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Old 07-04-2010, 18:38   #1
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Aluminum Stanchions ?

Hi Group,

As many may recall I am fortunate enough to have a complete CNC home shop. Mainly I like working with the soft metals, i.e. aluminum...bronze etc.. As I build out my Ingrid 38 I am facing the question of aluminum or stainless stanchions. I like the idea of aluminum as I can adjust each stanchion so that the stanchion post is straight and has been adjusted for the camber of the deck. I also like the idea of aluminum as it reduces the the boats general galvanic signature by keeping a similiarity of metals (mast and lifelines).

The group as a whole is far more versed in this matter than am I and I'd truly like to hear your thoughts about the viability of this method of constructing lifelines.

I have already designed the cutting program for my opening portlights and decklights, which are also planed to be cut from 6061 T-6 aluminum.

Your comments and sugggestions would be greatly appreciated.

Glen
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Old 07-04-2010, 18:58   #2
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I would worry about the ductility of aluminum to take the abuse that is placed on the standard lifeline. Now if you're talking stanchions and bases of one solid piece........I like it!!!!
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Old 07-04-2010, 19:18   #3
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Sailmonkey,

Actually, I was thinking of aluminum tubing with a near .25 wall. It specs out better than the standard thinner wall stainless. The bases would be cut individually so that each stanchion stands tall. I will likely go with welded horizontal tubing vice stainless cable lifelines. If I do not weld to the stanchions I will do a butress join where the tubing can be bolted to the stanchion. However, the bow and stearn will be welded tubing.

Glen
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Old 07-04-2010, 20:12   #4
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I have never seen aluminum stanchions and it does make me wonder why. A couple of potential reasons might be cost, lifeline material, ductility, repeated cycling. Aluminum tends to cost more although it does machine much easier. In addition, the lifelines themselves are made of stainless and since they are not fixed at each stanchion, you will have rubbing between the two metals. Having steel and aluminum rub together will wear away the aluminum extremely quickly so you couldn't run bare steel lifelines. You could definitely deal with the ductility and strength issues with aluminum by changing wall thickness. However, aluminum has issues with fatigue. I don't really have that good of an idea of what the cyclic loading on stanchions is but maybe there are enough cycles with enough stress to have fatigue? If you use any weld joints, fatigue would definitely be a concern. This is the reason that aluminum trailers are very rare since the welds constantly crack (I know, I tow one a lot and spend a lot of time with the welder).

You are very lucky to have CNC machines at home.
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Old 07-04-2010, 20:27   #5
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If I were in your position I would find it attractive too. However, I'd say pick up a tig welder and learn to polish stainless. You'll increase your earning potential as well as being able to DIY.

Aside from the other things already posted, cosmetically it just takes more work to keep it looking nice and it does not start out with the luster of polished stainless.

I walked the docks looking for aluminum on boats. Found very little and what I did find (I'm talking non painted, non anodized) just couldn't hold a candle to the polished stainless. The welds turn dark gray and the pitting was heartbreaking. It's just not the optimum material for the job IMHO.
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Old 07-04-2010, 20:30   #6
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I believe mine are cast but they're alloy, not straight aluminum which would be much too easily bent etc. There are plenty of alloys with a lot of strength, that are not ductile to anything like the extent that the native metal is.
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Old 07-04-2010, 20:58   #7
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Aluminum is fine for stanchions, in my opinion, you'll want to make them somewhat larger diameter to compensate for the lower. A calculation or test will be needed. S/S stanchions are not all that strong, a strong person can bend one past it's yield point by hand...

Aluminum has a special beauty that the french seem to admire....
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Old 07-04-2010, 20:58   #8
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Guy's,

Thanks for the great responses. I also have a MIG and TIG system, but chose not to be a welder other than for my own use. I've built several tube and fabric airplanes and honed my gas skills there.

6061 T-6 aluminum is a alloy that is widely used in aircraft production. I have a really big garage, and not only have all CNC equipment but my own powder coating facilities as well. Mostly I turn out metal art, weather vanes etc..

The cost of 1.25OD aluminum compared to the same 316L stainless is pretty minimal. I just checked my suppliers website and a 3' section of sch 80 T-6 with a .188 wall was $14.00 where a 3' section of 316L with a .90 wall was $80.00 and with a .190 wall went up to $160.00.

Glen
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Old 07-04-2010, 21:02   #9
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Assuming you've got the ketch version, you have 16 outboard chainplates on the Ingrid 38. Visually, that's a tough match. Are those chainplates bronze?

I haven't eyeballed an Ingrid 38 in a few years, but if I remember correctly, the last one I got close to had white awlgriped masts. Is this the same on your boat?

If you have the white masts and bronze chainplates, I'd be worried that aluminum stanchions might detract from the boat's classic good looks. Otherwise....
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Old 07-04-2010, 21:26   #10
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Bash,

Mine is the cutter version. It's actually a Bentley which is an Ingrid with a raised coach roof. Most folks know what an Ingrid is so that's what I call it.

I like the traditional look of the Ingrid but not the chain plates runnning down the sides. Mine are mounted at deck level and the loads carried below via distribution plates to the deck shelf, 1st horizontal stringer and to the adjacent bulkheads using 1/4" plate that is both galssed and bolted into place.

The mast is white and I'll likely match the railing and bow sprit to that.
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Old 07-04-2010, 21:55   #11
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I had sched 40 on mine and they held up well for the 15 years I had the boat. One time a 450 lb guy pulled himself aboard out of the dinghy holding on to one. With a good baseplate it'll last forever.
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Old 07-04-2010, 22:56   #12
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Quote:
Originally Posted by Randy View Post
One time a 450 lb guy pulled himself aboard out of the dinghy holding on to one.
Good testimonial. I'm picturing the cringe on your face and your boat heeled over.
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Old 07-04-2010, 23:01   #13
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Or you can use bronze and chrome it....

On aluminium: use Spectra for the lifelines instead of wire; we do that on stainless stanchions too.

ciao!
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Old 07-04-2010, 23:15   #14
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Good Lord,

I can't imagine the stress that a 450 pounder would put on a stanchion using it as a lever to hoist himself aboard.

The responses are great, with much to be learned. Spectra does make a lot of sense, I had not thought of that. Put a pass thru in the stanchion tube and a cove edge on the inner surface to reduce abrasion, it would last a very long time. That is a great idea. Any thoughts on the size of the Spectra?

The wall of sch 40 is about 5/100th thinner than sch 80, I am amazed that it stood up so well for that long.
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Old 08-04-2010, 00:28   #15
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I use 10mm for upper and 8mm for lower lifeline. Dynex Dux would be pretty optimal but Amsteel Blue is great too. Mine is double-braid with polyester sleeve (10mm pure Spectra is overkill).

Instead of turnbuckles I use lashings of 1/8" Spectra.

cheers,
Nick.
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