Planning to unknown depths

[BarryNL]

I understand that DIR rejects computers in favour of planning, but how do you plan a dive in a new location if you can't get information about the site from other divers?

Do you simply plan a few different profiles and make sure you're equipped for the deepest/longest, or do you dive with a plan which covers you for deeper/longer than anything you expect to encounter and abort the dive if it turns out your plans are insufficient?

 

[RTodd]

I understand that DIR rejects computers in favour of planning, but how do you plan a dive in a new location if you can't get information about the site from other divers?

Do you simply plan a few different profiles and make sure you're equipped for the deepest/longest, or do you dive with a plan which covers you for deeper/longer than anything you expect to encounter and abort the dive if it turns out your plans are insufficient?

Getting some information about the site, to the extent it is available is part of proper pre-dive planning. But, if none is available, plan gas and deco for a set max depth and plan for contingency shallower depths. If bottom profile is significantly off your worst case max you probably don't have the right gear to do the dive anyway and it is time to turn.

 

[nadwidny]

I understand that DIR rejects computers in favour of planning, but how do you plan a dive in a new location if you can't get information about the site from other divers?

Do you simply plan a few different profiles and make sure you're equipped for the deepest/longest, or do you dive with a plan which covers you for deeper/longer than anything you expect to encounter and abort the dive if it turns out your plans are insufficient?

Except for exploratory cave diving where one is laying line, one can usually found out what range of depths to expect and make plans from there. In open ocean there are charts that can be consulted or one can use sonar to check out the area before the dive. There is always a way to find out what to expect and make plans from there, especially with regards to gas choices. Nobody needs to jump in the water not having a clue what to expect for a depth. When we are checking out a new area, we set a maximum depth and don't go past it. If things aren't going as expected then it's time to thumb the dive.

As for tables, for dives in the 130ish-200ish range we use ratio deco. For 200-300 we cut some tables and put those in our wetnotes. We always plan around a maximum run time so bottom time is adjusted according to what gets us out at the planned run time.

I actually did such a dive last week. We were checking out rumours of a wreck off a rock in Cape Breton, Nova Scotia. We used a chart to look at the bottom profile so we knew where to get in and what depths to expect. We had a planned maximum depth (250), a planned maximum run time (80). As it turns out that's pretty much the way the dive went. Our exploratory dives don't always turn out this way but they usually do. It pays to do the homework before the dive.

 

[limeyx]

Getting some information about the site, to the extent it is available is part of proper pre-dive planning. But, if none is available, plan gas and deco for a set max depth and plan for contingency shallower depths. If bottom profile is significantly off your worst case max you probably don't have the right gear to do the dive anyway and it is time to turn.

Exactly, and this is one of the big benefits of standard gases
All I really have to do is say what depth do I reckon the site is (approx)

then I have
up to 100 feet -- singles or doubles with 32% or 30/30 (assuming a no deco dive) +100% O2 if deco
100-150 21/35 or 18/45 and 50% (doubles)
150-200 18/45, 50% and 100%

Pretty easy really -- sure, if you expect it to be 150 and it's a 60 foot reef, you might be upset that you are burning $65+ fill on a shallow reef, but you will know for next time!

Also, I sometimes take 21/35 in the backgas, and a stage of 32% (probably about to get called a non-DIR strokery wizard at this point). If you are on a boat with a sounder and the expected 150 dive turns into 60 footer, take the stage, if not, take 50% and dive that way.

I dont see it being at all different without a computer -- the critical issue is what gas, and how much of it you bring -- computer isn't going to help with that.

The only times you get into weird problems are if you do "best-mix" then you are more limited to some extent I guess.

 

[RTodd]

Also, I sometimes take 21/35 in the backgas, and a stage of 32% (probably about to get called a non-DIR strokery wizard at this point). If you are on a boat with a sounder and the expected 150 dive turns into 60 footer, take the stage, if not, take 50% and dive that way.

Not a stroke move at all. Back gas for a deeper than achieved depth is not a problem. DIR doesn't worry to much about optimizing O2 content particularly below 100'.

 

[countryboy]

Plenty of on-line resources to get you "in the ballpark"..

Office of Coast Survey - NOAA Electronic Navigational Charts

MarinePlanner.com

Also, check for tide tables and currents...

 

[lamont]

Plenty of on-line resources to get you "in the ballpark"..

Office of Coast Survey - NOAA Electronic Navigational Charts

MarinePlanner.com

Also, check for tide tables and currents...

Puget Sound Bathymetry for Puget Sound

 

[Doc Intrepid]

Barry,

Wanted to post this trip report in this thread for your edification, but needed to get Mikey's permission first:

http://uwex.us/DOPUSSVA.pdf

This is an AUE trip report to a battleship (USS VIRGINIA) sunk by Billy Mitchell as a demonstration of the anti-naval capacity of air power. The team thought she lay in ~340 fsw. Upon getting to her, she actually lay in closer to ~390 fsw. Mike gave an interesting talk that included this dive when he was at the VBTech meeting in Virginia Beach in 2005.

One of my favorite trip reports, this one illustrates many of the pitfalls faced by teams operating with incomplete information, despite access to (NOAA) best available data from charts and sonar. It also tells a good tale about wreck diving off the Carolinas, and weather and other issues unique to this part of the eastern seaboard.

I also recommend you PM Curt Bowen, who is active on this board. Curt does a LOT of expedition trips to explore caves where little to nothing is known about the depths he will encounter. His experiences are well documented in his Advanced Diver magazine.

Enjoy,

Doc

 

[rjack321]

The funny thing is that Mike and AUE give rather short shift to the depth changes. This is IMO a reflection on:
1) proper training to understand the relationships between depth, BT and deco time and how to they interrelate for standard gasses
2) understanding the general shapes of standard gas deco curves, how and where they get longer or shorter
3) not anticipating an exact depth and running into MOD issues from a "best mix"

Overall a 50ft depth excusion was no big deal to them.