Backyard Aquaponics
A place to discuss aquaponics

I was also thinking the plywood should be on the inside, to have it push the water pressure onto the vertical studs. Having the plywood on the outside of the studs I imagine would pull out the screws or the heads of the screws would just rip through the plywood. I guess the plywood is on the outside because it is the stakes that really support the sides? The friendlys troughs seem to be less than a foot deep. You could maybe make slanted braces from the sides into the dirt like flying buttresses.

The plywood is really thin, and doesn't have much structural integrity. It is there to protect the insulation and the liner from random kicks, cart legs etc.
The studs and the soon-to-be-placed bracing supports the sides.

Zman, do you mean along the sides, or on the bottom? For along the sides, I answered in reply to DD. On the bottom, I don't see a need for the ply if the foam is under the cross bracing.

Maybe put bracing across the top too. Might interfere with the plants I suppose. Cable could work to do it. Are you going to fill this first one up before making more troughs?

Hi Karen i was referring to the bottom.

The other thing I wanted to mention is that your vertical studs would support the sides better if they were rotated ninety degrees. The nails or screws that hold them on could bend out with the studs oriented along the trough rathe than perpendicular. HTH!

The thin plywood, is it luan like for spacing for putting down flooring? Another alternative might be to use thick staples to attach wire mesh to the inside of the studs. That would distribute weight to the studs and would be tough.

Get those bracings before the long sides bend out. Imho the srtucture is not stable like this.

OK I thought about this some more on my morning commute. If you allow tension in the liner or maybe some other thing like wire mesh or other then you can support the water weight with zero side load. In cross section the trough sides would look like a suspension bridge. Most of the liner would be flat on the ground but near the sides would form an arc, up to the top rail. Depending on how much slack or tension is in the liner then the sides could be pulled in, or bow out or be pulled straight down into the ground. With this you would only need posts maybe a foot into the ground, and a top rail of 2x4s, and then maybe pinch the liner between the rail and another 2x4 or other. No side walls would be needed for support, and if the posts were in the ground then you wouldn't need braces across the bottom either. If you can't put some tension on the liner then I think a wire mesh could be used to make the suspension on the sides. Maybe a roll of 4' wide wire mesh, with one edge stapled to the top rail and the other end pegged into the ground with landscape fabric wire pegs. The liner weight on the part of the mesh under the liner would probably keep the mesh from slipping outward from the tension.

The threads getting a bit confusing so I Thought I would bring some sanity back .

I don't believe that you would really be certain how much tension you acheived on the liner so I would steer clear of messing with this very much.

+1 more cross bracing would have been good (but may not be needed depending on the water depth and the bracing of the 1" square tubing).

+1 Turning the vertical 2 x 4 sections to have the 3.5" section (they just call it 4 ) going in toward the center would give better support against the weight of the water. I can see that if you did this you wouldn't be able to put the insulation in as easily.

+1 It might be a good idea to use cable across the top of the beds as Dave mentioned earlier - this would help stabilize the sides.

If your metal supports are frequent enough I can't see any problem with your design. I say this because ultimately it is these supports that will counteract the force of the water.

2" by 4" is the size of the rough cut before it is kiln dried and surface smoothed. You "take off" 1/2" on all board measurements. Not that it's relevant or anything...

Ok on page three of this thread is a picture of a friendlys trough with white liner that is deeper than the other ones. You can see the liner held in tension by the rim, so the sides are not necessary to keep the liner from bowing out. Is that how you're attaching the liner Karen? I worry because I care xoxox LOL

+1 on the Radius (3rd picture in Dave's diagrams) I do believe it is how you keep from having the water pressure push or bow your sides out but it does require very secure attachment of the top edge of the liner.

In the friendlys picture it looks like they were using plywood strips, I imagine screwed into the rail to clamp the liner. Btw I think this would be a great way to make a homemade FT of whatever size you wanted, just liner a rim and posts, no expensive plywood needed.

This may work for a foot or two deep water but for a deep tank you may be asking a bit too much of the liner to resist ripping out and bowing out anyway.