Initial OW Dives

[rshreader]

Hello-

I just got back from Jamaica, where I did my OW dives, and more, for my NAUI and PADI certifications.

I have a question about buoyancy and weight.

On two dives I started ascending too quickly. On the second I was able to dump air in my BC quickly enough to correct the ascent rate. On the first of the two, when I started to ascend too quickly I was unable to dump air quickly enough and the DM had to grab me to keep me down until I was able to dump enough air.

Afterwards, the Instructor and the DM stressed the need to release air early and noted that, if your Buoyancy Control hose passes through a velcro keeper lower on the BC jacket, as mine does, it can create a pocket of air that is difficult to dump. They said that, when ascending I should disconnect the velcro keeper so the hose may be extended higher above the BC and release air more efficiently.

I learned to start dumping air early on an ascent. Sort of like clearing my ears on the way down, early and often.

I was wondering if I may have been carrying too much weight. In the pool, before I left for Jamaica, I had 6 and then 8-9 pounds. On my OW dives I was carrying 16 pounds. I was thinking that, in order to become neutrally buoyant at the bottom, I had to put a proportionately greater amount of air in my BC. With more weight, you need more air to obtain a neutral buoyancy. Therefore, when ascending I have more air in my BC to expand as I ascend causing my ascent to be proportionately more rapid.

I liked the weight distribution of 4 lbs in the back upper pockets and 12 pounds in the dump-able weight pockets along the cummerbund, but perhaps I should reduce the overall weight next time.

Of course, I will remember to dump air earlier on the way up as well.

Thanks for any and all comments/advice,

Read

PS Scuba is incredible! I had a great time and enjoyed exploring the reefs.

 

[ScubaSpicher]

Well one thing you need to consider the difference between diving in fresh and salt water. In fresh water with a 3mm fullsuit I need 8lbs for accurate bouyancy, but in salt water in the same suit I would wear 16lbs. That is the major difference you are forgetting. Besides that just remember that whether or not your hose runs through the velcro strap, you need to make it the highest point on the BC. So if you are horizontal and lift your arm to shoulder height, it would not be high enough. Try tilting to the side and releasing air that way, ensuring it is your highest point.

Your still new... as am I ... it just comes with practice and dives!

PS I got certified in Jamaica too, good diving, but it only gets better!

 

[SlowRain]

You might want to do a search as this subject has been discussed many times.

Short answer is there probably is some info lacking here. Did you have a wetsuit on in the pool? If so was it the same thickness you used in Jamaica? Same BC? All things being equal, if you had the same thickness wetsuit you doubled your weight which seems a bit excessive to me even converting from fresh to salt water...as there is a difference there.

There are lot of methods you can use....the old stand by of empty your BC at the surface, tank at 500 psi, see if you can float with water at eyeball level with full breath and when you let it out you sink is one test.

Personally what I do is a tank with around 500 psi at 15 feet. If I can get neutral with a minimum of air in my BC at that depth I feel pretty good about it.

Your experience is correct though...when you begin your ascent, you do need to start bleeding air early. Waiting until you are in a "runaway" situation is too late. It just takes practice and diving more....you will get there in no time I am sure.

 

[marinediva]

If you are ascending to quickly and your BCD hose is taking to long to expel air I suggest you start to use a dump value.

 

[Colliam7]

On the first of the two, when I started to ascend too quickly I was unable to dump air quickly enough and the DM had to grab me to keep me down until I was able to dump enough air. Afterwards, the Instructor and the DM stressed the need to release air early and noted that, if your Buoyancy Control hose passes through a velcro keeper lower on the BC jacket, as mine does, it can create a pocket of air that is difficult to dump.

Very reasonable advice (vent early; position your equipment to allow effective venting). I have observed more than a few divers who ascend using their BCD (i.e. putting air in to start their ascent), or start their ascent either neutral or slightly positive, which can contribute to an increasingly rapid ascent if venting doesn't occur early. If anything, I prefer to start my ascent by venting a small amount of air to become just a wee bit negative, and swimming up, so I am very slightly negative for much of the ascent - staying just a little ahead of the venting curve. It is a matter of fine tuning. But, the good advice you received is that you should prepare to vent like you should vote - early and often.

