More Movement: Spelljammer 5e Conversion

This post has been updated to correct another math error. That’s becoming a habit

Welcome back to my Spelljammer conversion for 5e. This post will cover a few more items related to ship movement that I missed in the first movement post. I may have underestimated just how much ship movement is a part of this campaign setting. However, traveling through space is what Spelljammer is all about so it all needs to be addressed. 

There were actually two types of travel in the original Spelljammer rules; tactical and long-range travel. The SR rules that I converted in the first post apply to tactical movement and travel within the atmosphere of a celestial body. There is an entirely different matter of taking off or landing on a planet. There were ten different classes of planet in Spelljammer each distinguished by their diameter.

Ships taking off or landing on these different size planets were assumed to be moving away from or towards the surface in a straight line. The time taken to land or take off did not take into account the SR of the ship. Instead it was determined based off the size class of the planet. For example, it took a spelljammer ship 40 minutes to take off from a Size E planet which is roughly Earth-sized.

I think it is actually simpler to set an atmosphere limit above a planet that must be broken through in order to reach Wildspace. I’m going to just make up a multiplier of 10 times planet diameter here based on 62 miles (100 km) being the widely held beginning of space on Earth. This isn’t right. The distance to space is about 1/100th the diameter of Earth. I’m going to use 1/10th the diameter for this conversion. This change has been made in the rules below.

The DM can figure out from the table below how long it takes a ship to reach Wildspace based on their SR.

Ships that are traveling in Wildspace have broken free of the gravitational pull of these bodies and are able to obtain greater speed. A spelljammer ship traveling in a straight line and avoiding any gravity fields will reach a speed of 4 million miles per hour (6437376 km/h) regardless of SR rating.

This should mean that a spelljammer ship can travel 100 million miles (160934400 km) through Wildspace in a single day of travel, but of course it’s not that simple. The original rules allowed for an individual to operate a helm for 12 hours without tiring. After 12 hours the operator may continue to use the helm, but with an SR decrease of 1 per hour. After 24 hours of use the operator passes out and must be fully rested before using the helm again.  I think this is a good area to bring in the exhaustion rule from 5e.

The travel speed of a spelljammer ship changes based on where the ship is being operated. The SR granted by the spelljammer helm and operator applies when a ship is being operated in the atmosphere of a celestial body or when the ship is engaged in combat. The boundary between planetary atmosphere and Wildspace varies between different planets, but generally rests at a distance of 1/10th of the diameter of the world.

Celestial Body Size Classification

Size ClassDiameter in MilesDiameter in Kilometers
Size ALess than 10Less than 16
Size B10-10016-161
Size C101-1000162-1609
Size D1001-40001610-6437
Size E4001-100006438-16093
Size F10001-4000016094-64374
Size G40001-10000064375-160934
Size H100001-1000000160935-1609344
Size I1000001-100000001609345-16093440
Size J10000001 and greater16093441 and greater

Distance To Reach Wildspace

Size ClassMiles Above SurfaceKilometers Above Surface

A spelljammer ship in Wildspace or the Phlogiston is not restricted by its SR. A ship traveling through Wildspace and avoiding any gravity fields will reach a speed of 4 million miles per hour (6437376 km/h) regardless of SR rating. The Phlogiston contains dense rivers of flammable ether that flow between Crystal Shells. Ships traveling in these currents can achieve speeds that are beyond measure. Generally a ship may travel between crystal spheres within 10d10 days.
However, travel is always limited by the endurance of the helm operator. A spellcaster may operate a spelljammer helm continuously for 12 hours without tiring. At the end of each hour thereafter the character must make a Constitution saving throw. The DC is 10 + 1 for each hour past 12 hours. On a failed saving throw, a character suffers one level of exhaustion (see appendix A in the PHB). Each exhaustion level gained from spelljamming reduce maximum SR by 1. This penalty persists until removed by an appropriate amount of rest.  Regardless of exhaustion level after 24 hours of continuous operation of a spelljammer helm the operator will pass out and be unable to use any helm again until after a long rest.

We aren’t quite done with movement yet. For the next post I will begin to convert over rules for ship to ship combat with Maneuverability Class. I have a small admin note as well for those of you that read all the way to the end.  I will adding all of the bold texted items in these posts to a separate Spelljammer page on the blog. This will be a living document while I do the conversion and most likely all the way my group’s Spelljammer campaign.


5 thoughts on “More Movement: Spelljammer 5e Conversion”

    1. It really depends on the game and the DM. You can hire a crew for a ship including a magic user to work the helm. Piloting the ship from planet to planet may seem like a waste because it drains your spells, but you’re not usually going to land and then jump immediately into combat.

        1. Ship to ship combat is typically done with onboard armament like ballista or catapults. You end up fighting over greater distances than normal melee or ranged combat because it’s space. I will get into specific rules for combat at some point that cover some of this.

    2. Most of the Spelljammer campaigns I saw back in the day did that. That let the party have a ship that moved at a decent SR because of the umpteenth-level wizard who actually “owned” and drove the ship from place to place. But that also led to a lot of DM “railroading” because the DM always decided where to go next and the players just rode along…

      The “you lose your memorized spells/spell slots” was not a thought-through mechanic. But then, people working at TSR at the time were forbidden to playtest anything they were writing because that would have been “playing games on company time” (yes, really).

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