Why not go to 100' ?

[Kevrumbo]

I’m going to be in the Caribbean next month for a few days of diving, and some of the dive ops I’ve contacted about a 2-tank boat dive typically do the first dive to about 100 fsw, and a second shallow dive. I have only the basic OW certification and have avoided doing dives much deeper than 60’ on all of my 25 previous dives, and that’s worked out fine with the other divers. I’ve actually been to a bit over 70’ on a couple of dives, and really did not notice any difference. A couple of the ops I contacted said I could stay up at 60’ while they are down at 100, but I will be diving as a single and usually buddy with the DM. Being 40’ more shallow would make me essentially a solo, and I won’t do that. But other than faster air consumption, shorter NDL, and possibly some narcosis (I don’t know how I’d be affected having not gone that deep yet, but feel nothing at 60’) why not go to 100’ with the DM? I tend to be very relaxed when I dive, not at all anxious, check my air and NDL frequently, have pretty good buoyancy control, and a fairly low rate of air consumption (after years of playing sax and practicing controlled breathing). So why not go for it? I suppose I could arrange for some deep dive instruction first, but really don't want to spend the money if going to 100' is not that a big deal.

Your opinions are greatly appreciated.

SAC is your (Surface Air Consumption). SAC is influenced by lots of different things, so knowing your personal rate is important. The beauty of knowing your SAC is that you can calculate your consumption rate for any depth. This is a useful bit of planning for any dive, but it becomes increasingly more important the deeper you go.

Just a quick example. Let's say your SAC is 0.7 cf/min. If you dive to 100' you would be at 4 atm of pressure. 4* 0.7 = 2.8 cf/min. So at 100', you're burning gas 4 times faster than at the surface. If you have an 80 cf tank, then that tank will last you 80/2.8 = 28.5 min on the bottom. Of course, you need to plan for having plenty of gas reserves for: descent, ascent, safety stop, and some "just in case." So obviously no one would plan to stay at 100' for 28 minutes with that gas volume and sac rate.

Whatever dives you do, I recommend that you start to figure out your SAC. To do this, spend some times on your next dives with a slate. When you reach the bottom, on your slate write down your: Depth, bottom time, and tank pressure. When you finish the bottom portion of your dive, just before you begin to ascend, write down those three pieces of information again. After the dive you can use this information to calculate your SAC. Use your average depth for the bottom portion of the dive, and then see how much gas (pressure) you consumed for the time you were on the bottom. You can convert pressure to volume long-hand or you can use the nifty little app (SAC rate by Elliot apps).

Do this on multiple dives as your SAC will be influenced by work load, stress, temperature, etc. After doing this for a while, you'll start to get a good sense of your average rate.

Here's a great tutorial on how to figure "Rock Bottom"/Emergency Minimum Gas Reserve for a 18 meters/60' dive, and a 30 meters/100' dive:

Below is another example of the contingency gas plan for this dive to 30m/100' that you should be aware of, but as a Basic Open Water Diver not yet having the formal training and instruction AND most of all -experience! -to undertake safely with confidence & competence. The point is, there are prudent reasons for holding the Basic Open Water Diver to a limit of 18meters/60feet Max depth while gaining the experience of logged dives and undergoing further advanced training.

How much gas reserve is needed for Air Sharing in an Emergency Out-of-Air Contingency for two divers at a depth of 30 meters/100'?

Given: For each teammate using an 11 liter/bar tank (an AL80 cylinder), and having a volume Surface Consumption Rate (SCR) of 22 liters/min -same as 0.78 cuft/min in US Imperial units (a reasonable breathing rate for beginning to novice divers)- using a NDL air profile dive to 30m (4 ATA) depth for 10 minutes bottom time.

Emergency Minimum Gas Reserve/"Rock Bottom" air calculation, from 30 meters to 15 meters at an ascent rate of 9 meters/ min and from 15 meters with one minute stops every 3 meters to the surface:

Depth (ATA) x SCR (Liters/min*ATA) x Time (minutes) = Liters
4.0 x 22 x 1 = 88
3.7 x 22 x 0.3 = 24
3.4 x 22 x 0.3 = 22
3.1 x 22 x 0.3 = 20
2.8 x 22 x 0.3 = 18
2.5 x 22 x 1 = 55
2.2 x 22 x 1 = 48
1.9 x 22 x 1 = 42
1.6 x 22 x 1 = 35
1.3 x 22 x 1 = 29
1.0 x 22 x 1 = 22

Sum Total Volume: 403 liters

Divide by the tank rating of 11 liters/bar (an AL80 cylinder) equals 36 bar --> round it up to 40 bar Emergency Minimum Gas Reserve/Rock Bottom absolute reading remaining on your SPG at 30 meters -->this is the pressure (40 bar) needed for one person in an emergency contingency to reach the surface with the above arbitrary conservative ascent profile.

