A very large proportion of those involved in maritime accidents do not drown but die of hypothermia. My suggestion is to provide something which acts like a scuba diver's suit but which also can be packed in the same space as would be used by an ordinary life jacket. A scuba diver can remain relatively warm and active for up to half an hour in water that is no hotter than two degrees Celsius. A person in ordinary clothing in the same temperature of water is likely to become hypothermic in less than fifteen minutes. A scuba diver's suit is less than two millimetres thick.
The survival unit consists of a piece of PVC drainpipe which serves the double purpose of storage container and heat pump, and a multiple layer polythene bag assembly which is stored as a rolled up ring inside the drainpipe.
When an emergency occurs, the polythene bag assembly is pulled out of the pipe and the person steps into the ring of rolled-up polythene. If immersion is imminent, the person should inflate the upper part of the ring which acts like an inflatable swimming ring used by children. This ring will provide flotation to prevent drowning. When immersed, the person should inflate the ring further. This will cause a series of tubes to inflate and act like the extending blow toy used at parties. These tubes will cause the rolled-up polythene bag assembly to extend downwards forming a cylinder around the person.
The inner bag assembly is made like bubble-wrap with slightly
porous bubbles. Inside each bubble is a small amount of cellulose
wallpaper paste. This material swells in contact with water, causing
the bubbles to become inflated with wallpaper paste. With the
correct porosity, water molecules will pass into the bubbles but
the moistened cellulose molecules will not be able to escape.
Cellulose molecules are very much larger (typically 1,000 times larger) than water molecules and will not disperse through the porous layer.
The insulation qualities of cellulose (wallpaper paste) can be tested very easily. Get two identical buckets filled with cold water. Put a packet of wallpaper paste into one of them and mix it in well. Wait until the paste has stabilised and is ready for its normal use. Put one (bare) hand into the bucket of cold water and the other into the wallpaper paste. Keep both hands still. Check which hand stays cold and which gradually warms up.
The wallpaper paste trapped within the polythene forms a layer of "immovable" water which acts as a reasonable insulator without causing much flotation. It is thought that the survival system will work best if the person is more or less vertical in the water.
The outer bag is connected to a simple water pump which is activated by wave action or the person. The pump inflates the outer bag with sea water. As the outer bag fills, it compresses the inner bag inwards so that it becomes a relatively close fit around the person. The combination of the two bag assemblies is to isolate the person from free-flowing sea water and thus reduce the rate of cooling.
The person can also make use of the heat pump. The person puts his or her feet into the loops at the bottom of the pipe and pulls the handle. The pump is a linear version of James Joule's mechanical equivalent of heat experiment. When the handle is pulled upward, a vacuum is formed under the double piston unit. Water can only get to the lower part of the pump through small holes similar to those in a coffee percolator filter. Perforated flap valves open to allow a strong rubber band to pull the piston down again. The mechanical effort to pull the piston upwards is converted into heat. This helps to warm the space within the bag assembly. The exertion of the person will also produce more heat than would be generated if the person was inactive. It is estimated that an average person could raise the temperature of the water around him or her by around ten degrees centigrade in twenty minutes. This would significantly lessen the likelihood of hypothermia - even in near arctic circumstances.
Additions to the basic design include a pair of long-sleeved polythene gloves which will help to reduce heat loss in the person's hands and arms, an inflatable hood which will help to shield the person from wind and spray, and an inflatable kite. The kite is made of coloured polythene so that it will aid searchers in finding the person. It will also act as a means of ensuring that the hood is kept on the windward side of the person.
The heat pump could also be operated by wave power with a balloon attached to the handle with an inverted "parachute" below to act as a drag anchor. A one metre diameter balloon in one metre high waves could theoretically generate more than 800 watts of heat.
The wave powered water pump acts in a manner similar to the air pump illustrated.
In warmer seas the bag assembly will tend to reduce the distribution of the electrical disturbances caused by a person in the sea which could attract the attention of sharks. At the same time it would be effectively accoustically transparent to relatively friendly porpoises and dolphins.
Many people died in the Estonian Ferry disaster through hypothermia. The effects of hypothermia were shown in the film "Titanic".
Copyright (C) W. H. James 14/6/1998 Wilf James,106 Jarden, Letchworth, Herts. SG6 2NZ, UK. Please send your comments to me at my new email address: wilf dot james at ntlworld dot com Note: Because I get so much spam I use the word Convention in the subject line as a filter. Please put the word Convention in the subject line of any email to me. It does not matter if the subject has nothing to do with conventions. Unexpected emails usually get mixed up with the trash and can be lost. The Convention filter keeps such emails out of the trash.