Constant Movement and round based combat

This question came up the other day during a session where we have an airship that is basically a hot air balloon attached to a ship and is powered by elementals (Fire elemental for the balloon and air elementals for the propulsion).

While we were on the ship we were attacked by a dragon which landed on the ship. This was fine because we hadn't started moving yet. During the fight one of our PCs initiated the ship bringing it into constant motion. This wouldn't be a problem except that the dragon repeatedly flew off the ship to get a better angle for its breath weapon then landed back on the ship before its turn was over. The reason this was an issue is that the ship moves faster than the dragon. Since it was the dragon's turn it just ignored this as if the ship were standing still even though it was in constant motion.

Is there a good way to solve the problem of moving on and off something in constant motion or are we and the DM just missing something in the rules?

Some furhter details: The dragon has a fly speed of 80ft and never dashed while the ship has a speed of 220ft per round. There was no driver for the ship. The PC started it up and returned to combat. It was traveling through the air in a straight line. Relative motion wouldn’t apply due to the dragons ability to fly against the direction the ship was traveling and still catch back up.

• Related 3.5 question rpg.stackexchange.com/questions/63913/… - about spells, but the key here is framing the encounter or the battlefield. Sep 20, 2017 at 23:37
• Are you familiar with relative motion? Sep 21, 2017 at 2:46
• Relative motion wouldn’t apply because the dragon could fly against the ships direction, breath, then fly back over and land on it. Oct 1, 2017 at 19:04

Easiest to treat this as 'Difficult Terrain' for flying movement

Although D&D's round abstraction isn't meant to be completely realistic: the dragon is launching itself from a moving platform, so it could believably even be ahead of the flying ship briefly before landing again (assuming a winged creature the size of a cottage is believably airborne to begin with)... similar to how someone could say, jump 20' forward while on a flying ship without worrying about their jump speed compared to the ship's speed. It's just in the dragon's case: it has some serious wind resistance to contend with (not unlike flying around in strong winds)

Treating this as difficult terrain for flying would be a simple (and supported) method that would halve the distance the Dragon could fly without losing its 'ride' (i.e. something it should probably be able to do briefly). And of course: if it doesn't land on its turn, the ship would move away.

But let's explore a different example: say a melee fighter wants to jump off a very-fast moving wagon, attack someone, then jump back on before the wagon leaves. The DM might decide to use the mounted combat rules as a basis for adjudication: "Once during your move, you can mount a creature that is within 5 feet of you or dismount. Doing so costs an amount of movement equal to half your speed."... which could make the stunt pretty unlikely without further allowances.

• How does this solve the issue? Sep 20, 2017 at 21:58
• @András By allowing the dragon to jump off a moving ship then quickly land back on it - which a dragon ought to be able to do - while also accounting for the fact that such a maneuver would be more restricted than if the ship were actually stationary so the fact that the ship is moving isn't totally ignored. Sounds good to me. Sep 20, 2017 at 23:02
• Given the concept of relative motion, the dragon begins at the same speed as the ship. Thus, I'm not sure adding difficult terrain for flying is entirely appropriate. Sep 20, 2017 at 23:42
• Correct me if I'm wrong, but during a single turn, your melee fighter can either jump off or jump on, not both, no? Per quotes: "Once during your move . . . you can mount . . . or dismount". @Wyrmwood, I think it's about the mentioned wind resistance. Sep 21, 2017 at 8:59
• @KtX2SkD I'm still pretty certain it would be relative; unless the ship itself is blocking a significant amount while perched. Sep 21, 2017 at 15:02

The ship is not moving when the dragon takes its turn.

Sorry, but this is just how the abstraction of turns in the game happens. D&D is not a physics simulator, and never intended to be.

The vehicle moves when it is the driver's turn (just like a mount). On all other turns, the vehicle is considered stationary for all purposes.

So when the vehicle moves, everyone on board of the vehicle move together with the vehicle. Everyone not on board is just left behind and must use their own movement to catch up.

One good strategy is to try and make vehicle move when the dragon is not landed.

The driver can even attempt a maneuver using the vehicle proficiency to shake the dragon off, then move the vehicle. It should be a contested roll, the dragon versus the driver.

On this one the DM should adjucate what ability makes more sense from the roleplaying and description of the maneuver.

Maybe even the PC can use their actions to try and impose advantage / disadvantage on the rolls. Be creative.

This problem also happens during a chase (think a spy vs spy tailing scene in the city alleys). Use contested rolls of stealth, deception versus insight and perception to either tail or shake off the tail.

• If I may, while many times games don't/can't seek 100% realism, it does not necessarily devalue cases where games do/attempt being realistic in certain aspects. In fact, almost any game must fundamentally have a level of realism & correlation to our world, it just boils down most of the time to practicality and/or taste. If I DMed such a situation, I'd investigate all possible alternatives to this... circus of time-freeze... probably not easy, but what's easy about D&D anyways :) Sep 21, 2017 at 9:17
• @ktx2skd #RantModeOn what baffles me is that people are OK with the HP abstraction: I am a lv 10 barbarian, and I will stand completely still and let my lv 10 fighter friend swing his greataxe at me. For keepers. Green Knight style. There is zero percent chance I'll die. Heck, at lv 20 a barbarian can dive from stratosphere, land on his face, and stand up to fight. but when it comes to the other abstractions the game made to be playable people need to read the book on a headstand to see if they get it. #RantModeOff Sep 21, 2017 at 13:29
• Lol, that's news, I'll check the books next time I'm around them for these scenarios. One other example that bugged my taste the most, is the death save system. It's surely not science-based, as I can't fathom a medical injury that without intervention becomes either terminal or not in 30 seconds max., and a corresponding first aid practice that can be "fired & forgotten" after possibly 6 seconds of work. Still pondering it every once in a while... :P Sep 21, 2017 at 13:53
• @ktx2skd a first aid practice that can be executed without sterelization or implements of any sort with medieval knowledge in 6 seconds. But again, the real world ancient egypt "medics" could predict the gender of a baby from early pregnancy with pinpoint accuracy, so I heard. Sep 21, 2017 at 14:06

The driver should ready an action

If the driver readies an action to move the ship away from the dragon when the dragon tries to land back on the deck, they should be able to escape the dragon. Note that the movement may provoke an attack of opportunity from the dragon, and depending on speed the dragon may be able to hit parts of the ship with its breath weapon the next round.

If the driver fails to do this, the dragon can land on the ship.

D&D's rules generate a very different metaphysics from the world we live in. Turns are a thing, as much as people would like to pretend that combat rounds happen simultaneously over a 6-second period. You can't remove the effects of the turn-based nature of the combat system without completely replacing the combat system. The ability of the dragon to do this sort of thing is baked into the system and is something you're just going to have to accept, not have the dragon take advantage of, or use a different system.

• Although all of the driver comments are good and make sense the point of the post is that there was no driver, the ship was traveling in a straight line through the air with more fly speed than the dragon but the dragon could just fly off, fly behind the ship in the opposite direction the ship is traveling then use its breath and fly back onto the ship as if it was standing still. This is why i accepted difficult terrain as the answer. Oct 1, 2017 at 18:53