Ahhh, you all beat me to it! I've been meaning to post about the targets I've been building recently, but I hadn't gotten around to typing it all up and taking photos. This post was motivation to finish that, so here goes with my current recipe....
HOOPS
The hoops are made from PEX, a hollow plastic tubing which I bought in 10ft (3m) sections from the local big box hardware store before finally scoring a better deal on a 100ft (30m) roll off Amazon and making a similar deal with a local independent plumbing supply outlet. If I were starting from scratch knowing what I know now, I'd stalk the best sales I could find on 100ft (30m) rolls - or bigger, depending on how many you want to make. Buying in large quantities also helps with color consistency since different batches / types of PEX seem to vary slightly in terms of color shades. Not a big deal, but they definitely look nicer if they're matchy-matchy.
HOOPS > PEX TYPES
Use the cheapest PEX you can find, at least for temporary use. Since these won't be used for potable water and won't be under pressure, the differences between PEX-A, PEX-B, and PEX-C don't really seem to matter. If you're doing a permanent installation, maybe the type of PEX does matter in terms of leakage and color-fastness...but I don't have any data on that yet. I've used a mix of PEX-A and PEX-B here; they've performed identically for my purposes.
HOOPS > PEX COLORS
PEX seems to come mostly in white, blue, and red. I've blended all three, as seen here, and the result works fine for my informal needs. I could see a strong argument to go with exclusively white PEX (and blue cross members) if you're building for a formal competition. Also, PEX seems to take paint fairly well; too much work for me, but that's an option. Again, buy in bulk to ensure consistent colors.
I tried a few variations and ended up settling on red for the outer circle and blue for the inner with white connectors. I'm not sure it matters much for personal training. These are visible enough on water at 60-70ft even in lower light, so they're satisfactory for my purposes. The darker colors do get lost in the grass in low-light; white would probably work better, but deep grass seems to be a problem no matter what color you use.
HOOPS > PEX SIZE
I've used 1/2" hose here since it was cheap and I was trying to prove the concept. It seems to be visible enough even in the 60-70ft range, but bigger would definitely be better. The same design will work - it'll just be more expensive. If you're trying to match some ICSF or ACA standard or placing them in rougher water, maybe you need hose with a bigger diameter? Not sure, check your guidelines.
HOOPS > DIMENSIONS
I was trying to keep this simple, so I didn't bother cutting those 10ft (3m) sections; each yields a target with a diameter of roughly 100cm (38-40") depending on how round it happens to be when you measure it. PEX generally keeps its shape, but the hoops can get squished between outings depending on how you store them. A little manipulation and they'll get back to almost-round-ish, but the outer diameter still varies somewhat.
That said, I liked the easy math: a 100ft roll will give you 10 targets with a ~100cm diameter. That was good enough for me, but do your own math if you're trying to build rings for a particular competition. PEX isn't the easiest stuff to measure without help or hardware, so definitely "measure twice, cut once" if you'll need to meet tight tolerances for ring diameter, and don't forget to include the connector(s) in your calculations!
My middle rings are ~60cm (24-26"), and that inner one is ~30cm (12-13"). Again, I was going for easy and symmetrical, and these are fine for me - but do your own math!
CONNECTORS
After a few experiments, I've settled on plastic T-shaped "push connectors" knockoffs of the "SharkBite" design. I went with cheap plastic for their light weight and low price, and because, as mentioned above, we aren't deploying these under pressure or for drinking water. Most of the official "Sharkbite" models seem to be made from metal (or much smaller), and they're too heavy for this application - definitely go for plastic.
Here's the best part: although they're watertight, these connections aren't permanent - you can squeeze the collar down and detach the hose from the connector. There's a trick to it, but it's not bad once you get the hang of it. That'll help some folks with storage and transport, although for me it's been easier to leave them in hoop form.
Note that I'm not really recommending this brand - there are lots of choices out there on Amazon and other sites, and they all seem to be interchangeable. But that's what you need to surf on: 1/2" (12mm) PEX plastic push connector, tee (or use larger diameters or "cross" instead of "tee")
CONFIGURATIONS
Once we figured out how to use the tee-connections to make connections between the nested loops (my kid cracked that one - can't take credit for it), it opened up a bunch of design possibilities. You can use longer or shorter pieces for each ring, and even modularize them by adding more braces by using shorter pieces of PEX and more connectors. I haven't done that yet because these designs (with a single connector running between the interior loops) have been sturdy enough for my purposes so far. The connectors are the most expensive parts - see below, but each additional connector adds roughly US$1 to the cost. If you need them to be rock solid, this approach will work - it'll just cost a bit more. If you're going for super-sturdy triple-nested rings, you'll probably want to use cross-shaped connectors on the middle ring; I've got some coming, will post photos soon.
ANCHORS
See those smaller holes in the tee-connector? They're the perfect size for paracord. A simple overhand knot secures a parachord anchor, and you can use anything for weight. I had these leftover SCUBA weights sitting around in the garage, so I used those. It would be easy to add multiple anchors for each target, but I wanted to keep my hoops portable and to be able to detach the anchors easily for use on grass - this solution works very well for me. They drift a little on the pond, but hey, real fish drift around as well.
COMPLICATIONS
I thought that fluff flies and leaders might get caught in those connectors, but so far it hasn't been a problem. A few wraps with electrical tape would solve that issue if necessary - probably a good idea for formal competition.
I worried that the pieces might disconnect spontaneously during placement or retrieval on water, but so far the connections have been quite robust. Again, tape or glue would make them more permanent, but I've wanted to keep mine collapsible.
COST > HOOPS
If you shop carefully, you can get 100ft/30m rolls of PEX (white, red, or blue) for ~US$25-30 on Amazon or at a plumbing supply shop. Since you can get roughly 10 hoops of 100cm diameter each out of each roll, figure your cost per hoop to be ~US$3. Less for smaller hoops, of course - I figure my middle hoops cost $2.50 each, and $2 for the inner rings. Those are rough numbers, but they're good enough for my purposes.
COST > CONNECTORS
The going rate for packages of 10-15 plastic tee push-connectors seems to be US$11-14 on Amazon. After buying several different batches, I'm fairly convinced that all the brands are made in the same factory somewhere in China, and it doesn't really matter which you buy. I've gotten my costs down to roughly $1 each, regardless of whether they're straight, tee, or cross. Again, your availability and cost may vary.
COST > TOTAL
- Single 100cm target with straight connector: ~US$4
- Double 100cm > 60cm target with two tee connectors: US$8
- Triple 100cm > 60cm > 30cm target with three tee connectors: US$12
As mentioned above, adding more braces and connectors would improve stability and add $1.25 or so for each additional brace.
Hope that helps!