Is it ok to do 2 deeper dives following a shallow dive?

[s.s.seafan]

Hi,

I'm going on a vacation trip next week with family, will want to do some diving. The dive shop (recommended here on the travel board) offers diving at 8am, 10am, 1pm. The 8am dive is for wreck at 100', as I'm still quite new (OW certified 2 years ago, 30+ dive so far) and not trained in wreck diving, I'll skip that. The 10am dive is 20', and 1pm is two dives at 45' and 60'. Is it ok to do the 2 dives at 1pm following the 10am dive? I think I learned somewhere that to never follow a dive with deeper dive - not sure if that's the rule?

thanks,

Jason

 

[Jim Lapenta]

Work it out on the tables and see what you come up with for NDL's. Reverse profiles are not necessarily a no no. But they may result in considerably less time on the latter dives.

 

[muzikbiz22]

Work it out on the tables and see what you come up with for NDL's. Reverse profiles are not necessarily a no no. But they may result in considerably less time on the latter dives.

I was going to suggest Jim Lapenta's reply from this prior thread on Scubaboard, click here. Also in that same thread, is a reply/link to DAN Europe's response to reverse profiles. Or you can search "reverse profile" and find a plethora of info.

 

[flots am]

I'm going on a vacation trip next week with family, will want to do some diving. The dive shop (recommended here on the travel board) offers diving at 8am, 10am, 1pm. The 8am dive is for wreck at 100', as I'm still quite new (OW certified 2 years ago, 30+ dive so far) and not trained in wreck diving, I'll skip that. The 10am dive is 20', and 1pm is two dives at 45' and 60'. Is it ok to do the 2 dives at 1pm following the 10am dive? I think I learned somewhere that to never follow a dive with deeper dive - not sure if that's the rule?

There's no evidence that doing the shallow dive first causes any physical problems or is any better/worse than doing the deeper diver first.

That said, all the tables and computers I'm aware of will penalize you for doing so, which means that the reality is that even though there's nothing wrong with it, you might not be able to fit it in to whatever table or computer you're using.

To get an actual answer you would need to plan your dives according to your preferred method and see if they're possible.

flots.

 

[Mustard Dave]

The reverse profile rule is something that made it into training manuals but nobody could explain why. There is no research that shows it poses any risk - you'll be fine.

 

[Damselfish]

no idea where these dives are, but is the wreck dive meant to actually penetrate the wreck, or just one where you swim around and see it from the outside rather than going in? Swimming around outside a wreck like that is pretty common and doesn't require special wreck training. You may not wish to do it do to depth or conditions, but that's another matter.

 

[Kronek]

Just ran some numbers in the eRDP. Times could be a little off, but.

20ft for 45min PG I (205min NDL)
SI 120m - PG After SI B
45' for 45min PG S (67min NDL)
SI 60min - PG after SI G
60' for 30min PG U (34min NDL)

With all that, go for it. After the 2 hours Surface Interval between Dive 1 and 2 you are almost desaturated so you dont lose much bottom time.

However you have significantly[ higher NDLs if you can do the 60ft first.

60' for 40min PG U (44min NDL)
PG After 60 min SI H
45' for 45min PG S (52min NDL)

Because I am bored. I ran some dives for if you did the 100ft dive first.

100ft for 15 min (20min NDL) PG J
SI 140min - PG After SI B
20ft for 45min (186min NDL) PG M
SI 120m - PG After SI C
45' for 45min (63min NDL) PG T
SI 60min - PG after SI G
60' for 30min (34min NDL) PG U

You can easily do all of them in the same day. Just going to be exhausted by the end of the day.

 

[DivemasterDennis]

I agree with Kronek. Doing you pre-and post-dive ndl calculations to confirm your computer will remove anxiety, if you have any. Reverse profiles, erratic profiles and lots of other things happen all the time on liveaboards or when Debbie and I are shore diving. Just adhere to no decompression limits, do a safety stop on every dive ( except the one to 20 feet max) and there should be no problem. Be safe, and have a great time!
DivemasterDennis

 

[ScubaSteve]

Just ran some numbers in the eRDP. Times could be a little off, but.

20ft for 45min PG I (205min NDL)
SI 120m - PG After SI B
45' for 45min PG S (67min NDL)
SI 60min - PG after SI G
60' for 30min PG U (34min NDL)

With all that, go for it. After the 2 hours Surface Interval between Dive 1 and 2 you are almost desaturated so you dont lose much bottom time.

However you have significantly[ higher NDLs if you can do the 60ft first.

60' for 40min PG U (44min NDL)
PG After 60 min SI H
45' for 45min PG S (52min NDL)

Because I am bored. I ran some dives for if you did the 100ft dive first.

100ft for 15 min (20min NDL) PG J
SI 140min - PG After SI B
20ft for 45min (186min NDL) PG M
SI 120m - PG After SI C
45' for 45min (63min NDL) PG T
SI 60min - PG after SI G
60' for 30min (34min NDL) PG U

You can easily do all of them in the same day. Just going to be exhausted by the end of the day.

To the OP, the only thing I would suggest is that you be careful of in running your pre-dive plans to see if you believe you will be safe is to be realistic in your numbers. If a shop runs dives at 8:00, 10:00 and 1:00 and you go on all three, I highly doubt you will see a 2 hour SI between dives 1 and 2. If the SI time is unknown, I will rarely use an SI of more than 1 hour so that it is one more layer of conservatism. I have also never been on a boat that had me back in the water after anything less than 45 minutes so I use that as my experience.

 

[spectrum]

Jason

What is your air consuption like as a new diver. You may be inherently exposure limited.

Pete