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In my world there is a strip of ocean which is uncross-able due to extreme currents and storms.

The solution has been to simply go underneath this particular strip (which is very narrow; only a few miles across) and then resurface on the other side.

To this end, ships which can go underwater have been built. However, the technology level of this world is similar to our medieval to early renaissance periods (with some differences in the resources available to its inhabitants).

How would a submarine operate given this constraint?

Consider:

  • Method of propulsion (including an energy source)
  • Method of life-preservation (Oxygen)
  • Method of navigation
  • Method of diving and surfacing*
  • Carrying capacity (Crew and weight)
  • Materials (For resisting water pressure)

A true submarine would be best (something which can remain underwater for long periods of time), but in theory a submersible which can go below for a short amount of time is good enough (since the strip of ocean is so narrow).

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  • $\begingroup$ What depths are you talking here? And are the subs intended to operate outside of this limited range? $\endgroup$ – Twelfth Apr 2 '15 at 18:05
  • $\begingroup$ How about having a chain/rope pulley system across the channel, and the ship or submarine grasps it to get across, a la the cable car system in San Francisco? $\endgroup$ – Seth Apr 2 '15 at 18:57
  • $\begingroup$ Seth, its not a channel its open ocean so there would be nothing to tether to. @Twelfth, let's say that the current is relatively shallow, so something like 100-150 ft below the surface $\endgroup$ – Dider Apr 2 '15 at 22:26
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Your first problem is the currents you mention. Currents are rarely just on top. If they are strong enough to severely affect ships you are going to have to dive reasonably deep otherwise it will just carry you away. And there is no guarantee that you can dive below them.

So first issue, I would guess that it would have to be human powered, like this. Apparently in 1620 a Dutchman build three different working submarines. They used oars to move the vessel, but I think it would make more sense to use 'bicycle' like apparatus to turn a screw in the back. I think there was an early civil war sub that did this.

Going to deep, I would say much more than 50ft. in rough water, would make it pretty hard to see for navigation.

The 1620 subs had a tube attached to a flotation device that allowed for air to circulate, you could even have two of them, with a 'fan' or bellows sucking air down up and forcing air up the other. the float would have to be well done so that water doesn't fill up the sub.

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  • $\begingroup$ Drebbel reportedly also had chemical air purification that allowed one of his subs to stay down for extended periods of time; He is known also for chemical discoveries as well, but he didn't publish so we can only guess as to exactly everything he did discover and how he managed all his feats. $\endgroup$ – John_H Apr 2 '15 at 18:21
  • $\begingroup$ "Now that for which I mention this story is, that having had the curiosity and opportunity to make particular enquiries among the relations of Drebbel and especially of an ingenius Physician (Dr Kuffler) that marry’d his daughter concerning the grounds upon which he conceived it feasible to make men unaccustomed to continue so long under water without suffocation, or (as the lastly mentioned person that went in the vessel affirms) without inconvenience, $\endgroup$ – John_H Apr 2 '15 at 18:24
  • $\begingroup$ I was answered that Drebbel conceived, that ‘tis not the whole body of the Air, but a certain Quintessence (as Chymists speak) or spirituous part of it, that makes it fit for respiration, which being spent, the remaining grosser body or Carcase (if I may so call it) of the Air, is unable to cherish the vital flame residing in the heart; $\endgroup$ – John_H Apr 2 '15 at 18:25
  • $\begingroup$ so that (for ought I oould gather) besides the mechanical contrivance of his vessel, he had a chemycal liquor which he accounted the chief secret of his submarine navigation. For when from time to time he perceived that the finer and purer part of the Air was consumed or over-clogged by the respirations and steams of those that went in his ship, he would by unstopping a vessel full of this liquor, speedily restore to the troubled Air such a proportion of vital parts as would make it again for a good while fit for respiration, $\endgroup$ – John_H Apr 2 '15 at 18:26
  • $\begingroup$ whether by dissipating or precipitating the grosser exhalations or by some other intelligible way I must not now stay to examine." - Robert Boyle $\endgroup$ – John_H Apr 2 '15 at 18:26
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So in our world in the early renaissance period there was in fact one of the last great alchemist, for he wasn't yet a scientist, did in fact build submarines that did in fact travel underwater for some time.

Cornelius Drebbel for King James I of England in 1620's built submarines and Robert Boyle, one of the first scientists very highly regarded hims and investigated the subject:

Now that for which I mention this story is, that having had the curiosity and opportunity to make particular enquiries among the relations of Drebbel and especially of an ingenius Physician (Dr Kuffler) that marry’d his daughter concerning the grounds upon which he conceived it feasible to make men unaccustomed to continue so long under water without suffocation, or (as the lastly mentioned person that went in the vessel affirms) without inconvenience, I was answered that Drebbel conceived, that ‘tis not the whole body of the Air, but a certain Quintessence (as Chymists speak) or spirituous part of it, that makes it fit for respiration, which being spent, the remaining grosser body or Carcase (if I may so call it) of the Air, is unable to cherish the vital flame residing in the heart; so that (for ought I oould gather) besides the mechanical contrivance of his vessel, he had a chemycal liquor which he accounted the chief secret of his submarine navigation. For when from time to time he perceived that the finer and purer part of the Air was consumed or over-clogged by the respirations and steams of those that went in his ship, he would by unstopping a vessel full of this liquor, speedily restore to the troubled Air such a proportion of vital parts as would make it again for a good while fit for respiration, whether by dissipating or precipitating the grosser exhalations or by some other intelligible way I must not now stay to examine."

See further discussion here: http://todayinsci.com/D/Drebbel_Cornelis/Drebbel-OriginOfSubmarine.htm

Given that one of the theories as to how he did this was via containing Oxygen that he had cooked out of Saltpeter and that the Chinese knew about Saltpeter long before that time period than it seems entirely reasonable to have there be submarines previous to that point in time back in the middle ages a little ways. The ability to have the man power and ship building to construct the vessels may be more of a limiting factor, as the Spanish Armada was sunk in 1588 by what was largely the English fishing and merchant fleet to the point that there were laws dictating the eating of fish.

I actually think that if you are wanting a fixed point to point navigation in a current then you may wish to consider having them use some sort of pully system; this would greatly increase the ease of navigating and put the power as being perhaps teams of oxen on either side so that the amount the vessel could hold would be increased. I am thinking that a chain system would actually be more reliable and cheaper for the day than anything involving rope as the links can be inspected and fixed by a blacksmith rather than having to have a rope walk and you are dealing with being subjected to water nearly constantly.

Drebbel's submarine held 16 people, I assume that having breathable air may have been the limiting factor. That gives something like 3000 pounds as the carrying capacity; you could probably assume that it is able to hold quite a bit more in terms of cargo carrying capacity than that if it were designed to carry cargo as cargo wouldn't necessarily need "a certain Quintessence (as Chymists speak) or spirituous part of" Air.

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  • $\begingroup$ Could you please elaborate on the "pulley system"? $\endgroup$ – Dider Apr 2 '15 at 22:27
  • $\begingroup$ Who is to say that he "wasn't yet a scientist"? $\endgroup$ – Galaxy Feb 24 at 4:05

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