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Pfuller

Buoyancy, trim and streamlining

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I'm fairly new to Scuba diving, and did a lot of my UW photography on snorkel for the past couple of years.

 

Now i have switched to scuba, i'm finding that having a tank on my back (12 litre/100cft steel with a backplate/wing) really alters my centre of gravity. I use to be able to nail macro/supermacro focus by setting the desired focus, and rocking back and forward to get the focus sharp. I'm finding this much harder with a tank on my back which i find accentuates your movement much more (we're talking millimetres here, which obviously matters with 1:1 plus macro shots).

 

Does anyone have any advice on how to setup thier rig to improve your centre of gravity? I just read about V or P weights. Does tank weighting help? What are peoples opinions on the best weighting placement for photographers doing macro work?

Edited by Pfuller

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I used to have the same problem. I listened to some freinds advice and switched to a wing, harness and use a SS backplate - i find that this enables me to keep relatively still and also means that my weight never shifts around as it used to when i used a Weight belt, all my weight is distibuted evenly across my back and secured with the harness. I also add trim weights to balance myself - normally 1 kg on the lower tank strap. This seems to work regardless of the port / lens combination that i am using and helps me to keep horizontal.

 

Although i have ordered some bouyancy arms and i am looking forward to trying those - although in reality it is save my wrists more than for trim :)

 

The other thing that really helped me was use of correct breathing techniques. As we all know your lungs and the way you use them can have a big effect on your position in the water. Once i have locked focus i hold my breath until i have pressed the shutter this way you eliminate any out of focus shots from rising as you inhale or sinking as you exhale.

 

Regards,

 

Alastair

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I'm fairly new to Scuba diving ... Does anyone have any advice on how to setup thier rig to improve your centre of gravity?

 

I think the key is lots of diving ... I'm sure there are things you can do with your equipment, but if you are new, then nothing is gonna help like practice ...

 

I've spent lots of dives simply practicing movement and buoyancy for photography with my camera topside.

 

One thing I found helpful once was a bit of leg weight ... I dove a few times with one lb weights around my ankles and I kinda liked it ...

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Once i have locked focus i hold my breath until i have pressed the shutter this way you eliminate any out of focus shots from rising as you inhale or sinking as you exhale.

 

It's not "holding your breath" as much as "not breathing in and out at that time". I know of several scuba training agencies that would have kittens if they saw anyone recommending to a new diver that they ever "hold their breath". :)

 

To the original question of improving the center of gravity - it's going to depend on your personal build, your kit, where you're diving etc. One thing that make a huge difference is to get your weighting right in the water. A lot of people have too much weight, which means that they have to add more air to the BCD to offset this. That makes it harder to have a nice, simple, stable center of gravity.

 

The only way to dial this in is to try it out over the course of several dives, adding or removing weight as needed. Do a weight check at the end of the dive during your safety stop. With your tank relatively empty (500-700 psi left) you'll be at your most buoyant.

 

A lot of people learned to do their weight check at the beginning of the dive. While that can give you a good starting point, I find that if I have a wetsuit on that it can hold a lot of small bubbles on the surface when it first gets into the water, and this adds a fair amount of lift. If you can have 1-2 lbs of weight that you can remove and hand to a dive buddy at during the safety stop while hanging near the line, you'll quickly find out if you really need it or not.

 

James.

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Thanks for the suggestions!

 

I have two cam bands around my single steel tank, so i might try moving some weight from my belt to the tank and see how that goes. The cam bands enter the centre slot of my backplate (and i assume this is standard), but i'd like to try to use another couple of straps to anchor down the tank to the outside of the backplate as well, and possibly prevent any sideways rolling of the tank which i think is a influence. (DIRer's probably wont like this idea)

 

I also have plastic fins, and i only just read last night about the benefits of using negative rubber fins. I'm hoping that a good pair of rubber fins should eliminate the need for leg weights, but its a good idea while i have my plastic fins, because i do find my feeting floating off sometimes.

