see also subpage Dehydration and Sharks
Ocean (from Ωκεανός, Okeanos (Oceanus) in Greek) is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface (an area of some 361 million square kilometers) is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas. More than half of this area is over 3,000 meters (9,800 ft) deep. Average oceanic salinity is around 35 parts per thousand (ppt) (3.5%), and nearly all seawater has a salinity in the range of 31 to 38 ppt.
Seawater is (impure) water from a sea or ocean. On average, seawater in the world's oceans has a salinity of ~3.5%, or 35 parts per thousand. This means that every 1 kg of seawater has approximately 35 grams of dissolved salts (mostly, but not entirely, the ions of sodium chloride: Na+, Cl-). The average density of seawater at the surface of the ocean is 1.025 g/ml; seawater is denser than fresh water (which reaches a maximum density of 1.000 g/ml at a temperature of 4°C) because of the added weight of the salts and electrostriction.The freezing point of sea water decreases with increasing salinity and is about -2°C (28.4°F) at 35 parts per thousand.
Accidentally consuming small quantities of clean seawater is not harmful, especially if the seawater is consumed along with a larger quantity of fresh water. However, consuming seawater to maintain hydration is counterproductive; in the long run, more water must be expended to eliminate the sea water's salt (through excretion in urine) than the amount of water that is gained from drinking the seawater itself.
This occurs because the amount of sodium chloride in human blood is actively regulated within a very narrow range of 9 g per L (0.9% by weight) by the kidney. Drinking seawater (which contains about 3.5% ions of dissolved sodium chloride) temporarily increases the concentration of sodium chloride in the blood. This in turn promotes sodium excretion by the kidney, but the sodium concentration of seawater is above the maximum concentrating ability of the human kidney. Eventually with further seawater intake the blood concentration of sodium will rise to toxic levels, removing water from all cells and interfering with nerve conduction ultimately giving seizures and heart arrhythmias which become fatal.
Of note, various animals adapt to harsh living conditions. For example, the desert rat, is able to concentrate sodium far more efficiently than the human kidney, and therefore would be able to survive by drinking seawater.
Survival manuals consistently advise against drinking seawater. For example, the book "Medical Aspects of Harsh Environments" (Chapter 29 - Shipboard Medicine) presents a summary of 163 life raft voyages. The risk of death was 39% for those who drank seawater, compared to only 3% for those who did not drink seawater. The effect of seawater intake has also been studied in laboratory setting in rats. (Etzion and Yagil; Metabolic effects in rats drinking increasing concentrations of sea-water. Comp Biochem Physiol A. 1987;86(1):49-55.). This study confirmed the negative effects of drinking seawater when dehydrated.
The temptation to drink seawater has always been greatest for sailors who have expended their supply of fresh water, and are unable to capture enough rainwater for drinking. This frustration is described famously by a line from Samuel Taylor Coleridge's The Rime of the Ancient Mariner:
Although it is clear that a human cannot survive on seawater alone, some people claim that one can drink up to two cups a day, mixed with fresh water in a 2:3 ratio, without ill effect. The French physician Alain Bombard claimed to have survived an ocean crossing in a small raft using only seawater and other provisions harvested from the ocean, but the veracity of his findings was challenged. In Kon-Tiki, Thor Heyerdahl reported drinking seawater mixed with fresh in a 40/60% ratio. A few years later another adventurer named William Willis claimed to have drunk two cups of seawater and one cup of fresh per day for 70 days without ill effect when he lost his water supply.
Most modern ocean-going vessels create drinkable (potable) water from seawater using desalination processes such as vacuum evaporators, flash evaporators, or by the use of reverse osmosis. However these processes are energy intensive, and most were not available or practical during the age of sail.
Treading the water to keep warm in a survival suit improves the chance
of surviving an accident at sea. When a boat capsizes, when a helicopter
is forced to land on water, or when some other accident takes place at
sea, the rule of thumb has been: stay close to something that will float
and do not waste energy on moving to keep warm. Now, however, research
conducted at SINTEF Unimed shows that moving in the water for about five
minutes every twenty minutes or so is sufficient to maintain the body's
core temperature - providing, that is, that you are equipped with a survival
suit. After several tests with subjects in a pool with waves and cold
water, researcher Hilde Færevik concluded that a person's core temperature
falls dramatically if the person remains still even when equipped with
a survival suit.
Perhaps the most difficult survival situation to be in is sea survival. Short-or long-term survival depends upon rations and equipment available and your ingenuity. You must be resourceful to survive.
Water covers about 75 percent of the earth's surface, with about 70 percent being oceans and seas. You can assume that you will sometime cross vast expanses of water. There is always the chance that the plane or ship you are on will become crippled by such hazards as storms, collision, fire, or war.
As a survivor on the open sea, you will face waves and wind. You may also face extreme heat or cold. To keep these environmental hazards from becoming serious problems, take precautionary measures as soon as possible. Use the available resources to protect yourself from the elements and from heat or extreme cold and humidity.Protecting yourself from the elements meets only one of your basic needs. You must also be able to obtain water and food. Satisfying these three basic needs will help prevent serious physical and psychological problems. However, you must know how to treat health problems
that may result from your situation.
On November 23, a German U-boat intercepted and torpedoed the ship. As the ship was sinking, Poon Lim took a life jacket and jumped overboard before the ship's boilers exploded. After approximately two hours in the water, he found an empty life raft and climbed into it.
The raft had several tins of biscuits, a ten-gallon jug of water, some chocolate, a bag of sugar lumps, some flares, two smoke pots and an electric torch.
Poon Lim initially kept himself alive by drinking the water and eating the food on the raft, but later resorted to catching rainwater in a canvas tarp and fishing. He could not swim very well and often tied a rope from the boat to his wrist, in case he fell into the ocean. He took a wire from the electric torch and made it into a fishhook, and used hemp rope as a fishing line. He also dug a nail out of the boards on the wooden raft and bent it into a hook for larger fish. When he captured a fish, he cut it open with a knife he fashioned out of a biscuit tin and dried the fish on a hemp line over the raft. Once after a large storm had spoiled his fish and fouled his water, Poon, barely alive, caught a bird and drank its blood to survive.
On two occasions other vessels passed nearby: first a freighter, then a squad of US Navypatrol planes. Poon contends that the freighter saw him but did not
pick him up because he was Chinese. The Navy planes did see him, and
one dropped a marker buoy in the water. Unfortunately for Poon, a large
storm hit the area at the same time and he was lost again.
Book: Sole Survivor
In memory of giant....