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Old 01-09-2008, 18:29   #1
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Chainplates

I need to replace my port chainplate. It is 2" x 3/8" x 23" aluminum. I cannot find a replacement so I am going to have some made. Does anyone else need custom chainplates? It will be 6061 T651 aluminum alloy, min 42,000 psi tensile strength and a yield strength of 35,000 psi. I know it is overengineered. They used this alloy in the Pioneer space craft. so I think it will be OK for a sailboat. Let me know.
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Old 02-09-2008, 09:08   #2
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Contact JSI, The Sailing Source . They made matching replacement chainplates for us that were very inexpensive and a perfect match. Further, I don't believe aluminum would make a very satisfactory chainplate as it generally doesn't have particularly good compressive strength compared with Stainless and pin loads, even on relatively small rigs, can be substantial.

FWIW...

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Old 02-09-2008, 09:29   #3
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We have aluminum chainplates but I will probably change them out one day with SS. Rig by Offshore Spars and work completed by Palmer Johnson.
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Old 02-09-2008, 15:01   #4
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Originally Posted by svHyLyte View Post
I don't believe aluminum would make a very satisfactory chainplate as it generally doesn't have particularly good compressive strength compared with Stainless and pin loads, even on relatively small rigs, can be substantial.

FWIW...

s/v HyLyte
316 stainless and 6061 T6511 aluminum both have the same yield strength of 40,000 psi and the aluminum weighs 1/3 of what 316 weighs. The aluminum also costs 1/5 of what the stainless costs. I am going to have 4 6061 T6511 aluminum chainplates made for less than cost of 1 316 stainless chainplate. I was just trying to help the community.
I misquoted the yield strength in the thread starter. 35,000 psi was shear strength.
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Old 02-09-2008, 17:38   #5
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I'm with svHyLyte on this. Aluminium, including 6061 of whatever temper, is a poor and not recommended choice for chainplates due to the potential for corrosion where bedded to the hull and also wear/compression at the clevis pin.

This potential corrosion issue does not, of course, exist where the chainplate is part of the structure of a vessel constructed of aluminium but even then for any half decent job the chainplate will be bushed with stainless steel bushes for the clevis pins for the reasons svHyLyte states.

This only mentioned in case it is of interest to any who were considering taking up Easterly's offer.
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Old 02-09-2008, 18:36   #6
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Stainless steel is preferrable over aluminum. Yeild strength is different from hardness, and aluminum is definately a softer metal. Try scratching a piece of aluminum, and then try scratching a piece of stainless steel - the stainless is difficult to scratch. Now think of the pressure the clevis pin puts on the top of the hole in the chainplate....the aluminum hole will elongate much faster than the stainless one will. Aluminum and stainless steel next to each (stainless steel clevis pin through an aluminum chain plate) other will start to corrode due to the different metals in contact with each other - just like a stainless stee screw in a mast.
Just think about it....if aluminum were a better choice AND CHEAPER than stainless steel, wouldn't all sailboat manufacturers be using aluminum.
Stainless steel is the way to go.
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Old 02-09-2008, 20:33   #7
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I agree, I prefer a SS chainplate, but think about it guys what are the tangs on your mast made out of?

Just make sure on SS chainplates that used 6mm and then doubled it up where the pin goes through that there is no horrizontal weld done UNDER the pin.

This makes a weak point

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Old 02-09-2008, 21:08   #8
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I know there are plenty of boats out there that have aluminum chainplates. I agree with some posters that SS is harder but it also fails differently than aluminum. If both yield at 35,000 psi whats the diff? Aluminum will stretch, SS will break. Aluminum does corrode faster but I can carry spares and replace them more often for less money. Here are some pics of one of my chainplates, unknown age, that if they were SS would have failed. Notice no elongation.
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Old 02-09-2008, 21:23   #9
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Just think about it....if aluminum were a better choice AND CHEAPER than stainless steel, wouldn't all sailboat manufacturers be using aluminum.
Brian Stetler
Just a guess here but Schaffer is the only company making (mass producing) chainplates. They are all made of SS. Kind of like Lewmar, the only company making winches. Once you corner the market.........
I do know of talk about composite chainplates, what's next hybrid boats??
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Old 03-09-2008, 07:32   #10
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Different ships, different Long Splices.

