I am constructing a frame to hold a screen to keep fish from going down a spillway. Most of it will be completely submerged, the other parts will always be in contact with the water.
My question is whether pressure treated wood or premium cedar would be more durable over the long haul.
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Replies
How about Trex or something similar, the composites?
...The unspoken word is capital. We can invest it or we can squander it. -Mark Twain...
Be kind to your children....they will choose your nursing home.
I've worked with Trex and really don't like it, but I've only used it once so I'm a rookie. Also I am unfamiliar with the dimensions available. I'm planning to use 4X4 or 6X6 for the main supporting members.
the composites would be my first choice.. if it's got to be wood.... what about cypress ?
Is cypress readily available?
don't know...
probably a regional thingMike Smith Rhode Island : Design / Build / Repair / Restore
Trex would have a lot of flex. How would it hold a series of staples or whatever to stitch hardware clothe onto it?
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If that was a concern you could sandwich the hardware cloth, chicken wire, what ever, between to pieces of the material.
Composites are likely not to have the strength you would need.
cypress or white oak would be traditional for this.
The white oak would be my choicebecause of strength and some cypress nopw is weaker than old growth. I have used some cypress that was very splintery and hard to work. The joints might be weak at corners.
PT would be a very bad choice. The treatment chemical could be bad for the fish and other natural organisms and the current generation of PT is well known for causing corrosion in metals other than stainless steel.
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Most folks would just use regular PVC for this. I used a white flour. light grate cut to size to keep my goldfish from 'going over the falls'.
Daniel Neuman
Oakland CA
Crazy Home Owner
JZ
I would use aluminium bar stock.
Chuck S.
How big of a screen frame are we talking?
You can readily find 6x6 composite beams (those black ones used for landscaping). Technically not structural but if we're only talking something like a 4x4 frame, It might work just fine.
Yeah, cypress is probably what you want, or maybe teak or some other tropical. Treated won't really hold up that much better than regular wood, and it's toxic to fish, of course.
Black Locust.
Local mills here produce it in a multitude of dimensions. Very hard. Verrrry rot proof. Cheaper than cypress or white oak.
My own personal preference for such a project is to see wood in my stream, not PVC, trex, etc... Not for functional reasons, just aesthetics.
Ithaca, NY "10 square miles, surrounded by reality"
I design fish screens for a living, for a shop that has been building them for fifty years. The only thing that holds up is stainless screen on stainless frames.
If I could find aluminum or fiberglass screen with the opening size I need, that was strong enough to hold up to the debris without the hole size changing, I might try aluminum frames.
That said, I would go with cedar, before I used pressure treated. The pressure treated is pretty toxic on marine life. Constantly submerged wood actually holds up pretty well. We run into irrigation headgates made of doug fir, pretty frequently that are in decent shape after ten years.
I don't know exactly how these are used, but it seems like impact resistance would be a part of theoverall consideration. Cedar is a brittle wood for the most part, so it doesn't fir into my mental image of requirements. Is the impact thing why you use all SS?
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Piffin, we are screening to prevent salmon and steelhead fry from going down irrigation ditches and dying in fields. The holes are 3/32-inch on 9/32 staggered centers. This gives the highest percentage of open area, of any material we can get.
There is debris impact on some of the screens during high water in the spring, but the rest of the year it is negligible.
The screens I design are self cleaning, using a paddlewheel drive in the screened water as it leaves the screen structure to go down the ditch. (As an aside, there hasn't been any good engineering design information on plane old undershot paddlewheels published since around 1880. I went nuts trying to locate any good design information that wasn't just "rule of thumb")
In the past stainless mesh on mild steel frames was tried, but there were serious issues with dissimilar metals corrosion. It is really hard to keep metals from corroding when you are immersing them in water, and then drying them off twenty or so times an hour.
As part of our installation we remove, the irrigator's headgates, and diversion structures. I was amazed at how well the doug fir was holding up, so long as it was constantly submerged.
Also, while cedar may be brittle when dried back to 12% moisture: when submerged it is saturated, and probably almost as flexible as if it were steamed.
Thank you
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Ipe.
Beer was created so carpenters wouldn't rule the world.
I agree with Jigs N Fixtures. Wood constantly submerged holds up very well. Here in the Bay Area there are redwood pier pilings that have been in place over 100 years. I'm not sure where you are but if redwood isn't available, cedar would probably work just as well.
Having spent a lot of time working at a large public aquarium i can tell you a lot of PVC gets used for such purposes, this is what MadMadScientist reccomended.
The stainless that Jigs-n-Fixtures reccomends would work but what are your primary considerations?? Aesthetics, backyard pond for relaxation or durability like in a commercial fish farm setting or the cost and ease of workability??
Certainly a sandwich of wood over hardware cloth wouldbe the easiest to build and if fully submerged the list of acceptable species is long. If you need some extension above the water surface to prevent jumping(a real consideration depending on the species of fish) then i think a non-organic material is in order.
good luck
actually a number of things you could use--------
look at the cape hatteras light house on the outer banks of north carolina
built I think in the 1860's-brick-over 190 feet tall-it stood untill just a few years ago on wooden cribbing sunk in the sand and constantly submerged in sea water.-what was the wood-can't recall-probably the local SYP.( due to erosion of the barrier island it sits on-the lighthouse was jacked up and moved inland a bit a few years ago)
also recall reading a book written by a carpenter in England-probably before WW1( walter Rose, i think- he talked about the wood he used to fabricate farm pumps and water pipes etc.-------Elm?????
a lot of things would work-question iwhat would work that is close to you???
Stephen