Safety Stops

[JOHN DE KLERK]

Hello Divers. I am a new diver (PADI Open Water). Can anyone advise on safety stops. I did one dive in which it was extremely difficult to say at 3m for the safety stop- the moment I approached that level, I just shot upwards to the surface. What did I do incorrectly? What must I watch for? Help ! I don't want a repeat episode.

 

[Halthron]

Fresh OW divers tend to have a problem with bouyancy. It's nothing to be ashamed of but is something you should work on improving. Consider it incentive to be able to stay below the surface when a boat is coming your way

You most likely were either underweighted or had too much air in your BC. Remember that a properly weighted diver will have good bouyancy with 500 PSI/30 Bar in their tank at the 15 ft/5m safety stop and an empty BC. The key is to find out how much weight you need.

 

[spectrum]

Hello Divers. I am a new diver (PADI Open Water). Can anyone advise on safety stops. I did one dive in which it was extremely difficult to say at 3m for the safety stop- the moment I approached that level, I just shot upwards to the surface. What did I do incorrectly? What must I watch for? Help ! I don't want a repeat episode.

Halthron prety much summed it up. This is something you need to practice on your next dive, especially towards the end when your cylinder gets light.

At the end of the dive you want to be just barely bouyant with 500 PSI in your tank, your BC empty, bobbing plumb in the water with still legs, cross them if you have to. You should be bobbing at eye level with a moderate breath. A deep breath in and out will probably expose and then sinnk your entire mask. Adjust weight as needed. Having a float with spares or a buddy can help. If you think you are light bring some extra removable weights on the dive.

Once you have this right you will only need a few feet of depth to get enough suit compression to let you stay down. You may need to do a bit of a duck dive to get down again but that's fine. The bottom line is that you will be able to hang at 15 feet with little to no air in your BC.

Pete

 

[shugar]

i know exactly what you're going through... i still have that problem every now and then... solved it for the most part when a DM friend of mine gave me this advise

at 30' dump all my air in the bc... i'll be relatively lighter anyway with the tank almost gone... as you ascend slowly to the safety stop dump more air (air expands as you go up)... you may be heavy at this point (most fresh OW divers are overweighted... i suggest you begin the dive with more correct weight) but i found that i had a much easier time controlling my bouyancy/ hovering since i wasn't fighting nature's urge eject me out of the water...

in other words i found it easier to keep UP to 20-15 rather than force fin myself down to 15-20... a tiny puff maybe of the BC allowed me to hover pretty ok...

hope this helps

Jag

 

[markfm]

I "cheat".

Personally, I want to be able to stay neutral even if something goes bad and the tank is going to go empty. Say there's been a bit of a problem with gas, and you've been at 30m, a depth where that "safety stop" becomes mandatory. I want to be able to suck my tank down to near empty, without becoming a cork. To do that, I compensate for that last 500 psi -- add another 1 lb of weight (500psi in an AL80 is just under 1 lb of weight).

I totally agree with Shugar -- going slightly negative, really working to dump air on the final ascent is very handy, only adding that little bit of air once you reach your desired stop depth.

Good luck!

 

[drew52]

It does sound like you maybe slightly light so perhaps try adding an extra half kilo.

If you're diving in South Africa as per your profile you're probably using a steel cylinder in which case you shouldn't have to much of a weight/buoyancy difference at the end of the dive. If you are using an aliminium cylinder then add a little extra weight for the difference in buoyancy at the end of the dive. Do the the buoyancy check with an empty aluminium cylinder to check what weight you need.

Having said that Shugars suggestion of getting negatively buoyant early on is a great way to ensure you don't just shoot past your safety stop. I usually have no air in my BC at 5 meters if I do its usually because I'm carrying extra weight in case someone struggles to descend.

Practise makes perfect so don't stress these things have happened to most of us.

 

[spectrum]

you're probably using a steel cylinder in which case you shouldn't have to much of a weight/buoyancy difference at the end of the dive. If you are using an aliminium cylinder then add a little extra weight for the difference in buoyancy at the end of the dive. Do the the buoyancy check with an empty aluminium cylinder to check what weight you need.

The cylinder material or size has nothing to do with this as long it it the same for every dive. Air consumed will cause the same weight and buoyancy shift regardless of cylinder. Air weighs .08 LC/CF no mater what it is contanied in. Consuming 70 CF from an 80 CF cylinder will make any diver 5.6 pounds lighter and more buoyant at the end of the dive.

Pete

 

[markfm]

Edit -- Spectrum covered some of what I posted, so I modified this.


To get a better appreciation of this, look at the tank data available from Huron:
http://www.huronscuba.com/equipment/scubaCylinderSpecification.html

The buoyancy full and buoyancy empty columns to the right of the table are the important thing. A steel tank may start less buoyant, be negative compared to an AL80 of equivalent size, but the buoyancy change in pounds is the same.

I have faith in the math -- nothing esoteric, just weight of air. That's why I'm comfortable with doing the alternate weight check, getting neutral with a full tank then adding weight. If I'm neutral at the surface, breathing out sinks me, then I look at my SPG and add weight based on that; 3000 lbs on my SPG means I would need 6 more lbs to be neutral if I emptied my tank, 2500 psi showing means I would need to add 5 lbs to be neutral at the end, etc.

The idea of getting neutral with a full tank, then add 5 pounds, is not an old wives' tale, lazy, or anything bad. It just means they use the underlying physics. (Neutral at 3000, add 5 pounds, means you would be neutral at 500. My choosing to add 6, which compensates down to an empty tank scenario, is a personal choice to take care of contingencies.)

 

[drew52]

Sorry guys wrong terminology above. Not going to argue the maths, but having done buoyancy checks before and after the dive with both steel and aluminium cylinders I have found that usually a person may require extra weight to have correct weighting at the end of the dive when using an aluminium cylinder. With steel cylinders they usually don't.

Best thing to do is do the buoyancy checks.

(As far as I know most aliminium cylinders become positvively buoyant when empty whereas steel ones are generally still negatively buoyant when empty, could be wrong on this)

 

[in_cavediver]

Halthron prety much summed it up. This is something you need to practice on your next dive, especially towards the end when your cylinder gets light.

At the end of the dive you want to be just barely bouyant with 500 PSI in your tank, your BC empty, bobbing plumb in the water with still legs, cross them if you have to. You should be bobbing at eye level with a moderate breath. A deep breath in and out will probably expose and then sinnk your entire mask. Adjust weight as needed. Having a float with spares or a buddy can help. If you think you are light bring some extra removable weights on the dive.

Once you have this right you will only need a few feet of depth to get enough suit compression to let you stay down. You may need to do a bit of a duck dive to get down again but that's fine. The bottom line is that you will be able to hang at 15 feet with little to no air in your BC.

Pete

I would strongly suggest that you strive for neutral with empty tank/BC at the surface, not 15ft as recommended above. The last thing you want to do is be positively buoyant at any part of the dive. Also, you should not need to duck dive down. Simply carry a couple extra pounds. Remember, you should be in control of your position during ALL phases of your dive and the last ascent is one of the most important phases. That means you will start your dive somewhere around 6-7lbs negative and end the dive 1-2lbs negative depending on your tank pressure. (think, neutral with zero PSI in tank).

Mike