Rebreather bouyancy... back 2 n00b basics

[almitywife]

hi all

i said in another thread that almity1 has asked me to tape him diving so he can reveiw his trim and bouancy as he is still fooling around with his weights

as you can see, at the beginning he face was in the sand and maybe he can specifically talk about what he has been doing with his rig & weights to make changes but here is some vid that you can see he is improving.

anyone else can tell us how you are working/did work on your trim when you first started out and any hints to help

cheers

http://www.youtube.com/watch?v=x2iUpeJiaC8

 

[Mr.X]

There are a lot of factors involved with trim from RB setup to RB setup. The easiest fix here might be to change the type of fins he is using as he seems to originally have a heads-down attitude. Adding bailout would probably change his attitude too, probably offsetting the normalizing effect of the fins. Useful ballast (argon) inside the Narked stand might make a difference too and make him tail-heavier.

When I first used the Meg I had a heads-up attitude and had to get rid of my rubber Jet fins and move towards the floatier Mares Quattro. Also, I am 98% in a drysuit and can always manipulate my buoyancy one way or another. The Narked stand that I use from time to time is typically neutral in its effects.

One last item - I sometimes have students use a super heavy backplate with the Meg. 16-18 lbs! Makes a difference.


Best,

X

 

[PacketSniffer]

Which counterlungs?
There is definitely a difference in the type of counterlung utilized. I noticed that when I started out with the cordura lungs I got to the point that my trim was spot on; completely horizontal with legs up in a stationary position. Now that I've switched to the neoprene lungs, I have head up/feet heavy trim. If I stop finning, my head rises/feet fall. I can manage it somewhat in a dry suit but there's no hope in a wet suit. This is with the following parameters:

TLS350 with socks and Rock Boots/Thinsulate 200 undies + Polypro base
DSS SS 7lb BP and 30lb singles horseshoe wing
Jet Fins
Luxfer S40 sidemounted on left for bailout
Salvo 21 HID on right
Valves down
Minimum loop volume in lungs

I'm now in the process of trying some different wings with a bias towards the rear so it will help trim out just right without thinking about it. With those neo lungs, trim is always on my mind and I can't stand that. I want it back to the way I had it. "It just happens" so I can focus on the dive/tour.

I've also tried using the DSS Kydex plate and placing two trim weights at the very top of the plate. It works for diving dry. But, for diving wet, I'm too heavy in overall weight.

Other things that I'll be trying:
OMS Slipstreams (slightly lighter than Jet Fins)
Wings: DiveRite Venture, Dive Rite Rec, Oxycheq Mach V 40lb, Halcyon CCR35
Syntactic foam - As a last resort, I'll place a block of this in the bottom of a stand to offset the negative trim at the feet. See Ouroboros thread on RBW.

These are some of the things I'll be trying. Maybe there is something here that you can grab to resolve your issues.

Good luck

 

[DiveTub]

Get deeper! trying to work out trim in 10-15m is a real PITA. Lung + Wing + Drysuit volume just changes way too much at these shallow depths, even a slight up or down can be a deal breaker with buoyancy.

Get out and do some 20-30m stuff it will make all the difference and is much easier to work on finer trim.

Cheers
Chriso

 

[Mr.X]

Get deeper! trying to work out trim in 10-15m is a real PITA. Lung + Wing + Drysuit volume just changes way too much at these shallow depths, even a slight up or down can be a deal breaker with buoyancy.

Get out and do some 20-30m stuff it will make all the difference and is much easier to work on finer trim.

Cheers
Chriso

Let's think about it - at what depths do you really want to have the best trim and buoyancy? It's certainly not 30M.

X

 

[JD White]

When I did my course the first thing we did was sort trim out in the (salt water) pool. With the Inspo, this was having 3lbs in each trim pocket and 4lbs in the pocket on top of the unit. Once this was done (only took about 10 mins) I had no trouble with buoyancy at all. I was expecting that this would be the most difficult part of the program, but I found it really easy once I had the trim sorted.

JD

 

[almity1]

When I did my course the first thing we did was sort trim out in the (salt water) pool. With the Inspo, this was having 3lbs in each trim pocket and 4lbs in the pocket on top of the unit. Once this was done (only took about 10 mins) I had no trouble with buoyancy at all. I was expecting that this would be the most difficult part of the program, but I found it really easy once I had the trim sorted.

JD

Thanks Jarrod and everyone else.

