best metal for underwater use. All the best, Robert Gainer
It’s good that RAD can make a recommendation
It’s good that RAD can make a recommendation for someone that is familiar with both stainless and boating. There are a lot of different types of stainless and they all react differently to welding and saltwater. The 304 stainless is stronger then the more corrosion resistant 316 and type L stainless handles welding and corrosion better then non L types of stainless. The picture you posted shows corrosion along the weld line of the turning box. That may be from the damage the heat does to the structure of the metal. If you can electropolish and passavate the metal after welding you won’t get that corrosion in stainless weldments. In our shop we dipped stainless after all drilling, machining and or welding was done in an acid solution with a 12 volt DC current going through it. This took the steel impieties from machining off the surface and prevented the weld zone from rusting. In this application I think you should stay with bronze pipe and unions because of the interaction of the stainless wire and the fittings. You don’t want a metal rubbing on the wire strands that is harder then the wire. With tension the wire should not touch the sides of the pipe but it will at times and you don’t need the strands being abraded from rubbing on stainless. All the best, Robert Gainer
It’s good that RAD can make a recommendation for someone that is familiar with both stainless and boating. There are a lot of different types of stainless and they all react differently to welding and saltwater. The 304 stainless is stronger then the more corrosion resistant 316 and type L stainless handles welding and corrosion better then non L types of stainless. The picture you posted shows corrosion along the weld line of the turning box. That may be from the damage the heat does to the structure of the metal. If you can electropolish and passavate the metal after welding you won’t get that corrosion in stainless weldments. In our shop we dipped stainless after all drilling, machining and or welding was done in an acid solution with a 12 volt DC current going through it. This took the steel impieties from machining off the surface and prevented the weld zone from rusting. In this application I think you should stay with bronze pipe and unions because of the interaction of the stainless wire and the fittings. You don’t want a metal rubbing on the wire strands that is harder then the wire. With tension the wire should not touch the sides of the pipe but it will at times and you don’t need the strands being abraded from rubbing on stainless. All the best, Robert Gainer
I take it you work in a fabrication shop
I take it you work in a fabrication shop as well........ No Greg, not now, but I owned and did most of the design work for two boat repair and building shops for about thirty years. Now I just work as the Small Boat Program Director for a maritime museum, “The Hudson Fisheries Trust” and I design/build replicas of significant small boats with high school children doing most of the work. We also teach small boat building/design and history but it’s all traditional stuff using copper rivets and steam bent frames mostly. I did some high tech stuff when I was in the business such as the rig for one of the BOC solo round the world racers but mostly run of the mill stuff and lots of repairs. I am also on the staff at “The Beacon Institute for Rivers and Estuaries” as their “Maritime Specialist” and although that sounds good I’m not sure what it means. And at one time, long, long ago I was the youngest person to solo across the north Atlantic in an unpowered 22 foot sailboat. I also get a mention in the second edition of Richard Henderson’s book on single handed sailing. So I know just enough to get into trouble and no more. All the best, Robert Gainer One of our recent projects, www.offsoundings.info/clare.htm
I take it you work in a fabrication shop as well........ No Greg, not now, but I owned and did most of the design work for two boat repair and building shops for about thirty years. Now I just work as the Small Boat Program Director for a maritime museum, “The Hudson Fisheries Trust” and I design/build replicas of significant small boats with high school children doing most of the work. We also teach small boat building/design and history but it’s all traditional stuff using copper rivets and steam bent frames mostly. I did some high tech stuff when I was in the business such as the rig for one of the BOC solo round the world racers but mostly run of the mill stuff and lots of repairs. I am also on the staff at “The Beacon Institute for Rivers and Estuaries” as their “Maritime Specialist” and although that sounds good I’m not sure what it means. And at one time, long, long ago I was the youngest person to solo across the north Atlantic in an unpowered 22 foot sailboat. I also get a mention in the second edition of Richard Henderson’s book on single handed sailing. So I know just enough to get into trouble and no more. All the best, Robert Gainer One of our recent projects, www.offsoundings.info/clare.htm
All bronzes are not 'true' bronzes ....
