Trampoline attachment buttons

[Stumble]

Looking at the picture it's pretty clear what the problem is. The stainless bolt is corroding the aluminium button. I doubt that anodizing will do much of anything to help this.

[Cotemar]

Originally Posted by Stumble

Looking at the picture it's pretty clear what the problem is. The stainless bolt is corroding the aluminium button. I doubt that anodizing will do much of anything to help this.

Just look at your anodized mast for the answer to that question.
Your anodized mast will last the life of your boat.
Your mast has plenty of SS harware bolted to it.

[Stumble]

Cotemar,

Anodizing aluminium doesn't change it's galvanic properties it just created a thicker aluminium oxide coating than would develope normally under normal conditions.

The reason your mast lasts until it wears out (generally) is because the size difference between the mast and the stainless bits is huge, providing a lot of surface are for the damage to be dispersed thru.

[Cotemar]

Originally Posted by Stumble

Cotemar,

Anodizing aluminium doesn't change it's galvanic properties it just created a thicker aluminium oxide coating than would develope normally under normal conditions.

The reason your mast lasts until it wears out (generally) is because the size difference between the mast and the stainless bits is huge, providing a lot of surface are for the damage to be dispersed thru.

If that were true then all your anodized aluminum cleats and anodized cat cross beam would be dust right now. An it is not, so that idea does not fly.

[tamicatana]

Cotemar,

I've seen quite a few masts and x-beams I could show you to demonstrate that Stumble is correct. The engineering term for it is 'white stuff.' ;-).

Anodising may help, but it doesn't prevent galvanic corrosion. Tef-Gel will help too.

btw, freshwater rinsing helps as well

[Jim Cate]

Not personally familiar with these bits, but they look pretty simple in the picture. I wonder if it would not be fiscally sound to take one to a hungry machine shop with basic numerically controlled tools and have a couple of hundred run off in a suitable alloy. Have the central hole sized to accept the little nylon inserts used commonly in genoa fairlead tracks... this should minimize the galvanic corrosion issues.

Cheers,

Jim

[Dragon Lady]

Originally Posted by Jim Cate

Not personally familiar with these bits, but they look pretty simple in the picture. I wonder if it would not be fiscally sound to take one to a hungry machine shop with basic numerically controlled tools and have a couple of hundred run off in a suitable alloy. Have the central hole sized to accept the little nylon inserts used commonly in genoa fairlead tracks... this should minimize the galvanic corrosion issues.

Cheers,

Jim

Yeah I'm thinking about it Jim, judging by the response there is a market there.
Just one question, where do you find a machine shop that does repetition machining in Oz these days?

[Cotemar]

Originally Posted by Dragon Lady

Yeah I'm thinking about it Jim, judging by the response there is a market there.
Just one question, where do you find a machine shop that does repetition machining in Oz these days?

Don't have to. I can have him send them to you. Have 150 of them spoken for so far.

[Cotemar]

Originally Posted by tamicatana

Cotemar,

I've seen quite a few masts and x-beams I could show you to demonstrate that Stumble is correct. The engineering term for it is 'white stuff.' ;-).

Anodising may help, but it doesn't prevent galvanic corrosion. Tef-Gel will help too.

btw, freshwater rinsing helps as well

Using Tef-Gel has always been a given when installing SS bolts into aluminum to minimize galvanic corrosion.

These PROBLEM buttons are NOT ANODIZED. As you can see in the picture that the SS to aluminum interface is not where the button is corroding.

Properly ANODIZED parts installed properly will last a life time as in the picture showing the anodized aluminum cleat with SS through bolts and the anodized hatch with SS hing bolt. These both look like new and they are just a foot away from the un-anodized buttons that are corroding.

[Jim Cate]

Originally Posted by Dragon Lady

Yeah I'm thinking about it Jim, judging by the response there is a market there.
Just one question, where do you find a machine shop that does repetition machining in Oz these days?

G'Day DL,

Sheesh, I dunno! But there must be some around that can handle such a simple job. There are heaps of them in the States, but that isn't much help here, is it?

Or you could outsource them to China and get them for 3 cents each!! Good quality, too... just like the originals...

Sorry I can't be of help there.

Cheers,

Jim

[Dragon Lady]

I'm actually thinking of using some of these:-

99 cents each and plastic so no corrosion.

[tamicatana]

Originally Posted by Dragon Lady

I'm actually thinking of using some of these

There ya go! the only thing I can see is that like all things plastic, UV will probably eat it, but maybe you can put something on it to help prevent that.

Here's another lateral solution: since there are apparently already holes in that railing to accommodate the screws for these washer things, why not chamfer/fair them and just lace right through the holes? Seems to me there'd be less crap to hurt your feet when walking on the trampoline, and lose a bit of weight, and simplify the boat.

Something similar to these buttons came OEM to the Farrier trimarans, but amongst the modifications to my trimaran include such a change - her trampolines lace right to the flange. My F-boat doesn't squeak when I walk around, unlike the other F-boats I've been aboard (another plus). That could also be because I don't use covered line, I use single braid for trampoline lacing...

[Stumble]

Cotmar,

I deal with galvanic issues all the time, anodizing has little to no effect on galvanic corrosion. If you want I can refer you to the corrosion engineer I work with on offshore parts you are welcome to call his firm and pay for his opinion. Or you can read almost anything from credible engineering sources about galvanic corrosion. If you would like to cover this in detail free free to start a thread on it.

Anodizing World: Corrosion between anodized aluminum and steel




Tamicat,

I know Corsair trimarans use plastic buttons instead of aluminium. The problem with them is that the stainless bolts are a little on the small size, and have a constant problem with snapping from crevice corrosion. I just replaced all of the steel bolts on mine with titanium bolts and reinstaled the plastic buttons.

[Cotemar]

Originally Posted by Stumble

Cotmar,

I deal with galvanic issues all the time, anodizing has little to no effect on galvanic corrosion. If you want I can refer you to the corrosion engineer I work with on offshore parts you are welcome to call his firm and pay for his opinion.

The problem with believing everything you and your buddies think is that eventually even logic does not make sense to you.

I show you three aluminum parts that are in the same salt spray environment with stainless steel bolts through each of them all within a foot of each other and one of them is corroding. The buttons are not anodized, so they are corroding not at the SS to aluminum interface but on the outside edge where the salt water soaked line is holding moisture.

Also if you had looked a bit closer you would have seen that the un-anodized corroding button is mounted on an anodized L bracket that is in great shape under the same salt spray conditions.

This is real world, not in a lab.

Oh, and let me just clue you in. I am and engineer also.

[tamicatana]

I'm not clear, apparently. My point is to replace buttons etc altogether and completely solve the problem. Please see below photos for examples:

My trimaran. Removal of bolts etc, installed grommets, laced through. No owies on the feet, simpler. I'm going to do this to my Catana:





How it's done on the Catana at present. If you look generally lower right, you can just see the stainless eyebolts which are bolted through the flange, with washer backers. I hate these things, but they're better than the buttons if you ask me





Underside view, showing backers: