1" Stainless tubing strength? Solar panel mount Q

[Chuck in WA]

Hi All,
I'm attempting to design a support structure for 4 solar panels, fabricated from 1" SS tubing (Bimini/handrail stuff, .065 thickness). My boat is a "sundeck" style, and my plan for the structure is to attach the fwd tubing to the radar arch, then run the tubing aft to the end of the sundeck, where it will 90* down and attach to the existing railing. When the panels are installed, it will almost create a "hardtop" of sorts above the sundeck. My concern is the length of span (around 10'), which will be otherwise unsupported, so I wanted to solicit your thoughts about this aspect. The total weight of the panels will be under 200 pounds. Attached is a "God's eye view" drawing of my proposed construction (not to scale).

I've had 6" of wet/heavy PNW snow on my bimini (of similar dimensions) before with no adverse effects, but the bimini is supported differently and the bows are slightly curved (the solar mount will be flat), so perhaps apples to oranges.

In the picture, black lines=SS tubing and green lines=solar panel position.

One thing to note regarding my attached image before comments begin - it does not show any aft lateral support I will build in, simply to keep the picture a little cleaner.

TIA for your thoughts!

 

[Comodave]

I would go with 1.25” tubing. It is has much more strength and you can get bimini fittings to put it together with. I put a hardtop on my boat with the 1” s/s tubing from the bimini and it was very loose. I had some tubes bent out of 1.25” and it is solid as a rock. The hardtop weighed less than 100 pounds but is quite large. The difference was amazing between the 1” and the 1.25”.

 

[jleonard]

I'd put a pitch on the panels to help shed the snow no matter what size tube you use.

 

[GoneFarrell]

Chuck,
Comodave's advice for 1.25" dia tubing on the unsupported runs is good.

1.25 tube is almost twice as stiff as one inch (0.050 vs 0.026 in^4)

My back of napkin calcs: 10 foot span, 100 pound point load in the middle of the span:
117,000 psi at mid-span for 1" tube, 61,000 psi for 1.25" tube. Yield for 316SST at 73,000 psi or better, say 85,000 psi.

If you can come up to mid-span from the aft or fwd mounts with a tube at 45 deg you could use 1" tube, otherwise your structure will flap around a bunch more than you would be comfortable with.

I used to design cranes and stuff, hope this helps!

I'm working up mounts for 2 x 110 watt flex panels as we speak (type!)

 

[DDW]

The ASTM spec for minimum yield on annealed 316 is about 30,000 psi (less, for 316L). If you buy it with a cert most of it will come at 40 - 45 ksi tested. Ultimate will be 80 or 85 ksi, but this is after it has distorted and stretched 30% or so. Tubing is usually in the same condition, but that depends on the manufacturing process.

Annealed 316 is pretty soft material.

 

[GoneFarrell]

DDW, thanks for catching that, back of napkin is dusty!

I was assuming tubing would have cold-working level spec from being drawn/sized.

 

[mike66]

A couple of 45 degrees runs from the radar arch legs to the first cross span will add some rigidity against the lateral momentum of the panels as the boat rolls. Otherwise some of that force will have to be countered by the panels and their mounts. Don't know how much twist the panels can take.

 

[Ka_sea_ta]

I looked at a similar design attaching solar panel mounts to a radar arch. My concern was that the arch tended to move independently of the boat in rough sea state. Its a large FG arch and it doesn't move a lot but I could never figure a good way to isolate the panel mounts from the arch movement... Hopefully your arch is more rigid and this is not an issue.

 

[Group9]

I would go with 1.25” tubing. It is has much more strength and you can get bimini fittings to put it together with. I put a hardtop on my boat with the 1” s/s tubing from the bimini and it was very loose. I had some tubes bent out of 1.25” and it is solid as a rock. The hardtop weighed less than 100 pounds but is quite large. The difference was amazing between the 1” and the 1.25”.

I agree. We built our solar racks on our last boat out of 1" SS tube, and it wasn't long before I wished we had gone with the 1.25 inch. The one inch tube just isn't strong, or stiff enough, for that much weight.

 

[Larry M]

A couple of 45 degrees runs from the radar arch legs to the first cross span will add some rigidity against the lateral momentum of the panels as the boat rolls. Otherwise some of that force will have to be countered by the panels and their mounts. Don't know how much twist the panels can take.

Another Forum member, hopefully we’ll hear from him, didn’t add any cross members and ended using straps as a temporary fix. As Mike pointed out, the lateral movement was pretty severe before he added the straps which worked but weren’t a permanent solution.

