Traveling the Astral Sea
An Astral Drive is a magical engine fitted to a flying vessel. It lets the ship leave one plane from open air, enter the Astral Sea, travel there, and then cross over the destination plane’s Periphery to emerge into its airspace.
Introducing Concepts
The Astral Planeship
An typical astral planeship has the following statistics.
Astral Planeship
Gargantuan vehicle (100 ft. by 20 ft.)
Creature Capacity: 20 crew, 40 passengers
Cargo Capacity: 30 tons
Travel Pace (aerial): 30 miles per hour (800 miles per day)
Travel Pace (astral): Astral voyage speed is determined by the Astral Voyage rules below
Cost: 100,000 gp
Vehicle (Astral)
Vehicle (astral) is a new vehicle proficiency. When these rules call for a Vehicle (astral) check, use Wisdom by default and add proficiency if the creature is proficient with Astral Vehicles. The DM can substitute Dexterity for delicate close handling or Intelligence for technical maneuvers.
Crew Roles
A ship making Astral Passage needs two officers:
Navigator. This character makes Intelligence (Arcana) checks to determine the route to travel.
Pilot. This character makes Vehicle (astral) checks to steer the trip along its voyage.
Other crew can use the Help action when their assistance makes sense.
A Plane's Periphery
The Astral Sea is coterminous and coexistent with every plane it touches. A plane's Periphery marks the boundary between the plane on one side and the Astral Sea on the other, in both respects. The drive catches this border to tear the ship free of one plane and cast it into the Astral Sea.
An Astral Ship within a plane can exit by either flying to the Periphery— if it's physically approachable— and passing through it, or by crossing over to the Astral Sea in-place by shifting planes. One method may be easier than the other depending on the plane.
Arrival works the same way in reverse.
A plane with no open air, or one sealed against Astral Approach, can be reached only through a designated breach site, harbor, sky-gate, floating island, or similar special entrance.
The Astral Voyage
An Astral Voyage is the process of traveling through the Astral Sea between planes using an Astral Drive. An Astral Voyage has four steps:
Plot the Route. The navigator charts a viable course to the destination plane.
Engage the Drive. The pilot activates the Astral Drive to pass through the periphery of the current plane and enter the Astral Sea.
The Astral Voyage. The pilot steers the ship through the Astral Sea along the plotted course with help from the crew.
Attempt Arrival. The pilot reaches the destination plane and pass through its periphery to emerge at the intended location.
During an Astral Voyage, the navigator plots the course and interprets Astral currents, after which the pilot guides the ship through the Astral Sea. Resolving an Astral Voyage uses the following process.
Step 1: Plot the Route
To begin an Astral Voyage, the navigator must first plot a route. Plotting a route takes 10 minutes at a chart table, astrolabe, shrine-compass, sky map, or similar station. The navigator makes an Intelligence (Arcana) check. The base DC is 15. Apply the following modifiers:
| Modifier | Circumstance |
|---|---|
| +2 | The navigator has never visited the destination plane |
| +2 | The destination is hidden, sealed, or known only by rumor |
| +2 | The route crosses a hostile Astral Region |
| -2 | The ship carries an accurate chart for this exact route |
| -2 | The navigator has successfully made this exact voyage before |
Determine results as follows:
Success: The ship has a workable route.
If the navigator succeeds on this check by 5 or more, they gain 1 temporary action point. This action point lasts until the end of the voyage and may be spent on any skill check or ability check made to operate, navigate, or repair the ship. The navigator and the pilot they are guiding share this action point. If the navigator rolls a natural 20 on this check, they also gain 1 such action point.
- The action points mechanic mechanic from 3rd ed. Eberron is a points-based system similar to Inspiration. If you're not using action points, then just award Inspiration that can only be used for the Astral Voyage.
Failure: No usable route is found. The navigator cannot make another attempt until they have gained fresh insight into the error from another source, or benefit from the Help action by another character who has Arcana. A different navigator can make a separate attempt.
Step 2: Engage the Drive
Engaging the drive takes 1 action by the pilot. The pilot makes a Vehicle (astral) check. The base DC is 15. Apply the following modifiers:
| Modifier | Circumstance |
|---|---|
| -2 | The pilot is following a well-charted Astral Lane or a route the pilot has successfully flown before |
| -2 | The pilot is receiving guidance from a functioning beacon, harbor signal, or fixed Astral Landmark |
| +2 | The ship is passing through an Astral Storm, psychic squall, or other hazardous Astral Weather |
| +2 | The ship is damaged, poorly trimmed, overloaded, or short-handed |
Determine results as follows:
Success: The ship and everything aboard vanish from the current plane and appear in the Astral Sea. The Astral Voyage then begins.
Failure by 4 or Less: The drive fails to catch. Nothing happens, and the drive can’t be engaged again for 10 minutes.
Failure by 5 or More: The ship suffers an Astral Mishap. (See below.)
Step 3: The Astral Voyage
During an Astral Voyage, long-distance travel is resolved as a skill challenge relying on Vehicle (astral) checks made by the pilot. The DC is figured as in the Engage the Drive step. Other crew members can attempt skill checks to give the pilot advantage on the primary check.
