MSDT Prep Questions

[tursiops]

You have just discovered the problem of diving with tables, and the value of the computer.
You can plan the dive with tables, but it is rare that you can actually do that dive....the real dive will be something else.
You can also plan the dive with your computer, using planning mode.
By now you should have figured out how to do that on your computer, and that tables will be of little help to you in real diving.

 

[sabbe]

I was just going back into my log book and filling in some notes. Decided to look at the tables and compare to what the computer showed. The computer had a safety stop for 3 minutes (which is always for that depth) not 8 or 15 so had no reason to believe anything was wrong.
Just trying to figure out where I went wrong and how to correct the action.
If the computer is always making adjustments and still shows everything with in limits then how are you supposed to dive? Like your taught by the tables or just let the computer deal with it?

Decompression theory is just that, a theory. Unfortunately, there are not 100% guaranteed hard and fast rules. Instead tables are around 99.8%. You can follow the table or the computer and still for some reason we science doesn't yet understand still get bent.
I'm getting those numbers from here, I don't know if they're exactly right but the intent is there's no guarantee.
Probability in Relation to “The Bends” – Changing the Way We Think About Dive Safety | Modern Decompression

Because we don't know everything we reduce risks, stay hydrated, avoid physical activity, get enough sleep. You can set your computer more conservative or stay well inside your NDL.

Technically it's safer to never dive, and it's even safer to never leave your house but that comes with other issues.

Sam

 

[Edward3c]

@Stephen McCallister Even when I’m diving on holiday with a dive operator I always want to know the maximum depth and time, with some indication of the profile. That way I can make an appraisal of whether the dive is one I want to do, additionally, I calculate my gas requirements. As a diver I’m responsible for knowing whether I’m capable of doing a particular dive - not the dive operator or guide. So no, you don’t “just let the computer deal with it”.
The thing I see a lot, is people jumping in and doing just that without any idea of what the dive profile should be.

 

[KenGordon]

I didnt plan the dive, it was a guided dive and from the school. The dive briefing on the boat never gives you depth or time at depth, or time at the site to allow you to do any dive planning.

Ask. They have a clue. They will know the depth and they will have a max time. Your actual time will be limited by the speed you use your gas which depend solely on the depth.

Depending on the place your profile might be square or a reef style gradual ascent. You can find out which by asking around, although some specific sites may vary, for example there is a square wreck dive in Cozumel although mostly they are more triangular reef dives. Guided reef dives almost always manage to start deep and end up shallow.

Have a plan A, eg 20 minutes at 30m, and then a plan B for it being shallower quickly. The main thing is to plan to leave the bottom with enough gas. Arriving at the surface with too much gas is not a terrible outcome. Make sure you and your buddy agree both plan A and B and the contingencies of having more gas/NDL than expected so you are on the same page when adapting in the water.

All this stuff is the equivalent of life experience for divers. 92 dives is like being 19.

BTW, if doing four dives a day, start earlier and finish later. Have longer SIs. Understand that the computer models are just models. Don’t assume that a Suunto is conservative just because people on SB say so.

Once you get medical clearance I suggest doing a load of diving. Leave participation in the PADI instructor pyramid scheme until you think you have reached a plateau in your own diving.

 

[UCFKnightDiver]

It sounds like you're trying to rationalize why you got a DCS hit - I would be too. However, as others have said, the tables and algorithms the computers are based on are just models based on theories of what we think the body is doing (e.g., different compartments or tisues in your body on gassing and off gassing at different rates) and are not going to be accurate 100% of the time. You also have to take into account individual differences in physiology, conditions that day, temp, hydration, etc.

Regarding the tables vs. computers point. Tables are going to be based on a square profile where you descend immediately to your max depth, stay there and do your dive, and then surface. Most dives are not square profiles though, so a computer is going to sample depth/pressure close to continuously and take that into account when calculating your dive time which often leads to longer NDL times, or less nitrogen loading, etc.

