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Underwater Survival

Copyright 2000 A. Scott Moore

Edited by R.C. Kirkland for The Guild Companion

"The sea was angry that day my friends…like an old man trying to send back soup at a deli."
George Costanza - Seinfeld

We all know that the ocean is a dark, mysterious and vast place that takes up 3/4 of our planet's surface. Blah, blah, blah. We get the point: It would be a fun place to run an adventure. The intimidating thing is that we want our adventure to be somewhat convincing and realistic (otherwise, we could find systems a lot simpler than RMSS). The following suggestions are not "written in stone" or a prerequisite for fantasy adventures, but it does provide a good basis for creating new races, unique vehicles, weapons, etc. that adhere to the basic laws of underwater physics.

The Behavior of Water

The landlubber's primary concern once he encounters the ocean is buoyancy. An object that is lighter than the amount of water it displaces will float. An object that is heavier than the water it displaces will be unable to testify at trial. But not all water is created equal. Salt water has minerals dissolved in it that make it heavier than regular old H2O. The saltier the water, the easier it is to float in.

Another big factor in the behavior of water is the tide. The tides on earth are caused by the moon, but are influenced by currents and wind. If your home grown Rolemaster world is without any large satellites, then your players needn't bother developing the skill Surfing.

One rule of thumb to follow regarding waves on a large body of water is that the wave will be no taller than 1/7 of the wavelength. Therefore as the wave nears shore, the wavelength necessarily gets shorter and the wave height can no longer be sustained and the wave breaks.

Tides only occur in large bodies of water because they have the flexibility of movement to allow for large bulges on their surfaces (i.e. high tide). Lakes (even fairly large ones) seldom have more than a few ripples, caused by the wind, to lap at their shores. All of that extra water movement causes erosion and the dissolving of minerals in the water and thus the higher salinity of the ocean.

Water density does more than make for a relaxing float on the surface. It makes moving through the water rather difficult and at least inefficient for the hydrodynamicly challenged. For example, fighting under water with most conventional weapons is all but impossible without a little magical assistance.

Oh, The Pressure

Obviously, water weighs more than air. But how much more? On earth, if you took a column of air from sea level to the top of the earth's atmosphere and put it on a scale, you could balance it with a column of water of the same diameter that was a mere 33 feet tall. That unit is called one atmosphere. So if you dive under water to a depth of 33 feet, you have twice as much weight pressing in on you than you did when you were standing on the beach. If you've ever felt that pain in your ears when you dive to the bottom of the pool, that was a taste of the immense pressures that await those who dare to plumb the depths of the oceans.

All that pressure can have some rather unpleasant effects on the humanoid body, most especially caused by breathing pressurized air. Air that is breathed in at the surface will cause no ill effects to a diver. You can breathe out of a tube that pokes above the surface pretty much indefinitely with no problems, other than the fact that you'll look like a prune. Of course, it is all but impossible to breathe through a tube that is more than about three feet long because you won't be able to circulate enough fresh air through its volume with only your lung power.

That's why people in the "real" world need a way to carry air with them to deeper depths. Historically this has been accomplished in two ways: the submarine (or diving bell) and the scuba tank (or diving suit). The principle difference between these methods is whether the vehicle or the diver is absorbing the pressure of the water. Whether either of these two methods are available to the characters depends entirely on the GM and his world. Both take some rather sophisticated technology, but magic can be a powerful substitute.

Leaving aside for a moment the interpretations of the spells that could be used, I'll discuss the physical effects that accrue in the real world. Physiologically, being aboard a submarine is not much different than standing on dry land. The hull of the vessel is taking all of the pressure of the ocean and that pressure is not transmitted to the occupants. Unless of course there is a hull failure, in which case that pressure will be transmitted in one merciless instant.

Scuba diving is not such an all or nothing affair, but it is fraught with other, potentially just as deadly, dangers. These dangers result from the fact that the pressures of the depths are being directly applied to the diver. This causes the nitrogen that makes up over 70 percent of the air we breathe to be absorbed into the bloodstream with unpleasant effects.

The first effect is called Nitrogen Narcosis. It is a feeling of intoxication that closely resembles being drunk. It is caused when the gas bearing capacity of our blood is being partially taken up by nitrogen and allowing less oxygen carrying capacity. This by itself is not deadly and is easily remedied by ascending somewhat and reducing the pressure. This frees some capacity in the blood for more oxygen. Unfortunately, Nitrogen Narcosis affects your judgement and you may not do what is in your best interest. Stabbing a passing shark with your knife may seem like a perfectly logical move, while suffering from nitrogen narcosis.

The second ill effect from nitrogen dissolved in our blood is called decompression sickness or, more commonly, the bends. It results from breathing pressurized air at depth and ascending to the surface too quickly. If ascension is too rapid the nitrogen doesn't have time to dissolve out of the bloodstream and exit the body in the form of exhaled air. Instead the rapid reduction of pressure causes the nitrogen to "boil" out directly into the bloodstream. In the least extreme cases, this causes considerable pain mostly around the joint areas where the blood vessels are constricted (that's why it is called the "bends"). In more extreme cases it can cause nitrogen embolisms in the bloodstream which can lead to heart failure or an embolism reaching the brain. Without appropriate medical treatment, severe decompression sickness nearly always leads to death or permanent brain damage.

The only effective treatment for decompression sickness is to get the victim under pressure again to allow the nitrogen to be redissolved in the bloodstream and then gradually released through the lungs. This is usually done in a hospital with the use of a hyperbaric chamber. In a pinch, the diver can be taken back under water to regain pressure and gradually ascend again, but this method tends to be less effective in severe cases.