A route requires a certain number of voyage successes before the ship accumulates the number of voyage failures shown for that route on the following table.
| Voyage Distance | Successes | Failures |
|---|---|---|
| Close crossing | 4 | 3 |
| Common crossing | 6 | 4 |
| Long crossing | 8 | 4 |
| Remote crossing | 10 | 5 |
Each attempt represents one watch of about 8 hours. At the end of each watch, the pilot makes one primary check and the crew may make one or more support checks.
Primary Check
Each watch, the pilot makes a Vehicle (astral) check. The DC is calculated as above in the Engage the Drive step.
Success. The ship earns 1 voyage success.
Success by 5 or More. The ship earns 2 voyage successes instead.
Failure by 4 or Less. The ship gains 1 voyage failure.
Failure by 5 or More. The ship also suffers an Astral Mishap.
Critical Failure. Roll twice on the Astral Mishap table and apply both results.
Support Check
One other creature may attempt a support check appropriate to the situation.
On a success, the pilot makes the primary check with advantage. On failure, nothing happens. A failed support check never causes a mishap by itself. The same creature can’t make the same support check in two consecutive watches unless circumstances clearly changed.
Intelligence (Arcana). An Arcana check can be made to read Astral Currents, dominions, and planar signatures. The base DC is 15. Apply the following modifiers:
| Modifier | Circumstance |
|---|---|
| -2 | Ship is following a well-recorded route or using a reliable Astral Chart |
| +2 | Region is crowded with planar echoes, overlapping dominions, or false signatures |
| +2 | Ship has journeyed into a dangerous region of Astral Weather or other hazard |
Wisdom (Perception). A Perception check can be made to spot danger, drift, or false shores. The base DC is 15. Apply the following modifiers:
| Modifier | Circumstance |
|---|---|
| -2 | Ship is approaching a bright beacon, major harbor, or other obvious landmark |
| +2 | Visibility is hampered by Astral Haze, drifting debris, psychic glare, or similar interference |
| +2 | Hazard or landmark is actively concealed, motionless against the void, or disguised |
Wisdom (Survival). A Survival check can be made to keep bearing through storms and dead zones. The base DC is 15. Apply the following modifiers:
| Modifier | Circumstance |
|---|---|
| -2 | Ship is moving through a stable Astral Lane with clear, familiar conditions |
| +2 | Ship is crossing storms, dead-water, hostile currents, or turbulent border regions |
| +2 | Route passes through a shifting or trackless region where bearings won’t hold for long |
Skill Challenge Outcome
If the ship reaches the required number of voyage successes first, it arrives at the destination plane’s aerial Periphery and can attempt Arrival.
If the ship reaches the route’s failure limit first, it is lost in the Astral Sea. It remains adrift in a dangerous region. To recover, the crew must complete a new voyage challenge to a known destination, starting from its current Astral Position.
Step 4: Attempt Arrival
Piercing a destination plane’s aerial Periphery takes 1 action by the pilot. The pilot makes a Vehicle (astral) check. The base DC is 15. Apply the following modifiers:
| Modifier | Circumstance |
|---|---|
| +2 | Pilot wishes to arrive over a specific city, harbor, tower, or other landmark |
| +2 | Pilot wishes to arrive over a moving target, or in a place the crew has never seen |
| -2 | Ship is arriving at a well-known Astral Harbor, sky-port, or beaconed approach |
| +2 | Ship is arriving through severe weather, heavy cloud, smoke, or other obscuring conditions on the destination plane |
| +2 | Destination point lies within a warded, concealed, or magically distorted region that interferes with planar approach |
Determine results as follows:
Success. The ship emerges on the destination plane in the intended general region.
Success by 5 or More. The ship arrives within 1 mile of the chosen point.
Success by 10 or More. The ship arrives directly over the chosen landmark, or as close as terrain safely allows.
Failure by 4 or Less. The ship still emerges on the destination plane, but 5d10 miles off course.
Failure by 5 or More. The ship remains in the Astral Sea near the destination and suffers an Astral Mishap. The crew can try again after 1 hour.
Astral Mishaps
When a mishap occurs, roll on the following table, and apply the resultant effect or effects.
| d100 | Mishap Name | Description |
|---|---|---|
| 01–13 | Psychic Whiplash | Each creature aboard takes 2d6 psychic damage and gains 1 level of exhaustion |
| 14–26 | Hull Shear | Ship takes 5d10 force damage to its hull |
| 27–39 | Component Damage | Ship takes 3d8 force damage to a major exposed component |
| 40–52 | Astral Lee | Ship falls into a dead zone in the Astral Sea; no voyage or Arrival checks can be attempted for 1d4 hours |
| 53–64 | False Bearing | Pilot has disadvantage on their next two voyage or Arrival checks |
| 65–76 | Wrong Shore | Ship is cast to the wrong landfall; it appears at a dangerous open-air point on the intended plane |
| 77–88 | Wrong Plane | Ship is cast to the wrong landfall; it appears at an open-air point on a thematically related plane |
| 89–100 | (reroll twice) | Reroll twice, ignoring any further results of 100 |
If a check fails by 10 or more, treat the mishap as severe and roll twice.
Lost, Drifting, and Broken Helms
If the ship’s helm or Astral Drive is disabled while in the Astral Sea, it can no longer make voyage or Arrival checks. It drifts until repaired, towed, or otherwise rescued.
If a ship is lost in the Astral Sea, finding a way back requires beginning a new Astral Voyage.