Running on water

[Ambrus]

Superheroes do it all the time. With the right combination of special abilities and magic a D&D character could likewise move at astounding superhuman speeds. So, anyone care to hazard a guess how fast a bipedal character would likely have to be moving to tread upon the surface of a body of water without sinking or slowing down? Would such a feat even be realistically possible if one ignores the issue of the means by which a human could be made to run at such speeds? Any of you physics-gurus care to tear the idea apart?

 

[Mark Chance]

Excessive speed isn't needed. What you need is a 5th-level cleric and water walk.

 

[Celebrim]

Speaking in terms of physics, the forward motion of a walking entity isn't as important to staying afloat as much as the force and speed of the step and the amount of water displaced by the slap (bigger feet work better).

To really be realistic about it, we'd have to introduce to D&D the concept of 'negative encumberance', but I've played using GULLIVER rules and while its very useful for a game ref to have seen these concepts, I can speak from experience in saying that that much realism doesn't make for good game play. (Might be better if you had a computer doing all the work.)

However, going fast and thereby being able to walk on water is a fantasy staple (of a certain sort of fantasy) and it does have some factual basis (in that if you could move your feet fast enough and push the water hard enough, you could do it). But with human sized feet and typical human body weight, it would have to be very fast indeed. Just because it's a round number, I'd say a runner with a base land speed of 300' per round could do it (translates to a running speed of about 170 mph). In actuality, that's probably too slow but I don't know the physics involved enough to calculate a number and covering 1500' in a single round is going to be hard enough under the core rules.

Or, you could just make a balance DC check of 90 to stand/walk on water.

 

[Claudius Gaius]

Straightforward displacement calculations (shove foot into water, exert force to displace water, reaction force keeps you up) depend on how deeply your foot goes (and thus how much water is displaced), how much drag you get removing your foot, and number of footfalls per second. It then translates into speed by multiplying the footfalls per second by an average stride length. Lacking practical measurements, these numbers are all subject to a wide variety of assumptions - but most of the calculations for come out at somewhere around the speed of sound.