Does anyone know what spec aluminium should be used for a spinni pole and boom?

I'm specifically looking for the 60xx number for Nacra F18 spinni pole, and a Spitfire spinni pole & boom (appears to be the same tube is used for both, certainly in diameter and thickness).

I've identified a supplier of 6082T6, 16swg, 1.5" OD, anodised. Another has mentioned 6063T6. Should I give a damn?

This is for myself and a few mates with a mix of boats as above, who are finding breakages expensive!

Thanks, Simon

The normal alloy for this application is 6061 or 6063 T6. The 2 alloys you mentioned are about 80% as strong.

If I am looking for aluminum, my 1st choice is 7075 T6 or T651 with 6061 T6 2nd.

7075 is about 1.5 times as strong as 6061 but it is normally hard to find, is not available in all sizes and expensive. I have stumbled across some deals at surplus yards.

For any al tube you should treat the inside with a long life corrosion protection. Like Boeing Boeshield T-9 or CRC Heavy Duty Corrosion inhibitor. These look like a wax when dry. One reason highly stressed metal tubes fail so quickly in salt water is corrosion in micro surface cracks. Keep it clean.


There is a difference between suppliers and there are many grades of al tubing. Each alloy has an allowable range and the range is pretty big. The more expensive tubing has tight quality controls and is tested.

The best tubing is name brand like Reynolds. For strength it will test out at the top or even above the allowable range

Next is mill spec. Tubing sold for spinnaker poles is normally mil spec and will test out in the top 80% of the allowable range for the alloy.

Below mil spec is a big group of quality tubing. This is normally sold in big lots to manufacturers. Most dealers will just look at you blankly when you ask about it. There are a few dealers you deal with hobbyists that can help.

At the bottom is cheap generic tubing. It is probably the alloy listed and strength can be anywhere in the allowable range

If you can, I would use carbon. It is a lot more durable

Simon

From those specs I would guess you are based in the UK, I'm going to respectfuly disagree with Carl, I beleive the normal alloy for this application in the UK is 6082-T6. Most reputable manufacturers use 6082-T6 for masts, booms, beams etc.

6082-T6 is superior to 6063-T6 in terms of strength, but most grades are similar in terms of stiffness.

Check if the anodising is on inside and outside of tube, if only on the outside you may want to follow Carls advice.

If you want more info on the different materials mentioned try using http://www.matweb.com

All that said, 6063-T6 is probably cheaper, so if your components are breaking in compression then you may not see any real difference in terms of strength.

You pay your money you take your choice.

All the best

Gareth
www.fourhulls.com

Carl, Gareth, Thanks for your feedback. This forum never ceases to amaze me in terms of the expertise that's available out there. Yep, I am based in the UK (Cheshire, sail at the Dee SC).

I realize I didn't answer your question.

6061,6063,6082 will all work. Your pole is probably 6063 T6 since that is what Forespar and some others makes their poles out of.

Don't buy cheap al tubing. Buy from a marine distributor or an established metal distributor and be sure to tell them what you are planning to do with it.

If you are doing this because you just don't want to pay NACRA prices, 6063 is a good choice.

If you are doing this because your pole is not strong enough Try 6082,6061 or even 7075.

Try to look at a pole right after it breaks. If there are cracks with white powder near the break, I would definitely treat the inside of the pole to prevent corrosion. The surface and the anodize is cracking allowing salt to corrode the al. It would have probably broken without the corrosion but the corrosion makes it break faster

If the poles always break at the same place, try splicing the pole. Use a 2 ft tube whose OD is the same as your poles ID but twice the wall thickness of the pole. If the pole breaks again somewhere else, it was cheap.

Why not a used carbon fiber windsurf mast for both applications? They work well for both (but aren't class legal).

Chris.

Ditto for 2024 which is much easier to find. The trouble with these 'higher' alloys of aluminum is that they corrode like mad; terrible fatal intergrannular corrosion with the slightest provocation. This is espeially true of 7075. That's why you don't see them used in marine extrusions very often. Anodizing would be absolutely mandatory; paint would just not cut it. I've seen 7075-T6 go from uncorroded bare clean metal to intergrannular (trashed) in a month by sitting outside in weather. And not on the beach, mind you but at an inland airport! We had to instruct our paint crew to carry a spray can of green primer to 'touch-up' any bare spots at the end of each work day in case the job got held up so as not to create a bunch of skin repairs! What a nightmare!

Also these alloys are not weldable, if that matters to you. 6061 happens to be the strongest weldable alloy. Also 6061 has a much better fatigue life than either 2024 or 7075. There's a reason the marine industry uses what they use. If you want stronger/lighter, go with carbon. Since 7075 is used almost exclusively by the aircraft industry, it costs about like a carbon pole anyway, unless you just happen to find the right size in a surplus store or scrap bin.


IMHO

Jimbo

Hi all,

Chris you beat me to it.

My friends and I use Sailboard Masts almost exclusivly in both Carbon and Alloy, they have proven to be more than up to the job for booms and poles. The tapers allow you to reduce weight and windage at the outer ends where the stiffness is not needed.

Second hand one piece Sailboard Masts are very cheap in OZ, of course you have to look closely at what you are buying but misuse is generaly easy to see. The Alloy masts are getting harder to find, but if you can find Serfiac a european brand which I believe where very popular in UK as well as OZ they are excellent, anodised models are very resistant to corosion. The carbon mast vary alot in stiffness and strength racing mast are stiffer, wave masts are stronger.

Regards Gary.