Posts Tagged ‘Technical Dives’

CDT Fourcault promo

Wednesday, June 15th, 2011
CDT Fourcault

A while back, I spent some time on the CDT Fourcault diving shipwrecks of the North Sea. The trip was a blast, and I met some really wonderful divers. There were groups from Belgium, UK, USA, and Italy (actually only one diver from Italy). All were fine divers, and many great sea stories were told over the dinner table.

Since that time some of us have kept in touch, and exchanged photos and videos of the trip, and other dive events. The latest was a promotional video made for the vessel CDT Fourcault. There are clips from our trip, and even a shots of me.

How Long can a Scuba Diver Stay Underwater?

Sunday, January 30th, 2011

I provided a simple answer to this question in a post last winter.  Over the past year, this post received a large number of hits, so it’s obviously this is a question that is often asked.   Therefore, I wanted to expound on the previous post.

There is no short answer to this question.  Ultimately, the limiting factor is either available gas, or environment.   The environmental factor here is cold.  Water transfers heat 25 times faster than air.  Even 80 degree water robs your body of heat.  This is why exposure protection is needed.  For the rest of this discussion, let’s assume there is sufficient exposure protection for the given water temperature.

Now the time limit is just a function of the available gas.  Let’s breakdown the answer based on type of diver.

Free Diving: Here the divers plunge to some amazing depths on one breath of air, and stay for several minutes before returning to the surface.  The limiting factor is the individuals tolerance for low Oxygen, and high CO2. I believe the current record is 124 M unassisted.  The maximum duration for static (resting) breath hold is 11 minutes 35 seconds.

Basic Scuba Diving: Here there are two limits:  The available gas in the diver’s tanks, and the no decompression limit for the depth.   There is a detailed explanation of the factors involved, but an average diver can stay between 60-80 ft for about an hour.

Technical Diving: Divers are limited by the number of tanks they use during the dive.  Some exceptional dives have been for over 18 hours.  Clearly a great deal of planning is required for these types of dives.  More routinely Technical Divers often go to 150-250 ft with durations around 90-120 minutes.

Rebreather Diving: A rebreather (as described here) removes the gas limitation, but imposes a limit on the duration of the scrubber material.  Based on the construction of the rebreather, this is usually between 3 and 11 hours.  The limiting factor here is the number of tanks a diver is willing to bring in case of rebreather failure.

Commercial Diving: These divers are provided gas from a surface vessel or station.  This technique also referred to as surface supplied, does not have a limit on the gas available.

Saturation Diving: In this case the divers body is completely saturated with inert gas.  In some cases the divers will utilize a habitat between dives.  This provides an area where the diver can warm up, and take food and liquids.  In essence there is no limit to the duration that a diver can live in saturation.  The down side is the extremely long time needed to decompress.

I hope this helps answer the question.   If you have any questions on this subject, send me a comment below.

Class Photos, Fall 2010

Wednesday, December 15th, 2010
Shooting a bag while maintaining buoyancy

Shooting a bag while maintaining buoyancy

This fall in the Northeast was a bad season for blowouts and poor visibility.  Several hurricanes passed by, stirring up the surf.  Often, this can help the conditions by mixing the surface water with the cooler water below the thermocline.  Unfortunately this fall it cleared out the plankton on the surface, then just stirred up the bottom into soup.  At this point, the surface had over 50 ft of visibility, but the bottom would drop to less than 5.  That’s on the days we could make it out.

On the plus side, this gave me the opportunity to drag some students up to Dutch and finish up classes.  Once most of the drills are done, I dragged the camera along to grab a few shots.   After this fall, I needed the practice or I’d forget how to work the housing.  Also, I’m playing with a new lenses/port combination that takes some getting use to.  For what it’s worth, here are some of the photos that came out well.

Count the Counter lungs

Tuesday, October 12th, 2010

A friend just asked an interesting question:  Why have two counter lungs vs one?

I must admit, that no one ever told me an answer to this question, but here is my reasoning for 2 vs 1:
One counter lung only lets the scrubber work during half of the breathing cycle.
If the lung is on the exhale side, then it inflates on exhale, but gas only passes through the scrubber on inhale.
If it’s on the inhale side, then gas passes through the scrubber only on the exhale.

If you have two counter lungs, half the gas passes through the scrubber as you exhale, and half passes through as you inhale. This makes the gas pass through the scrubber slower, (aka dwell time)  and therefore the scrubber is more effective.  I would also assume that the slower gas movement would decrease the work of breathing of the unit.

Missed the Varanger… Again

Sunday, September 12th, 2010

After years of trying, I still have not made it to the Varanger.   However this time we were close!

Besides the Varanger issue, I’ve been trying to get together with some fellow instructors to schedule some student dives in the proper depth range.   It’s been hit or miss over the last year, but we were finally able to coordinate schedules.   Unfortunately, none of my students were available.   It figures.   I’ve never been on the Atlantis before, so I just headed out to check out the boat and crew, and hopefully get in some fun dives.

NOAA was calling for rough seas around a front of storms coming through.  The front generated a fantastic sunrise, but the old “red sky in morning” told us NOAA might be right this time.  We could see the front to the south, so we headed north to out run it.    This plan worked well.  We never saw more than 2 ft seas, and we had a fresh water rinse for our gear on the trip home.

The Atlantis is located right inside the Absecan Inlet with parking next to the AC Aquarium.   She’s a large comfortable boat with lots of deck space, and room inside for passengers and dry gear.   Geoff has been trying to get me down to AC to try it out.  I must say, I was impressed.

Shortly we arrived on the Southern Lillian.  The crew had a grapnel on the wreck quickly, and Geoff jumped in to secure it.  Once secure, divers started dropping in.  As usual, I was helping everyone in, hoping to hear a bottom report before dragging my camera into the water.  Geoff reported that below the thermocline, the clear surface water gave way to dark muddy bottom conditions.  Visibility was estimated at 5 ft at best.

With most fish out of season, I rolled in to look for scallops or lobster.   Geoff was right, below the thermocline the temp dropped to 47, and the vis made it difficult to even read gauges.  Once on the bottom I tied off and started the search.  I’ve been on this wreck several times, but in the current vis, I had no idea where I was.  I pulled out a few lobsters with eggs, and finally scored a couple legal ones.   Most of the fish darted away from my light as it approached.   There was one notable exception.  Off in the distance, I could see a large white object.   On closer inspection, it was one of the largest Tog I’ve ever seen.  It was not intimidated by my light or me.   As I approached within a few feet, it slowly swam over the top of the nearest deck plate, and disappeared.

Satisfied with my catch, I headed back to the line.  for some reason, there were large “clumps” of vegetation.   No one was sure what it was, but in some areas of the wreck it was piled up like tumbleweeds.  Reeling up the line involved pulling out wads of this stuff.   The thermocline at 70 ft felt great, and I could immediately see the boat, and the fact that it was raining.

Most divers went in for a second dive.   I opted for one long dive, and was happy with the harvest it produced.

Many of us slept on the trip home.   There are six bunks below, and lots of space inside to stretch out.   Our wet gear got a fresh water rinse on the way, and we still made it back to watch the rest of the game.

It was not the Varanger, but it was still a fun day of diving.