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Old 16-04-2018, 04:34   #1
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DIY solar arch/bimini from mild/carbon steel

Hi folks,

I'm toying with the idea of buying a steel vessel. I'll need an arch/fixed bimini for solar panels, stern anchor, antennas, beer cans, fishing rods, the usual...

Decent stainless steel is ridiculously expensive over here.

So why not just build the thing from ordinary steel?

Just use U or T Profiles so it doesn't trap water and paint the thing just like the rest of the boat. Won't be pretty, no nice bends and stuff but cheap and easy to manufacture, just beveled cuts & welding.

If When I want to do modifications during cruising I just pull out the old stick welder, angle grinder and maybe a vise and I'm all set.

Or even use pipe with drainage holes and use a nozzle / hose for painting on the inside. Big ships have rails made of pipe as well without corroding away instantaneously.

Has anyone done this before? Any experiences? Am I missing something terribly obvious?

Thanks, Andi
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Old 16-04-2018, 05:03   #2
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Re: DIY solar arch/bimini from mild/carbon steel

so ... the reason to use stainless is every edge and corner will get whacked constantly ... meaning you'll spend the rest of your life touching up chipped paint.

then again, steel boat ... you'll spend the rest of your life touching up paint anyways ... so ... go ahead.

Not sure you need to paint inside steel pipe ... if you seal it it won't rust, if you don't seal it put weep holes in the low points and spray it inside with a lot of fish oil. Think about it ... do bicycles get inside paint jobs?
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Old 16-04-2018, 05:23   #3
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Re: DIY solar arch/bimini from mild/carbon steel

I did. I used 1-1/4” (or 1-1/2”?) schedule 40 galvanized electrical conduit. For bends I used standard elbows. I first just assembled it using couplings but find this problematic so I welded the couplings. I made sockets I welded onthe deck. I added cross pieces of 1” EMT to stiffen, connected with pipe hangers. I joined the two arches with flat bar.

The only problem was the flat bar rusted like crazy, I just replaced that with heavier 304 ss, not all shiny but very practical. I have a 400 watt wind gen, 630 watt solar, and radar mounted on it. It carries the outboard and a Fortress FX-37 stern anchor. It would serve as davits but the wind vane is in the way.

Being galvanized rust is greatly reduced. Still some where welds were. You could build the thing and then find some place to hot dip it before final attachment.

I drew it up on CAD first making a profile of the boat to get the shear and angles correct. That took a good bit of fiddling around.

It came out looking OK. It’s not all blingy but easy on the pocket and much more stable and functional than some “kit” arch installations I have seen.

Every time I fret about cosmetics my wife tells me to stand in front of a full length mirror naked for 30 seconds. It does the trick.
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Old 16-04-2018, 05:37   #4
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Re: DIY solar arch/bimini from mild/carbon steel

Why not use aluminum? If properly isolated from the steel, you don't even need to paint it. Keep the weight in mind, it could affect the trim of the boat.
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Old 16-04-2018, 05:47   #5
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Re: DIY solar arch/bimini from mild/carbon steel

Where is "over here"? We use galvanized pipe on a daily basis, and have even used it in coastal areas with great success. My preferred pipe carries the designation SS40, or SPS40. It is slightly thinner than schedule 40, but it's higher tensile steel and Class III galvanized instead of hot dipped. It welds clean and is plenty strong.(You still don't want to inhale the yellow smoke!) We have had some of these posts powder coated, which is nice, but does make welding a bit more work. We give the welds a good coat of cold galvanize and get several years until they need another coat. Our supplier also makes square/rectangle stock in similar wall thickness. Good luck with your project, and keep us updated if you buy the boat and build a solar arch.
I've attached a few photos of the steel we use.





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Old 16-04-2018, 05:53   #6
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Re: DIY solar arch/bimini from mild/carbon steel

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Originally Posted by SVTatia View Post
Why not use aluminum? If properly isolated from the steel, you don't even need to paint it. Keep the weight in mind, it could affect the trim of the boat.
Saltwater resistant Aluminium (AlMg4,5) is crazy expensive as well, more difficult to weld and you'll probably need a welding process with shielding gas (expensive, difficult to source under way, dangerous to store (heavier than air)).

The weight difference isn't all that high either, Al is not as strong as steel and even if I use some ridiculous length like 100ft/30m of steel pipe it's still only 60kg.
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Old 16-04-2018, 06:02   #7
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Re: DIY solar arch/bimini from mild/carbon steel

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Where is "over here"?
Germany and without buddies working in the business or some other source which gets bulk rates. So salt water resistant stainless pipe (33mm / 1.5in) would run around 7USD per ft / 20EUR per Meter.