many bronzes on the market today are not true bronzes and have too much iron and zinc added to make them 'free machining' bronzes .... good/easy for machining purposes but BAD for corrosion resistance. A 'true bronze' is a royal bitch to machine. Too much zinc (making the metal a 'red brass') in underwater applications will because of electrolysis cause the zinc component to be consumed as an anode (if otherwise not adequately protected elsewhere by proper anodes), leaving the base metal of the 'bronze' weakened/'spongey'. If you buy bronze for underwater, insist on 'true' bronzes such as admiralty bronze, NickleAluminumBronze, etc. .... or a bronze 'with certifications' that shows minimum or virtually zero zinc content !!!!! Too much 'crap' bronze is being imported ... and its actually 'red brass'. ditto concerning the huge worldwide consumption of 300 series stainless ... lots of inferior crap is showing up due to the intense asian consumption and market pressure of stainless - beware. Get certifcations and 'mill specs' whenever possible if the part is 'important'.
many bronzes on the market today are not true bronzes and have too much iron and zinc added to make them 'free machining' bronzes .... good/easy for machining purposes but BAD for corrosion resistance. A 'true bronze' is a royal bitch to machine. Too much zinc (making the metal a 'red brass') in underwater applications will because of electrolysis cause the zinc component to be consumed as an anode (if otherwise not adequately protected elsewhere by proper anodes), leaving the base metal of the 'bronze' weakened/'spongey'. If you buy bronze for underwater, insist on 'true' bronzes such as admiralty bronze, NickleAluminumBronze, etc. .... or a bronze 'with certifications' that shows minimum or virtually zero zinc content !!!!! Too much 'crap' bronze is being imported ... and its actually 'red brass'. ditto concerning the huge worldwide consumption of 300 series stainless ... lots of inferior crap is showing up due to the intense asian consumption and market pressure of stainless - beware. Get certifcations and 'mill specs' whenever possible if the part is 'important'.
You are right and a lot of junk is out there
RichH, You are right and a lot of junk is out there. For things like screws and bolts Silicon Bronze is a common choice and for underwater castings or other hardware Manganese Bronze can’t be beat. I think Nickel Aluminum Bronze is most often used for bearings and such. I don’t see it used much on marine applications and not at all for underwater in a saltwater environment. Terms like gunmetal and admiralty bronze tend to be most often used in England and not heard so much here. You can't buy in the USA using a name like Admiralty Bronze. All the best, Robert Gainer
RichH, You are right and a lot of junk is out there. For things like screws and bolts Silicon Bronze is a common choice and for underwater castings or other hardware Manganese Bronze can’t be beat. I think Nickel Aluminum Bronze is most often used for bearings and such. I don’t see it used much on marine applications and not at all for underwater in a saltwater environment. Terms like gunmetal and admiralty bronze tend to be most often used in England and not heard so much here. You can't buy in the USA using a name like Admiralty Bronze. All the best, Robert Gainer
Any 'red metals' supplier who deals with the
Chemical Process industry will have admiralty, etc. bronzes. They are are becomming increasingly rare since the virtual collapse of the US red metals industry (due to cheap/inferior asian supply) but they do exist; and, there has been a mini-resurgance of 'quality' mini-foundries. My choice for saltwater is and has been Nickle Aluminum Bronze ... is and was a navy standard for critical applications from as far back as the 60s. There has also been the developement and availability of some innovative stainless grades that better handle saltwater, etc corrosion. I think I'll wait a bit as I remember all too well how the 300 series were touted when they were developed .... only to discover much later on that they were quite flawed when it came to corrosion and fatigue concerns. In any event for wetted stainless: grind the welds flat, mirror polish (to a an extrememly FLAT micro-inch surface profile), then passivate/electropolish to remove any surface irregularities, etc. ..... and then design for 30% of UTS stress to be sure that youre well under the 'fatigue endurance limit'. If you design 90ksi stainless beyond ~30ksi stress .... its eventually going to fail by fatigue if you apply cyclical loads to it. Most boat rigging design I see today is still well above that 'magic' ~30Ksi design limit .... and is vulnerable to catastrophic fatigue failure.
Chemical Process industry will have admiralty, etc. bronzes. They are are becomming increasingly rare since the virtual collapse of the US red metals industry (due to cheap/inferior asian supply) but they do exist; and, there has been a mini-resurgance of 'quality' mini-foundries. My choice for saltwater is and has been Nickle Aluminum Bronze ... is and was a navy standard for critical applications from as far back as the 60s. There has also been the developement and availability of some innovative stainless grades that better handle saltwater, etc corrosion. I think I'll wait a bit as I remember all too well how the 300 series were touted when they were developed .... only to discover much later on that they were quite flawed when it came to corrosion and fatigue concerns. In any event for wetted stainless: grind the welds flat, mirror polish (to a an extrememly FLAT micro-inch surface profile), then passivate/electropolish to remove any surface irregularities, etc. ..... and then design for 30% of UTS stress to be sure that youre well under the 'fatigue endurance limit'. If you design 90ksi stainless beyond ~30ksi stress .... its eventually going to fail by fatigue if you apply cyclical loads to it. Most boat rigging design I see today is still well above that 'magic' ~30Ksi design limit .... and is vulnerable to catastrophic fatigue failure.
