Subterranean sailing?

[Drul Morbok]

Hi everyone,
reading the page about the dwarven race, I stumbled upon the following sentences:
"There are a number of underground rivers, lakes and even seas in the vast underworld of Khoras. The dwarves sail these subterranean waterways in squat, thick hulled vessels called durogars. These sturdy vessels have broad bellies, are typically three levels tall, are tiller steered and have two square sails."

This made me wonder about subterranean wind conditions.
I can easily imagine even strong winds in narrow tunnels, but I guess that a cavern would have to be rather huge to feature air circulation within it, and for air currents passing through a cavern, the narrow entrances should pose some kind of bottleneck for the amount of passing air, so in the wider sections of the cavern, there should be close to no wind.

But then again, my assumptions might apply only for rather regional underground complexes, and not for continent-wide underworlds, or I might fail to consider other wind sources like geothermal heat, magma reservoirs and the like.

As with all my questions, I aim for an open discussion about game world mechanics rather than for judging right or wrong.

[tanis]

That's actually a good question. I hadn't thought about that until you pointed it out, but you're right, that does seem a bit strange.

Though, one of the nice things about fantasy as a setting is that we have the opportunity in this sort of situation to ignore concerns about plausibility, and come up with a cool explanation for how exactly this can work.

Maybe Dave can find a cool thing to add to Khoras, or dwarves, or whatever, now!

[David Roomes]

That's an excellent question. And you already struck upon one of my chief answers... geothermal energy. I think geothermal energy could heat air in a large cavern (perhaps one end of a very large underground cavern) and cause a weather system where one end of the cave is consistently higher temperatures and higher pressures which might result in a constant gentle wind that blows all the time across an underground lake.

Keep in mind that when I say "very large cavern", I'm talking about truly stupendous, gargantuan caverns that simply dwarf anything we have on Earth and equally huge underground lakes. The largest underground lake on Earth is Dragon's Breath cavern in Namibia. However, I'm thinking of something like that scene in The Two Towers where Gandalf and the Balrog are falling and fighting for a very long time and then suddenly emerge from the roof of a vast cavern holding an immense lake. THAT is the kind of underground lake I'm talking about. Caverns and lakes measured not in feet, but in miles. So big that we have no equivalent on Earth that we can even study. It's possible that a cavern that large could experience strange atmospheric effects that we aren't aware of. Maybe.

Other possible sources of wind: fast moving underground rivers, underground water falls, tunnel caverns that connect to the surface, leaking gas fissures, subsurface volcanic activity and so forth.

However, you bring up a very good point. There would probably be only select places in the underground world where there would be enough wind to justify the use of sails and the dwarves would obviously only put sails on vessels on lakes that have sufficient wind.

Most places probably wouldn't have enough wind and the dwarves would be forced to use other methods. This strikes me as an opportunity. Rowing, of course, would be an option. But the dwarves are ingenious engineers. Perhaps they would have invented some kind of primitive propeller system and turn their shafts using coal-fired steam engines! The dwarves, no doubt, have access to vast coal reserves.

[tanis]

Good point. Get a large enough cavern, and concerns about temperature equalization become less significant.

Also, it sounds like Dave just confirmed steampunk dwarves. XD Arcanum, anyone?

I kid, but still, that's cool.

[David Roomes]

I like the idea of steampunk dwarves...

[Drul Morbok]

Yes, good point, if the cavern is high enough...maybe a domed ceiling with an upward shaft in the center...hot air will rise above heat sources, and if it is moist air - let's assume water meeting lava at certain intervals - there might even be rainstorms.
I guess even lightning is possible if you're creative about iron ore deposits and the like.

Such caves might not be the norm, but they might be the most likely ones to be inhabited and therefore most relevant for shipping.

But yeah, steampunk dwarves rock, so early steamboats would be a lot cooler than sails 
Or a complex system of mithril ropes pulling ships across lakes and along rivers...powered by waterwheels and able to pull ships upstream.