Just to go into detail aout the video.

It is divided into 3 parts

The first part was when I had 7 or 8 hours up on the unit, that is the first dive out of training.

During training I was using a set of ally tanks, and I ended having 3lbs in each counterlung along with 3lbs in each counterlung and everything was OK, things could have been better but I knew I could finish training and work on the intricate details later.

When I got and put on the Steel Fabers I kept my weights the same, and the results were what you see in the video, more on that later in the third part.

The second part was my wife taking video of different parts of the rebreather to see how it was positioned, especially how I was hitting my head on the top there. More on that later.

The third part of the video is me with less weight in the counterlungs and I was ability to get things into position. This was after 10 hours.

Since then, things have dramatically improved.

I have no weight in the counterlungs at all, it looks like the Fabers have the weight in them, not like the allys. I have positioned the Backplate in relation to the canister that it sits more on my shoulders and my back, this did change my center of gravity, and it was only a couple of inches on the backplate.

My weight in the pouches totals 10 lbs and I will be trying less. I did try 12 lbs total on the weekend , and I found I was a little heavy.

Close to 20 hours now, and its great to be able to have fun and just dive, there is a little more work to do, as I am seeing on how to handle my camera while on a RB. But as I am diving it is working itself out.

That is the key, go out and have fun, dive your respective unit and it will be shown what direction to take.

 

[DiveTub]

Let's think about it - at what depths do you really want to have the best trim and buoyancy? It's certainly not 30M.

X

Beg to disagree on that one.

Anyone can hang on a line or under a bag at 5m and be a little negative plus work on trim while they go, something to do on saftey stops and deco.

Good trim at depth is paramount to an enjoyable dive, maximum conservation of gas and not running into stuff.

Cheers
Chris

 

[Mr.X]

Beg to disagree on that one.

Anyone can hang on a line or under a bag at 5m and be a little negative plus work on trim while they go, something to do on saftey stops and deco.

Good trim at depth is paramount to an enjoyable dive, maximum conservation of gas and not running into stuff.

Cheers
Chris

Trim and buoyancy are both components of RB competency, and as such shouldn't be depth dependent. Not everyone can hang onto an anchor line, or bag. In a worst case scenario where there is no anchor, or heavy bag the diver may have to perform a longish deco. without reference - something to hang onto. I've also seen many a diver positive on their deco., or end of dive. The only thing saving them was the fact they had something to hold onto. Thankfully, most DIR/Fundies folks are terrific at this aspect.

As RB's are typically less affected by tank pressure changes, the variables on deco.would be drysuit/wetsuit, empty bailout or BC. Again, at which depths do you want your trim and buoyancy skills to be sorted and spot-on?

X

 

[DiveTub]

Trim and buoyancy are both components of RB competency, and as such shouldn't be depth dependent. Not everyone can hang onto an anchor line, or bag. In a worst case scenario where there is no anchor, or heavy bag the diver may have to perform a longish deco. without reference - something to hang onto. I've also seen many a diver positive on their deco., or end of dive. The only thing saving them was the fact they had something to hold onto. Thankfully, most DIR/Fundies folks are terrific at this aspect.

As RB's are typically less affected by tank pressure changes, the variables on deco.would be drysuit/wetsuit, empty bailout or BC. Again, at which depths do you want your trim and buoyancy skills to be sorted and spot-on?

X

You forgot
Counter Lungs
Bailout bottles
O2 and Dil bottles


And you are right any diver that is doing any sort of Deco should have their buoyancy dialled in. If you have "also seen many a diver positive on their deco” then maybe you should be reporting their instructors to their training agency for incompetence....

However case in point we are talking about a new CCR diver that is a long way from being qualified or doing any sort of Deco at all. Hence it is far easier to work on getting your trim and buoyancy sorted with a bit of depth as you are having less changes to the following air spaces Counterlungs, Drysuit and Wing, now that is plenty of gas expanding with even minimal depth change in shallower water. So a bit more depth gives you more room to move to get your trim dialled in, from experience a new CCR diver has less trouble with holding shallow stops after being at a bit of depth, rather than just jumping into 5-10m and mucking round with three sources of buoyancy.

Buoyancy on a CCR is complicated enough without trying to master it in the top 10m where the pressure varience is greatest. Drop down to 20m and its a whole world easier to work on the trim. Being upright on your ascent is no big deal, horizontal ascent just comes with practice.

Cheers
Chris