Circadian.

This is coolbert:

Once more from Joel at Bubbleheads we have the tip, American submariners for DECADES operating their vessel using and EIGHTEEN HOUR DAY while on patrol, the accepted practice now under review?

"The Stupid Shall Be Punished"

"Are Eight Hour Watches The Way To Go?"

"According to this Navy Times article, the Navy is studying if the current 6 on - 12 off watchstanding cycle practiced by Submariners is detrimental to our health and well-being, or if we should shift to something else."

And from various other sources including Prometheus:

"The submariner's day lasts 18 hours: three 6-hour watch cycles, 1 on and 2 off. He stands a duty watch, then has the next 12 hours for everything else: repair and maintenance tasks, study, relaxation, eating, and sleeping. Then it's back to the duty watch."

"There are four meals a day: breakfast, lunch, dinner, and midrats. There is always plenty of food. Crew members usually get about six hours of sleep per day; most people fall to sleep very quickly because they are tired after a long workday. The days pass without sunrises and sunsets"

That eighteen hour day with the sub crew operating in three shifts [watches] of six hours each thought to be that schedule allowing for the greatest effectiveness and alertness.

Humans as almost all [?] living being having adapted through eons to a circadian rhythm of twenty-five hours that is almost exactly the same as the twenty-four hour rotation of the planet, that eighteen hour day poses problems [?] and is being evaluated as a result of new science.

Other environmental factors aboard a submarine such as LIGHTING [artificial] also a source of difficulty, remedies not being easily found. From Prometheus:

"We also talked about lighting onboard which some percentage of sailors complain bitterly about. The new 'broad spectrum, low level fluorescent lighting used onboard many submarines gives some headaches, and honestly does not adequately represent enough light to approximate what one might expect of the spectral benefits of daylight."

ONLY until the advent of the nuclear powered submarine those submariners for the most part operating on the surface, having access to the natural environment, able to observe the rising and setting of the sun, the phases of the moon, etc. That no longer possible and the normal bodily functions as related to the natural cycle disrupted?

Seems the eighteen hour "day" regimen has worked well for many decades now? And yet a better way is being sought to improve things. "BETTER IS THE ENEMY OF GOOD ENOUGH?"

And this thought has occurred to me too. Those two Virginia class submarines to be "manned" with total female personnel with have a crew each and everyone of those young women having a natural biological clock built into their system. THEY will know with a certain exactitude how long the patrol has lasted without having had access to the sun and phases of the moon!!

coolbert