no SI

[scuubaadoo]

I have been on two trips recntly, one to the Bahamas and the second to the FL Keys. Both times the dive crew told every one it was ok to get back in the water as the second dives were less than 25 feet and so "its like doing a long deco stop". I took my time until I was told get in now or you won't be allowed in. This usually put me at about a 45 minute safety stop. What do you think of their rationale?

[boulderjohn]

In many cases with shallow dives you really don't need much surface interval. If you took the traditional PADI OW course, there is a question on Knowledge Review 5 to that effect. It asks the minimum SI between two dives. The correct anser for the imperial numbers is 4 minutes; the correct answer for metric is 0 minutes.

Let's look at the PADI RDP. For a 35 foot dive, your maximum bottom time for a first dive is 205 minutes. That means you could do 3 consecutive 65 minute dives at 35 feet with no surface interval at all if you wanted.

[Dirty-Dog]

You are ALWAYS wrong to 'do as you're told' when you feel uncomfortable with the dive plan. What if they're wrong? It's YOUR life, not theirs.

The question shouldn't really be about THIER rationale, it should be about yours. Don't you know how to plan a dive? Even the most rudimentary dive planning skills would give you the answer. As a test, I presented your question to my friend Kim, who has just finished her PADI OW certification. She has no dive experience other than a resort course and her certification dives. She was able to answer, correctly, that at these depths you would be offgassing, and that reaching the NDL would require a tank the size of a winnebago.

Your SB profile lists "scuba" as your occupation, implying that you are a dive professional. That a dive professional would need to ask this scares me a little. I hope your profile is in error.

[gmanstan]

Dang Dirty D , that was a little harsh. By his post I would guess fairly new diver if not in years by number of dives. Maybe its just time for a review of his "Books".It never hurts to re-read ,and I would suggest he does his "Tables" in log book with his dives, if nothing else for practice . But it would give him a better idea of NDL limits,SI times ,PPO ect.

[Dirty-Dog]

Perhaps it could have been worded more gently, but is there any part of what I said that you actually disagree with?

Do you think it is ever smart to dive a plan you are not comfortable with? A brand new OW diver ought to know this answer.
Do you think that any certified diver ought to know at least the basics of dive planning? I.E how to look at a computer or table to see what the NDL would be on a repetitive dive given the current SI (even if the SI is 2 minutes).

While the question would indeed indicate a new diver (and one with what I would call frighteningly inadequate training), the profile would imply that this is a dive professional. Do you think it is frightening that a dive professional would post this question?

[gmanstan]

well he might be Scuba Professionally(cleaning boats, retrieving golf balls ??) Or maybe just filled out "occupation" wrong. But your post was right on ,just sounded like how my Dad used to get on me...lol
But like I said maybe a lot of dive years but only 1 or 2 vacation dive trips each year. Its always a good time to review your study material or at least keep up with training refresher course or when in doubt ask. I think he was at least in the position of " Err on the side of caution", so I gotta give it to him for posting and asking. Now its time to apply whatever words of wisdom he might gleam from these post.
You know

[Dr Deco]

Hello scubaadoo:

As previous posters have said, that is a simple series of dives that can be checked with readily-obtainable tables. If you were suspicious of the advice for, the boat operators/ dive master, you should check. Sometimes it is only necessary to clear a misconception. It is one of those “AhHa” moments where you then see it all clearly.

For other readers, it is necessary to be able to use these dive aids. Writing Scuba Board for dive tables is pretty “late in the game.” The PADI RDP is helpful

Dr Deco

[scuubaadoo]

Sorry if the question was not asked correctly. Please reread the question. I was not looking for a rehash of what tables may or may not tell you to do. The question was 'what do you thinkof he rationale" of dive operators not to allow divers to do a longer SI if thats what they wish to do. Since irregardless of what table may of may not say the greatest volume change in a bubbler is the last 33 feet to the surface and more importantly the last 15 feet. Dirty dog no matter how many times you reread the question do not ever reply to any post I put forward. The fact that your friend can blindly read a dive table is more proof that divers blindly follow with no thought as to what is going on behind the tables or what they read. Your mean spirited, stupid kneejerk reaction saddens me that I came here to have an open dialogue and this is what I get.

[Thalassamania]

If you are diving a computer, no problem.

If you are diving any other system, too short a surface interval will invalidate any repetitive group calculations and thus make future correct dive calculations impossible.

Will you get bend ... doubtful.

[JahJahwarrior]

Dive boats are a business, typically they have to move a certain number of divers through the boats to stay afloat (pun intended, to lighten the mood) To do this, they typically plan dives out to allow for two trips each day. This leaves them with a range of sites they can visit to keep the dive time plus the SI times plus travel time to under half a day.

So, as a business, if you feel that tables are not accurate and you wish to be more conservative, you might lose out on that second dive. It's certainly fair for them to run their business this way. Think of it like a bar: they give a call for last rounds before they close. You either buy then, or you don't buy, because they have to close.

Now, if the operator took you to sites that required a longer SI, then demanded that you enter the water again, that might be something to complain about. But if they used Navy tables, or anything more conservative, then I don't see what the problem is, with them planning for a trip that had a 45 minute SI.

I've been on boats that had shorter SI's, and longer SI's, it depends on the trip schedule. Typically, if you take the boat for the day, you dive deeper sites, or more sites, and have more SI, but you also pay more because you kept them from running two trips.

I don't get your argument about bubble size change, because tables are based on bubbles and size changes, and on preventing DCS. I have a feeling the tables took into account the pressure change Divers don't necessarily need to put thought into what goes on behind tables, that why we have tables. I agree, it's good to understand, but the fact remains that only a few people are "smarter" than tables. If you blindly follow tables without knowing anything about what science is behind them, you are statistically about as likely to get bent as the person who created the tables, using years of research and science dives. ie, nitrogen bubbles don't care how smart you are, but they do seem to respond well to following the tables.

I understand why you might find the reaction knee jerked and slightly mean spirited, but it's a sad fact that most divers can't even read tables. Heck, a lot of them can't even read a dive computer! I think the post which you took as rude was really meant to say "if you can't read tables, learn how, because it's important." when your original post seems to say "I know how to read tables, but I don't trust them"