Since there doesn't seem to be a lot of details on how to build these, here's the info on the system I put together. I got the general idea from a system one of my dive buddies had put together using PVC pipe. This is not a competion grade setup. The main goals of my system are to allow for easy adjustment of the bottom plate between dives, and to make it easier to recover a lanyarded diver, compared to the single downline setup we normally use.
The
crossbar I use is a pole made of marine grade aluminum.
It is commercially available here for US$40...
shurhold.com/telescoping-handles
It holds the lines 9' (~3M) apart. If you buy two units, three of the sections can be joined together, to hold the lines 12' (~4M) apart. It collapses down to 5' (~1.3M) sections for easier transportation in your car.
I drilled three holes through the pole, for eye bolts, using existing holes where possible. Two for the floats/pulleys, and one for an anchor line attachment point.
For attachment points I used 1/4"x 2” (~6mm x 50mm) stainless steel eye bolts from the hardware store. ( 1/4” x 2-1/2” for the anchor point ).
There are better options ( e.g. marine eye bolts & eye nuts, or ones with larger eyes), but my budget limited me to the hardware store. I used nylock nuts to ensure the nuts do not spin off, and the eye bolts stay securely attached to the pole.
For
pulleys/blocks there are many options, just make sure they can handle the weight & line size.
- The first picture below is the basic pulley I use. US$20 each
www.seattlemarine.net/productcart/pc/viewPrd.asp?idproduct=10999
- Second picture is a snatch block which allows for weight/line deployment retrieval without having to thread the pulley each time. This one runs US$45 each
www.seattlemarine.net/productcart/pc/viewPrd.asp?idproduct=3352
- Best of all may be a cam block, as it includes the brake. But the US$150 each price is steep
www.fisheriessupply.com/productgroupdetail.aspx?cid=6063
As far as
floats go, there are also many options...
- diving floats
www.leisurepro.com/Prod/AQUFC.html
- boat bouy/fenders
www.polyformus.com/
- as well as many others...
For a
brake you can use one of the following...
- I currently use a basic rope cleat which can be clamped or bolted to the pole. I'll upgrade to one of the other options as resources become available. The cleat option works, but can be tricky to master a quick “secure & release” of the line under load. I use a half figure 8, which works okay for how we've been using the system.
- Here are links to some pre-made rail mounted cleats. I'm not sure how well they would work...?
www.downwindmarine.com/Rail-Mount-Cleat-Pair-4-5-16-Black-Nylon-p-37512.html
or
www.downwindmarine.com/Rail-Mount-Cleat-Add-A-Cleat-p-105435.html
- 2 opposite facing clam cleats is another inexpensive option at US$13 each. But an additional mechanism is required to ensure the rope stays in the grooves. Maybe a velcro strap?
www.downwindmarine.com/Clam-Cleats-p-1-c-5883.html
- 2 opposite facing sailing clutches is the deluxe setup at US$70 each
www.sailingsupply.com/index.php?id=33&prod=75
- 2 cam blocks, replacing the need for pulleys is also a nice (and expensive) setup at US$150 each
www.fisheriessupply.com/productgroupdetail.aspx?cid=6063
For a
bottom plate I use a yellow frisbee with a hole drilled in the center for the down line. Additional holes were drilled in the frisbee to reduce drag while raising and lowering. If you use this, avoid placing a jam knot just above the plate, as the divers lanyard can catch on it when tuning at the plate. To keep the plate flat, I added a U-braket to the bottom of the frisbee.
I use 25lbs(~11Kg)
bottom weights at each end of the downline. For me it's a good balance (no pun intended) between having enough weight for pull downs, and not too much weight for recovering from 130'(~40M) at the end of the day. (note: it's not really enough weight for FIM)
We've tested manual recovery of a diver using the system, and it works well. It may not meet the 1M/s AIDA standard, (Todo: conduct recovery rate test.) but it's certainly better then no counterweight. We have not deployed it with a recovery weight, so it is not currently suitable for competition. Adopting a recovery weight, should be just a matter of beefing up the attachment point hardware, and making sure you have enough floatation at the heavy end of the crossbar.
The rope, floats, weights, and bar length in the images below are just for illustration. No, I don't really use kiddie floats for my counterbalace ;-)
Anyway, I hope this is helpful.