How to determine whether my dragon hunting trophy can stay afloat on a lake?

Question

Continued from Can a person covered in mud survive an ordeal with fire breathing dragon?

Miraculously my protagonist managed to subdue the fire breathing dragon and knock it unconscious. He then tied up the creature which is as big as a double decker bus with a wing span measuring 50 meters from tip to tip. The only thing left to do is to take it back to the village, which is conveniently just across the lake, alive.

Suppose soon there will be a high tide - in the next hour or so. My protagonist wishes to make use of this opportunity to float the dragon and use it as a ferry to reach the other side of the lake. How can my protagonist make sure that his hunting trophy will not drown during high tide? Is there a way to determine the buoyancy of an uncooperative dragon?

This is not a freshwater lake.

Answer 1

Your biggest problem is the dragon itself: you need to quickly decide if it can float or not, so you don't have time to build a measuring ground to weight it and also measure its volume.

Also chopping out a sample of its flesh to measure its density is going to make it more angry, so it's a no go.

Force its wings open, put some floaters below them and navigate to the other side.

Examples of what you can use as floaters:

• some banana boats
• some conventional boats (this would also provide you with propulsion)
• wood logs (I am sure the battle cut some trees down)
• [...]

Answer 2

It will work, probably

• Human body density is between 1.028 and 1.021 g/mL, which is just low enough to float in salt water (1030 g/ml).

• Horse density is of 0.95 g/ml, which would also float.

• Reptiles and other dragon-like creatures can float sometimes. Think also of crocodiles.

So, your dragon, if built similarly, would also probably float.

What you can do to be sure

• If you can afford to wait a bit. Put it close to the shore, and when the tide goes up, see if it float. If not, pull it ashore. If yes, everything is fine.
• Attach floating material to it. Wood. Air filled skins/hoses from other animals you hunted.
• My favourite (and it's serious): Feed him with food that cause gases, it will help him float. For instance artichokes, broccoli, leeks or cauliflower.

Determine density

Otherwise it is very difficult to guess your dragon’s density without putting it in water or in another fluid. Basically, you have two parameters to define density:

• Weight
• Volume

Weight is “easy” to determine, if you have or can build a scale. But the volume is difficult to determine. Usually it is done by putting the object in a fluid and seeing how much fluid is displaced. So, if you are able to build a big bathtub to find the dragon volume, you could as well build a boat to cross the lake.