Hello there,
I have been reading about RDP but got lost in calculating surface interval.
Question: you dive at 70' for 30min and then make a second dive to 50' for 4min. What would be the minimal surface interval to perform these two dives safely?
So, Why the answer is is 24min
I know that 70' 30min is Group O then I got lost. Can some one explain me like if I was 5 years old? Thanks for your help.
The missing surface interval exercise breaks down into three questions:
1) what group am I when I finished my first dive?
and
2) what group do I need to be at the START of the second dive in order to not exceed the NDL?
and
3) how long do I need to wait between dives to go from the group I had after dive #1 and the starting group I needed to do dive #2?
What you have discovered already is that you can answer the first question.
So let me lead you through this case so you can see how to answer questions #2 and 3.
// full solution.
Question #1 is what my group is after the first dive? You already worked it out to "O". that is correct.
Question #2; what do I need to be in order to make the 2nd dive without exceeding the NDL? For this you need to flip the table over and use the back side. The dive is to 50ft so you need to find 50ft on the table (see image). 50ft is the black circle on the image. The next thing you need to do is to find the NDL. Your dive needs to fit in an NDL of 4 min. So read to the right until you find 4 min (or more) on the blue line... the adjusted NDL. I circled this in blue; read up to see what group this is
Question #3; how long to you need to wait to go from group "O" to group "W".
In this case, from O to W means you don't need a surface interval at all. You can make these dives back to back.
If the second dive had a bottom time of 47 or 48 minutes instead of 4 minutes then you would have needed to be a group J (see if you find this). In that case your surface interval from group O to group J would have been a minimum of 24 minutes.
R..