Deep stop hand signal?

[ToneNQ]

So if you went to do a half depth stop for a 25m dive, would you stay 3mins at 12m in addition to a stop at 6m?

I can't speak for Mares, but circa 2008 with a Suunto, the deep stop only kicked in well beyond recreational limits. Even when there was decompression it was still unlikely there'd be a deep stop. We did a swag of 20min 42-44m dives with no deep stop. We did a 10min 60m dive and the first stop was around the 30m mark for 1min. I think the next stop was 18m, then 12m, pretty standard after the deep stop.

To the OPs point, I'd use standard deco stop signals previously described. The deep stop is inarguably a deco stop, the entire theory behind them is about off-gassing. Signal we go up to a level, signal the depth, signal the time. Definitely rethink why you would want to stop deep, the research is pretty clear that the theoretical benefits aren't realised and it's best to get shallower.

 

[boulderjohn]

Having done considerable research, I have come to the conclusion that there is considerable difference between deep stops on decompression dives and deep stops on NDL dives. Here is my article on decompression diving, which to my knowledge has the latest research. A recent article with a title suggesting it has a "fresh look" in favor of deep stops on decompression dives is absurd; the "fresh look" is a few very old studies of NDL dives and no research whatsoever on decompression dives.

The idea of deep stops on recreational dives began with two of those studies mentioned above, but it was only really accepted by one agency--NAUI. Unless it has changed positions in recent months, NAUI is the only agency I know of that advocates deep stops on recreational dives. GUE does advocate a series of stops starting at half the maximum depth for recreational dives, but the GUE instructor who explained it to me as an official representative of the agency said clearly that it is not because of a belief in the value of deep stops. The purpose is to make the ascent slower when closer to the surface. Half the maximum depth was chosen because any idiot can supposedly calculate half the maximum depth.

Do deep stops help or hurt on an NDL dive? I don't know. All I know for sure is that there is nowhere near enough research on this to tell. Let's look at two dive profiles to trigger some thought. (All numbers are made up off the top of my head and do not reflect actual dive profiles, but they should be close enough.)

1. Tom dives to 90 feet until he is within 5 minutes of NDL. He ascends to 45 feet and does a 2-minute deep stop. He ascends to 15 feet and does a 3-minute deep stop.

2. Sally dives to 90 feet until she is within 5 minutes of NDL. She ascends to 45 feet and pokes around 10 minutes, exploring that section of the reef. She ascends with 10 minutes of NDL, stopping at about 30 feet to explore that section of reef for another 10 minutes. She ascends with her computer telling her she has 45 minutes of NDL remaining and does a 3-minute safety stop at 15 feet.​

 

[BlueTrin]

I can't speak for Mares, but circa 2008 with a Suunto, the deep stop only kicked in well beyond recreational limits. Even when there was decompression it was still unlikely there'd be a deep stop. We did a swag of 20min 42-44m dives with no deep stop. We did a 10min 60m dive and the first stop was around the 30m mark for 1min. I think the next stop was 18m, then 12m, pretty standard after the deep stop.

To the OPs point, I'd use standard deco stop signals previously described. The deep stop is inarguably a deco stop, the entire theory behind them is about off-gassing. Signal we go up to a level, signal the depth, signal the time. Definitely rethink why you would want to stop deep, the research is pretty clear that the theoretical benefits aren't realised and it's best to get shallower.

My understanding is that @racerx_ would add a deep stop only because it was required by his Geo and he claims that he feels better, hence why I asked him to clarify.

You are talking about a deco schedule generated probably based on a more common algo which is different from his approach and this is why you don’t have deep stops.

 

[tursiops]

My understanding is that @racerx_ would add a deep stop only because it was required by his Geo and he claims that he feels better, hence why I asked him to clarify.

It is only required if you set the Geo to require it. The default is no "deep stop."

 

[boulderjohn]

Strongly recommend you read Deco for Divers by Mark Powell (make sure you get the 2nd edition).

Mark's opinions on deep stops has shifted over time, including after the 2nd edition of this book. Here is something he published two years ago on the topic.

Mark just led a webinar on the topic (they are saying their goodbyes as I type). The topic was primarily deep stops in decompression dives, but his position is pretty much identical to the one I expressed in my article last year. There is really no good definition for deep stops, some of the profiles that people have been doing stop too deep, and we still need to do more research to find the ultimate first stop. (I used the term "first stop" because I agree with his opinion that we should stop using the phrase "deep stop" because it is meaningless and confusing.)

This past year Mark worked with DAN Europe on a small study that has not been published yet. They compared a profile using a relatively deep first stop with one using a shallower deep stop. (Not a seriously huge difference between the two, though.) Unlike the NEDU study, there were no DCS cases to define the study, so they looked to other measures. The one significant one was something that I had never heard done before. They compared bubble scores for divers when they got out of the water and found them to be similar, but they also compared bubble scores in 15 minute intervals while the divers were off-gassing on the surface. The difference was huge. The deep stops group actually had higher bubble scores after they were first measured, and 90 minutes later the bubble scores were not highly reduced. The shallower stops group started slightly higher, but dropped rapidly, and at 90 minutes their bubble scores were significantly lower.

Mark revealed that for decompression dives, he is currently using GFs of 50/75.

 

[tursiops]

Need more info to make sense of this. What were the profiles in the DAN study? If they were constrained to be the same dive time, but one had a profile that spent moire time deep, the results are not surprising.

 

[BlueTrin]

Link for Mark Powell’s webinar (thanks to the Diver Medic for organising)

 

[boulderjohn]

Need more info to make sense of this. What were the profiles in the DAN study? If they were constrained to be the same dive time, but one had a profile that spent moire time deep, the results are not surprising.

The had the same total dive time, meaning that the distribution of stops tended deeper in one group and shallow in the other. That was achieved by changing the GFhi. I remember they used Mark's practice of 50/75 for the shallower profile, but I don't recall the deeper one precisely (30/85??). It is in the webinar above.

 

[Celt]

I don’t know what signal you might give halfway through an ascent with the intention of doing a stop but I know the signal you’d get back.

 

[EFX]

How do you make a deep stop hand signal?
For example, telling your dive buddy that you're going to a do a deep stop at certain depth for a certain duration.

For hand signals in general, and this would cover any signals for stops (see rjack321's post #4 for details) I would recommend the book "Hand Signals for Scuba Diving" by the NACD (National Association of Cave Diving). You can get it online and it covers a wide variety of signals for every category you can think of (basic communications, trouble signs, signs relating to buddy positioning, signs relating to the environment, etc.). Though written by the NACD these signs can easily be used for recreational diving. I use these signs in my own recreational diving and they have been easy to learn.

The advantage of using the NACD hand signals is they can be done with one hand, an advantage to those who carry equipment. Most, if not all , of the signals are intuitive. If you adopt these signs you will have to give up some cherished signs like the safety stop (a horizontal hand on top of a three fingered second hand) or the thumbs up (let's go shallower) sign.

Since the signs are from the NACD for use in overhead environments the thumbs up means "let's turn the dive" i.e., leave the overhead environment for open water. Since the safety stop is the raised pinky finger, in open water I've changed the thumbs up sign to mean I'm going directly to the surface right now bypassing any needed safety stop. It means I have a problem, not necessarily an emergency, that I cannot fix under water. Afetr the safety stop it means let's finish the dive and surface. The NACD sign for "go to a shallower depth" or get off the floor of the cave/cavern is a palms up hand with the hand going in an upward motion. This can be followed by signed numbers for the shallower depth.