6061-T6 vs. 6063-T6 aluminum

[Seattle Scott]

Specs for my boat call for a 17 ft spinnaker pole. Off the shelf this is at least $1,500.So I build up plastic pipe with epoxy and kevlar cloth for about $150 (and 15 hours)and now have a pole that weights a ton (see pic). So then I price aluminum tubing through Forespar and they have 6063-T6 aluminum tubing "clear anodized to military specs, triple commercial" for about $550.00 for a 15 ft length (3.5 inch diameter). I find a local supplier (see link)they have 6061-T6 aluminum and can cut to my length (16.5 ft) for about $115. The local supplier says 6061 is "harder" than 6063 but not as bright or good looking as 6063. I'm thinking if I don't like the looks I can paint. Per ft they weigh the same.But does anyone know if 6061 is as suitable or better than 6063 for spinnaker pole use? Is one "stronger" or which one is going to snap first?

 

[Glenn]

6061 vs 6063

Heat Treatable (Strong) Alloys6061-T4 or T6 - High strength allow provides good formability, weldability, and corrosion resistance. May be difficult to perforate or bend.6063-T6 - Highly corrosion resistant with good formability. Softer than 6061-T6 and easier to bend. Finish is pleasing and is the most suitable for anodizing

 

[Commanderpete]

6061 Is Fine

I have some technical drawings that show Pearson used 6061-T6 aluminum for the mast and boom on the Triton, Ensign, Ariel, Commander, Alberg 35 etc. (and probably later boats). No doubt its strong enough.However, it doesn't look like the aluminum on that website is anodized for corrosion protection.The trick is going to be finding anodized aluminum in that length from a local supplier so you can avoid shipping charges. I'm thinking of making my own pole also. I'll probably try calling local fabricators to see if they can get the material for me.I'd be interested in what you find out.Peter

 

[Seattle Scott]

So what is anodized?

Isn't aluminum pretty non-corosive, in that it always has thin layer of oxidation that retards the whole process. Is paint a fair substitute for anodizing?

 

[Alan]

Nope!

Anodizing puts a hard protective coating on the aluminum to help prevent oxidation. Paint will help, but anodizing does a better job of adhering and protecting than paint.

 

[patrick]

Aluminum is subject to corrosion

Especially when scratched. Anodizing and alodining treatments will make it a lot harder to scratch. It will etch easily with caustic.Check out this link for some interesting info.http://www.focuser.com/atm/anodize/anodize.html

 

[Chuck Bussey]

My Opinion

I make my living by Blacksmithing. My knowledge of metalurgy is based on experience and research that I do for projects. I almost did'nt answer this post because of the mis-information already present in postings; there is not a complete explination for any of the facts and other information appears to be copied from commercial descriptions. Let me clear up some mis-conceptions.Aluminium corrodes like most metals. This corrosion or oxide is clear and very hard as in aluminium oxide (a common abrasive used in sandpaper). Anodizing it is used mainly for color but can be used to build up the thickness of the oxide for the purpose of protection. When aluminium "pits" it is usually due to the presence of a different metal attached directly to the metal and the cause is galvanic. Chemically the metals are reacting with each other and the result is the softer metal looses.The bottom line on oxidation is that if you want to paint it go for it but not completely necessary for the protection of the metal. It is very corrosion resistant anyway. Be careful of what hardware you use for the fittings (galvanic corrosion).The T-6 only refers the hardness. (T-6 is the hardest) Regardless of the descriptions for 6063 or 6061 as to drilling etc. You will have no problems. Regarding heat treating, big deal. It is such a pain in the ass to harden aluminium anyway and the stock you mentioned is already hardened. This just means that it will not bend easily (this is desireable for this application). Be careful about any heat (if I remember correctly >400c) because this will damage the hardness.I would be more concerned with the wall thickness as being enough for the stress loads. Bottom line... 6061 T-6 is used for airplane building, cheaper as you found it and perfect for this application.I hopes this clears this up for you.Just my $.02 worth,Chuck

 

[robert taylor]

material certifications

get both suppliers to provide the material certs for their product....if the yield strength is similar, go with the cheaper one. wall thickness and moment of inertia are the important factors to consider for bending resistance. for thin wall tubing, the moment of inertia is appoximated by the formula (pi x diameter cubed x wall thickness divided by 4). the point is a larger diameter with a thinner wall is stronger. i agree with the posters that favor 6061. you may also check around for a damaged boat with a boom you could use.

