Trouble dialing in weight

[Matt S.]

Sorry in advance for rambling on here...

I am a new (new!) diver, and have only done cold, rainy, Seattle drysuit dives so far. I learned how to do a weight check in my OW class of course--and I did class in my drysuit and personal gear--and I ended up needing about 40 lbs. (My gear and specs at the very end.)

Diving on my own, with rental tanks, I check the tank specs and adjust weight as needed. But now I think I may have been overweighted from the beginning. Here's why.

On my last dive, I rented a new kind of tank, and adjusted my weight accordingly. I was told it was a particular kind of Faber HP 80, which is about -13 lbs when full. So, the way it worked out, I needed to drop 8 lbs of lead from my last config. But when I got in the water, I had to kick a bit to get down. I must have had the wrong tank specs, because on my last dives, I sunk easily when I deflated my BCD. This time I was clearly under weight compared to last time. (but, the dive went OK and I didn't go Polaris at the end. I also felt pretty agile under water, compared to before.)

This long preamble is just so I can ask this: when properly weighted, how hard do you have to work to get down that first 5 or so feet? Or is deflating the BCD like hitting the elevator down button? I'll do another weight check, but it would help to know how it should feel at the beginning of a dive with a full tank.

It seems like you should be negative at the beginning of your dive by the weight of the air that you will consume--5 or more pounds--and being that negative ought to make you sink pretty easily.

I would rather be a few pounds over than under, but at the same time, now I am wondering if I am carrying an extra 8-10 lbs that I don't need.

(As an aside, I am surprised that dive shops don't mark the buoyancy specs on the tanks, or at least post the data somewhere. It's important information! And sometimes it is hard to tell the make of tank from the markings.)

 

[dschulte]

Sorry in advance for rambling on here...
This long preamble is just so I can ask this: when properly weighted, how hard do you have to work to get down that first 5 or so feet? Or is deflating the BCD like hitting the elevator down button? I'll do another weight check, but it would help to know how it should feel at the beginning of a dive with a full tank.

You should have your dry suit empty and your BC full when on the surface. As you begin your decent, empty your BC fully and begin to add air to your dry suit to achieve neutral buoyancy and compensate for suit squeeze. Your decent should be effortless, just a partial exhale should get you past the first 2-3 feet, and then you should have your BC empty and begin filling your dry suit. Now you are not going to put a ton of air in, just enough to counter the squeeze and become neutral. I dive with about 18 lbs in my dry suit; this includes the 6 lbs plate and the 12 on my belt. I set my weight by emptying my BC, slightly inflating my dry suit, enough to get the color to inflate, then hold a breath and see if I am at eye level in the water. Do not go too light on the weights, air in your suit is your friend, not waddling blimp:fruit: , but a layer to ensure thermal protection. Try to get some pool time and play with your weighting, it is more comfortable and safer than in open water.

Good luck and welcome to the dry club.
:monkeydan

 

[JohnnyH]

It's good that you are thinking about finding your proper trim. That's half the battle (rather than just strapping on more lead) With 80cu ft of air you are correct in thinking your weighting will change by about 5lbs when you are at around 500psi (i.e. end of dive) and therefore for optimal weighting you should do your buoyancy check with 500psi rather than a full tank.

Breathing and the volume of air in your lungs is an important factor too. There's been plenty of talk about this on this forum. Try practicing breathing off the bottom of your lungs to reduce displacement from your lungs while descending. Also there is always plenty of trapped air about you, your BC and drysuit that only water pressure will be able to eliminate - so unlike when you are ascending, when you descend after entering the water you will be extra buoyant. Therefore make sure to fully vent the suit, try dropping your right shoulder to make your left shoulder (and inflator hose) the high point of your rig to help dump the gas, and relax the body - watch what your fins are doing - they shouldn't be doing anything.

And keep thinking - that's the best tool. (Would sound trite if it wasn't so true)

John

 

[Peter_C]

I was told it was a particular kind of Faber HP 80, which is about -13 lbs when full. So, the way it worked out, I needed to drop 8 lbs of lead from my last config. But when I got in the water, I had to kick a bit to get down.

Sounds to me like you went from an aluminum 80 to a HP (High Pressure) steel 80

Swimming down at the begining means you are weighted about perfect if you are diving steel tanks. :14: Since you were not corking at the end of the dive, then everything sounds about right.