So ideally for a two person buddy team, multiply 40 by 2 which is 80 bar needed for both to reach the surface (sharing Air in a buddy Out-ot-Gas contingency).

But realistically, for two novice divers stressed: 80 bar plus 30% of 80 bar equals 104 bar Rock Bottom SPG reading. A full AL80 cylinder is 207 bar/3000 psi, so with nominal exertion in a normal dive, this Dive Team has a usable amount of roughly half tank each (100 bar/1500 psi) at 30 meters, before encroaching on the Emergency Minimum Gas Reserve/"Rock Bottom" SPG reading of 104 bar.

Ten minutes bottom time at a depth of 30m/100' would result in 80 to 90 bar of Air consumed for the Novice Diver (i.e. A Depth Consumption Rate at 30 meters of 8 bar/min); start a normal ascent with no less than 100 bar (1500psi) SPG reading and no more than 15 minutes bottom time (NDL at 30m being 20min). Spend the remainder of your dive & air supply at 15m/50' depth or shallower, before final ascent to safety stop and the surface.

Lastly if you physically over exert yourself at 30m/100' for whatever reason and begin hyperventilating with increased work-of-breathing & narcosis (Hypercapnia), abort the dive at max depth and ascend to the shallows with your buddy for the remainder of the dive. Relax and take time to regain a normal breathing pattern. . .

 

[Freewillow]

take a deep diving course. The idea to solo dive 30 feet above the others is a STUPID one

 

[KeithG]

You will be diving in a group and with a guide. If you are told that the dive will be to 100' and you don't want to go that deep, don't go on the dive.

Remember: Plan your dive and dive your plan. If the dive is planned by the DM to 100, that's where it's going.

Or, go on afternoon dives, which are often shallower.

Or, do the deep dive, stick with the guide, and follow his or her instructions.

an additional suggestion: if you are doing a group dive, make sure you formally buddy up with another diver, not the DM. As a buddy team you can then agree to dive together above the "maximum allowed" depth. communicate this plan to the DM before you hit the water. with 70 to 100 foot visibility and no current, the DM will be okay with this.

DM led group dives for vacation divers are almost always a cluster (which is why we try to avoid them if at all possible). there are divers below the DM, divers, above the DM, divers ahead of the DM, divers way behind the DM. a herd of cats. And all of them think the DM is their personal buddy. The DM can only be the buddy for 1 diver, not 8 or even 3.

on a recent trip a fully certified and trained rescue diver had a panic attack about 10 minutes into the dive (insert snarky comment about poor training standards) The DM eventually noticed (the diver was lagging behind and above the cluster) and responded appropriately, eventually taking the diver to the surface. During this interval the DM had no ability to "service" any other diver. The DM was no longer anyone elses buddy.

If you are doing a group dive and every diver thinks the DM is their buddy, then no one really has a buddy.

 

[Nikole]

Did you check your O-gind before the dive? Walls it already damaged?

What exactly happened after the O ring burst?

Diving deep is easy and fun- until it isn't. Have you ever dealt with a burst o ring while in the water? I did, on my fifth dive after certification, right after buying my brand new regulators. I was in about fifteen feet of water and it was a bummer because it ended a day of diving.

On dive fifteen, my log book reminds me that I lost a fin in about 35' of water. New spring straps on new boots. Turns out your fins and boots have to fit each other. You change your boots, you have to make sure your spring straps fit the same as they fit on the old boots. Who knew? It's not in the manual... Hey, did your open water class teach you that you can efficiently swim with one fin? You can. Just cross your legs and dolphin kick. You can even use your finless foot to hold the strap of the foot with the fin. Good to know.

Which is why new open water divers might want to get some experience in relatively shallow water. We humans get task loaded sorting out new and novel problems. Once divers have some experience solving problems under water, they are less task loaded. In shallow water, you can always CESA on a single breath.

