Have you ever been diving from a boat in high swell and/or current? Well, like most divers you probably have and you found that holding on to the anchor/descent line when doing a safety stop can be difficult. By using a jon line you can eliminate the shake that occurs from holding onto an anchor/descent line.
The jon line was named after Jon Hulburt who came up with the idea of attaching a 1m to 5m line to the anchor/descent line instead of holding on to it with your hand. This allows you to hover in the water while the anchor line rises and falls with the waves, so you can maintain easily your safety or deco stop.
Is it a good idea? Definitely, I hate being pulled up and down violently when trying to do my safety stop or drifting away when there is a strong current. I remember a story that my friend, who is a tec diver, told me about recreational diving in the Red Sea. It was quite a stormy day with a lot of current, when they came up to do their safety stop there was no room on the anchor line to do their stop, so he pops out his jon line and attaches it and anchor line. They were able to sit back and relax in the water while the other divers bounced up and down due to the conditions. If that isn’t a good advert for it, I don’t know what is.