The ship in question is a cog or a carrack, double-masted, and the technology and ways of sailing available are similar to those found during the renaissance (1300-1400).

In comes a wind-generating stone with no recoil, that blows air from one polished side (so if the stone is square, it blows from one side only). Normal sized stones can generate a strong wind, while larger stones can generate powerful gale. The stone's power can be quelled simply by covering it with a special pouch, and the power does run out of charge after a while.

  1. How would a stone like this change the way people sail?
  2. Where would this stone specifically be kept on a ship in order to maximize it's use? For example, would it be kept behind the main mast, foremast, or mizzenmast (if there were three masts)? Would a special device be needed in order to hold and move the stone to more favorable angles?

You will set the stone under the boat, submerged in the water.

If the stone generates recoil (wind produced pushes stone backwards) then those forces will cancel each other out when you put the stone topside blowing onto the sail. The force pushing forward on the sail will be counteracted by a force pushing backwards on the stone.

But if that is the case you can use it for propulsion. Put it on the back of the ship and let the recoil on the stone push you along. That becomes like an airboat or fan boat with a big fan throwing air back. I think it would work even better under the boat because the water offers more to push against.

If there is no recoil you could have it blow on the sail. Yes, yes, how droll. But if you put your recoilless stone on the front of the boat blowing into the water it would blow the water there out of the way. You are not pushed backwards because front mounted wind stones are recoilless, remember? Your ship would fall into hole in the water displaced by air. You would make a perpetual wave in front of the boat to ride. It would be a surfboat. Cue Ventures, please.

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    $\begingroup$ If recoilless then you can also fasten one to a man with a parachute for endless Fun! $\endgroup$ – Joe Bloggs Jul 9 '20 at 16:23
  • $\begingroup$ @JoeBloggs what other things could be done with such technology besides flight and travel? $\endgroup$ – Ebi Jul 9 '20 at 22:21
  • $\begingroup$ @Ebi Anything that uses a difference in air pressure. Depending on your definition of ‘wind’ they could make incredibly efficient compressors for air, which can then be used for mechanical power transmission for all sorts of machines. $\endgroup$ – Joe Bloggs Jul 10 '20 at 5:38

Here is your answer!

It covers things pretty comprehensively when the stone blows from behind. However it seems to show that it's more efficient to remove the sails and just have the stone (I mean fan!)


Rather than describe a video in words right now, I will simply give the link to it.

In order to better fit in with the rules, I'll see what I can do in the way of a short transcription (can't do it tonight!)


There is an interesting possibility that, by using an efficient modern Bermuda rig, you could actually utilise the Bernoulli effect to produce lift from the sails and thus progress forward even if Newtonian reaction occurs. I suspect this might be more efficient than the method shown in the video. You would face the stone at right angles to the direction of travel and direct it at the sails. The equal and opposite reaction of the stone on the deck would actually serve to keep the boat more upright than it would be as a result of an external wind. A good keel is of course essential. However that possibly doesn't answer your question which specifies a cog and a coracle. I need to investigate more to see if anyone has done this or if it could work.


The same guy in his previous video accidentally demonstrates the Bernoulli effect at one point although he doesn't realise it!

  • $\begingroup$ do you think that this wind-creating stone element I'm trying add is too complicated? Like if it could be used on a ship, what else could people use it for (example: flight?) $\endgroup$ – Ebi Jul 9 '20 at 0:50
  • $\begingroup$ btw...AWESOME VIDEO! good find, thank you! $\endgroup$ – Ebi Jul 9 '20 at 0:54
  • $\begingroup$ direction of travel and direct it at the sails. The equal and opposite reaction of the stone on the deck OP says the stone has no recoil. $\endgroup$ – The Square-Cube Law Jul 9 '20 at 5:26
  • $\begingroup$ @Renan - It doesn't really matter. If I'm right it should work either way. I was just trying to retain as much science as possible in order to keep the need for magic to a minimum. $\endgroup$ – chasly - supports Monica Jul 9 '20 at 11:29

i am going to add to the other answers, in that trips would be cut in half as ships would now be able to travel on a schedule. it'll not be all that different with the first steam ships when they became viable.


Although a lot suggest blowing the sails, it would actually be better to completely lose the sails. At least where other wind can't reach. Why? Because it makes to sense to blow into sails. Sails would only complicate matters as it will interfere in most cases with your direction, making you need a large crew that sailing ships have to still float the right way as efficiently as possible.

