Question Only Instructor wears dive computer (extra charge if I want one)

[JMarc]

so I would just use a bottom timer that shows me the average depth

You better then have the max depth very quickly after immersion and then follow a strictly ascending profile. You need to be very careful for the average depth to be safe for table lookup.

 

[rongoodman]

I assume there's some mapping between the letter groups and the degree of saturation of the compartment running the show?

 

[JMarc]

I assume there's some mapping between the letter groups and the degree of saturation of the compartment running the show?

One compartment. 60min for DSAT RDP, 120 min for most (all?) other tables.

 

[tursiops]

I assume there's some mapping between the letter groups and the degree of saturation of the compartment running the show?

Yes, that's how tables and pressure groups work.

 

[jborg]

You better then have the max depth very quickly after immersion and then follow a strictly ascending profile. You need to be very careful for the average depth to be safe for table lookup.

I mean, you don't need to be that enormously careful -- an on average ascending profile will tend to result in less saturation than a corresponding square one. For example, a 20m/30min/EAN32 square profile results in ~60% SurGf according to Subsurface:

An initial drop to 35m for 5min and then a zig-zag ascend over time ends up with the same average depth at 30 minutes and a SurGf of ~48%:

(The/an agency actually teaching the use of depth averaging for anything will, as far as I know, say that the average starts when you reach the bottom -- excluding the descent -- which is even a tad more conservative than what Subsurface calculates here.)

 

[Centrals]

Hi there, for some perspective I am quite new to diving and finished my advanced Open Water Diver in December.
I am now on vacation and wanted to do a wreck dive, but the dive Center I wanted to do it with charges 50$ extra If I want a dive computer.
It’s 2 tank dive with one to the wreck and one to a reef.
I haven’t done a dive without it being a lesson yet and I wondered If it’s normal and If I’ll be fine without a computer.
Thanks in Advance for your answers!

$10.00 for a day rental is acceptable but $50.00!!!! It is nothing less than robbery.
Find another operator.
Put forward the $50.00 for a new computer because you will need it sooner if not later.

 

[tursiops]

It is nice of everyone to keep making suggestions to the OP, but he has not looked at SB since his first (and only) post to start this thread.

 

[JMarc]

I mean, you don't need to be that enormously careful -- an on average ascending profile will tend to result in less saturation than a corresponding square one.

Time weighted average depth of ascending level is mathematically safe. There are other profiles which would work, but I don't think anybody published a less constraining characterisation.

The case I worry about more isn't an irregular ascent, it is the one where the descent is not rapid. This morning dive for instance I reached the max depth at about 1/4, 1/3 of the dive. I don't know if it would have been safe to use the average depth for that profile, but the more you are moving the deepest point towards to end of the dive, the more risks you are taking if you use the average depth for table lookup.

 

[L13]

You better then have the max depth very quickly after immersion and then follow a strictly ascending profile. You need to be very careful for the average depth to be safe for table lookup.

You don't have to be that careful. It actually takes some effort to generate a profile that isn't more conservative with average depth and time.

However, every diver should either be:

1. planing their dive with tables (and following the plan using their own a depth gauge and timer)
2. using their own dive computer.

Since option 1 costs a significant fraction of option 2, while being much less convenient and harder to execute correctly, I always strongly recommend option 2.

The first item a new diver should buy (after items required for initial training) is a dive computer. any modern computer will be good enough. Second should be a mask if you didn't already have to buy one for initial training.

 

[Chavodel8en]

It is nice of everyone to keep making suggestions to the OP, but he has not looked at SB since his first (and only) post to start this thread.

While this is true, this is still supposedly a thread in response to his question. Obviously this thread has been hijacked, but we need not all go along with the hijack. Part of the reason the OP may not have re-posted here is bc he may have read some of the responses and decided they were not helpful to him.