The US Navy does use nickel-aluminum bronzes
RichH said, “My choice for saltwater is and has been Nickle Aluminum Bronze ... is and was a navy standard for critical applications from as far back as the 60s” The US Navy does use nickel-aluminum bronze for minesweeper propeller shafts, propellers for ice-breaking service, submarine propellers and high pressure pump body’s or other high strength forgings. And MIL-B-24480 is a Navel spec for nickel-aluminum bronze casting. I guess all of this is a critical application in the Navy but it doesn’t make it the best choice for a small craft that doesn’t need the particular properties in that metal. Nickel aluminum bronze is approximately 10 per cent lighter in weight than manganese bronze, and can be designed to make thinner propeller blade sections because of its higher strength and its resistance to notch sensitivity make it a great high stress propeller material. But I shudder to think what it would cost to have a custom propeller cast for my boat because it casts more per pound and its not found in standard propeller shops. Most yachts use propellers cast from manganese bronze. Because they have lots of money and can afford it the Navy can use it for some applications where it would not be appropriate in a yacht and besides I don’t have an Ice Breaker so I don’t need a custom propeller and I don’t have a Minesweeper so I can use a stronger stainless shaft instead and I don’t even intend to look at getting a submarine so I don’t need to forge any pump bodies or have a custom propeller for that either. RichH also said, “Any 'red metals' supplier who deals with the Chemical Process industry will have admiralty, etc. bronzes” That may well be true but I don’t get any of my hardware from the Chemical Process Industry so I can comment about that. We have no problem getting metal for the casting we do and sheet and bar stock is a standard item but the term admiralty bronze isn’t used by anyone I know in the US and I know of just a few parts made from nickel aluminum bronze for small craft but offhand I can’t think of any examples. Maybe you can point some out? All the best, Robert Gainer
RichH said, “My choice for saltwater is and has been Nickle Aluminum Bronze ... is and was a navy standard for critical applications from as far back as the 60s” The US Navy does use nickel-aluminum bronze for minesweeper propeller shafts, propellers for ice-breaking service, submarine propellers and high pressure pump body’s or other high strength forgings. And MIL-B-24480 is a Navel spec for nickel-aluminum bronze casting. I guess all of this is a critical application in the Navy but it doesn’t make it the best choice for a small craft that doesn’t need the particular properties in that metal. Nickel aluminum bronze is approximately 10 per cent lighter in weight than manganese bronze, and can be designed to make thinner propeller blade sections because of its higher strength and its resistance to notch sensitivity make it a great high stress propeller material. But I shudder to think what it would cost to have a custom propeller cast for my boat because it casts more per pound and its not found in standard propeller shops. Most yachts use propellers cast from manganese bronze. Because they have lots of money and can afford it the Navy can use it for some applications where it would not be appropriate in a yacht and besides I don’t have an Ice Breaker so I don’t need a custom propeller and I don’t have a Minesweeper so I can use a stronger stainless shaft instead and I don’t even intend to look at getting a submarine so I don’t need to forge any pump bodies or have a custom propeller for that either. RichH also said, “Any 'red metals' supplier who deals with the Chemical Process industry will have admiralty, etc. bronzes” That may well be true but I don’t get any of my hardware from the Chemical Process Industry so I can comment about that. We have no problem getting metal for the casting we do and sheet and bar stock is a standard item but the term admiralty bronze isn’t used by anyone I know in the US and I know of just a few parts made from nickel aluminum bronze for small craft but offhand I can’t think of any examples. Maybe you can point some out? All the best, Robert Gainer
Oh brother, ......
I did not say that NiAlBronze was cheap nor abundantly available for the hobbyist, etc. It is a very difficult metal to produce correctly; hence. it can be costly. It is commonly available from the remaining quality manufacturers and distributors that deal in it .... get off your ad-hominem duff and do a Thomsregister, etc. websearch. Any area that is breaking naval ships will have it as scrap. Its not only strength characteristics but strength and corrosion resistance in saltwater that make NiAlBronze the 'best' of the bronzes (as least as my memory serves from back when I was a member of the team that developed the first successful commercial offerings for Navy, Chem. Process and aerospace applications). Admiralty is common in Chem Process, especially heat exchangers, etc. ... again get off your duff and do a search. The original poster asked which material is best. That answer remains (true) bronze and the best 'true' bronze is still NiAlBronze for seawater service.