 

I do breathe hold (when there no chance of depth changes), since i've been use to doing this from topside telephoto photography and on snorkel (where you have no option : ) But holding your breath at the neutral (or negative) point is something i'm sure i can improve.

 

Next thing is to get my housing and strobes neutral and balanced!

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Pfuller, all of these questions - trim (center of gravity), buoyancy, gear setup, how you propel yourself - are interrelated in ways that, well, complicated.

 

For example, take your ability to pivot in place, known as the

.

 

If you're the typical advanced recreational diver, and are trimmed out (balanced) in a long, strung-out straight legged position, this will happen:

 

  • You are hovering in place
  • Bend knees to begin helicopter
  • This alters CG (trim) and you begin to tilt head down
  • You inhale to correct perceived sink
  • Begin to rise
  • Swear

 

The fix for all this, and more is to acquire the skills that were woefully left out of your basic Open Water scuba class. You'll find these in a GUE Fundamentals class, or, a UTD Essentials class.

 

Since you're in Victoria, I'd suggest giving Liam Allen a call, at + 61 414 405 598. Tell him what your problems are and what you want to accomplish. A Fundamentals class will cost you maybe US$350, but possibly be the best money you've spent on diving yet.

 

Not to mention, when you're done with the class, you'll have some skills that will make other divers scratch their heads saying "how'd he do that?"

 

 

All the best, James

Edited by fdog

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What are peoples opinions on the best weighting placement for photographers doing macro work?

 

The best weight placement for macro work is the placement that works for you. Figure out where to put weights so that you can stay horizontal, face down, without moving, and use as little weight as possible.

 

Many people need to add ankle weights because their legs and fins are too buoyant. I suffer from heavy feet, and use an ankle weight around the top of my tank to make it easier to stay horizontal. Distributing weights top to bottom is important, and you need the correct distribution for your body type-- there is no one-size-fits-all approach.

 

Another issue is distributing weights around your back and front. If you get this wrong, you can end up doing accidental half barrel-rolls. My torso is more buoyant than my BC-tank-integrated weights, so my natural position is lying face up in the water (heavy tank and weighted BC are down, beer belly is up). Although you can get some nice Snell's circle pictures from this position, there's not a lot of macro to focus on. I distribute weight in my BC to the front pockets so that I can either be face up or face down, with a very slight tendency towards face down. Distributing weights front to back is important, and you need the correct distribution for your body type-- there is no one-size-fits-all approach.

 

Basically, my advice is to move your weights top to bottom and front to back in the way that works for you. Most people need more weight low and behind them. I have an unusual body type, and I need more weight high up and in front of me. Do what works for you, not what other people do. Back plates are great for some people, but not helpful for others.

 

Although this might seem complicated at first, once you get it right, you won't need to alter your weighting scheme again. Suddenly all diving will be easier, and hovering motionless for macro pictures will be effortless.

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Like Jeremy said, it really takes a lot of diving/practice. While I haven't taken the class, James' Fundies suggestion is a worthwhile one. I'd go easy on the weights given the fact that you are diving a steel 100, particularly so in tropical water. I do a bit of North Florida cave diving with double 100's (and don't need an ounce of extra weight with those!); it took a bit of practice at first to get the trim sorted. Buoyancy and trim are critically important in caves and an important skill on a reef as well. Good luck with it, try and lose as much extra weight as you can, and practice, practice, practice!

 

Wendy

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Good day mate,

 

I tried weights on my tank but found that it didn't work for me. What I did find was the actual positioning of the tank on my back made a big difference to my trim so I have now worked out where to strap my tank. Also I found that the standard weight belt also didn't work for me so I use a harness weight belt called a 'Weight and Trim 2'.

 

Ultimately I think as a new diver you will have to try a number of combinations to get it right, which is a pain in the butt, but once you do it is worth it. Also I am not one to push any particular agency but I know PADI have a peak bouyancy course (cost about $120 here in Perth) so it might pay you to find a LDS or Instructor that you feel comfortable with and try that course. If you were here in WA I know a couple of very good Instructors that would help you out.

