How to plan second dive of the day using a computer

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FPDocMatt

Contributor
Messages
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Location
Middletown, Maryland, USA
# of dives
25 - 49
I just bought my first dive computer, haven't used it yet.

After the first dive, while we're on our way to the second dive site on the boat, the dive operator tells us how deep we're going on the second dive, and for how long.

If I had used my RDP table for the first dive, I would know my dive group after the surface interval, and be able to tell whether the dive was safe.

How do you do this with a dive computer?
 
Most dive computers have a planning more. Sometimes it is called 'simulation'. It'll be accessible through your computers' user menu/interface.

At a minimum, on entering the mode, you will input your remaining surface interval, followed by the depth of the dive. It'll give you your maximum NDL for that depth.

Some computers may have a more detailed planning mode, allowing multi-level profiles to be plotted. Some computers may allow you to plan more than one dive in advance.

I don't think any computer will give you an end 'pressure group'. This is quite irrelevant, as computer algorithms will not match your tables and you don't need a pressure group really. Computers and tables are not strictly inter-changeable. You just keep planning a dive, doing a dive etc.

A quick glance at the resulting NDL for a planned depth will give you a clear indication of what you can achieve on the dive and what your max limit will be. If the time is too short, then just plan a shallower dive... or accept the need to multi-level the dive to extend the time underwater. As you scroll through the depths (shallower to deeper) in planning mode, you'll see how the NDL gets shorter. This'll also give you an indication of what sort of NDL you'll get at varying depths. Use that knowledge to 'paint a picture' for the dive ahead with respect to formulating a strategy for multi-leveling.
 
Your computer can not be used to plan a future dive if you have any nitrogen (or oxygen) loading. It can only be used to see the limits of a dive that immediately starts. Of course, you can extrapolate those results a bit and you will get better at this with more experience.
 
Wel definately read up on your manual. I encounter too many people who use their computer as a "magic box" and don't know it's functions and limits. Do you know what you're computer will do if you go into deco? Do you know what your computer will do when it goes in error / SOS? Do you know what model it uses? Do you know how to set it more conservative?

Anyway when using a computer to plan a dive you have a couple of options:
- Look at the plan function of the computer... most will give NDL limits for all concerned depths based on model/conservative setting and current desaturation time (successive dives). This way you already know your NDL for the following dive.
- Some computers have a simulation mode which can be used to simulate a dive and even simulate decompression stops.

Of course when doing deco-dives or even deeper NDL dives you always need to look at a backup decompression source. This can be your buddy's computer (if you've done previous dives together), or a bailout plan based on your computer sim or plan mode. In any case it makes sense to carry within your buddy team a spare gauge that can show depth and time.
 
Most dive computers have a planning more. Sometimes it is called 'simulation'. It'll be accessible through your computers' user menu/interface.

At a minimum, on entering the mode, you will input your remaining surface interval, followed by the depth of the dive. It'll give you your maximum NDL for that depth.

Ah I see, thanks. So before every dive you go to PLANNING, and enter the surface interval since the last dive, and the info about the dive you're about to do, and it tells you how long you have at that depth. Cool!

I went to the website for Dive Computer Training, and it said I can't do the training without an activation code, that I can't purchase the activation code, but rather have to get it from the store that sold me the computer. So I emailed the outfit in Spain that sold it to me to get it. We'll see how that goes.

I read the manual, but didn't understand it. I'll try reading it again. The manual is pretty minimal, and seems to assume that you already know how to use dive computers.
 
Your computer can not be used to plan a future dive if you have any nitrogen (or oxygen) loading. It can only be used to see the limits of a dive that immediately starts. Of course, you can extrapolate those results a bit and you will get better at this with more experience.

Are you saying I can only use the computer to plan the first dive of the day? Then what good is it? That makes no sense. In that case, why does it ask me for a surface interval?
 
Yes, every computer I've used has a surface "planning mode" that will give you in real time the allowed non-deco time for each depth, taking into account your surface interval offgassing. If the first dive was deep or had significant nitrogen loading the general rule is to do a surface interval at least an hour to minimize microbubbles, regardless. As Andy points out pressure group is a table terminology not used in computer diving.
 
Your computer can not be used to plan a future dive if you have any nitrogen (or oxygen) loading. It can only be used to see the limits of a dive that immediately starts. Of course, you can extrapolate those results a bit and you will get better at this with more experience.

I'm not sure what you mean by that? Enter plan mode, input SI, scroll through depths... see the NDLs. Works fine on multiple dives. That basic function, or more, has existed on every dive computer I've used.
 
the computer should scroll through all the options you have . it will give a depth and time @ that depth . the manual will give you a basic giude through all the functions. It is all ways a REAL good thing to thouroughly read the manual while you are reading go through your functions on your computer
 
If your computer allows you to input an SI, then it might support future subsequent dive planning based on ongoing off-gassing. None of mine do that. I use either current outputted dive limitations, tables, or past experience to plan subsequent dives. What computer are you using?

What good is it? Invaluable for safely getting the most dive time out of a current dive.
 
https://www.shearwater.com/products/peregrine/

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