 

[Tim C350 April IV]

Scott in Seattle

Scott - I notice you are in Seattle - you might take a look down at Boeing Surplus in Kent for an appropriate (or usable) piece of tubing to play with. They have an amazing array of *stuff* there. Open Tues-Sat.Tim BroganApril IV C350 #68Seattle

 

[patrick]

If you go to Boeing Surplus,

you might want to consider titanium as an alternative to aluminum. If you are buying it by the pound, it is probably a better choice. You can improve the strength of whatever material you choose by filling it with urethane foam. It also will make it float.You might also check eBay. I am going to list a few boat items soon including a couple of poles. Last but not least, plan to attend the Fisheries swap meet (in April or May?). Get there in the wee hours of the morning (2 AM +/-) and you will find a place to park and a more than a few bargains.

 

[Seattle Scott]

Thanks All

Obviously my pole project will not be enginered, so I am just following along with Forespar does. I forget where their length break is as to when you go from a 3.5" OD tube to a 4" inch tube, but for 16.5' pole they use 3.5" tubing Forespar's 3.5" OD stock has a wall thickness of .120". The local supplier for 3.5" tubing has .125" wall thickness, so I'm OK if I go with the local 6061 for about a 75% savings. Since Chuck says corrosion not a big issue, I'll probably go with the local 6061, and paint just for sake of keeping up with the Jones. I'm parked next to a Swan. Like the foam idea. The pole ends I'll swap out from the "prototype" ie, heavy as sin pole, are Forespar's plastic (there is a fancy name with composit in it) ones, so no memtal to metal contact with these. But I will need to bolt/screw the ends on and will try to isolate the SS bolts/screws from the aluminum. I live 10 blocks from Fisheries Supply in Seattle, so thanks for the swap meet heads up.

 

[Don Radcliffe]

Been there, broke mast

Just a word of advice on going up in pole diameter... when **it happens, something has got to give, and a $115 pole section is a whole lot cheaper than your mast.

 

[Alan]

6061 T-6

What a great discussion! I'm in the process of building a retractable sprit pole for my Akite out of 3.5" 6061 T-6 with 1/4" wall thickness that will be unsupported at the outboard end. Originally I was concerned about the amount of load this pole could carry for a 6' sprit with 1400sqft a sail on it. But after talking to a structural engineer and Hal Spars I think this thing will be more than strong enough. I'd love it if this project turns out to be a J105 killer.

 

[Ed]

dia. issues

Dont forget to concider the od of the fittings and the id of the pole. you need to be careful to get a compaible size or you will have to machine the inside of the pole! Thats what i had to do, not brite enought to check the fittings first! I used a stop sign post for a few years. worked good but heavy.have fun

 

[Alan]

Ed

Thanks for the heads up. What did you use? How big was the pole and what did you finally go to? Not sure I understand about 'the fittings'??

 

[ed]

fitting size

I did this almost 20 years ago so im a long way from remembering the sizes. the problem i had was that the forespar end fittings for the spinaker pole would not fit into the alum pipe i selected. fortuatly i had access to a machine shop, they thinned the wall of the pipe from the inside so the end fittings would fit a standard size pipe. So im saying before you buy the pipe check the diameter of the fittings you want to put into it. and select pipe accordingly

 

[Alan]

OK Ed,

I understand. Pipe is measured in ID while tubing is measured in OD. I'm using a 3.5" pipe so the ID is 3.5 and the OD is 4" with a 1/4 " wall. Being that this is a sprit pole, the only thing going on the outboard end is a block attached to the surface of the pole to carry the adjustable tack line.

 

[Bob B.]

Tube/Pipe Sizing (edited twice)

Hello to Scott & contributors:I realize that your project is well in hand so this information is for others who might be contemplating pipe or tube projects. I worked in a chemical plant for 30 years so couldn't help but learn something about pipe. Pipe (SS, Al,& other) is manufactured in "Nominal" ID pipe sizes. The actual dimensions may not be that close to the nominal size. All pipe in one size has the same OD but of course depending on the wall thickness has many different IDs. The wall thickness is designated by the pipe Schedule & can be from Sch 5 to Sch 160 & even the heavier XX Strong.Schedule 40 is regarded as "standard pipe". This changes for sizes over 12". As pointed out already, tube size is the actual OD dimension. Tubes can be telescoped. Tube wall thickness is different than pipe wall thickness & must be specified.Scott. In your reply #10, the two Aluminum stock examples:1. Forespar's 3.5" OD stock with a wall thickness of .120". (This is 3" Schedule 10 pipe). .226" thickness would be Schedule 40. 2. The local supplier's 3.5" tube with a wall thickness of .125". (This is 3.5" tube). Available in other thickness'You need the pipe/tube sizing charts to recognize the difference. Do a "Google" on pipe sizes.Regards, Bob B.