I did not say that NiAlBronze was cheap nor abundantly available for the hobbyist, etc. It is a very difficult metal to produce correctly; hence. it can be costly. It is commonly available from the remaining quality manufacturers and distributors that deal in it .... get off your ad-hominem duff and do a Thomsregister, etc. websearch. Any area that is breaking naval ships will have it as scrap. Its not only strength characteristics but strength and corrosion resistance in saltwater that make NiAlBronze the 'best' of the bronzes (as least as my memory serves from back when I was a member of the team that developed the first successful commercial offerings for Navy, Chem. Process and aerospace applications). Admiralty is common in Chem Process, especially heat exchangers, etc. ... again get off your duff and do a search. The original poster asked which material is best. That answer remains (true) bronze and the best 'true' bronze is still NiAlBronze for seawater service.
A quick look at the McMaster-Carr
catalog will reveal that they are a source for all of the bronze alloys mentioned here and a few more with a discussion of the mechanical and chemical properties, and complete listing of the available shapes and the price per unit,weight, length, or piece.
catalog will reveal that they are a source for all of the bronze alloys mentioned here and a few more with a discussion of the mechanical and chemical properties, and complete listing of the available shapes and the price per unit,weight, length, or piece.
Why??
RichH, You and I must see the purpose of a forum like this very differently. You are correct in what you say and if you want to use it go for it. But I feel an obligation and responsibility to give an answer that is both useful and realistic instead of just showing how clever I can be. The person who asked the question obviously doesn’t have a machine shop and he will be asking someone else to fabricate any parts for him. Why would I recommend a “non standard” more expensive metal instead of something available off the shelf that does the job and is used all the time for a good reason? You say, “The original poster asked which material is best. That answer remains (true) bronze and the best 'true' bronze is still NiAlBronze for seawater service” First, there are many true bronzes. Second, the best choice takes into account every aspect of the job. Don’t select a material based on one property of the material to the determent of other factors. And don’t select a material that solves a non existent problem. Manganese Bronze, also a true bronze, is what’s used in this case and it has been used for quite some time now so what do you gain with a more expensive solution? You want the part to last 50 years longer then the boat? You want to spend just so you can say you spent extra? I wonder why Manganese Bronze is the most common metal for struts, propellers, rudder bearings and Pintles and Gudgeons and other underwater fittings. As far as a source goes I don’t need to look it up anywhere. My supplier can handle it and I have used exotic metals and materials on a lot of jobs where it made sense. Some racing boats have very fancy and expensive fittings but that’s not what’s needed in this case. Again, I am in the marine industry not the Chemical Processing business. If Admiralty Bronze is a term you find in common use in the chemical business then that’s great. But in the American marine business it’s not a term you hear unless you are on the phone with an English company. All the best, Robert Gainer
RichH, You and I must see the purpose of a forum like this very differently. You are correct in what you say and if you want to use it go for it. But I feel an obligation and responsibility to give an answer that is both useful and realistic instead of just showing how clever I can be. The person who asked the question obviously doesn’t have a machine shop and he will be asking someone else to fabricate any parts for him. Why would I recommend a “non standard” more expensive metal instead of something available off the shelf that does the job and is used all the time for a good reason? You say, “The original poster asked which material is best. That answer remains (true) bronze and the best 'true' bronze is still NiAlBronze for seawater service” First, there are many true bronzes. Second, the best choice takes into account every aspect of the job. Don’t select a material based on one property of the material to the determent of other factors. And don’t select a material that solves a non existent problem. Manganese Bronze, also a true bronze, is what’s used in this case and it has been used for quite some time now so what do you gain with a more expensive solution? You want the part to last 50 years longer then the boat? You want to spend just so you can say you spent extra? I wonder why Manganese Bronze is the most common metal for struts, propellers, rudder bearings and Pintles and Gudgeons and other underwater fittings. As far as a source goes I don’t need to look it up anywhere. My supplier can handle it and I have used exotic metals and materials on a lot of jobs where it made sense. Some racing boats have very fancy and expensive fittings but that’s not what’s needed in this case. Again, I am in the marine industry not the Chemical Processing business. If Admiralty Bronze is a term you find in common use in the chemical business then that’s great. But in the American marine business it’s not a term you hear unless you are on the phone with an English company. All the best, Robert Gainer