I was wondering if I may have been carrying too much weight. In the pool, before I left for Jamaica, I had 6 and then 8-9 pounds. On my OW dives I was carrying 16 pounds.

As several have mentioned, it would probably help to have a bit more detail. If you used the exact same exposure suit, BCD, fins and tank for OW as in the pool, you should not require as much additional weight as you used (16 lbs vs 8-9 lbs). The buoyancy of sea water is only slightly greater than that of fresh water. But, we often put on more neoprene in OW, or use a different BCD and need not only additional weight to compensate for the sea water difference, but also for the additional positive buoyancy we have taken on in our gear.

I was thinking that, in order to become neutrally buoyant at the bottom, I had to put a proportionately greater amount of air in my BC. With more weight, you need more air to obtain a neutral buoyancy.

Not exactly. Yes, on your OW dives, you are going deeper than you did in the pool. So, there is possibly an element of neoprene compression, and slight loss of positive buoyancy, to compensate for. And, you can figure in the fact that it will seem you are adding more air to your BCD at depth, because of the compression of the air in your BCD by the depth. But, the only reason to need more weight is because you are more positive in sea water to begin with, and possibly your rig is more positive. Therefore your overall buoyancy (the balance between how intrinsically positive you are and how much weight you are carrying), should not change dramatically just because you are in salt water. While playing armchair DM is always a bit dangerous, I think you may be on to something in wondering about whether you were overweighted.

 

[Rand]

You want to get your weighting sorted out as others have posted above. Without further info, my best guess is that you were overweighted.

If you own your own BC, check and see if it dumps air by pulling down on the inflation hose. Many styles have a cable that runs the length of the hose and connects to a shoulder dump valve. Venting this way prevents you from having to worry if the velcro strap is trapping air or not. Just dip your right shoulder down when you vent it, making the left shoulder dump valve the highest point (assuming you are ascending in a vertical position). If you are renting, it may or may not have that feature.

Get in a pool or quarry if you can't get some more ocean dives in and practice. It's all about becoming familiar and comfortable with the gear.

 

[diver 85]

When we were taught in '85, I had a little short acronym I used right before starting the final ascent----AT........A for air(dump your BC) & T for time ie stop your stop watch(that was end of BT)...Something I've done on every dive (just about) since.......

 

[don Francisco]

Read- You will probably be able to shed weight on your next dives, but since you seem happy with your trim you should keep the distribution similar.

The ultimate test of weighting is being neutral at 15 feet with 500psi in the tank, no air in the BC, and your lungs about 1/2 full. You'll be able to dial it in over time, by shedding a pound or 2 every few dives. Another indicator of overweight is dropping like a rock as you start the dive. If you're properly weighted you wouldn't be that far from neutral & would descend fairly slowly.

One secret to avoid accelerating ascents is to remember that you'll gain bouyancy as you rise, so vent your BC and start ascents by swimming up against slightly negative bouyancy & continue to vent to remain slightly negative as you rise. Your instructor is right about venting the air trapped in the inflator hose loop. On most BCs you can also vent that by pulling down on the hose which opens a dump valve at your shoulder.

One technique I suggest to all new divers is to ascend in steps, stopping every 10 feet & re-establishing neutral bouyancy. This will ensure that imbalance & momentum won't accumlute and cause a runaway ascent. Moreover, if you hesitate at each 10 foot level for 20 secs it will gaurrantee that your ascent rate cannot exceed 30 feet per minute.

 

[rshreader]

Thank you all for your comments and advice.

FYI-I was using my own SeaQuest Black Diamond BC, inherited from my brother's closet. I was not using a wetsuit in the pool or in the 82 degree ocean. I did have on a dive skin.

Thanks

Read