Place the stone as close as possible to something that holds as much of the wind as possible. The further the stone is away from pushing something, the more it can be diluted or change direction from other currents. So as close as possible so it'll spent as much of it's power to thrust. If you blow it now, it'll force as much of the wind into the small solid, like a sail or just a slightly bend piece of metal. You can just place it in a box. Fix all this to something sturdy and you have all the propulsion you need. It can be anywhere in the hull, but at the center or in the front makes sense for a lot of builds. But look at cars for different effects of front or rear drive.

Now 2 ships will be created. One for speed, with a more normal hull for the period, making it aerodynamic (waterdynamic?), making it move easily through the water at high speeds. The other is simply round. Think any useful variation of a pancake with a round bottom. The stone in a box can easily be turned in these ships, giving them thrust in any desired direction. This gives them high flexibility.

Not needing a lot of sails or crew to manage it all frees up space and weight, giving you a lot of room for cargo, men or attack stuff.

The circular one could have a square on top if it's an attack ship. With 1 extra stone in a box the whole ship can rotate and keep 2 sides of the triangle at you, while pelting the enemy with all cannons. The oblique angles are perfect to make enemy cannon's have glancing blows instead of direct hits.

I could go on an on, but I'll leave the rest to you. Unless there's more questions.

Edit: @Renan gave an interesting point about placing the stone in centre mass. But if you place it behind, the front might get out of the water. This could be advantageous, as there is less water resistance and with no sails you'll not lose energy from not being completely straight.

Extra edit: the stone could be completely sealed off in a box. The wind it thrusts can be used again,making it a loop. If it actually generates wind it would need to let the air out, but this can be used in the thrust as well. You just need to be able to let it escape without pushing backwards for maximum thrust. But placing it under a boat could even be reminiscent of a jetski.

  • $\begingroup$ Can't place it in a box, because the wind that bounces off the front wall will then bounce off the back wall. I think. Intuitively I think something like a satellite dish shape, right in front of the stone, is best. $\endgroup$ – workerjoe Jul 9 '20 at 15:59
  • $\begingroup$ I think a thrust forwards in a closed system will always to in the thrusts way. Any air would loop, and as the thrust would also make a lower pressure area in front of the stone, any push back would be nullified. In the end, regardless of pressure agaibst the back of the box, it would go forwards. But maybe you're right. How does a box in water behave if you put an externally powered fan in there? Even so. You can put holes in places or put it on the top deck with a dish in front like you suggest to make it work without the box. $\endgroup$ – Trioxidane Jul 9 '20 at 17:53

If the magic does make it recoiless, violating Newton's third law, then the best place for the stone is close to the ship's center of mass. Place some canvas or wooden wall there and point the stone at it.

The reason is that by having the thrust vector passing through the cebter of mass, all of the energy is applied as forward motion. On a sail ship the push of the wind also tends to push the vessel into a rotation, with the front going down and the rear going up (though ships are built to resist this). By blowing on the sails attached to the masts you are not being as effective with the stone as you can.

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    $\begingroup$ Doesn't even need canvas. Point it right at a solid wood plank. $\endgroup$ – workerjoe Jul 9 '20 at 15:40
  • $\begingroup$ @workerjoe you're right, I'm editing the answer. $\endgroup$ – The Square-Cube Law Jul 9 '20 at 15:56

The fastest point of sailing for a traditional multimast square rigger is somewhat off the wind, a broad reach (around point 135), when the most sail is exposed to the wind. Modern sloop rigs tend to be fastest close hauled (~point 45 depending on design).

Your wind stone used in a direct fashion, mounted aft of the hull and blowing forwards, would always leave the ship on a dead run, straight before the wind.

This means that direct use of the stone on a large square rigged vessel would not be as fast as using the equivalent real wind slightly off the stern.

This leaves you with multiple options

  • build an outrigger spar (probably mounted on the mizzen) to hold the stone so it's always at the best point off the hull
  • use trade winds when they're available and use the stone for
    • in the doldrums
    • making way for navigation and harbour maneuvering
    • sailing against the wind

The last is actually highly significant in many situations as vessels traditionally were bound to navigating on prevailing winds only, meaning the Spanish Armarda after their confrontation with Nelson in the Channel had to sail round Scotland and Ireland to get home, losing many more men and ships on the way. With access to your stones they'd be able to sail directly home.

In theory you could also delay the dominance of the sloop rig for smaller vessels, but that depends on the availability of the stones to ordinary people.

  • $\begingroup$ Excellent, thank you $\endgroup$ – Ebi Jul 11 '20 at 3:07

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