Surface interval on boat dive

[serambin]

On a recent 2 tank dive we had a short SI. Let me give details and ask if this is a good procedure.

Dive 1:

Max depth 51fws
Time 40 Min
A square dive to depth an only a small deviation during the bottom time.
No safety stop.

23 min SI

Dive 2:

Max depth 48 ft
Time 38M 30S
3 min stop at 15 ft.

Again a square profile dive.

My Genesis React Pro stopped on the max green level before caution after the second dive.

I understand that a dive boat has to do its job reasonably fast, but the short SI concerned me. Also, the lack of a stop on the first dive. I'm sure the dive master has completed these exact dives many times, but is this the right way?

thanks,

Stan

 

[NorCalDawg]

Stan, what do your tables say? I don't have mine handy but that doesn't sound like you were in any danger of exceeding the NDL's for your repetitive group.

One thing you should always do is PLAN YOUR DIVE. The Dive boat is just there to get you to the dive site. If you need to stay out a few minutes longer on your SI, then you are free to do so. Don't feel pressured to jump right in just because everyone else is the second the boat gets to the site. If you feel you need a longer SI, tell the Divemaster. It sounds to me like you just jumped in the water without doing your own planning. That's where the problem lies.

 

[rawls]

serambin...

I see you are PADI certified so using the PADI RDP you will see that after your dive to 51 ft for 40 minutes you are an Q diver. After a 23 min SI you become a L diver. An L diver going to 48 ft can make a dive for 42 minutes (Total NDL of 80 min-RNT of 38 min). In the Navy dive tables you are a G diver after your first dive. After a 23 min surface you are still a G diver. Your RNT is 44 minutes after a 23 minute SI. Your next dive is to 48 ft. You have 56 min of residual nitrogen. Your NDL is 100 min based on the Navy tables, so you could make a 44 minute dive (100-56). So both the RDP and the Navy tables allow you to make a 48 ft dive for 38' 30" within the NDL time. Although a 3 min stop at 15 feet is suggested, it is not required. Remember...You are the peson who decides whether you are going to do the dive or not. If you do not feel comfortable with it then you do not have to make the dive. For myself, I would have had no problem doing this profile.

 

[Kamchatka]

I didn't get the tables out so if this is wrong - tear into me. After trips to somewhat deeper wrecks (80-120', kinda like the Speigel Grove) we've gone to a shallow reef, maybe 25-40' with a short SI. A couple of times newbies asked (nothing wrong with that) if we needed a longer SI. The DM or skipper asked them to compute their bottom time for the anticipated profile. The tables invariably indicated times well within the NDLs. (OTOH, don't take the word of those people who run the dive ops; they're just no ****** good.) One other thing. Word on the street is that safety stops are a good thing. Not doing one would concern me. And slow ascents are good. Especially as you get closer to the surface. How did you feel about your green lantern still being in the green, albeit close to caution line? (As a comparison, from an old TV show: "Almost late? We have a phrase around here for that. It's called 'on time'".)

 

[SkullDeformity]

Blah, I hate short surface intervals. Sometimes I wonder if I go on boat dives for the diving or the social aspect.

 

[fppf]

We always shoot for an hour. Most diving sources recommed at least an hour between dives.

We also ALWAYS do a safety stop. Just because the DM blows off a safety stop does not mean you and your buddy need to blow it off as well. Did the DM call for a safety in the breifing? If not did you ask about one?

Only place we did not do a full hour SIT was in KeyLargo. But those dives where only 25 feet for an hour on 36 nitrox. And yes we still did a 3 min stop while we watched everyone else trying to get back on the boat in 10 foot seas.

Seems like an odd question from some that has over 500 dives?

 

[drbill]

Although we don't know the details as to when in the open gate time each dive was made, I would not go out on a boat that offered less than a 30-min surface interval (and preferable set aside one hour). Although your dives are reasonably safe based on the tables, I think it is a very bad practice for a boat operator to offer dive trips where reasonable surface intervals are not allowed between dives. Of course here off Catalina, it is very easy to do repetitive deep dives necessitating longer surface intervals for safety, and the boats I dive offer a minimum of 60 min almost all the time.

 

[Steve50]

Why no safety stop ?

 

[serambin]

I did not no that there would not be a stop after dive 1.

I knew that on my computer, I had 14 min NDL time left after dive 2.

My tables were in my BCD pocket, and never left it.

I quess my question is more along the lines of, "if we had a 45 min. SI wouldn't it have been safer and for that mater, easier on our bodies?

Thanks,

Stan

 

[Steve50]

Longer si would have been better, but don't let anyone stop you from doing your safety stop unless the safety stop is not safe ;-)