@randythawkins
I am still intrigued by the frame for your net cover..... Any ideas/suggestions for making something similar, but on a larger scale? Anything I've tried to come up with doesn't have enough strength to span our pond. I recall from a previous post, you said you focus on triangles as the strength of your design.
.....but I was never good at geometry. Would you mind posting a drawing that shows
HOW you fit the PVC pieces together, and what you would maybe do different for something say, 15' x 10'.
Mmathis - It has been awhile since this request and the length in time is not because I forgot - I have just been trying to figure out to best respond. Well, I really don't have a good plan so I figured I would just start and see where my typing leads me. So, here goes...
A primary goal when I built the net was to have a way for leaves NOT to collect on top of the net. I have seen many instances where people placed nets over their ponds stretching them flat and letting them float on top of the water. Whereas this would prevent leaves from sinking to the bottom of the pond the leaves would still collect at the top of the water and would still sit in enough water to make a yucky mess. I wanted a design that would allow the leaves that landed on the net to either roll off or blow away. The obvious solution to this is a sloped approach. Because my pond is round my slope would be highest at the center. The next step was to design a frame which would be higher in the center and I quickly started doodling plans similar to roof trusses.
A well designed roof truss is able to span large spaces and is self-supportive to prevent drooping in the center. The secret sauce is the cooperative way the sloped top and the flat horizontal bottom work together. I found this page which does a good (basic) job of explaining this interaction -
http://makezine.com/2010/06/10/ask-make-how-do-trusses-work/. It also presents the idea of the triangles I have mentioned in the past. The triangles prevent the structure from racking to one side or the other which plays a major role supporting the span over the open space (in my case, the water).
Although my implementation is round/circular the same fundamentals can apply to a square/rectangular build. If you were to cut my structure in half, top-to-bottom and down the center, and look at it from the side you would see that my frame is similar to a basic roof truss -
(Please ignore the measurement numbers. I found this image on google and borrowed it as a reference.)
If you were to build a net frame of a square/rectangular shape you would create several segments like that image above. In my case, since mine is circular, all of my segments share a common center high point.
So, with that somewhat convoluted description of the mechanics of my design, I will move on to the construction...
My pond is about 9' across. While at Lowe's I took various pieces of their 10' PVC pipes, ranging from 1/2" to 1.5", and supported either end to see how much droop I would have. They all tended to droop about the same. I decided to go with 1" as I felt it would give me the rigidity I needed at an acceptable cost. I could have gone with the larger size which would have provided minimal "better rigid support" but an significant overall undesirable increase in weight of the completed project. I really did not have a drawn-up design so I purchased a bunch of the 10' pipe and several handfuls of various fittings - T's, 90, 45, and 25.5 degree elbows and headed home.
I started the build by deciding how many sides I wanted on the lower outside ring and played around with the lengths of those side pieces until I was happy with it.
I then moved it to a flat surface where I could step anywhere I need to. Once there I made an alteration for the rise over the skimmer box.
Everything I did to this point was dry-fit. Nothing was glued as I was constantly taking apart and reassembling things. The rocks helped keep things from shifting as I worked - I wanted it to be equally circular and not oval shaped.
I cut into the sides and ran the lower cross members. Then I started working on the top angled part. In the very center would be my vertical post. Due to the limited options given to me by the various PVC connectors I decided to create a smaller circular part at the top and then run the vertical post from that.
Then, I measured, cut, and placed the top angle pieces.
Once I felt good about the results it was time to glue things. With all the angles I was concerned that I would not realign pieces correctly after applying PVC glue and that those subtle variations would add up and not end well so I decided to just use some super glue. I got the thinner stuff as opposed to the thicker gel because I wanted it to flow into the joints and not glob on the outside edge. It took awhile as I was careful not to miss any connection but I eventually got them all pretty well glued and, so far, it has held up very well.
So, my design was more driven by the connectors and the puzzle they presented for getting everything together more than any historically proven methods (other than keeping with the basic similarity to the truss shown earlier in this write-up).
With the net frame in place over the pond it has only a slight droop in the center which is not enough to concern me (right now). I will continue to watch it over time and see how the weather elements affect it. Oh, speaking of weather...last Winter here in Atlanta we had several snow/ice events and the net did collect some of that stuff. My intentions were to remove the net before those events as I was concerned what the additional weight would do but it showed no negative results.
That covers the mechanics of what I built along with, hopefully, a better presentation of the why it all works.
Mmathis - you say your pond is about 15'x10'. For that I would probably try building 4 roof truss shaped pieces - 2 for either end and 2 equally spaced in between. Wrap a PVC frame around the bottom and then some at the peek of the "trusses". Here, similar to the net frame I built to go over my settlement chamber:
That is much smaller than your needs and would certainly require a vertical post in the centers but, hopefully, that can provide a good visual starting point. Give me a couple of days and I will get on google Sketchup and see if I can draw up a few ideas there.
Did any of this help?
]. When you said triangles, I literally thought triangles, ha! But of course, finding the appropriate fittings -- another matter. I like the truss idea -- the problems I've had in the past have had to do with support issues.