 

Hope this helps.

 

Karl

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I spent an hour or so in the water changing the position of my tank, and observed an emormous difference in the positioning of the tank. Having said that, i found that the original position my tank was the best position. I decided to try moving a couple of kilograms from my belt to the backplate. I cut up some old lead flashing and have attached it to the holes down each side of my backplate. I haven't tried this out yet so i'll see how it goes. Hopefully its not distributed too widely to accentuate body roll.

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as mentioned bouyancy is key for macro work, both of yourself and of your camera.

 

you say you're diving a 100cf steel tank, thats quite a heafty load. i assume the diving in victoria is cooler water and you're diving with a thick suit. otherwise a 100cf steel is a bit of weight overkill in warmer waters with a thin suit. try different trim options, but i'd think that moving weight up to the backplate or tank with such a heavy back load will only accentuate the tendancy to roll over on your back. you likely need weight on your front to counter balance the heavy tank.

 

also, balancing your camera is key. when setup for macro, my rig is quite negative, and trimmed to point lens down. a couple pieces of foam noodle placed over the strobe arms gets the trim in place, so you can have it neutral and simply guide it with your hands, instead of supporting its weight.

 

and always be aware of your surroundings, if you're stopped in a spot to shoot some macro, know where the bare rock, sand and, more importantly, coral/life is so you don't accidentally knock anything while balancing yourself, especially behind you by your legs. cheers,

 

chris

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First of all, never never hold your breath. I know there are situations when you think or are sure that you can get away with it, but all it takes is one slip up and you can get hurt or even killed. You can suffer a fatal AEG (arterial gas embolism) after an uncontrolled ascent of just 3-7 feet by holding your breath to get a shot. Especially in shallow water, sudden surge caused by wave action can cause this. IF you get into a habit of holding your breath while shooting, sooner of later you will get so wrapped up in the shot that you will begin pushing the limits of good judgment. It just ain't worth the risk.

 

Instead, practice your buoyancy, experimenting with the amount and placement of ballast, without a camera, until you are able to hover in place comfortably while maintaining steady controlled breathing. The advice to check your weighting at the end of a dive during a safety stop with a about 500psi remaining in your tank is exactly what you need to do to fine tune how much ballast you need. You should have just enough to remain neutrally buoyant at 15 feet with very little air in your BCD.

 

Your buoyancy is radically different in full scuba than when snorkeling, so give yourself time to adapt before adding the challenge of photography.

 

When setting up how you are distributing your weights, be very careful about how much undroppable weight you use. Always have enough of your weight attached to you in a good easy to dump system in case of an emergency that requires you to achieve positive buoyancy to get to or remain on the surface. Your statement about adding lead flashing to your rig via a home made set up makes me nervous. Give yourself time practicing before you go and start modifying your gear. In addition to potential safety hazards, you will also be voiding your warranties!

Edited by Aquashot

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Victoria water temp is quickly dropping off at the moment, sitting around 19c at the moment, and will get down to about 13c at the end of winter/spring. So i'm wearing a 5mm wetsuit at the moment, and its double thickness at 10mm around the body, so steel tanks are recommended. (and i stil have signiifcant weight on a belt). I dived over the weekend with the lead on my backplate and i think it was accentuating roll a bit more, but i was only shooting wide angle so didn't get to test out its benefits/drawbacks on macro. A balanced camera rig is something i definently need to work on. Its difficult though getting it right for every different port/strobe/snoot configuration though!

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Good advice about the breath holding...i only hold after exhale when i'm negative, but its not a good habit to form.

 

And re: backplate weight.. If I persist with this setup i will organise a better system, but at the moment its just for testing on shallow shore dives with ample droppable weight on my belt. Do backplates even come with warranties? :beer:

 

My bouyancy is pretty good at the moment, but its more about trim and having a well balanced centre of gravity. Its something that i'll have to work on and i'm sure practice makes perfect!

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