Fuzzmutton:
I would appreciate some constructive feedback on improving my diving (and just in case someone suggests it---No, I will not take up golf instead
)
Tennis perhaps? Kidding aside, you probably have figured out the basics of what went wrong, but here's my impressions on a few things.
We have been used to mainly diving in a shallow area where it's almost impossible to get into trouble, the few boat dives we have been on have been with someone who stepped up like they were running the show and said we are going to this depth until our PSI gets to here then we surface and then we will spend this much time on surface interval. Everything done by the numbers.
Although you didn't explicitly say so, it sounds like you were diving as part of a group on a guided dive. It's easy to get complacent and rely upon the DM or guide to do the dive planning.
It also sounds like it is a case where you are diving in a different envirionment than before. Any big changes -- temperature, ocean vs. quarry, boat vs. shore, big tanks vs. small one, deep vs. shallow -- adds in additional risk and adds in unknowns that you have to work harder at understanding. Unfortunately, too often we don't know what it is that we don't know until it causes problems.
Did we just forget everything we had been taught in class about the RDP, using it, planning your dive and diving your plan? Duh!
In this case, it sound like you were doing something fairly close to square profile, so you should have been able to compare the dive plan to what your (and your buddy's) computer was showing for NDL at that depth. Going back and forth between the RDP and your computers isn't going to work in the real world, so you need to compare the dive plan to your computer.
If the dive plan is multilevel (E.G. "OK, we're going down to 80' for 20 minutes, then up around 50' for 15min or so, then on up to 30 or shallower for the rest of the dive") then you'll have a problem evaluating the dive unless you have done a similar series of dives in the past, or you have a fancy computer with a simulator function. Unfortunately, what your were taught in class about the RDP doesn't help much in the real world if you are doing multi-level dives. The wheel is one method to evaluate such dives --- I wouldn't call it "plan", because if it is a repetitive dive, then you don't really know what pressure group you are starting in.
In practice, I find it sufficient to see what my computer says is NDL at a couple of depths to approximate my starting pressure group, and then trace the various segments on the back of the RDP using the "zero SI method", where you treat the dive as a series of back to back dives with 0 minute surface intervals between them. Yes, it's messy and not all that accurate, but I have yet to come up with a better way to evaluate a potential dive.
In any case, you should make an attempt to evaluate the dive and determine limits rather than blindly relying upon the planning done by someone else. If you know that you will probably be hitting deco limits, then it won't come as a surprise during the dive that you are deco limited rather than gas limited.
"Yeah, my last dive ran into deco, but I didn't have enough air to stay down. I surfaced with about 6 minutes to go."
With a slow ascent and the 3 minute safety stop that you did, this means that he probably had around 10 minutes of deco obligation when starting up. Deco in and of itself is not bad. Having a deco obligation and not having the gas to meet that obligation IS bad.
More specifically, each of you should have enough gas to support both of you through the entire required decompression period. The most basic underlying rule about gas planning is that
each diver, at any point in the dive, should have enough gas for
both divers to safely abort the dive. This is so that a complete tank or regulator failure of one diver still leaves the buddy team with enough gas for a safe abort.
Part of your diving planning is figuring out the minimum pressure you will have before starting the ascent. If this minimum pressure, often called "rock bottom" was based upon the assumption of no deco obligation, then going into deco will cause you to go beyond safe gas limits.
Obviously, going into deco when that was not planned shows either poor judgement or lack of awareness. The same goes for violation of agreed upon gas pressures for turning around and for ascending.
Going into deco and not letting your buddy know is a violation of buddy protocol / inconsiderate / ............ (fill in other pejorative phrase of choice).
Your doing the final ascent without acknowledgement by your husband is another basic buddy violation. A simple exchange of up signals should have been done. On his part, if he should have stayed down longer to complete a deco obligation, he should have vigorously informed you, and even grabbed you as you started to ascend without him. A simple signal usually understood even by buddies that I've just met that day on the boat is simply to move my hand back and forth horizontally, palm horizontal. Just about everyone intuitively understands that as "level off" "stay at safety stop" "I plan on staying at this depth xxx minutes" or something similar, depending upon the context of the situation.
I checked out my dives and was horrified to see that I had gotten two different violations for not enough surface interval, THEN went on to make a second deeper dive.
Were these "violations", or was this just a case of doing a dive using a Suunto computer that was showing the "attention" signal or something? A less than 1 hour SI may reduce NDLs, but it shouldn't be prohibited by your dive computer.
Don't beat up yourself or your husband too badly for the incident. You are analyzing and trying to prevent a repeat performance. We have all done stupid things. Most of us just aren't brave enough to post them in a public forum.
Charlie Allen
