The is a lot of discussion about tethers, mostly about how to make them neutral buoyant and still minimize the drag. I started with a 30m tether consisting of 16 cat5 wires and two 16 gauge speaker wires. You can review the electronic post to see the purpose of the wires. I have rejected the idea of putting floats on the tether for buoyancy because of the difficulty with reeling it in and storage. I will probably go no more than 50' deep so I think closed cell foam (polyethylene) in tube form is the answer. It is flexible, not overly bulky, and durable. The problem I have is knowing what size I need for the wires I am using. I don't live the USA so I can't get a sample and test. I am going to encase the foam and wires in PET expandable sleeving to keep everything together. I chose that over ski rope because of the reports that the ski rope retains water and is quite wet when it is retrieved. I will also run a small nylon rope down the tether to attach to the ROV. That will facilitate retrieval in case the ROV stops working. I am going to use disconnect plugs so I can remove the tether from the ROV. The tether has 16 wires (2 for power, 8 for relays, 2 for depth gauge, 1 for LED negative, 1 for video, 2 for power to camera), the rope, and the foam. The disconnect plugs work great and the sleeving keeps everything nice and tidy. In the beginning I thought I would need up to 18 wires so I bought and used two 10 wire connectors. I had already cut the holes in the PVC cap for those when I realized I could have got by with just one 16 wire connector. That is why the connectors attached to the ROV are different from the one connected to the control box.
UPDATE: the quick disconnect plugs aren't working out. The saltwater is causing a short with the power cable which is causing a power drop and corrosion. They might have worked if the positive and negative were further apart. I am not going to test that. Instead I am going to try these connectors. Other IP68 rated connectors cost at least $100 which is way too much.
I used the 1/4" foam tube which turned out to be just about right. Snaking the sleeving down everything was a chore. If you do this you will need to wrap tape around everything about every 2-3 feet. If you don't then snaking the sleeving will stretch the foam to the point of breaking. The tape helps keep the foam in place. I started out with 100' of sleeving. After I got in on I ended up with about 28m of covered wire.
UPDATE: the quick disconnect plugs aren't working out. The saltwater is causing a short with the power cable which is causing a power drop and corrosion. They might have worked if the positive and negative were further apart. I am not going to test that. Instead I am going to try these connectors. Other IP68 rated connectors cost at least $100 which is way too much.
I used the 1/4" foam tube which turned out to be just about right. Snaking the sleeving down everything was a chore. If you do this you will need to wrap tape around everything about every 2-3 feet. If you don't then snaking the sleeving will stretch the foam to the point of breaking. The tape helps keep the foam in place. I started out with 100' of sleeving. After I got in on I ended up with about 28m of covered wire.