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I was considering the possibility mermaids might make use of sailing ships similar to the USS Monitor, but with sails and supposedly wood.

Now, the mermaids wouldn't mind the ship being filled with water, in fact they'd prefer it. Water is heavy: you don't want your ship filled with water. The air in the ship also has a lot to do with it not sinking.

Please review and criticize my idea for a mermaid’s boat.

To the point

My curiosity is about ship designs they could utilize. One idea I had was what if you took out the back/stern (or most of it) of a ship? It would fill with water, but the weight of the water inside of it shouldn't create drag when the ship moves forward? If you tried to move it backwards, of course, that would go poorly, and this may also affect turning speed.

You would need some way to maintain buoyancy, and keep the sails above water and level enough. Also, depending on the size of the hole in the back, you'll want to make sure nothing in the ship falls out that you don't want to fall out.

This idea may well be useless, but I hope that it can inspire some mermaid ship design of interest. Thank you.

Design Idea

1: The Air Decks. Size may not be representative of the real thing. It would be filled with air to keep the ship buoyant and the sail/rigging above the waves. It would also be used as dry storage. The air decks also extend out further than the Submerged Decks, I thought this may be necessary for the ship's buoyancy. There's also the question whether extra buoyant materials should be added to the vessel to counteract the water.

2: The Submerged Decks. Water flows in through the opening in the stern, and it is not closed off so it can freely flow out when the boat moves forward. Note that a grating is likely placed here, so that it isn't easy to fall out by mistake. Mermaids hang around here with cargo that doesn't mind being wet.

3: The sails. The question of how mermaids will handle rigging comes to mind, but that's for another time.

4: The sea. It needs to not totally wash over the air decks. This creates some issues. If you have sensitive cargo in the dry decks, you don't want seawater getting in. Which implies the water doesn't get that high, or there are no windows, which will make things quite dark. You could have lanterns for lighting, but that comes with dangers. You could try to have lighting come down from the top deck with some grates, so that as long as the waves aren't crashing over your boat things will remain pretty dry. Sealing off certain cargo rooms so no water can get into them is also a possibility.

5: I was considering the type of opening you would have in the stern. You'd want it elevated above the keel I'd expect. For one thing you would want to make sure the rudder is adequately supported. How a rudder would work on a strange ship like this is questionable.

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    $\begingroup$ Besides some typos and unorhodox punctuation, the post never actually stated a question. I added a sentence to the intro in line with the implicit request. You should review my changes. $\endgroup$ – JDługosz Oct 16 '16 at 15:52
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    $\begingroup$ On first read of this question, I immediately thought about the Wasp Class carriers of the U.S. Navy. These ships have a stern gate allowing smaller vessels to launch and recover inside the ship. $\endgroup$ – cobaltduck Oct 19 '16 at 17:17
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It's not (primarily) the weight of the ship, or what's in it - water or cargo* - that creates drag, it's pushing the water out of the way. Your open-backed boat would be worse than a conventional boat with tapered stern, because the abrupt break at the end creates turbulence, which means additional drag.

But you have another problem with a mermaid ship, assuming it's crewed exclusively by mermaids. How do they get into the rigging to handle the sails?

*More cargo (or water) would cause the hull to ride lower, so there'd be more drag because of the increased submerged area. See e.g. Plimsoll line http://oceanservice.noaa.gov/facts/plimsoll-line.html

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  • $\begingroup$ I hadn't considered turbulence. It's probably better as you and Chris pointed out to have a normal boat with water in the lower decks. For the rigging, they might pick very strong mermaids, or they might arrange some elevator like pulleys that a couple of mermaids can use to help one up.It might be something like a hanging crow's nest, which can be pulled over to either side of the ship, and fasted to nearby rigging while the mermaid works on it. $\endgroup$ – J. Doe Oct 16 '16 at 17:57
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    $\begingroup$ You might do better with a trimaran-like design, with two air hulls and a water hull. $\endgroup$ – jamesqf Oct 16 '16 at 22:08
  • $\begingroup$ That is a good idea. It makes them unique, it has a plausible reason for why they're using a less common design, and it might help them to deal with the difficulties that come with a water filled boat (less buoyancy). $\endgroup$ – J. Doe Oct 16 '16 at 22:28
  • $\begingroup$ "assuming it's crewed exclusively by mermaids." Besides, they spend all day luring sailors to their death. Best to use mermen instead... :) $\endgroup$ – RonJohn Feb 27 '18 at 1:21
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Sailing boats/ships depend on the fact that they are floating on the surface of the water to work. In a nutshell the resistance of the hull in the water (especially the keel) provides a restive force which allows you to sail in a range of directions other than the direction in which the wind is blowing (in some cases almost directly into the wind). Contrast this with a hot air balloon which is entirely at the mercy of the wind and can only control its direction by ascending or descending to find different wind directions.

