Gearing Up

Salt water freezes at a lower temperature than freshwater. Seawater's freezing point decreases about 0.5 degrees Fahrenheit for each five parts per thousand increase in salinity. At 35 ppt sea water will begin to freeze at 28.6 degrees Fahrenheit. McMurdo Sound seawater has a nearly constant mean annual temperature of -1.86 degrees Celsius (28.65 degrees Fahrenheit) and temperature doesn't vary much with depth or season -- 0.2 degrees Celsius (0.36 degrees Fahrenheit). Typical dives lasted an hour with some shallow-depth dives stretching to ninety minutes underwater. Cold hands can be a limiting factor for many divers scuba diving under the Antarctic ice. Everyone's internal thermostat dictates their own comfort level with remaining underwater; some people put out more body warmth and can last longer than others. Divers may not be cold right away, but given time and even the best diving gear, the cold seawater will triumph.


What does a diver wear to stay warm in such cold water ? ........ A drysuit !

Here a diver wearing a DUI drysuit is standing over the dive hole inside a dive hut putting on a neoprene hood.

For warmth, the diver wears a drysuit with several layers of undergarments. Unlike the more familiar wetsuit, the diver stays dry within a drysuit. No water can enter inside the drysuit due to seals at the wrists and neck; there are no seals at the diver's ankles since the drysuit has attached booties. A special watersealing zipper enables the diver to enter and exit the drysuit. At the back of the diver's head is this drysuit's attached latex hood which will be pulled over this neoprene hood in order to seal out water (the diver's hair stays dry underwater).

On the diver's chest is a drysuit inflation valve. The diver lets air into the drysuit from a scuba tank hose through this valve in order to counterbalance external water pressure and maintain neutral buoyancy. The diver's left upper arm has a drysuit exhaust valve for releasing air when ascending or descending in order to maintain proper buoyancy.


Following is a description of the dive gear we used. This is what worked for us. There is a wide variety of dive gear and opinions, so many different gear configurations will work. Several of the Antarctic recreational dive trip operators offer equipment advice; you can link to their sites from this site's list. We saw a lot of variety in other dive teams, so there are multiple approaches to diving in Antarctica. We sought advice from a variety of people, brought down some extra gear to experiment, and arrived at what worked best for us. Your mileage will vary.

Undergarments

Warm Wind Drysuit Undergarment It's what you wear inside the drysuit that keeps you warm; the drysuit only keeps you dry. The first clothing layer was regular or expedition weight polypro long underwear. Over that, the team wore a Warm Wind Thermal Liner Polartec® series 200 jumpsuit as a second layer. The team wore DUI 400G Thinsulate® (400 gm/m2) Type B nylon shell booties (shown here). Some wore only these booties; some wore polypro or US Antarctic Program issue socks in combination with these booties.

DUI Drysuit Undergarment A third and final layer was a DUI 400G Shell Type B Thinsulate® 400 gm/m2 Thermal Garment. The DUI 400G Shell Type B Thinsulate® 400 gm/m2 Thermal Garment worked really well as the top layer for general wear before, between, and after dives. Its wind-resistent shell kept out wind and its insulation combined with underlayers was warm as several layers of US Antarctic Program clothing.

Drysuits, Hoods, & Gloves

DUI drysuits The team used every model of DUI drysuit ranging from the TLS trilaminate models to the CF compressed neoprene models. They all worked admirably with no leaking. Drysuits were pressure tested and repaired as needed by DUI before Antarctic use. Trilaminate drysuits are advantageous for diving out in the open when it is extremely cold and windy. Trilaminate drysuits don't retain surface moisture as do compressed neoprene drysuits. Surface moisture on a compressed neoprene drysuit will freeze and stiffen the drysuit which makes it very cumbersone to maneuver in a drysuit topside. In addition, trilaminate drysuits tend to be lighter than compressed neoprene drysuits which helps in keeping overall equipment weight down for weight-limited helicoptering to remote field sites. The drysuit inflator valves on the drysuit air inflator line are specially modified at McMurdo to put a larger knurled brass collar on the valve end so that clumsy, cold fingers can easily pull that valve on and off. When first dropping into the 28 degree F water, there is no cold shock since there is almost no skin in direct contact with water. You can see here that only the diver's lips will be exposed to water! Shortly after beginning a dive, the diver's lips go numb a bit from the cold but since lips are well vascularized, it isn't a problem.