So... are you ready to solve problems at 100' ?

 

[LordElrond]

Diving to 100' in my opinion is no different than diving to 60-50-40 in terms of difficulty, but worse (less light and less time to enjoy the water or solve problems).

On my first dive after the course, still with my instructor, we went to 95', in a monstrous current and 60F water, swimming very low in the clearings of sand between seagrass in order to avoid the full force of the current. Another couple of dives I went to 90'.
No issues apart from the shorter bottom time, but at that depth, that is relatively moderate, you start to see the difference between skill levels due to training and experience, and it's a motivation to train and dive more. The other guys on the boat wore heavier undersuit because they knew they were going under the thermocline, had scooters so they didn't have to fin all the time against the current, brought their doubles so had more time to play and when it was time to go up I was very preoccupied since I knew that screwing up would have been quite dangerous, where those guys were totally relaxed and seemed to have an elevator that effortlessly took them from stop to stop.

I faced the same doubt in DR in August, since after a few dives the guide told us that if we wanted we could go to the St. George wreck, even if it was outside our certification limit of 70'.
A quick minimum gas calculation told me (considering emergency ascent with a buddy, 30l/min each of stressed SCR and two minutes to complete the gas share and start ascent) that with an AL80I had to start ascent with about 140 bar in the tank, for an estimated bottom time (with 20l/min of planned surface consumption, close to my real one of 18l/min) of 10 minutes, all to visit the shallowest deck of the wreck. With unfamiliar rental gear, air insted of 32% and close to the maximum END we are allowed, I chose to not dive that wreck.

Take this opinion keeping in mind that I have zero experience: if someone told me to go to 100ft to see a pretty coral for 5-6 minutes then ascending to 60', with my gear, no current, good viz and a 15l tank I'd go. If the dive is planned as a square profile at 100ft for more time I'd rather wait, take the relevant course and strap a small twinset on my back. I hope to have a lifetime of diving ahead of me, so no hurry =D

 

[NAM001]

This is one of the most friendly threads on this topic. I am a proponent of limits my self. And I under stand at least to my satisfaction the how and why of those limits. The most important factor is comfort and ability to deal with problems if they occure at greater depths. My wife got certed a couple of years ago and when she was done she was not functionally safe to go beyond 30 ft. After a year of shallow diving and engaging in having to deal with a number of problems that always happen to new divers, she became very comfortable with her self. I took her to vortex and we went to the entrance of the cave and she minimally spazzed when I asked her to look at her depth. Ok she got over that so there was no magic life and death line at 50 ft. She also had her first exposure to a tank not lasting all after noon as it did when going to <30' . She now watches her gages like she should. That opened the serious side of the world of diving. This year we went to grand cayman and she made a 100 ft dive. I was a bit concerned about it but I made the gamble that she could handle her self. She did fine. her first exposure with current was again an eye opener for her. She got over the fear that that jaws was somewhere down there waiting for her. Suddenly she became one with the water. Point is it takes a while for new divers to transfer the material covered in classroom lessons into real world experience. She has lost her tank a couple of times like so many newbe's have done and has learned the importance of predive checks, proceedures and the variety of skills from gear checks to shooting bouys. Unless you have a really good instructor you will probably will not leave the OW class with much more than a C card and a false sence of security. Im pretty proud of what she has accomplished. She cant tell you who boyle or henry is, but she knows what to expect in regard to the physics their names are associated with. She will be getting her AOW soon. She has had more exposure and TRUE interaction with the AOW skills than most divers with her dive count. Experience , comfort and confidence are the keys to doing advanced dives. OW teaches you to survive in depths <60'. If you are of the mind set that you can cesa frmm 100 feet like you did in OW class, then you don't belong at 100'. Get your AOW

 

[Aguablanco1]

I don't think the OP is looking for us to talk him into anything. It appears he is looking for advice, not affirmation of a preconceived conclusion.

My first 100'+ dives were done with DM'S doing the guiding and I felt comfortable. I did plan the dive myself for practice so maybe that helped. Do what is comfortable.
RichH

 

[KenGordon]

Grand Cayman is as good a place as any to get some depth experience. I am guessing your 100ft dive will be on a wall and will start deep and work up then finish on the shallow reef.

