Suppose we scale up a human to about 10m in height and their skeletal structure have evolved to ensure they won't succumb under their own weight. Due to their unique blood circulatory system they can remain conscious on land, however their weight would easily match those of the Titans in the prehistoric period. They aren't very intelligent so they don't build rafts, but I need them to swim across Lake Baikal. What other biological features must the giant have to become a swimmer?
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4$\begingroup$ Pretty much any animal can swim. Here is a swimming elephant. I'm sure many dinosaurs could swim. Your titan can probably also swim. $\endgroup$– kingledionOct 3, 2016 at 13:40
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1$\begingroup$ How did you resolve scaling him up? $\endgroup$– MołotOct 3, 2016 at 13:46
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2$\begingroup$ To whomever downvoted: Remember to always leave a comment explaining how the question can be improved if there's no comment currently that voices your reason (such as is the case right now). $\endgroup$– RangerOct 3, 2016 at 13:46
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1$\begingroup$ @Mołot I think you took that post out-of-context; that's asking for a feature request (mechanical force), I'm talking on being polite/helping people grow. If people are downvoted and nobody explains why, they won't improve. On a side note I'd like to point out that downvotes are (per the Help Center) reserved for "egregiously sloppy, no-effort-expended post(s)." I don't see those traits present in this question, so (arguable) somebody downvoted erroneously. $\endgroup$– RangerOct 3, 2016 at 13:57
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2$\begingroup$ @Molot While voting is anonymous, it's good to explain why a question/answer deserves a downvote (or a flag, if it comes to that). That way, the poster can improve it. This can also head off meta posts titled, "Why is my post getting downvoted?" $\endgroup$– AzuaronOct 3, 2016 at 13:59
4 Answers
Assuming they have the same mechanics as a human (which seems to be the case) they'll be able to accomplish basic stroke movements. Weight might be an issue, but the fix is easy; you just need to lower their density so it's less than water, and they'll naturally float. Alternately, just near the density of water and it'll be easy to stay above the water's surface.
Fat's density is about 910 kg per cubic meter. Density of water is 1000 kg per cubic meter. Assuming their biology as a whole is basically just a scaled up human, their density also should be basically just a scaled up human; this means being fat enough to more or less float (or at least not sink too quickly) is perfectly reasonable.
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$\begingroup$ I very much agree. The resultant density will depend on how the OP handled the scaling up of the skeletal structure; human-like bone is denser than water, so if this creature has a similar or even more compact skeletal structure than a human, buoyancy might become even more of an issue. But this is why I like your answer: regardless of how they handle the skeletal structure question, you correctly note that they must keep the creature's overall density low, and that's very much the basic, correct answer, here. $\endgroup$ Oct 3, 2016 at 14:19
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1$\begingroup$ @type_outcast agreed. If you want any semblance of realism in this titan, theri bones will have to be far more dense than regular Human bone, or made of non bone materials that are stronger and lighter. A purely Scaled up human would probably not be able to float due to this, but if they work around it, This titan does not have to float, just not sink too much. Just like a Bird in the air, they could use technique and muscle to overcome some sinking, meaning they could be moderately more dense than water, just that they would not last long swimming if they are too dense. $\endgroup$– RyanOct 3, 2016 at 18:06
Expand their chest to provide over-sized lung capacity (which could be evolutionary-justified as part of your augmented circulatory system). Then require that they hold their breath while the swim.
Built in flotation devices!
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$\begingroup$ From experience (don't ask) I would submit that the location of those air bladders will be very important to this big creature being able to keep its head above water (not to mention produce a reasonable amount of propulsion in the water). I can't tell you precisely where they should go, because the weight distribution of a creature this big isn't going to be the same as a human. If I had to guess, though, the air bladders should probably be more dorsal, and spread out laterally, so the big dude doesn't roll constantly. $\endgroup$ Oct 3, 2016 at 14:25
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$\begingroup$ I've done this in a pool with scuba gear as a demonstration of buoyancy control. That said, would not help keep the head above water. Not enough volume displaced, not in the right place, and breathing still needs to be done which means lungs will be "empty" on a somewhat regular basis/cycle. $\endgroup$– ivanivanMay 15, 2019 at 23:08
I'm not sure I see the problem. The density of a human remains the same if scaled evenly. Yes, there would be more bone (heavy), but also spread over a larger volume. Density is what allows something to float (less dense than water). Density is a factor of mass per volume. A perfect scaling would prevent the giant from succumbing to their own weight (look at elephants or dinosaurs - the bones are thicker to support the weight - but they still are roughly the same density), and would keep overall density without a pretty slim margin the same as for a normal-sized human.
Even if your giant is too dense to be able to swim, he could still make his way across the lake.
He simply knocks over a tree on one side of the lake, drags it to the water and uses the tree as a float as he kick-swims his way across.
If your giants regularly carry around a huge tree-sized wooden club (ie. a tree), then he can just use that as his floatation device.