aluminum vs stainless steal for radar arch

[BigB72]

i've got a duckworth that i want to put an arch or tower on. i looked into having an aluminum one custom made and powder coated and it will cost me about $2000. my wife's uncle owns a boat trailer business. my father in-law said that he could make one out of stainless steal with the stuff at the trailer yard for free. they have a nice paint booth too, so i would just have to pay for paint.

i understand that the stainless steal will weigh more, but is there anything negative about using stainless steal?

should i pay $2000 for aluminum or is this a no brainer?

[little doc]

Galvanic corrosion.

It's a problem for dissimilar metals in a corrosive environment, in theory at least.

Scott.

[BigB72]

will it make my boat corrode or just the arch?

[Bait O' Eggs]

If the stainless only cost me the paint I would go with stainless. Where you bolt it to the boat, put a spacer to keep the stainless from touching the aluminum.

Thin piece of UHMW, or rubber sheet or something like that to keep the dissimiliar metals apart.

[backlash442]

Why would you want to paint s.s.??

[HOGGEMIN]

I think Motion Marine charges $ 1,300 for there custom radar arch.

Also Roy Bait 'o' Eggs has it right for dissimmular metals a spacer is all you need to stop the problem.

[troybuz]

Galvanic corrosion. Will the stainless arch corrode my boat

Aluminum will corrode with most dis-similar metals...this includes the fasteners (Most marine fasteners are stainless). So, to answer your question, yes, to a degree. The more protection and care you use keeping any stainless from touching the aluminum the better off you'll be.
If you can build a nice looking arch with stainless that's the way I'd go. I think the bends, the design, and the quality of manufacturing are more important that is made from Stainless or Aluminum.
I made my tower tower from 6063.
Here's my tower making slide show: http://rides.webshots.com/slideshow/549361243xBhUNl

Troy

[BigB72]

Originally Posted by HOGGEMIN

I think Motion Marine charges $ 1,300 for there custom radar arch.

Where is motion marine? my price was from a custom fabrication shop in coosbay.

Might just end up going with s.s. if all i need is a spacer between the metals. i'm sure we could come up with something for this.

why would i paint it? why knot? it's not like it's going to cost a lot and it will look pretty sweet the same blue as my boat.

[Metal Manipulator]

Metal fatique in stainless is a factor too. As far as galvanic corrosion goes Alluminum is lower on the list of nobility right behind Magnesium, Zinc,cadmium, mild steel there fore sacrificing itself to others of greater nobility such as lead,Tin, Brass, Stainless Steel, Monel, Silver, Gold, Platinum.

Sealed and insulated with plastic and a product such as 3m 4200 for the bolts,will go along way's to prevent this corrosion in alluminum.

If you paint it It will start comming off very soon. If you want it coated and I am not sure why you would unless the stainless is not 316L then I would recamend a product called Plascoat applied the same way as Powdercoat but a much softer material that won't chip off like powder coat material.

[pugetplunker]

motion marine is in west linn. plastic spacer under the gunnels to help spread the load,also at motion they would tell you to use plastic incerts for the holes to keep the stainless fastners from comming in contact with the aluminum gunnel

[Critr Gitr]

Here is my aluminum one I had it built for under $1000 - includes powder coating PM me for details. You can even stop by for a closer look. All work done in Eugne area.

[BigB72]

thank you all for your input. it has helped me a lot. nice to have experienced people willing to help a beginner.

[Onokai]

wet fly said (Metal fatique in stainless is a factor too).
Thats why I vote aluminium as it can flex more without cracking. Painting S/S is nuts so give up that idea. Powder coat is ok on aluminum only if it cannot flex much as that will cuase it to come loose. Stainless will crack if it flexs at wields much. Free is nice but not always the best bet for things. Mark

[Chrome Bumper]

Either will be fine if you have a good welder and design. Since you will attach it with stainless fasteners in any event you have a mixture of metals. Most aluminum and stainless alloys are pretty close on the galvanic chart so the effects will be minor.

Even between different aluminum alloys you will have galvanic potential and most aluminum shapes used on boats are 6061, not the most durable in the a marine enviroment.

What alloy is the stainless, 304 or 316 maybe? What weld filler and method are you using?

[fyshndad]

Here are some pics of my $100 arch
It is nearly ready to install
It needs one more good coat of paint & some rubber trim to protect the reels

I too thought it would be cool to match the color to my boat trim

[backlash442]

S.S. cracking would be all about the workmanship imo. I know guys whose boats are going on 20 years and more w/out having an issue. On the other hand I know a guy with powder coated alum. and he hated it. Every season he had to repaint it due to chipping/flaking. He now has s.s.

Personally, I think the s.s. will look a lot better on your blue boat than painting it the same color. If you scratch it and the s.s. shows it's going to look very cheesey imo. Then again to each his own. Good luck.

[BigB72]

i understand free is not always best. but free would give me extra $ to spend on radar/chartplotter.

My father in-law is a perfectionist (so much that he can be a pain in the arse to work with) so i'm not too worried about the craftsmanship he would put into the arch. i am however worried about what i would get out of some one i don't know.

the mixed reviews are making it even harder to make my descision. i do know now that painting or powder coating are out of the question. i don't want the thing to look cheap when it is done.

s.s would be o.k. so long as we take care to use spacers to keep the metals from touching. i think we would be able to acheive this.

[Chrome Bumper]

Free is a very good price, 316L is a bit more corrosion resistant then 304L. Either will buff out fine. You want the L (low carbon) grade to minimize weld embrittlement problems, or oversize the weld joint design.

Dialectric isolation won't gain you a lot. Bedding, like 3M 5200 should reduce corrosion by not allowing water to collect in tight areas that don't get exposed to enough oxygen to initiate 'stainless' properties of the Al or SS.

Steel designs tend to be 'skinnier' and weigh a bit more since steel is stiffer and heavier than aluminum.

[Metal Manipulator]

This is he reason that you should use plascoat, it wont chip and if it gets nicked the corrosion won't creep under the coating. If it is stainless I still would not coat it but you will have to maintain it with polish and a sealer such as woody wax.