Free-diving (sage ability)

Free-diving is an amateur-status sage ability in the study of Athletics that enables characters to hold their breath and explore depths down to 100 ft. below the surface for periods of at least 6 rounds. Having honed their lung capacity, and using weights to drop quickly to their maximum depth, characters with this skill are vital in activities like pearl-diving, sponge collection and ocean salvage.

Free-diving has ancient roots and has been practiced throughout history, particularly in the Mediterranean, southern India and Japan. Divers take several breaths for 3-4 rounds to saturate their blood with oxygen before taking the final breath and submerging. With fins made of wood, bone and other materials to add propulsion, divers also use footwear of animal skins to further streamline their bodies, gliding as quickly as they can to the bottom. Additionally, experts are able to equalise their ears to conserve energy in their descent and ascent.

Unskilled

Characters must have this ability to perform this sort of diving. Without training in breath-holding and equalisation, there's an excellent chance that a character would take an uncontrolled swallow of water or be struck with the bends in a manner that would be life-threatening. The deepest depth a cliff-diver could achieve would be 15 ft., plus 1 ft. per 8 points of knowledge. Those without any diving experience could hardly go further than 12 to 15 ft. below the surface.

Depth

Free-divers are able to drive down to depths of 30 ft. once they've achieved amateur level of ability. Depth thereafter increases at a rate of 3 additional ft. for every 2 points of knowledge above 10. This allows an authority-status character to dive to 60 ft., while an expert could dive to 105 ft. No dive can be made below 120 ft., regardless of the amount of knowledge the character possesses.

Using weights a diver is able to descend up to 36 ft. a round, which is important in calculating how much available time is spent getting to the target depth. Swimming downwards can be performed at half this speed, 18 ft. per round.

In returning to the surface, controlled ascents were employed to alleviate the danger of shallow-water blackouts and other dangers. Characters employing these techniques may ascend safely at speeds of 15 ft. per round, and up to 30 ft. per round unsafely.

In the case of the latter, the character must make a constitution check or become incapacitated in some fashion that they have to be rescued by another. This rescue must occur within the time frame of the character's being able to hold their breath.

Strength	Base Rounds
3-5	4-5 (d2+3)
6-10	5-8 (d4+4)
11-13	6-11 (d6+5)
14-16	9-12 (d4+8)
17-18	11-13 (d3+10)
18% or more	13-14 (d2+12)

Time

The base number of rounds that a character can hold their breath underwater is based upon their strength. The range is rolled at the point of diving, with the diver being able to interpret messages from their body telling them how much time remains. For example, a character with a 13 strength dives and rolls a 6-sided die as shown; learning that there were 10 rounds available at the start, how long can be spent underwater, calculating depth against how long it takes to surface can be done accurately by the diver.

This number is then adjusted upwards by 1 additional round per 6 points of knowledge above 10. For example, a character with 31 points of knowledge (31 - 10 = 21) would add 3 additional rounds to every dive, regardless of his or her strength. As knowledge is accumulated, there's more opportunity to search an area or take part in some other activity.