I am not sure what actual skills an AOW course brings but what you need to be is aware of gas use, deco limits and narcosis. Being conscious that you might be narked is more important at these depths as the degree of impairment is significant.

Deco limits are significant. If you have been at 100ft for 15 minutes and see an Eagle raw further down the wall then you need to understand that you cannot go down to look at it. You will probably not have the gas, not then but later as a consequence. Of course being a multilevel dive you will probably lose the deco further up the wall. These are things that can be taught on a course or learned though experience.

Being a wall dive your buoyancy needs to be good. There really is no bottom as far as a diver is concerned. But, being a wall dive, it is perfectly fine to be above the group so long as your buddy is close to you. Discuss this with your buddy.

Be aware that you may end it in a train of divers, rather than proper buddy pairs.

I seem to remember, and it was a long time ago so may have changed, that in the afternoon all the operators assumed that divers would have been diving deeper in the morning and so only ran shallow trips.

Rather than jumping in for a 100ft dive first thing, I suggest doing an afternoon trip to get warmed up, then the following day doing a potentially deeper one.

Have a full and frank conversation with the operator, bust most of all have fun. Being scared is no fun.

 

[Freewillow]

This is one of the most friendly threads on this topic. I am a proponent of limits my self. And I under stand at least to my satisfaction the how and why of those limits. The most important factor is comfort and ability to deal with problems if they occure at greater depths. My wife got certed a couple of years ago and when she was done she was not functionally safe to go beyond 30 ft. After a year of shallow diving and engaging in having to deal with a number of problems that always happen to new divers, she became very comfortable with her self. I took her to vortex and we went to the entrance of the cave and she minimally spazzed when I asked her to look at her depth. Ok she got over that so there was no magic life and death line at 50 ft. She also had her first exposure to a tank not lasting all after noon as it did when going to <30' . She now watches her gages like she should. That opened the serious side of the world of diving. This year we went to grand cayman and she made a 100 ft dive. I was a bit concerned about it but I made the gamble that she could handle her self. She did fine. her first exposure with current was again an eye opener for her. She got over the fear that that jaws was somewhere down there waiting for her. Suddenly she became one with the water. Point is it takes a while for new divers to transfer the material covered in classroom lessons into real world experience. She has lost her tank a couple of times like so many newbe's have done and has learned the importance of predive checks, proceedures and the variety of skills from gear checks to shooting bouys. Unless you have a really good instructor you will probably will not leave the OW class with much more than a C card and a false sence of security. Im pretty proud of what she has accomplished. She cant tell you who boyle or henry is, but she knows what to expect in regard to the physics their names are associated with. She will be getting her AOW soon. She has had more exposure and TRUE interaction with the AOW skills than most divers with her dive count. Experience , comfort and confidence are the keys to doing advanced dives. OW teaches you to survive in depths <60'. If you are of the mind set that you can cesa frmm 100 feet like you did in OW class, then you don't belong at 100'. Get your AOW

Very well written and interesting topic, BUT FOR ONE THING. " If you are of the mind set that you can cesa frmm 100 feet like you did in OW class, then you don't belong at 100'."

CESA can be done from 100 feet, but every Cesa is potentially dangerous. If you have a competent dive buddy, there is NO REASON in the world to CESA. If your buddy is more that 10 feet away @ deep depth, you have the wrong buddy. Now compare 100 feet to the surface with HUGE pressure changes and your buddy @ a max of 10 feet .

FYI, my wife is my dive buddy. When we deco dive under 120 feet we are ALWAYS at touching range .

 

[NAM001]

Very well written and interesting topic, BUT FOR ONE THING. " If you are of the mind set that you can cesa frmm 100 feet like you did in OW class, then you don't belong at 100'."

CESA can be done from 100 feet, but every Cesa is potentially dangerous. If you have a competent dive buddy, there is NO REASON in the world to CESA. If your buddy is more that 10 feet away @ deep depth, you have the wrong buddy. Now compare 100 feet to the surface with HUGE pressure changes and your buddy @ a max of 10 feet .

FYI, my wife is my dive buddy. When we deco dive under 120 feet we are ALWAYS at touching range .

You don't do that cesa with no more experience than what you have out of OW class. It was taught as a <60' solution. and then from < 30 ft' depending when you took the class. You and your wife are dong deco ,, that alone is an entire experience level world away form those that have 25 dives under their belt with a card that has wet ink in it.