Hoods & Gloves Divers varied in hood setup, with some having attached latex or neoprene hoods on their DUI drysuits. The attached hoods reduce water circulation around the diver's head, and were pulled over a neoprene underhood. As underhoods,all divers use Henderson ice caps (see bottom left, aka ice hoods) that have a strip of neoprene running across the upper lip. These are thin 3 millimeter full face hoods that reduce the skin area that will be in contact with the water. See Henderson website http://www.hendersonusa.com/ for details. We ordered them from MAR-VEL Underwater Equipment, Inc.; 400 Elm Street, Woodlynne, NJ 08107. phone: 800-325-5711 or (856) 962-8719; fax: (856) 962-9084; Email: marvel@mar-vel.com ; Web: http://www.mar-vel.com/ ; size KH43 is large and sufficiently stretchy to fit an extra-large head size A diver with an attached latex pulled it over the ice cap, and then pulled a DUI Warm Neck Self- Venting Hood over that. A diver with an attached compressed neoprene hood used an ice cap under it. A diver without an attached hood used in icecap under a DUI Warm Neck Self- Venting Hood, and wore a neoprene collarpiece cut from another hood around his neck for additional insulation. Basically, two layers of insulating hoods were used by all. The team used dry gloves that were inexpensive concrete mixing gloves; these were tough and very supple, making it easy to stretch them down and over the dry glove cuff rings mounted on the drysuits. We also used Viking five-finger rubber dry gloves, which are less supple and more expensive than the concrete mixing gloves. Take two pairs of dry gloves in case you get a puncture. A source for concrete mixing gloves: Boss Manufacturing Co., 221 W. First St., Kewanee, IL 61443. phone: 309-852-2131. 1999 cost was US$37 for twelve. We knew it as "LtX GLV BLK RG035". Gloves are labelled R-1230 and also WR-1230-X. An unconfirmed source is Best Mfg. 800-241-0323 Under the dry gloves, the team used various combinations of fleece gloves or winter mountaineering glove liners. Take several gloves/liners and see what works best in the field. For example, a thin polypropylene glove can usually be worn inside a mountaineering glove/liner for extra warmth if needed. One team member used Marmot mountaineering glove liners. One team member used the inner pile liners from Black Diamond mountaineering gloves. One team member used Outdoor Research Expedition/Professional Modular Glove Standard Liners ( http://www.orgear.com/ These liners have extra thick insulation on the back of the hand and thumb/fingers, with curved fingers/boxed construction to minimize insulation compression and finger constriction.). In order to let the air equalize between the dry glove and the dry suit, a short length of cotton rope or Tygon® tubing was inserted under each drysuit wrist seal in order to break the seal a bit and let air exchange between the dry glove and the drysuit sleeve. Knot the rope at the ends to keep it from slipping all the way through the wrist seal.

The comfort level of the DUI drysuits, hoods, and undergarments was so considerable that team members (here Norbert Wu) could lounge in dive holes out in the open with subzero wind chill while waiting for gear setup or other divers.

Regulators

two modified Sherwood Maximus regulators

McMurdo Station modified its Sherwood Maximus regulators to avoid freezing and freeflow in the icy waters around McMurdo Sound (-1.86 degrees Celsius / 28.65 degrees Fahrenheit). A scuba diving air regulator has two pieces: the first stage (attached to the tank) and the second stage (in the diver's mouth and attached to the first stage by a pressure hose -- in lower right corner of this picture).

