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Old 02-05-2015, 08:30   #1
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6061-T6 Aluminium vs 316 grade Stainless Steel

Question for any metal techs out there

I'm building a Scarab Trimaran.
Working on the rudder atm, and it requires a SS Tube, 33,8mm OD, 6,35mm wall.
As a privat person, I cant get these dimensions in the length I need (I need like 1200mm, minimum amount I can buy is 6meters, which would be a bit costly)
Question now is, does a full 6061-T6 aluminium bar with dia 35mm be a good replacement for the SS bar?

Thanks

G
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Old 02-05-2015, 08:39   #2
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Re: 6061-T6 Aluminium vs 316 grade Stainless Steel

You can look up the properties of the materials in question @ www.matweb.com And if you do, you might notice that Aluminum is a LOT weaker than Stainless Steel. So odds are, it'd be a BAD idea.
Also, bare aluminum wont have anywhere near the corrosion resistance of stainless steel.

Talk to your designer for possible materials substitutions on critical items like that (and most other things, too). Plus, he may have POC's for suppliers that can get you more reasonably sized pieces of the spec'd material.

Also, on items like this, you can look for off cuts, & or talk to machine shops, boat fabrication shops & such. Odds are they'll have some, without you paying for a full sized piece.
Try NON-Marine fabrication & metal shops first, as the prices will be a Lot lower, & don't mention the words; marine, boat, etc. either, or the price will jump.
Plus, it's things like these which is part of the reason that folks form builders groups & such. So that you can do "bulk buys", & get decent rates on materials.
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Old 02-05-2015, 08:48   #3
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Re: 6061-T6 Aluminium vs 316 grade Stainless Steel

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Originally Posted by UNCIVILIZED View Post
You can look up the properties of the materials in question @ www.matweb.com But I wouldn't swap straight across on critical items like that until consulting your designer.

Also, on items like this, you can look for off cuts, & or talk to machine shops, boat fabrication shops & such. Odds are they'll have some, without you paying for a full sized piece.
Try NON-Marine fabrication & metal shops first, as the prices will be a Lot lower, & don't mention the words; marine, boat, etc. either, or the price will jump.
Thanks for the answer.
Prob is I'm in Europe. I checked around my country and all neighbouring countries, only found 1 supplier and he only delivers to companies.. And he doesnt even have it in stock (thats the supplier that could provide me with the 6m through another company)
It would cost me like 500 euro's for the pipe incl shipping, which I find a bit too much...
The 6,35mm wall is the odd one out. 2,5mm wall is the max size I can get all over.
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Old 02-05-2015, 09:19   #4
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Re: 6061-T6 Aluminium vs 316 grade Stainless Steel

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Originally Posted by ForSeTi View Post
Thanks for the answer.
Prob is I'm in Europe. I checked around my country and all neighbouring countries, only found 1 supplier and he only delivers to companies.. And he doesnt even have it in stock (thats the supplier that could provide me with the 6m through another company)
It would cost me like 500 euro's for the pipe incl shipping, which I find a bit too much...
The 6,35mm wall is the odd one out. 2,5mm wall is the max size I can get all over.
Do a search for the specific tubing section which you need. Start with Matweb, then Google, your designer, & the hundreds of other sources/manufacturers of that sized tubing, as there's NO WAY that only 1 metal supplier stocks that size in all of Europe. That & there have to be literally HUNDREDS of manufacturers IN Europe who make pipe in that size, it's not as if such is all imported for the entire EU demand. Otherwise, ONE glitch in the manufacturering or supply chain of it would shut down hundreds of companies, across the continent.

AKA common sense does apply here.
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Old 02-05-2015, 09:39   #5
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Re: 6061-T6 Aluminium vs 316 grade Stainless Steel

Follow this link

McMaster-Carr

to an English-dimension product with dimensions that approximate your described need. Should work. 316 SS...262 USD plus shipping and any UK fees you will need to pay.

