Recently I was in the south of France on the Mediterranean sea doing some freediving training. I got the opportunity to try for the first time a freediving sled. For those that have seen the epic freediving movie Le Grand Bleu you will remember the contraption that pulls the freedivers down into the deep. This contraption is the freediving sled. It has a break to slow down and stop it’s descent, a cylinder of compressed air with a valve and also a sac that gets filled with compressed air to lift it back to the surface. In the image below I am descending down to 25 meters.
Once you reach your target depth you activate the break and the sled comes to a halt. You open the valve and the compressed air starts to fill the sac. Once the sac is full, you shut off the valve to stop the flow of compressed air and the sled will begin to rise, at first slowly and then it will accelerate to the surface. You need to let go of the sled when you are about 10 meters from the surface and fin back up for the last 10 meters. In the image below you see me approaching the surface as the sled is accelerating towards the surface.
There are many advantages to going down using a freediving weighted sled one being that you go down very fast and without any physical effort, so you are conserving energy. Some use it to go down to a wreck, then they can swim around the wreck a bit and come back up again using the sled by being pulled up. Most of the accidents reported have happened on record attempts and individuals going deeper than they can safely go. At shallower depths if all safety precautions have been met, this remains very safe and is in fact commonly practiced in most freediving clubs of France.