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.

Human consumption of seawater

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:

"Water, water, every where

Nor any drop to drink."

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.

 

Into the cold water

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.
It is important to tread water (or move about in some other way, though only) at a moderate pace to avoid exhaustion, explains Færevik. The calculated intervals of five minutes every twenty minutes should serve as a guide.
It is essential that the accident victim moves around at regular intervals to maintain body temperature, continues Færevik. The same guideline does not apply to a person who falls into the water without a survival suit. When someone falls into cold water without extra protection, the peripheral veins will contract to keep the body's vital organs warm. Moving one's body in that situation will cause the veins to expand again, leading blood back into the extremities. As a result, the blood is cooled, the body temperature falls, and a critical point is reached earlier than it would be if the person remained immobile.

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.
Animated map exhibiting the world's oceans

Turn Salt Water Into Drinking Water

1. Get a pot and put an empty glass cup inside it in the center.
2. Slowly pour some salt water into the pot. Do not over fill. Stop well before the water level has reached the mouth of the glass. Make sure no salt water splashes into the glass while boiling.
3. Place the pot cover upside down so the highest point or handle is facing down right above and facing the glass.
4. Bring the water to a slow boil. A violent full boil can contaminate the drinking water by splashing into the glass.
5. As the water boils it becomes vapor, which recondenses in the air as steam and on the cover's surface as water droplets, which fall right into the glass. As you probably know, when water boils it becomes pure vapor, leaving behind anything that was dissolved in it.(this will probably take 20 minutes or more.)
6. Wait a little while before drinking the water from inside the glass, since both the water and the glass will be very hot.

• It really helps a lot if you can cool down the cover while the water boils so, as to make the recondensation occur faster. You can use cold salt water to do that, just change it when it becomes warm.
• This can also be done with urine if you're in the desert and water is hard to come by. If you do not have a pot, you can just dig a hole in the ground, do your business in the hole, place a glass/container in the middle and cover with something (plastic bag works). The natural heat of the sand will evaporate the clean water into the glass.
• This method of evaporating and condensing water is called distilling. It can be used with normal tap water whenever distilled water is needed.
• let a little steam come out so it doesn't explode.

133 Days adrift  (real survivor story - Poon Lim)

Hainan Island in 1918. In 1942, during World War II, he was working as second steward on the British merchant ship SS Ben Lomond, which was on its way from Cape Town to Dutch Guiana. The ship was armed but slow moving and was sailing alone instead of being in a convoy.
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.
He was also once spotted by a German U-boat, which had been doing gunnery drills by targeting seagulls. It did not offer assistance.
At first he counted the days by tying knots in a rope, but later decided that there was no point in counting the days and simply began counting full moons.
On April 5, 1943, Poon Lim reached land and a river inlet. A few days earlier, he had known that he was close to the land because the colour of the water had changed and was no longer the ocean deep blue. Three Brazilian fishermen rescued him and took him to Belém three days later.
During his ordeal, Poon Lim had lost 20 pounds, but was able to walk unaided upon being rescued. He spent two weeks in a Brazilian hospital, and the British consul arranged for him to return to Britain via Miami and New York. He later found out that only 11 others of the ship's crew of 55 had been rescued.

Book: Sole Survivor

In memory of giant....