They have great customer service and a phone call should answer any questions re shipping.

I am not affiliated but use them regularly...eg, I ordered a 2ft x 2 ft plate of quarter inch aluminum night before last and and it arrived at 1500 yesterday afternoon with standard shipping (UPS).
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Old 02-05-2015, 09:47   #6
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Re: 6061-T6 Aluminium vs 316 grade Stainless Steel

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Originally Posted by fryewe View Post
Follow this link

McMaster-Carr

to an English-dimension product with dimensions that approximate your described need. Should work. 316 SS...262 USD plus shipping and any UK fees you will need to pay.

They have great customer service and a phone call should answer any questions re shipping.

I am not affiliated but use them regularly...eg, I ordered a 2ft x 2 ft plate of quarter inch aluminum night before last and and it arrived at 1500 yesterday afternoon with standard shipping (UPS).
Thanks
I'll check
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Old 02-05-2015, 09:49   #7
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Re: 6061-T6 Aluminium vs 316 grade Stainless Steel

Aluminum is not a good choice for this application.


I don't like the hollow stainless tube route either, you're only saving about 8 lbs compared to solid bar.


The first place I clicked on in a search had sizes close to your requirements for less than 200.00 for a 4' section, and they ship worldwide...


https://www.onlinemetals.com/merchan...=902&top_cat=1


https://www.onlinemetals.com/merchan...id=7&top_cat=1
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Old 02-05-2015, 09:55   #8
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Re: 6061-T6 Aluminium vs 316 grade Stainless Steel

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Aluminum is not a good choice for this application.


I don't like the hollow stainless tube route either, you're only saving about 8 lbs compared to solid bar.


The first place I clicked on in a search had sizes close to your requirements for less than 200.00 for a 4' section, and they ship worldwide...


https://www.onlinemetals.com/merchan...=902&top_cat=1


https://www.onlinemetals.com/merchan...id=7&top_cat=1
So your saying if I use a solid bar with the same OD the diff would only be like 8 lbs?
And U would choose the bar over the tube?
Cause the solid bar I can get in 35mm OD no problem.

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Old 02-05-2015, 09:56   #9
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Re: 6061-T6 Aluminium vs 316 grade Stainless Steel

And by the way , I have a 26" piece of Vesconite rudder bearing stock material, raw dimension of 65mm od x 35mm id, left over from when I installed my rudder. Don't remember the cost but if you're interested I can find out and could send you 10" or so (enough for 2 bearings).


Just saw your post. yes and yes.
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Old 02-05-2015, 10:12   #10
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Re: 6061-T6 Aluminium vs 316 grade Stainless Steel

There's a (perhaps) critical question to be asked about substituting solid bar for the tubing. Was tubing specified (instead of bar stock) for an engineering reason that we don't know about?

Like, for instance, does the tubing have a bending moment, which in a collision, will let it bend, where as solid bar stock, given it's increased strength & stiffness, will cause some other critical item to fail?
Say, for example, if both were used as rudder stocks, protruding through a hull laminated.

Such entirely may not be the case, but on some things, unless common sense easily rules them out, it's worth a designer consult on the question. That, or if one has the inherent knowledge to make that kind of call, then no worries.
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Old 02-05-2015, 11:04   #11
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Re: 6061-T6 Aluminium vs 316 grade Stainless Steel

Perhaps a kinder way of me replying would be to inquire as to what application is this tubing/bar stock for, & are there any other spec's other than metal type, & wall thickness? As even within a metal type, there can be a lot of variables. Principally, it's yield & tensile strengths. Although if you consult Matweb, you'll see several others when you look up various materials. And as can be seen, they can vary hugely, as in by several X for one material, thus some of my comments about asking the designer more questions.

The more which you know more about both materials, as well as design, the better you'll understand you (and all) boats. In addition to working better with your designer, as you'll both be speaking the same "language". And one of you wont be dumbing down, as the other struggles to keep up.
It'll make it a lot easier for the 2 of you to make joint decisions, & for you to build things, down the road.

