Hey Charliehorse,
You pose a good question. This is something that is usaly a preference by th individule diver, as you may have noted by the assortment of replies. Most of which are good advise, and they all have there advantages. The last replie however is actualy the weighting that you would need for scuba diving not freediving. If you used 10% of your body weight, you would be extremly over weighted for freediving. If I went buy that I would were 18 lbs. With a full 3mm suit in fresh water I use 0 lbs. and in salt water I use 2 lbs. Sorry I don't know the conversion to Kg., but you get the idea.
The weight that you use depends on several things. Such as body fat (not so much body weight), salt or fresh water, suit and equipment. It all plays a roll. Here is what I mean by body fat instead of body weight. Lets say that you have 10% body fat and another diver has 26% body fat. You both are the same height and weight, and you both have the exact same gear. Because the second diver has more fat they will need more weight than you. Reason, fat takes up more space and displaces more water. Simply, it floats more. So what works for one may not work for another.
In the end, you will weight yourself for saftey or for preference. I weight myself for safty. Most freedivers, especialy spearfishers, over weight themselves. This is a preference, and if done right may not be bad. Say your speafishing in shallow water, you may want a little extra weight to help you stay down and conserve you energy. If you do this, I would recomend that you not push your limits and, as always, dive with a buddy.
I weight for safty. This is were you weight yourself so that you float incase of a black out. I have always done this but just recently found out that I was still over weighted. I recently took a PFI freediving course. It was well worth the money. Here is how they taught me to weight myself. Put on all the gear that you will be diving with. Get in water deep enough that you can not touch the bottom. Now take a full breath. How much of you is out of the water. With a full breath you want the water to be at the middle of your throat. If it is at your coller bone, you are too light. If it is at your chin, you are too heavy. If it is over your head, DITCH THE WEIGHT. Adjust your weight as needed. And remember, you will need to do this for salt water and fresh water if you will be diving in both. This is a good starting point. And if you want to be even safer, you can do as SanderP suggested and do this on an exhale instead of a full breath. To fine toon your weight, dive to 10 meters and hold. You should be neutraly bouyant.
And yes, get a rubber weight belt, it will save you alot of hassle. Also get one with a metal buckle, plastic ones tend to come loose. Try to get one with a clamping buckle instead of the belt buckle pin and hole type. You will have better adjustability.
Well I hope that this all helps, and good luck with your diving. Have fun and dive safe.
Brian