In order to float any object needs to displace a greater mass of water than its own weight. This is why you can make boats out of steel as long as the mass of water they displace (i.e. the volume of the hull below the waterline) is greater than the total mass of the boat).

What you could do is have a vessel which sits very low in the water (something like a barrel partially filled with water, just high enough to keep the sails and rigging above water and either have the cabins and crew accommodation submerged or have it tow a submersible.

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  • $\begingroup$ Great idea with submersible tows. Only thing is, you will need some mermaids or human hires in the towing ship to control the rigging and make sure all is well, and moving between the submersible and the ship may be difficult when the ship is moving (so if it's attacked or you're needed urgently, problem). I still think it's a good idea. As you point out, there is no need for an elaborate ship you've poked holes in, you could just fill the cabin area with water for comfort's sake (even if it is heavy). $\endgroup$ – J. Doe Oct 16 '16 at 10:28
  • $\begingroup$ I've added a more elaborate and detailed design for my bizarre ship above, if you would be interested in seeing it. The idea is probably filled with holes, the more detailed it gets, but I'll suppress the desire to not embarrass myself for the sake of learning. Thank you for the good answer you've already given. I feel I should set the green tick on you, but have hesitated in case it discourages others from answering. I'm still new to this. $\endgroup$ – J. Doe Oct 16 '16 at 10:31
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This is a bad idea, simply because you are going to be dragging that weight of water along with you as the boat sails.

A much better idea would be something like this:

Boom net riders

The sailing boat would be a catamaran, with two hulls and a sail mounted on a frame between them. The merfolk would use a net strung between the hulls or immediately behind them to hang onto or lie in while the boat is moving slowly. When it starts moving very fast they would haul the nets tighter to bring themselves more out of the water while still staying damp enough from spray etc to remain comfortable.

It could also look something a bit like this: Diver

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  • $\begingroup$ Like, net flooring? That would be a light way of making more deck space, and the splashing could keep them wet. Though on rough waters, I wonder about how comfortable being in a net suspends just on the water will be. I feel that part of the advantage of the triple bodied boat is that it can counteract the weight of water in the hull for more comfortable conditions. $\endgroup$ – J. Doe Oct 19 '16 at 12:56
  • $\begingroup$ @J.Doe If they are adapted to being in the water then they will most likely actually prefer that. In fact during a storm it wouldn't surprise me if they drop the masts and everything entirely to reduce the profile of the boat as much as possible and then they themselves just stay underwater as much as possible. The storm doesn't reach very far down. I've switched to a different image to show more what I have in mind. $\endgroup$ – Tim B Oct 19 '16 at 13:08
  • $\begingroup$ Ah, I see. I wonder how comfortable that is in rough waters. It does depend a lot on the shape of your boat, early boats were sometimes very uncomfortable even in good waters. Mermaids might be good at designing boats to not bounce around, potentially, and with three bodies I can see it being more stable in general. I probably overestimated the difficulty of the idea. Thanks. $\endgroup$ – J. Doe Oct 19 '16 at 13:36
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    $\begingroup$ Yes, I'm thinking a catamaran with the net slung between the hulls. You could climb the net to be out of the water or drop down on it to be more in the water as you wished. If going very fast you'd pull up to reduce drag, if travelling more sedately you could drop into the water more. $\endgroup$ – Tim B Oct 19 '16 at 14:24
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Much worse than the ships we have.

  • You need enough air to displace water of mass equal to mass of your sails. No room for changes here.

  • Submerged wooden hull with brass plating, tar, oils etc has mean density similar enough to water, and actual volume small enough, we can ignore its buoyancy for practical purposes.

  • Thus, what you would do, would be to get a ship as we have it, and add a lot of volume below water line. This would increase mass of your vessel, making it slower. Would increase drag, making it slower even more.

  • Opening on rear side only is mostly irrelevant for this drag. If there still is water inside when you're sailing, and you have no hole on the front to make it flow in, this obviously means you are carrying that water with your ship. Simple as that.

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  • $\begingroup$ The fragment «At best.» does not fit. I'd fix the punctuation but I don’t know which sentence it’s supposed to belong with! What’s it referring to? $\endgroup$ – JDługosz Oct 16 '16 at 15:57

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