 

[NDM]

Why can't you mount the solar panels on the sundeck's roof? If you are concerned about holes, there are ways to use adhesives. Look at how people do it on RVs. Leave a gap of an inch or so between the panels and the hardtop for cooling and mounting hardware. Also beware of shading from structures around the panels.

 

[CaptTom]

I'm following this. I'd like to do something similar; make a "hardtop" or Bimini out of solar panels over my sundeck. I don't have a radar arch, so it would be self-supported all around. Ideally, in the end it would be waterproof, about 10'x10', and allow attachments of side curtains to make a full enclosure.

Big project, and it's not likely to bubble to the top of the list anytime soon. But I'd love to see how others approach similar designs.

 

[Comodave]

I'm following this. I'd like to do something similar; make a "hardtop" or Bimini out of solar panels over my sundeck. I don't have a radar arch, so it would be self-supported all around. Ideally, in the end it would be waterproof, about 10'x10', and allow attachments of side curtains to make a full enclosure.

Big project, and it's not likely to bubble to the top of the list anytime soon. But I'd love to see how others approach similar designs.

I think that you probably will need to make the hardtop first if you want it to be waterproof and then mount the solar panels to the top of the hardtop. I have a Hardtotop hardtop on my flybridge and a fiberglass hardtop on my sundeck. I have thought about mounting solar panels on top of each. Not sure which way I will go. It will be a bit easier to mount on the sundeck since I don’t have to reach out over the flybridge hardtop. Not sure which way I will go since the solar panels aren’t at the top of my todo list yet.

 

[AusCan]

The 1.25" tubing is a good idea if you wanted to keep it flat.
A second option is install 1" but with 45 degree support to the vertical tubing and put a slight curve on the horizontal. A minimal curve will increase the load rating substantially.

 

[DDW]

DDW, thanks for catching that, back of napkin is dusty!

I was assuming tubing would have cold-working level spec from being drawn/sized.

It may - but get a certification! Many drawing processes anneal several times. Of course, the primary design criteria may be stiffness, which does not change with hardness condition.

 

[Group9]

Why can't you mount the solar panels on the sundeck's roof? If you are concerned about holes, there are ways to use adhesives. Look at how people do it on RVs. Leave a gap of an inch or so between the panels and the hardtop for cooling and mounting hardware. Also beware of shading from structures around the panels.

That's how we have ours mounted now. On the cabin top. Nothing but 5200 holds them in place. So far they have survived 65 mph winds and haven't budged.

 

[Chuck in WA]

Wow, you guys are fantastic! Thanks very much! As you may be able to see from the attached picture, the radar arch is rock-solid and will provide good support up front in all directions. For aft lateral support (when the boat rolls), I plan to run tubing at a 45*ish from the existing side rails on the boat to (what will be) the aft vertical tubing for the solar structure. The "beam" of the side rails in this area is 12.5 feet. Mike66, I also like your idea for lateral support and will investigate. Your idea would have the added benefit of additional support for the structure. The downside is it may create "headbanger" spots.

A "slight" curve at the apex is probably a good idea for added strength and rain runoff, while still keeping the panels reasonably flat. I don't intend for this project to create a waterproof seating area, but if I can avoid a surprise dousing I guess that would be worthwhile.

Comodave, I initially thought about putting solar over my flybridge Bimini, as I was lothe to cover my sundeck (there's a reason they call it that!). However, I would have no good way to keep bird poo off the panels on a regular basis, and I'd probably be unhappy with their performance as a result. Also, I would have more shadowing from antennas there. From my research, it doesn't take too much poo/shadowing to shut down a panel. I've convinced myself that a little bit of shade on the sundeck may not be too bad after all, and I will be able to easily stand on the flybridge steps with an extended brush to keep the panels clean and producing max power.

Thanks again to all!

 

[mike66]

Cross bacing anywhere would be helpful. If forward is a possible head banger, then move aft and also consider the rectangle under the panels as a place to cross brace. Good luck with the project!

 

[Scottwb96]

Someone mentioned early on about giving it some sort of pitch. Unless you plan to take them off in the winter, I would definitely consider pitch. As I am sure you're aware, PNW winters are ALL OVER THE PLACE (from no snow to 2, 3, 4' of snow). Flat surface may completely cave in. Another idea may be to add some sort of heating element to the mix, at least for winter to melt any snow... Just a thought... Good luck!!!

 

[MOJO]

Think about aluminum angle, maybe 2" x 2" x 1/4" or 3/8" thick. Stronger and lighter than tubing. Easily drilled and bolted together. Cross brace and it will be damn near bullet proof!