troubles with weight and bouyancy?

[Blue Kangaroo]

All great answers and I'd agree with most of the points.

However it's worthwhile having a think about the physics of diving and buoyancy.

Most newbies and some instructors (!!!!! @@@?!) believe that it's OK to overweight a diver because - well so what, you can compensate by adding a bit of air to the BC.

A big WRONG

Think how an inflated BC is designed to suport you - upright.

So more air means greater "tilt" and a less streamline profile in the water.

OK, so with this extra drag whats going to happen? You will have to work more for the same benefit - and when your muscels work you need more air, so you breath deeper, quicker. So now we have more air in the BC, and more air in the lungs - quickly the problem becomes a spiral.....

So back to the physics...as you all know when you start to assend the air expands making you more buoyant. If your BC is holding you at an upward tilt you will be inclined to swim upwards, or have to put effort in to stay down....effort means more air and greater buoyancy. As you rise the more air you have in your system - lungs and BC, the greater the change in buoyancy as the air expands. IE the more floaty you become.

This explains the yo yo effect as divers dump air as they breath hard and start to swim up ( on a shallow dive only a meter of two can have this effect), then reinflate to compensate for over weighting as they drop down again. Bouncing along the bottom is a classic symptom of overweighting.

Getting rid of weight is hard - esp if you've become good at managing it. On my advanced O/W course I try and get everyone to do Peak performance buoyancy. I'll strip off lead - almost every LB and make the divers control their buoyancy just with the breathing - it's not a way to dive but you can do it. I get down dive in a drysuit with virtually no weight. Not that I'd want to but it is possible. Ask an instructor to help you and try and visualise what is happening to your body. Minimise muscle effort - the less the body works the less air it uses, the better the buoancy, the less you have to work.....and so it goes round.

Think of breathing, trim in the water, the effect of extra air in the BC - they are all interlinked.

hope that helps

Cheers

 

[Thrillhouse]

Huge thanks to everyone who responded here... I read through the responses a couple times over, and it definately gave me some insight.

On the 25th our club has a dive to a local cove. There are a few wrecks at about 45 ft, an anemone garden and a bouey-chain that leads up and down... Sounds like a perfect opportunity to test out having less weight. I'll probably give 34lbs a go, since that's what I used during our OW. Also, huge relief to hear that the BCD should be used for boueancy instead of the drysuit... I always thought this was pretty common-sense, but we were told otherwise.

Right now I'm renting from the shop, and all their shellsuits are a uniform 'M'. I'd like to invest in my own but the bottom line is that suits are expensive. A well-fitting suit sounds awesome though... At 5'8 and 135lbs, I'm sure 'M' is a bit too big.

 

[Blue Kangaroo]

Ummmm....regarding the BC for buoyancy not the suit...THIS NEEDS A STRONG DOSE OF CAUTION.

Just be real careful here. Best practice - certainly in training is to use just one "device" to add and remove air from. You have to add air to the suit to aviod a squeeze, so we train folk to manage the buoyancy using the suit - after a while it becomes second nature. Ofcourse it's harder to dump air from the suit but that's all part of dry suit diving. However it's almost impossible to dump air from the BC AND the suit in the event of a runaway assent casused by a sticky valve, or accidental over inflation. I'm sure you can appreciate the problem. Making it a bit eaiser now can infact lead to potential problems with the inexperienced diver unable to manage 2 devices later on due to lack of training.

It's a bit like learning to drive - you never learnt with the radio on, and the hood down. Well if you did you had more fun that I did.... .

Try to stick with the best practice, but with the knowledge that you (later on with more experience) can change thnigs slightly yo suit your own needs.

Diving in cold conditions is a challenge but great fun too. Experiment with the weight, buoyancy and very soon you'll be an expert - really !

 

[Ber Rabbit]

Right now I'm renting from the shop, and all their shellsuits are a uniform 'M'. I'd like to invest in my own but the bottom line is that suits are expensive. A well-fitting suit sounds awesome though... At 5'8 and 135lbs, I'm sure 'M' is a bit too big.

Depends on the suit. I have a Viking Xtreme, my first one was a size 0 but a "wide" cut, at the time they weren't selling the "slim" cut here. Needless to say my body isn't "wide". When I bought my new suit I ended up with one that was one size larger (a size 1) but it was the slim cut. I was initially apprehensive about the larger size but the slim cut made all the difference and it fits great! BTW, I'm 5'7" and 137-141 pounds any given day.
Ber :lilbunny:

 

[creamofwheat]

Hey thrillhouse...there are a lot of us on this board from Vancouver...I also dive from UBC, I bet I know your instructor. At any rate, send me a PM and I would be more than willing to go dive with you and help you out.