Having a good idea of the tables is a good thing if your computer fails, but understand that they will not match a computer and you will almost always get longer NDL times/lower tissues loading with a computer vs. dive tables (dive profile and computer conservatism setting dependent). For a quick on the fly calc if your computer craps out, I like to use the rule of 120. For air, your depth plus your time should not equal more than 120. So if you're planning a 60 ft dive you have approximately 60 minutes of dive time. For nitrox 32%, subtract 10% from your actual depth to get your equivalent air depth (EAD), and use the same rule of 120. Of course you do need to know what your max depth is/was and to have a way to know your dive time. By the way this rule is more accurate in the middle of recreational depth ranges/tables (60ish feet) and breaks down as you move much lower and higher (below 30ish and above 100) so if you use it, it's a good idea to do a safety stop, especially for deeper dives. - Sorry, a little bit of a tangent with this last paragraph.

 

[Stephen McCallister]

Yeah you could ask but the answer was always "not sure until we get there because we might be changing locations based on conditions." So there was no way to know until you were actually at the site and they were getting you off the boat.I get that because on side of a dive site could have strong currents and the other side of it doesnt, then the depth changes between those two positions. That happened to about 75 % of the dives i went on there. Maybe it was the way that place operated, everything was a rush to turn dives around and get the boats back to resupply air and do it all over again.
I dive with a Suunto Zoop Novo. A lot of people have said that it is very conservative computer, even comparing mine to room mates at the school, mine always showed the least amount of dive time allowed and the shallowest depth. I dont like to really mess with any of the settings. I know what they do and how to change them but I have left them in default mode because i dont need to mess with them.

 

[Ben_3]

Maybe some of you can answer this. I should be going through the PADI IE this month. After that I would like to be able to teach some specialities, especially the popular local ones. This would help me pick up different courses and schedules at the shop.
What’s the best financial way to become a specialty instructor / msdt? To go through a CD or self certify? Finishing up Instructor so I kind of have spent a lot already. Any insight would be great.

 

[tursiops]

Maybe some of you can answer this. I should be going through the PADI IE this month. After that I would like to be able to teach some specialities, especially the popular local ones. This would help me pick up different courses and schedules at the shop.
What’s the best financial way to become a specialty instructor / msdt? To go through a CD or self certify? Finishing up Instructor so I kind of have spent a lot already. Any insight would be great.

The certification costs the same either way, per specialty. Plus, you pay the instructor if you go through him/her. On the other hand, you need only 10 dives in the specialty to go through a CD, but 20 each if you self-certify....which you can't do until you have given 25 certs. So there are tradeoffs, because those additional 10 dives in a specialty will also cost you, unless you already have them. Not to be ignored is the rather important fact that the CD might actually help you learn how to teach the specialty, and there are always tricks that are not in the Instructor Manual for the specialty nor do you know about them by self-learning. Some specialties are more needy of CD help. So, in part it depends on which specialties you are thinking of getting certified to teach; what is "popular" in your area? Note that you can always do a hybrid.....get some through your CD, and self-certify for some. Suggestion: get the REALLY popular ones immediately through your CD (so you don't need to have the 25 certs yet) because some of those will help you get your 25 certs. Nitrox, for example. If you are qualified for it, Equipment is another good one: no dives needed, can do in dead winter.

 

[Ben_3]

The certification costs the same either way, per specialty. Plus, you pay the instructor if you go through him/her. On the other hand, you need only 10 dives in the specialty to go through a CD, but 20 each if you self-certify....which you can't do until you have given 25 certs. So there are tradeoffs, because those additional 10 dives in a specialty will also cost you, unless you already have them. Not to be ignored is the rather important fact that the CD might actually help you learn how to teach the specialty, and there are always tricks that are not in the Instructor Manual for the specialty nor do you know about them by self-learning. Some specialties are more needy of CD help. So, in part it depends on which specialties you are thinking of getting certified to teach; what is "popular" in your area? Note that you can always do a hybrid.....get some through your CD, and self-certify for some. Suggestion: get the REALLY popular ones immediately through your CD (so you don't need to have the 25 certs yet) because some of those will help you get your 25 certs. Nitrox, for example. If you are qualified for it, Equipment is another good one: no dives needed, can do in dead winter.

Make sense. I don’t get the 25 certs thing though I will have to look that up.

 

[ChuckP]

Make sense. I don’t get the 25 certs thing though I will have to look that up.

If you're a divemaster, look in the back of your manual.

Basically states that to be able to self certify you need this:

Prerequisites
1. PADI Instructor
2. Certifed 25 divers
a. No more than fve from courses without dives.
b. No more than fve from PADI Seal Team or Master Seal Team registrations.

It's the same thing to become a MSDT but you also have to have five specialty certs that don't include the auto ones that come with being an instructor.