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Old 03-09-2008, 08:05   #11
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Aluminum is much more susceptible to fatigue from loading and from vibration. I would go with stainless if I had the option.
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Old 03-09-2008, 14:02   #12
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6061 is not "space age". It is common Home Depot aluminum. It contains copper which can cause internal corrosion in a marine environment The 5000 series, specifically 5052, 5083 and 5086 use magnesium as a hardening alloy which is closer to the base aluminum on the galvanic scale and normally used in marine aplications. If you have to stay with aluminum have them cut from 5083 plate. 316 Stainless is still far more preferable unless weight is a critical factor.
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Old 03-09-2008, 15:25   #13
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6061 is not "space age". It is common Home Depot aluminum. It contains copper which can cause internal corrosion in a marine environment The 5000 series, specifically 5052, 5083 and 5086 use magnesium as a hardening alloy which is closer to the base aluminum on the galvanic scale and normally used in marine aplications. If you have to stay with aluminum have them cut from 5083 plate. 316 Stainless is still far more preferable unless weight is a critical factor.
Just so you know there are several different grades of 6061. There is plain 6061, 6061 T4, 6061 T6, 6061 T651, and 6061 T6511. The T6511 is used in areospace and it was used in the pioneer space craft. So I would say that makes it space age.

The 50 series aluminum alloys are much weaker than the 60 series and do have some copper in them.
6061 T6511 is some of the most corrosion resistant aluminum.

The only reason they are not using it to make chain plates is there is no profit in it. If Schaffer sells you a 316 chain plate for $100+ and it costs them $50 to make, you have some profit. If it costs you $5 to make one from 6061 T6511 and you can sell it for $10, same profit margin, where's the money. Please read below and notice the marine uses.

APPLICATIONS

6061 is commonly used for structural components, screw machine parts, frames, brackets, jigs, fixtures, base plates, machine parts, couplings, hydraulic valve bodies, valves and valves parts, fuse parts, gears and shafts, worm gears, pistons, rectifier parts, fasteners, hardware, truck and marine components, marine fittings and hardware, electrical fittings and connectors, hinge pins, magneto parts, brake pistons, hydraulic pistons, appliance fittings, camera lens mounts, bike frames, etc. 6061 is used for heavy duty structures requiring good strength-to-weight ratio with good corrosion resistance. 6061 is easily cold worked and formed in the annealed condition. Cutting, stamping, bending, spinning, deep drawing, drilling, tapping, etc. are all readily accomplished using standard methods
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Old 03-09-2008, 15:44   #14
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Copper, for example, is used on spacecraft too but I suspect any sensible person would ridicule any claim it was a "space age" material as your definition of that would make it. In fact, copper and its alloys are among the oldest metals used by mankind.

Your understanding of the design issues seems to be very shallow and you make some unusual assumptions as to the business reasons why ss is used instead of aluminium - that's ok, you've made your own decision as to what material you are going to use for yourself long ago. My only interest in this is that the people you have invited to follow your example consider the good information provided by others before doing so and if still in doubt get some further professional advice.
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Old 03-09-2008, 15:57   #15
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Copper, for example, is used on spacecraft too but I suspect any sensible person would ridicule any claim it was a "space age" material as your definition of that would make it. In fact, copper and its alloys are among the oldest metals used by mankind.

Your understanding of the design issues seems to be very shallow and you make some unusual assumptions as to the business reasons why ss is used instead of aluminium - that's ok, you've made your own decision as to what material you are going to use for yourself long ago. My only interest in this is that the people you have invited to follow your example consider the good information provided by others before doing so and if still in doubt get some further professional advice.
Time out. My understanding of design issues are not shallow. It seems that most on this board have a single idea and won't accept anything else. The builder of my boat used aluminum, he was a racer, his son is the boatwright for the US olympic team. If you don't think T6511 is aerospace/spaceage why don't you come up here and visit a small local company, Boeing. I'd be happy to set up a tour.
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