SDI Solo Course Report

[mjh]

I would also question aborting a dive if one of my computers went down, and my goal is always to hit the shore, deck, etc.. with 500psi. For trim you might want to look at a tank weight. I dive with a 30lb pony, on a bracket on my right side w/drysuit. So my weight is center and left which leaves me with no weight belt and good trim.

 

[jonnythan]

Thanks for the tip divenut, I'll try that next time.

Johnnythan, it's just the opposite, 1/3 going out, 1/3 coming back, and save 1/3 for reserve...

JAG

Of course, I know the rule of thirds. Problem is you don't need 1/3 for reserve if you're in an OW environment when you can surface at any time. You don't need to start your egress with 2/3 of your gas in your tank.

I guess I'm just missing something.

 

[simbrooks]

Jon,

just a thought, but you might want to get back to your start point rather than surfacing and swimming to the exit. 50-50 gas management wont cut that and 40-40 (20 reserve) might only just if you have a delay or problem. Its not 1/3 for reserve for your buddy or to get you back out of an overhead if you have a problem like tech divers are instructed, but that last 1/3 can be used to ensure you have an easier or safer exit along the bottom than surfacing and swimming or at the very least a bit of extra safety if problems do come up - IMO.

 

[jonnythan]

50-50 minus rock bottom would cut that. Your rock bottom for this dive would be the amount of gas you need to deal with a problem for a minute or two plus ascend, including all of your stops. Say this is 1100 psi, and you're diving an Al 80. That least you 1900 psi to dive with.. take 950 psi for going and 950 for returning to your starting point. You're always going to have the 1100 psi you need to get to the surface in the event of an emergency.

Thirds doesn't make sense. Actually, now that I think about it, are they just teaching you to use the last 1/3 of your gas as your rock bottom? I've always learned thirds to mean 1/3 of what gas you have left after you take away that rock bottom.

If that's the case, is 1/3 always enough? Is it sometimes way too much? Why not do it a better way?

 

[jonnythan]

Oh, another question: did any of this even come up in your class? Did they teach you to calculate rock bottom, and gas needed for ascents?

BTW: at what depth was this instructor inflating your BC for you while you were on a pony tank and had your BC off with no mask on?

 

[simbrooks]

Thirds doesn't make sense. Actually, now that I think about it, are they just teaching you to use the last 1/3 of your gas as your rock bottom? I've always learned thirds to mean 1/3 of what gas you have left after you take away that rock bottom.

If that's the case, is 1/3 always enough? Is it sometimes way too much? Why not do it a better way?

I believe i understand your general thoughts and the generally accepted considerations of rock bottom, dont know about what this solo course teaches, but am i reading you wrongly here? That you are saying that the last 1/3 inculdes the rock bottom or are you saying that you work out your rock bottom and include it in your middle 1/3 (back and ascent)? I always thought the latter option.

Surely just thinking about this last 1/3 if it were to replace your rock bottom calculation amount and you actually required more gas than 1/3 your supply to exit/ascend, arent you diving too deep/far into an O/H with too air volume with you?? Particularly if it is >1/3 for ascent only (ie your rock bottom).

BTW, it does seem that the instructor was really having fun throwing this stuff at him. Working out many of the possible problems that could occur and putting them in multiple - not sure quite how i would cope with that many things happening at once. Surely the idea was to establish limits and show the guy what would happen if he let one thing go and problems compounded - i would imagine that IF he hadnt coped well with a certain amount of stuff, he might have "failed" the course if the instructor had to come in to help out - ie deep enough not to pop to the surface, but not excessively deep to really cause short NDL's and get some actual dive training time in.

 

[jonnythan]

I'm saying that leaving the very last 1/3 of your gas accomplishes nothing. You should figure out how much gas you'll need to get yourself to the surface at the deepest point/penetration in your dive, THEN you do thirds. This leaves you with the correct amount of gas for your egress (the rock bottom), as well as 1/3 of the remaining gas for an emergency. The other 2/3 of the "useable gas" (gas that's not needed for ascent) is for your dive.

Leaving the bottom 1/3 of your gas for "emergency" essentially reduces you to diving halves with an arbitrary rock bottom. If you use 1/3 for the dive and 1/3 for the return, you only have 1/3 of your gas left for an emergency and subsequent ascent. If you do it the other way you still have 1/3 of your gas left for an emergency, AND the correct amount for an ascent.

 

[jagfish]

jonnythan
You obviously know a lot about air consumption planning and it shows. Using my SAC (estimated at first, then one taken from the first dive) I was asked to calculate the total air supply I would need to complete the dive for the anticipate total dive time and maximum depth of the target site. We were wroking in bar, and I was asked to surface with the 1/3 (70 bar, or 1000psi). In this case, that was not much of a challenge, since the max depth of the dives in that area was only about 15 to 16 meters. I always came back with about 50 % more than that because the dives were only 50 to 60 minutes. I was running into my imposed time limit way before the air reserve.

In this light, I fully accept what you are are saying about the excessive gas reserve. For that depth, it was clearly more than needed. There was no talk of the term "rock bottom" so I cannot comment on the use of this concept in the training.

The excercise with the skills I had mentioned took place at 10 to 12 meters.

JAG

 

[fldivenut]

For trim you might want to look at a tank weight. I dive with a 30lb pony, on a bracket on my right side w/drysuit. So my weight is center and left which leaves me with no weight belt and good trim.

This raises another issue. If you don't have any ditchable weight you have to make sure that you can swim to the surface with the equipment you have on in case of a BC bladder failure/rapture. Or have a redundant bladder. In the case with a drysuit some regard this as an emergency float device and some don't, and that is a whole other discussion, probably already covered in the cave and tech forums.

As for solo diving you have to make sure you can surface without help of a buddy and the lift from your primary BC bladder. I don't know if they cover this in the solo course or not, it is a topic in intro tech diving though.

IMO the TDI Advanced Nitrox and Deco Procedures is a much better route to solo diving than the SDI Solo course. It seems to me that SDI just took the TDI Deco Procedures and removed the Deco Planning part of it and made it into the solo course. (I have taken the TDI courses and read the instructor standards for the SDI solo course.) If you go TDI tech make sure that you do the courses as a combined course, saves $$, and not only do you get the self reliant part for the solo diving but also the deep diving part. And this only for 4 more dives, the combined course is 8 hours academics and 6 dives. The combined courses start at $450 plus books and boat trips (3-4 for $45 each) here in S. Florida. You also need to have or rent equipment.

--A

 

[Mako Mark]

So what is the student to instructor ratio? Zero to one??

Who will be ripping your mask off or shutting your valves down if you are solo diving???

LMAO

How many people were in the class???? ONE....





Ahhhh, thats better,.... If I hadnt got that out I would have just burst.

Now on with the serious discussion..........