How to create travel speed for homebrew vehicles [closed]

Question

I'm working on a campaign where a giant forest covers the land where oceans should usually be. My party is going to have a vessel akin to a ship that will let them travel across this massive forest.

There are 3 forms of transport:

• a ship that uses mechanical legs to walk on top of the canopy. Rust would impede speed. Built for safe travel and transversing difficult terrain.

• A ship that has a giant keel that skims the top of the canopy. Pretty much a giant sailboat but out of water. Control Wind and Control Weather would increase the average speed. It's not meant for transporting people more than cargo.

• A ship that has hot air balloons connected to different parts of the ship to keep it above the canopy. Gas/Magic powered fuel. Medium/Slow speed. Used to travel across forests as well as land. Can carry cargo but more fuel will be consumed the heavier the cargo and the more weight the slower it will be.

I have never homebrewed a form of transportation or vehicle before and I have no idea how travel speed on a vessel of this sort would work because it's technically not a boat and more akin to a walking/floating cargo ship.

Factors like the weather would probably impede speed of these vehicles: things like tornados, strong winds, and thunderstorms. Vessels like these aren't affected in the same way as real ships are so I'm unsure of the speed of these vehicles. In addition to this, the weight of the cargo could slow down or speed up the ship depending on depending on if the load is removed or gained. I'm not sure how ships work so I'm not sure that the weight might even matter but if it did it would impact the speed of the vessel.

To sum all of this up into a sentence: How would I create accurate travel speeds for homebrewed vehicles?

I kinda figured out the general speed, like if the ship was slow or fast or in between, but I'm not sure what the average speed would be per hour or week or day.

Answer 1

Just modify existing transportation

Most of what you've proposed is analogous to existing seafaring transportation, many of which are given stat blocks in Ghosts of Saltmarsh. Note that these are updated from the briefer versions in the DMG (p.119) with multiple changes. Rather than trying to determine how fast your ship should be able to travel based on its movement mechanism, using existing ships will allow you to align your new versions with those designed for a typical D&D setting (and potentially player expectations.)

For example, consider the galley and the sailing ship. A galley (GSM p.187) is a ship that can carry "large amounts of cargo for merchants." Allow this to stand in for your floating cargo ship. Sailing ships (p.192) are "fast-moving designs focused on travel." This could be your expensive air ship.

The speeds of these ships are what you would expect from their descriptions.

• Galley: 4 mph, 96 miles per day
• Sailing Ship: 5 mph, 120 miles per day

If you'd like a greater difference between the speeds, you can easily modify them from there.

The point, though, is that you are asking for answers to the question "how fast should vessels of various speeds go in order to cross an obstacle the size of an ocean?" The answer, of course, is "exactly as fast as the vessels that already exist for that exact purpose." Whether they look like seafaring vessels or are described like that is irrelevant when looking at speed.

Answer 2

The first thing I'd point out is that the word "accurate" has no place here. (The word you're looking for is "plausible".) The vehicle you're describing doesn't exist in the real world, and (unless you go with option C and make it a dirigible) has little to no resemblance to any real-world vehicle. It's like asking whether the speed listed for dragons in the Monster Manual is accurate.

The second thing I'd point out is that it's entirely up to you. There is no "wrong" answer here. It's your world, so you can make it move as fast as you want and no-one can disagree with you.

With that out of the way, let me make some actual useful suggestions. The best thing to do is decide how fast you want it to be compared to other vehicles that already exist (either in the game or in real life). Do you think it should be faster or slower than a sailboat? A locomotive? A man on horseback? A bird in flight? (This will probably be easier, by the way, once you've settled on what the actual form of the vehicle is.) Then look up the speeds of other modes on transportation listed in the rules and use those as a guide. (You could also go beyond the core rules if needed. For instance, if you decide it's a walker, try to get hold of a copy of one of the Star Wars d20 games and look up the speed of an AT-AT or AT-ST.)

Answer 3

Not 100% sure if this is helpful but I would recommend taking a look at a few books I read in highschool with transportation nearly identical to what you are referring to. There's the Leviathan series by Scott Westerfield, Airborn by Kenneth Oppal, and of course the recently adapted into movie Mortal Engines by Phillip Reeve. They all have similar transports in one way or the other and give fairly good mechanical and mathematical info on the vehicles. It should be pretty easy to adapt to D&D merely changing out the chemistry for alchemy, and playing up the clockwork theme of it as well.