There are several books available which make it easy for a layman to get up to speed on such things, & that are handy to have around regardless of one's experience level/background.
And if you're keen on the idea, even a few basic classes in the area would help.
- Although you might have to speak to the university as to why you want to slot directly into say a Naval Architecture class, skipping several other things first. As well as showing them that you'll be able to keep up in such classes. Perhaps by taking a few validation exams, showing previous transcripts covering the basic prerequisites for that class or similar ones...

PS: If you do consult with your designer, you might check to see what other (if any) alloys might be viable - 304/306, etc. And what the pro's & con's of using each would be.
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Old 02-05-2015, 11:11   #12
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Re: 6061-T6 Aluminium vs 316 grade Stainless Steel

No one can get the length you need, metals come in stock sizes just like lumber. You need 26" of 2x4? You still have to buy an eight foot stick of it, and have it cut down. Doesn't matter who you are, you're buying the whole stick.


Whether you go to a metal yard, where they may charge you for the whole tube, or you use an online supplier who will cut to order but still surcharge you.


I would try the online suppliers like onlinemetals.com and if shipping that size to your location creates problems, ask them if they know any similar business closer to your corner of the world.


Sometimes if you have a metal yard located within an hour's drive, it can pay to ask them if they have a bent piece or other "scrap" that you can get a big enough good section from. Or a local welder or ironworker may have short cuts of the material in their shop, that they are willing to sell. Stainless is usually not stocked unless they work on marine parts or, more commonly, in the food service or hospital industry, where almost all the materials in a kitchen or surgical area may be made of stainless, and custom made to fit, by a local welding shop that specializes in that.
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Old 02-05-2015, 11:18   #13
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Re: 6061-T6 Aluminium vs 316 grade Stainless Steel

With a rudder stock the yield strength is what is important. A bend will jam the rudder.

The yield strength of 6061 is very similar to 316. Strength goes up significantly with the diameter. Get someone to do the proper calculations, but the yield strength of a solid 38mm section should be significantly higher than 35 x 6.3mm SS. The UTS is probably a little lower, but this is not much of a factor for a rudder stock.

6061 is often used for rudder stocks, but the corrosion resistance of 6061 is less than the aluminium 5 series or 316 so it is only an acceptable rather than ideal application, especially without any anode protection. One option is to consider anodising, which is not difficult or costly.

I would take this advice as very general only. Talk to the designer or at least an engineer before making the change.
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Old 02-05-2015, 11:31   #14
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Re: 6061-T6 Aluminium vs 316 grade Stainless Steel

Checking with the designer seems easy and is a very good idea, for the reasons stated above.

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Old 02-05-2015, 11:47   #15
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Re: 6061-T6 Aluminium vs 316 grade Stainless Steel

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With a rudder stock the yield strength is what is important. A bend will jam the rudder.

The yield strength of 6061 is very similar to 316. Strength goes up significantly with the diameter. Get someone to do the proper calculations, but the yield strength of a solid 38mm section should be significantly higher than 35 x 6.3mm SS. The UTS is probably a little lower, but this is not much of a factor for a rudder stock.

6061 is often used for rudder stocks, but the corrosion resistance of 6061 is less than the aluminium 5 series or 316 so it is only an acceptable rather than ideal application, especially without any anode protection. One option is to consider anodising, which is not difficult or costly.

I would take this advice as very general only. Talk to the designer or at least an engineer before making the change.
Typically, Stiffness, the sited (and, yes, Big) factor in a rudder stock, increases as a cubed factor of the thickness of a material.

As to the lifespan of anodization, on a bearing surface under almost continual high loads, while immersed. IMO, it's lifespan would be about on par with that of virginity on Prom night.
No offense intended to the suggesting party, for their recommendation of said metal treatment.
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