At the end of the dive with 500 psi you should be neutral at 15' with very little air in your drysuit and no air in your BC.

I doubt the tank is -13lbs, but probably closer to -9 lbs.

 

[FoSheZZie23]

My weight managment might differ from the norm but I like to be heavy. When i deflate my BC on the surface i want to sink, i dont want to have to exhale to sink the first 3 feet. I also dive dry and actually I didnt change my weight from when I wore a wetsuit. Depends on how many undergarments I wear. I wear a 25lb belt plus i have my steel HP100.

The main reason i like to dive heavy, and by heavy i mean 5 pounds overweight, is in the situation of an uncontrolled ascent all I have to do is dump my BC, with the extra 5lbs I have to keep some air in my BC at all times. They taught me in my drysuit class that at the bottom you shouldnt have any air in your BC only in your drysuit. Its alot faster to dump air out of a bc than a drysuit in my opinion. It also comes into play if you are diving with new divers that might not be weighted properly also, they are having trouble getting down or staying down, they wont have an uncontrolled ascent to the surface. I can help them fix the situation instead of a possible bad bends situation happening.

Thats just the way i think about it. I havnt noticed that being over weighted makes me any less agile in the water. Then again i like to take nice slow leisurely dives, so the extra might affect those who like to swim a mile underwater durning their dives...... just my 2 cents!

 

[Matt S.]

I was actually moving from a PST E7-80 to the Mystery Steel 80. Before I can figure this out I guess I need to talk to my LDS and figure out exactly what tank it was that I had.

 

[fisherdvm]

I am taking drysuit class in 2 weeks and worried of the same problem. I posted something called "dry suit and weight issue", and got some good response.

I wonder if your suit could be too big, and you can not empty enough air on the surface?? But I'll let the expert answer you... I know nothing about dry suit diving.

 

[spectrum]

This long preamble is just so I can ask this: when properly weighted, how hard do you have to work to get down that first 5 or so feet?

If you are weighted right and if the amount of air entrapped in your drysuit is comparable to what was in there for the weight check then vending your BC should make for an effortless drop. At the start of the dive your cylinder is a good 5 pounds heavier than than it will be when you reach your neutral weight check state. If you want to drop down near the end of the dive for something with like 750 PSI left in your cylinder then a little duck dive and a kick or 2 may be in order.

After you are in the water bob with your vent wide open spend a moment letting the water squeeze air out of your suit. Pay attention to keep the vent high. This will bring you to a fairly predicatable state.

Or is deflating the BCD like hitting the elevator down button?

As long as you don't keep going with the elevator metaphor, yes, dumping your BC air should make you drop with very little fuss. So you can keep up with your eirs add quick bursts of air to your BC. As you feel the suit start to constrict add a shot to the suit. After a while you will know when to do this. Don't let it get tight on you.

I'll do another weight check, but it would help to know how it should feel at the beginning of a dive with a full tank.

The initial drop should be easy. Of course relax your breathing and just as the BC finishes dumping make a deep exhale as a finishing touch and down you should go.

Be careful not to let a single data point throw throw you off. One odd cylinder spec or a sloppy job at venting excess suit air can make 1 dive awkward but need not invalidate all that you have learned.

Pete

 

[SparticleBrane]

Good gracious...40 pounds of weight? WITH a steel tank?? You sound way overweighted.

Here is a tank spec page. If you look, a PST HP80 is -9 lbs and a Faber HP80 is -13lbs. Note that these are actual HP tanks, not exemption (X-series, FX-series, or E-series) tanks.

 

[Matt S.]

> As long as you don't keep going with the elevator metaphor, yes, dumping your BC air should make you drop with very little fuss.

Good, good, that's what I need to know.

> Be careful not to let a single data point throw throw you off. One odd cylinder spec or a sloppy job at venting excess suit air can make 1 dive awkward but need not invalidate all that you have learned.

Good point.

> Good gracious...40 pounds of weight? WITH a steel tank?? You sound way overweighted.

That's how it worked out in class. Of course they are in a hurry, the student (me) is new, etc etc.

At this point I am pretty sure that I have been overweight but not grossly so. I'll do another check this weekend.

Thanks for the help!