To avoid the possibility of decompression sickness or nitrogen narcosis, the diver should avoid staying at deep depths for lengthy periods. For complete details of safe depth/time tables, consult any of the books about sport scuba diving. A general rule of thumb is that a diver can stay at 60 feet for 60 minutes without ill effects. A shallower dive will result in a longer safe time on the bottom while a deeper dive will result in much less time.


The Conductor on the Fast Train to Death

Another problem with water is that it is a far better conductor of heat than air, because of the much larger concentration of molecules. That's why you can cook a chicken in boiling water (212 degrees F, 100 degrees C) a lot faster than you can in an oven at the same temperature. This also means that 40 degree F water will cool off a humanoid body 25 times faster than 40 degree F air.

The life expectancy for someone in near freezing water is measured in minutes. Their effective time before exhaustion and unconsciousness is under 15 minutes. Even at temperatures as high as 80 degrees F, a person will succumb to hypothermia in a few days if they have no way to get out of the water at least periodically. If a person's body temperature drops as little as 5 degrees F, they will begin to lose cognitive ability and exhibit slurred speech.

Protective clothing will extend the effective time before exhaustion and unconsciousness as well as the time before death. A wet suit or equivalent provides good protection against the loss of body heat, but a suit that keeps the occupant dry is far better. Any opportunities to get out of the water even for just a few minutes will also extend life expectancy.

Treatments for hypothermia vary widely but all have the same goal: To raise the body temperature back to normal levels. This can be accomplished with a warm bath, hot blankets or even the shared body heat of another person. Consumption of alcohol, coffee and tea should be avoided (by the victim, others can have as much as they want). The victim should also not be massaged because that simply drives the colder blood near the skin's surface into the core of the body where it will cause a further drop in core temperature.

But What Treasures Lie Beyond the Horizon

As dangerous as the ocean is, why not just avoid it? Because it is a source of adventure, mystery and riches (prime motivators in every Rolemaster campaign I've ever been involved in). Aside from the tremendous bounty of food that can be provided by the creatures and plants that grow in the ocean, are the possibilities of trade, exploration and treasures of the deep. Any of these resources make a sound basis for an adventure and all of them together provide a solid foundation on which to build an entire campaign.

So the vastness of the ocean is not merely a mine full of resources for the fisherman, explorer or treasure hunter. It is also full of rewards for the bravest of individuals willing to plumb its murky depths: The Gamemaster.

Rules and Charts (surprise!)

Underwater Combat

Combat underwater is an extremely difficult prospect for those who have not had proper training, which is compounded by weapons not designed for underwater use. The GM must determine what effects short and long-term exposure to water has on equipment.

The greater density of water will obviously cause objects traveling through it to move slower and that includes your sword arm and your sword. There is also the problem of a lack of leverage that can seriously impact the effectiveness of a large weapon. Hostile Environments - Underwater can be used to reduce the maximum penalty for using a given weapon type underwater. This skill can never entirely remove the hampering effects of water on the combatant and there is a minimum OB penalty listed for each weapon type.

The best weapons to use underwater are those made for thrusting. Other weapon types can also be used in this manner, even if they were not specifically designed to do so, but this hampers their effectiveness. Any weapon less than three feet in length used for thrusting should attack on the dagger table. Any weapon over three feet in length used for thrusting should attack on the spear table.

Also note that any weapon that employs a flexible section such as a whip or flail will be utterly useless under water.


Underwater Combat Modifiers
Weapon TypeMaximum OB PenaltyMinimum OB PenaltyNotes
1-H Concussion-70-30Morning Stars are ineffective
1-H Edged-60-25
2-Handed-80-40Flails are ineffective
Missile-50-25Slings are ineffective / All ranges reduced to 1/4
Missile Artillery-50-25
Pole Arms-80-40
Thrown-100-60Spear only with maximum range of 20'


Decompression Sickness

If a character exceeds the safe diving limits for the time and depth to which he is diving (refer to the Navy Dive Time Tables), he will begin to suffer the effects of decompression sickness. Once the character has gone beyond the safe diving limits, he should make a RR versus a 10th level poison. Another RR should be required for every 5 minutes or every 5 feet by which he exceeds the safe limits with a -10% cumulative penalty for each RR.

The first time the character fails a RR, he has succumbed to nitrogen narcosis and will be at a -10 to all actions and at a -20 to spell casting or reasoning rolls. Ascending above the safe depth limit and ascending to the surface slowly (10 feet/minute) will alleviate the ill effects of nitrogen narcosis. Once a character fails three RR's, he is suffering from the bends and is in great danger.

A character suffering from the bends will, upon arriving at the surface, take an A Impact critical (one crit per round, ignoring results of broken bones) for every 5 minutes beyond the safe diving limits. The character will be in great pain and considered stunned during this period. These symptoms can be relieved by taking the character back down to a depth of approximately 15-20 feet and waiting there for 1 minute for each 5 minute period beyond the safe diving limits.


The chart below details the survival time for someone immersed in cold water. Keep in mind that if they are able to get out of the water for any length of time that these times could be lengthened considerably.

The GM should pick a time from the chart somewhere in the range represented. The exact time should vary based on the exact water temperature, clothing that the character is wearing, the amount of body fat the character has and other factors that he deems appropriate.

Also note that in cases of drowning in extremely cold water (below 40 degrees), it is possible that a person could be revived from a state of near death even after being submerged for an hour. The body's metabolic processes slow down to nearly undetectable levels and brain death can be delayed for a very long time. Physicians say, "You're not dead until you're warm and dead."

Editor's Note

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