SS is not normaly used under water
Stainless has the funny property that when you starve it of atmospheric oxygen it reacts with water to corrode. This is why it is not used under water or in locations that can get wet and not dry out for a long time. I though that you needed atmospheric oxygen for corrosion but apparently SS can actually separate the hydrogen and oxygen in water and the oxygen then reacts with the metal. Go figure
Stainless has the funny property that when you starve it of atmospheric oxygen it reacts with water to corrode. This is why it is not used under water or in locations that can get wet and not dry out for a long time. I though that you needed atmospheric oxygen for corrosion but apparently SS can actually separate the hydrogen and oxygen in water and the oxygen then reacts with the metal. Go figure
All this theory and detail about alloys and
metalurgy is great! I'm learning a lot, and it makes the gray day pass more quickly. Greg's question was "I can get the part in either SS or Bronze, which shall I get?" If the supplier is reputable, the bronze will (we hope) be a suitable marine alloy. So will the Stainless. Greg never asked for information on custom made (read expensive) pipe and fittings. He buys off the shelf, as most of us do. He'll take the alloy that's offered. Bronze is softer than Stainless, so where there is a chance that the SS cable or other metals may cut the pipe, consider SS. Bronze is more durable than SS -IN THIS APPLICATION-. This is demonstrated by the relative condition of the Bronze and SS fittings. So; Use bronze where you can, and SS where you have to. Keep it as simple as possible. Complication and redesign have an inverse relationship to likelyhood thst you will sail your boat this year.
metalurgy is great! I'm learning a lot, and it makes the gray day pass more quickly. Greg's question was "I can get the part in either SS or Bronze, which shall I get?" If the supplier is reputable, the bronze will (we hope) be a suitable marine alloy. So will the Stainless. Greg never asked for information on custom made (read expensive) pipe and fittings. He buys off the shelf, as most of us do. He'll take the alloy that's offered. Bronze is softer than Stainless, so where there is a chance that the SS cable or other metals may cut the pipe, consider SS. Bronze is more durable than SS -IN THIS APPLICATION-. This is demonstrated by the relative condition of the Bronze and SS fittings. So; Use bronze where you can, and SS where you have to. Keep it as simple as possible. Complication and redesign have an inverse relationship to likelyhood thst you will sail your boat this year.
Propeller shafts are somewhat protected
Propeller shafts are somewhat protected by the zinc anode and oddly enough the bronze propeller. Also shafts are commonly made from a better grade of stainless that is tougher then the common 300 series of stainless steel with a better surface finish then the common machining in most stainless parts. The surface roughness of stainless is a factor in crevice corrosion, the name for corrosion from oxygen depredation and polished surfaces don’t have as much of a problem as machined surfaces. But shafts are made from a type of stainless that isn’t suitable for making bolts or other parts. As a general rule it’s safe to say most types of stainless are not used underwater because of the crevice corrosion problem. All the best, Robert Gainer
Propeller shafts are somewhat protected by the zinc anode and oddly enough the bronze propeller. Also shafts are commonly made from a better grade of stainless that is tougher then the common 300 series of stainless steel with a better surface finish then the common machining in most stainless parts. The surface roughness of stainless is a factor in crevice corrosion, the name for corrosion from oxygen depredation and polished surfaces don’t have as much of a problem as machined surfaces. But shafts are made from a type of stainless that isn’t suitable for making bolts or other parts. As a general rule it’s safe to say most types of stainless are not used underwater because of the crevice corrosion problem. All the best, Robert Gainer
Fred,
Fred, I think he asked, "What is the best metal to use on a part of the boat that was going to be under salt water at all times" And that got things started. As far as the centerboard pennent goes I may have my priorities wrong but because the wire is made from a collection of small strands having some wear in the wire will cause a problem faster then some wear in the pipe. So I would use bronze for the pipe and preserve the wire. Also wrapping the pipe is a fast and easy way to control a small leak if you do wear the pipe but jamming or breaking the centerboard pennant is a greater problem and harder to deal with at sea, at least in my opinion. All the best, Robert Gainer
Fred, I think he asked, "What is the best metal to use on a part of the boat that was going to be under salt water at all times" And that got things started. As far as the centerboard pennent goes I may have my priorities wrong but because the wire is made from a collection of small strands having some wear in the wire will cause a problem faster then some wear in the pipe. So I would use bronze for the pipe and preserve the wire. Also wrapping the pipe is a fast and easy way to control a small leak if you do wear the pipe but jamming or breaking the centerboard pennant is a greater problem and harder to deal with at sea, at least in my opinion. All the best, Robert Gainer
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