Divers used two Sherwood Maximus regulators and they were attached to the air tank through a Y valve. One regulator has a single second stage attached and is the primary breathing supply; the other regulator functions as the backup air source and has the air pressure/depth console and drysuit inflator hose attached. A dive computer is very useful to track dives. The Sherwood Maximus regulators were selected after extensive testing; see Rob Robbins' report on this testing. The Navy Experimental Diving Unit tests regulators for cold water use; here are citations to some NEDU test reports.

Click to see a cut-away of the 1st stage.

first stage: The Sherwood Maximus 1st stage used for breathing becomes almost totally ice-encased during a dive (see picture above). The pressurized air moving and expanding through the first stage cools down the 1st stage and ice forms around it as a result. In one study, the air leaving the 1st stage of a regulator on its way to the 2nd stage in the diver's mouth dropped to -10 degrees F [1]. So it's no wonder that the 1st stage regulator comes out of the water looking like an ice cube, with ice almost a half inch thick around it ! The Sherwood Maximus 1st stage doesn't allow seawater inside its pressure-compensating mechanism which thus prevents problematic icing up of the regulator. The regulator senses the external water pressure (which a 1st stage regulator must do in order to deliver air appropriately) by an air bleed valve, a port that constantly trickles out tiny air bubbles which the regulator uses to sense ambient water pressure.

Click for a closer view of the 2nd stage.

second stage: the McMurdo- modified Sherwood Maximus 2nd stage has two interior metal pieces which act as heat sinks and transfer heat from the diver's exhaled breath to the air inlet orifice which is susceptible to freeze up. Heating of the inlet orifice is needed because air flowing through the restricted orifice in the 2nd stage inlet valve cools down. Any moisture present will freeze, thereby freezing the the inlet air valve, leading to a freeflow of air streaming into the diver's mouth, which can abort the dive. One metal strip inside the 2nd stage (copper-colored strip) leads into the mouthpiece, transferring exhalation-breath heat to the inlet valve; it is found in off-the-shelf Sherwood Maximus regulators. A second large metal plate (silver-colored stainless steel louvered plate, with edge strip running up to the inlet valve) was fabricated at McMurdo and fits over the exhalation ports, to further utilize exhalation-breath heat. This setup solved McMurdo's regulator freezeup problems. Divers open up the 2nd stage before leaving McMurdo Station each morning and use pressurized air to blow out any residual water from previous gear rinsing. Any water left inside the 2nd stage can freeze up and lead to a freeflow. If camping out in the field with no easy way to rinse, the gear is left untouched to minimize problems.

Tanks & Weights

ScubaPro 95 cubic foot steel tank McMurdo supplied ScubaPro 95 cubic foot steel tanks with a Y valve to use with two Sherwood Maximus regulators; the tank is mounted on a hardshell backpack. Generally no buoyancy compensating vest was used since the diver's drysuit can be used for buoyancy compensation (here Dale is using his Dive Rite BC). The backup Sherwood Maximus regulator hangs from a loop of surgical tubing tied to the right shoulder strap of the tank backpack. At Explorer's Cove, New Harbor, twin 72 cubic foot steel tanks were used instead of the 95 cubic foot tanks.

DUI Weight and Trim System weight harnesses McMurdo Station supplied DUI Weight and Trim System weight harnesses to the team along with lead weights and ankle weights. The harness holds the extra weight needed to be neutrally buoyant underwater. The yellow tube handles on the harness are a quick-release system to drop the weights quickly in an emergency. These DUI Weight and Trim System weight harnesses were easy to don and adjust. Divers could easily slip out of them while floating at the surface of the ice hole and then hand them up to someone out of the water. Divers can use ankle weights (as shown here) to distribute weight better on the body and to keep one's feet weighted down in order to prevent air expansion in the feet in an uncontrolled ascent.

1: Undercurrent 17(5):3, 2002

Text ©Peter Brueggeman. Photographs ©Peter Brueggeman, M Dale Stokes, & Norbert Wu. Photographs may not be used in any form without the express written permission of Peter Brueggeman, M Dale Stokes, & Norbert Wu.. Norbert Wu no longer grants permission for uncompensated use of his photos under any circumstances whatsoever; want more info?