If you're properly weighted at the start of a dive; are you over-weighted?

[EFX]

The issue of proper weighting or overweighting depends on other factors besides buoyancy changes. Two I can think of is initially getting to some depth quickly and the other is to get deeper quickly from a safety or deco stop in shallow water. An example of the first scenario is a group doing a drift dive where the surface current is higher than the planned depth. You want all the divers down quickly to minimize the seperation between divers. The second scenario is getting down quickly from a safety stop if a boat is coming. In either scenario being "properly weighted" for buoyancy changes will get you in trouble on the above two dives. Adding another 2 kg would be proper weighting and overweighting in other situations. Excluding the above scenarios tha answer to the op is no.

 

[herman]

No need for extra weigh, the average male has around 10 lbs (4.5 kg) of total buoyancy swing, +/- 5 lbs (2.5 kg) from half full lungs that can be put to use instantly. Adding a couple of "extra" lbs/kgs only serves to add drag to the diver and it takes time to dump that air. Learning to properly use your lung volume along with your fins are the proper way to control quick buoyancy swings, not manipulating the BC.

 

[EFX]

Not in my case. I'm properly weighted in that I can hold a safety stop at 15 feet with very little air in my BC. But at the start of the dive to get down I have to fully exhale until I'm about 8 feet down. Then, I can take a shallow inhale until I'm below 12 feet where there is enough wet suit compression where full lungs won't impede my descent. At the end of the dive I'm even more buoyant where I need to invert to get back down quickly.

 

[mrdre]

No need for extra weigh, the average male has around 10 lbs (4.5 kg) of total buoyancy swing, +/- 5 lbs (2.5 kg) from half full lungs that can be put to use instantly. Adding a couple of "extra" lbs/kgs only serves to add drag to the diver and it takes time to dump that air. Learning to properly use your lung volume along with your fins are the proper way to control quick buoyancy swings, not manipulating the BC.

It's depending where you dive. In warm waters - yes. In cold waters 7mm wetsuit (+ vest + gloves + hood) gets buoyant closer to the surface and gets compressed deep, so the lungs aren't enough to compensate for all the buoyancy changes. So you have to carry extra weights to compensate for wetsuit expansion near the surface.

 

[oldschoolto]

YOU all gave me a head ache.....

Jim....

 

[TMHeimer]

YOU all gave me a head ache.....

Jim....

Yeah...sometimes a simple question can get quite complicated, eh?

 

[cooperscuba]

Okay, now for the full s.p.

I posted the following yesterday on my center's FB page:

Pop Quiz - If you are correctly weighted at the start of your dive and you release all the air from your BCD, would you:

i) Float at eye level
ii) Sink slowly while exhaling
iii) Sink

I did plan today to post "The answer is iii) as you should start the dive slightly over-weighted" but, as this thread developed, I realized my wording of the question and my answer would open a can of worms. So instead I've posted the following:

The correct answer is actually iii)

If you cast your mind back to your Open Water course you'll remember the caveat that, if you perform the weight check with a full cylinder, you'll need to add 2 kg to compensate for the air you're going to breathe during the dive and the change this causes to your buoyancy (commonly referred to as 'buoyancy shift'). Therefore at the start of the dive, if you're properly weighted, you actually start the dive negatively weighted and something negatively weighted will sink.

However, the average male has around 10 lbs (4.5 kg) of total buoyancy swing, +/- 5 lbs (2.5 kg) from half full lungs, so some divers use their lungs (by exhaling hard at the start of the dive) rather than carry the extra 2 kg - Although this is really only applicable for warm water divers. A cold water diver wearing a 7 mm suit, gloves and a hood will really struggle to offset his equipment's buoyancy with this method.

Thank you for taking the time to answer. Much appreciated.

 

[drbill]

You might also consider the changes in wetsuit buoyancy at depth in answering this. Back in the "old days" (when I was much younger) we didn't have BCDs and weighted ourselves for the anticipated depth of the dive, and therefore started out a bit positively buoyant and had to kick down to depth.

 

[Freewillow]

You might also consider the changes in wetsuit buoyancy at depth in answering this. Back in the "old days" (when I was much younger) we didn't have BCDs and weighted ourselves for the anticipated depth of the dive, and therefore started out a bit positively buoyant and had to kick down to depth.

Hi Dr Bill, you remember me of a guy that had been diving forever. I think that he had a licence number of only 4 digits. He used to dive without a BCD. Was properly weighted for the depth he had choosen and was collecting bigger and bigger stones during the dive . He wanted me to dive on the Roreima, a wreck is Saint Pierre, Martinique at 50+ meters. I convinced him to buy a bcd before I would buddy with him though . That was some 20+ years ago. Almost yesterday.............................

 

[The Chairman]

Dr Bob's Weight Titration was taught to me in my NAUI ITC. At the beginning of a dive: With an empty BC as well as having hands folded and legs crossed: if the water just washes over your head with a full breath, you should be fine for the entire dive. Add a pound for every inch the head is out of the water and retest. Feel free to add two more pounds to this if you are anxious.

At the end of a dive (500 psi): With an empty BC as well as having hands folded and legs crossed: Your mask should just clear the water with a full breath and empty BC.

To descend: cross legs, let out air continuously until the water just washes over your head. Let go of the deflater button and exhale. You should drift slowly down and will keep descending until you take a breath. Be sure to assume the scuba position (horizontal) and repeat this process until you get to the bottom. If you're wearing 3mm or less, you probably won't have to adjust your BC any more. Simply vary your respiration to adjust yourself in the water column. To ascend, simply take a super breath (no holding your breath, now) and let the extra buoyancy take over. Keep that air way open and you should notice bubbles coming out as you ascend. Exhaling will stall the ascent. Again, do not hold your breath. Your glottis should always be open. Use only your diaphragm and chest muscles to pause your breathing. Practice this before you get in the water.

To test your skills at buoyancy: place ten 2 pound weights in a row. Pick up a weight and re-establish neutral buoyancy by only modifying your breathing. Keep adding weights and re-establishing your neutral buoyancy until it becomes impossible to do so. You're allowed a finger touch now and then as you work on being neutral and using your inflater for this exercise is cheating. Now reverse the exercise and drop the weight two pounds at a time. You should be able to maintain depth as you get lighter. Six pounds is passing and ten pounds is average. So far, I've had two students go up to 14 pounds with out cheating. On a good day I can do 16 and once I accomplished 18.