computers and surface intervals

[phoenix09]

I feel like I've been asking a lot of questions on here lately, but I'm a newbie and don't know most of this stuff yet...I'm also the only person among my family and friends who dives, so they have no clue about anything diving-related. Anyway, onto my question...

What's the deal with dive computers and minimum surface intervals? Is there any way to calculate this on a computer? Should I just look at dive tables so I have a general idea, then go by what my computer says for specifics once I'm in the water? I ask because I'm about to go on a trip with 7 dives over 2 days, mostly in the 60-80 ft range. The boat I'll be on requires a minimum surface interval of 2.5 hours between all dives...will this be long enough to take care of excess nitrogen, at least enough to do repetitive dives with decent bottom times?

 

[sasscuba]

I feel like I've been asking a lot of questions on here lately, but I'm a newbie and don't know most of this stuff yet...I'm also the only person among my family and friends who dives, so they have no clue about anything diving-related. Anyway, onto my question...

What's the deal with dive computers and minimum surface intervals? Is there any way to calculate this on a computer? Should I just look at dive tables so I have a general idea, then go by what my computer says for specifics once I'm in the water? I ask because I'm about to go on a trip with 7 dives over 2 days, mostly in the 60-80 ft range. The boat I'll be on requires a minimum surface interval of 2.5 hours between all dives...will this be long enough to take care of excess nitrogen, at least enough to do repetitive dives with decent bottom times?

2.5 hours will be plenty to do dives in the 60-80 foot range. Computer will automatically give you the next dive profile for the time out of the water. You can take a 10 minute interval and it will calculate the next dive profile but it will not be as good as a surface interval of 2.5 hours. Usually I see Dm's take about 45 minutes to 1.5 hours of surface int. between dives.

 

[wunat]

Dive computers will calculate your NDL considering whatever your surface interval is. Even if you just get back on the boat, change or fill tank and jump back into the water, it can will calculate as accordingly.

2.5 hours will be plenty for the type of repetitive dives you will be doing. Not sure what the dive operators onboard will do but we plan our dives with dive wheels (RDP). Dive computers are used as backup in monitor our dive plans.

 

[Jason Ooi]

dive computer calculated your dive time, SIT and NDL for repetitive dives

 

[Matsya]

Most computers have a "PLAN" mode that will give you NDL based on surface intervals and planned depth of subsequent dive.

Ideally you should look up the tables also as a back-up to confirm your computer's correctness. There should not be any huge disparity. As a practice run why don't you lookup the tables for a 2.5 hour surface interval after an eighty foot dive for 20 minutes to see which group that you fall under?

One issue is that since the RDP Tables don't provide for multi-level diving you cannot compare the results that your computer gives and the NDL of the table because the table is for a square profile. But I understand that you can use the wheel to plan multi-level dives and your computer will probably approximate the results that the wheel gives but I am not sure about this.

O.K. after all that, I think a surface interval of 2.5 hours is adequate to off-gas for the kind of dives that you are going to be doing and give you reasonable bottom time.