This will be the first Encounter Concept I’ve published. My hope is that this, and future encounters are detailed enough to provide everything a GM would need to use it, but also be adaptable to whatever system, or setting you prefer. That being said, I write my content using 5e basic rules as a framework for die rolls and check values.
Setting: Aquatic, Seafaring, On-A-Boat, Open Ocean or Sea.
Encounter Summary: You and your companions are aboard a mighty ship, lead by a seasoned captain and his loyal crew. It’s been a pleasant journey; the fresh air, the spray of the sea, even the crew cook helps to make this enjoyable for the captain’s guests. However, everything isn’t sea spray and glittering gold, someone is shouting “Man overboard!”. This encounter serves to provide inspiration and/or a reason for why.
Encounter Trigger: For this encounter, since events are on a table, it’s possible to simply select one ahead of time and further refine the encounter from there as it serves your story or group. Also due to the table, the event could be selected randomly with a die roll.
Usage Example: A group of four is sailing up the coast from one city to the next. The journey takes two to four days depending on wind and weather. As the DM, I would roll 1d4 to determine how long the trip takes them, re-rolling on a 1 (the winds wouldn’t be that favorable). Then, on each day of travel, each character would roll 1d12, my standard for encounters when traveling for a day or more at a time on the same mode of transportation. On a result of 11, the party would get a minor encounter, and for a 12, a major encounter.
For minor encounters I would roll 1d10, and for major encounters roll 1d20.
A drunken sailor, sing-slurring to himself teeters over the edge with an unremarkable splash.
While fishing, a crewman is pulled from the ship, he has hooked a Reef Shark, which now circles him in the water.
Two sailors in an argument get physical and one shoves the other off the ship. Some crew want to leave him in the water, others want to save him.
The captain of the ship has a prisoner/mutineer. That NPC has their hands bound, and are forced to walk the plank.
The rough waves induce seasickness. Each PC must make a DC12 CON save or be sick. Randomly select one PC who got sick. As they are throwing up, they slip over the railing into the sea.
A rogue wave bears down on the ship, but is noticed but a lookout. PCs may use their reaction to gain advantage on their DC12 DEX save to not be knocked off the ship by the wave.
A loud boom is heard in the distance and a second later the ship is hit with a cannon. The impact knocks a random nearby PC into the water.
There is a monstrous crunching sound and the ship lurches, having struck an underwater reef. Each PC must make a DC15 DEX save or be knocked prone. Any save rolls less than a 5 result in that player being thrown from the ship. The ship is also damaged as a result, and may need external repair out in the water.
A rogue wave arises out of nowhere and assails the ship. Each PC must make a DC15 DEX save or be thrown from the deck of the ship.
A storm rolls in, rain and waves but nothing too serious, until lightning strikes the deck of the ship. Randomly select one PC, they must make a DC15 CON save. On a fail, they suffer 3d10 lightning damage and are blown off the ship. On a save, they take half as much damage and are not thrown.
The ship is anchored to allow the crew and PCs time to swim and enjoy some time off from work. It’s restful, until a lookout on the ship yells to inform the swimmers of 1d3 Hunter Sharks approaching.
Amidst a terrible storm, a massive wave rocks the ship, knocking several crew members from the rigging, and throwing raging water across the deck. Each PC must make a DC18 DEX save or be thrown from the ship.
A crewman begins screaming wildly, he makes an attack against a
random PC, makes an attack against himself (auto-hits), and
jumps into the water. Another crew member yells out that it’s
just “ocean madness” and that the man is his brother and he wants someone to help him. In 2d2 rounds, there are 1d4 Hunter Sharks approaching the body/blood.
A rope slips loose, a mast creaks, a boom sways right into a random PC. They may make a DC18 STR save to hold onto the boom, on a fail they are thrown from the ship and suffer 2d6 damage.
A careless crewman left some powder where he shouldn’t have, and a drop of stray burning lamp oil triggers an explosion below deck. Randomly determine which side of the ship the explosion was on, and any PCs on that side of the ship must make a DC15 DEX save, or be blown from the ship and suffer 4d6 fire damage, or half as much and not be thrown on a save.
“Man Overboard!” A crewman yells, although as everyone looks to the water, it’s actually a woman who is overboard, who no one recalls seeing when they left port. As soon as someone enters the water and is within 10 ft (~3 m.) of her, she reveals her true form to be a Sea Witch, and combat begins.
One evening, just after the sun falls below the horizon, everyone can hear some faint whispers across the water. Any PC who makes a Perception check will hear the noise and identify it as singing, only too late. Any PC who makes a Perception check will hear the Siren’s Song and must pass a DC20 CHA save or be stunned, failing to reach DC15 CHA on the check will result in a PC using their full movement to move towards the siren (GM can decide where in relation to the ship the siren is).
From the captains quarters comes a loud commotion. The door bursts open, revealing the captain fighting with a mutineer. The mutineer throws the captain from the deck, and incites other crew members to mutiny. The crew divides in half and begins fighting each other. Some crew from both sides attempt to use/destroy the rowboat to rescue the captain.
Off the starboard side of the ship, there is a disturbance under the water, which a DC20 Perception check will reveal is a Young Sea Dragon barreling towards the ship. If the check fails, the dragon comes up quickly on the ship, and blasts it with Tidal Breath (see usual Tidal Breath rules, which includes 30ft. push which threatens to launch a PC into the water.)
From up in the rigging the party hears “MAELSTROM!” and the deck workers spring to life, the captain starts barking orders, and you can feel the ship lurch forwards, drawn in by the power of the massive whirlpool. Each PC may make two attempts at a DC25 STR check to steer the ship out of the current, PCs may roll one at a time and may stop rolling before each PC takes both their rolls. IF PASS, the ship, and everyone on it is safe, despite the force of the waves the PC is able to hold the helm against it, and get out of the maelstrom from the other side. If the check is NOT PASS, and each PC has taken both of their attempts (or yield their remaining attempts), the ship is unable to be controlled, and is forcibly drawn to the center of the storm before the surrounding water collapses in and destroys the ship, the maelstrom is no more, and all PCs and crew are left 60 ft underwater, with one level of exhaustion, and suffer 2d12 damage from water, debris, etc. If at any point during the checks, a natural 1 (CRITICAL FAIL) is rolled, the ships steering breaks, and the vessel is at the mercy of the ocean. The ship tips over, and collapses into flotsam as it is pulled further to the center of the whirl. The maelstrom will last a further 2d3 minutes. Each minute, each PC must make a DC20 STR check. On a save, they manage to remain above the water and conscious. On a fail, PC suffers one level of exhaustion, and is pulled underwater restricting their ability to breathe. Each subsequent fail adds a level of exhaustion and spends further time underwater. On a success, PC does not suffer, nor regain exhaustion, but is able to restart their breath timer. At the end of the 2d3 Minutes, the maelstrom dissipates, and PCs are left 60 ft underwater, with one extra level of exhaustion, and suffer 2d12 damage from water, debris, etc.
Hopefully this encounter gives you some sort of inspiration or ideas for when someone needs to get off the ship and into the water!