I'll definitely will do some blogging and post a link here when I get started on stuff, (anditainment.de | Stuff that entertains Andi… already has some old posts about travelling in grp boats and vans).
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Old 16-04-2018, 08:54   #8
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Re: DIY solar arch/bimini from mild/carbon steel

Steel boat? Use galvanized pipe. It's a no brainer. Avoids aluminum to steel issues and is economical.
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Old 16-04-2018, 09:19   #9
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Re: DIY solar arch/bimini from mild/carbon steel

Thanks so much folks!

So galvy pipe is on the top of my list...

If anyone ever tries to find it in germany, the electronic conduit is called "Stahlpanzerrohr" ("StaPa" in short, gotta love german abbreviations), seems to run around 7EUR / meter for 32mm od (1 1/4in), 2mm thick, 1,2kg / m hot dipped. "...auch für den Einsatz in agressiver Umgebung": also for use in corrosive environment. yep. I'm sold.

And it's PVC Counterpart costs 2€/m, maybe I use that stuff for templating and then recycle it as *drumroll* ... electrical conduit.
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Old 16-04-2018, 09:38   #10
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Re: DIY solar arch/bimini from mild/carbon steel

... and for painting (if I choose to do so) I probably use "Brantho Korrux 3in1", my favorite chip resistant paint (besides the horrible surface finish) and maybe some Polyurethane Truck Bed Liner on especially exposed bits / for de-rattling stuff like the anchor.

Cool. Now I only have to buy a boat. And a stick welder. And learn stick welding... I'll keep you posted. (don't worry, I grew up in a metal shop/foundry, I'll manage. I push comes to shove I have to resort to MIG Welding. But I'd like to learn stick, seems more appropriate for cruising).
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Old 16-04-2018, 10:07   #11
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Re: DIY solar arch/bimini from mild/carbon steel

@Fence Man: What type of electrode would you recommend?
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Old 16-04-2018, 10:08   #12
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Re: DIY solar arch/bimini from mild/carbon steel

Regarding Janww's comment, re: steel bicycles, I actually did run motor oil down the inside of the frame tubes to retard any rust. Complements the exterior paint...
Now have titanium bike and fiberglass boat
thnks
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Old 16-04-2018, 10:13   #13
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Re: DIY solar arch/bimini from mild/carbon steel

If you use galv pipe and tjen weld it you will get some rather nssty rust (and lowering of strength) at the welds. Why not use non-galb pipe, make your arch and yje 1)hot dip galv and 2) powder coat. It is an extremely effective finish. There are hot dip galv operations who have a powder coating line alongside which is the most efficient way of doing it. Just check with them first that they can handle the dimensions of yr finished arch. They might have to do what is called a double-dip which means they put one end in the bath , then turn it around and put the other end in the bath. It is still v effective, many people would never know unless you know what signs to look for and by the time it has gone through the powder coating line you would never know. It is truly a great finish and, in spite of a few chips over the years i would doubt you would need to be touching up with a paint brush for a good 20 years.
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Old 16-04-2018, 10:20   #14
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Re: DIY solar arch/bimini from mild/carbon steel

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I actually did run motor oil down the inside of the frame tubes to retard any rust.
In my understanding motor oil only works long test in correspondence with dust, preferably dry country road without tarmac. Thats how the old-timers do it. The modern variant would be stuff like Mike Sanders or Fluid Film (Lanolin) but I'd be afraid to use that in a warm environment, might just liquefy and seep out.

Maybe I just shoot the welds / the inside around the welds with some zinc primer. Has anybody else an opinion concerning drainage / no drainage? I tend to drainage holes bc I don't think the arch will become 100% air tight / I'm too lazy to pressure test it. Or maybe weld on some bungs+plugs and check every so often?
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Old 16-04-2018, 10:30   #15
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Re: DIY solar arch/bimini from mild/carbon steel

Hello Andy - I did exactly that. Welded the entire arch up, ground the welds clean and had the whole arch hot dipped. After dipping cleaned the arch with angle grinder (perfectly smooth ), left it unpainted for a number of months and finally primed and painted the arch. It's been 3 years now and no problems. If you nick the paint, touch it up - easy. When cleaning the arch after the galvanizing go carefully. If you see sparks you have gone too far. Other than the fact that it does'nt shine like stainless, it looks just as good painted a hammered bronze (I used hammerite as top coat). I would do it again - the finished product cost 6k (South African rands)
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