The Ghost Ship.

You have made a pact with one of the lost ships crewed by listless dead that wander the seas. Sailors see these ships, such as the Flying Dutchman or Ship of One Hundred, as portents of doom, but even in death the cursed crew and their damned captain retain a fierce love of their vessel—the only home known to their forsaken souls. The loyalty shared by captain, crew, and ship pierces the veil between life and death and grant you your power. Whether you are a member of the drowned crew sent alone on a mission, a stowaway who chose an unfortunate vessel, or a sailor rescued from a watery grave, the dead men follow you everywhere—and the spectral ship itself powers your spells.

Level 1 Features:

Crewmate Magic.

When you learn a spell of the appropriate level using your pact magic feature, you also learn the spells on the Crewmate Spells table. The spells count warlock spells for you, and do not count against your spells known.

Haunted Hull.

Starting at 1st level, you can manifest phantasmal fragments of the Ghost Ship on the battlefield, crewed by ethereal spirits with wispy skeletons and translucent flesh. You can use an action to manifest parts of the ship as one of the following effects. Once you manifest one of these effects, you can't use this feature again until you finish a short or long rest.
Crow's Nest. You manifest a single undead lookout, which hovers up to 120 feet directly above you for 1 minute. While you aren't deafened, you know the location of every creature within 120 feet of you, including those that are hidden, invisible, or on the Ethereal Plane.
Possessed Rigging. You manifest spectral ropes, which lash out at a creature you can see within 60 feet of you. The target must succeed on a Dexterity saving throw against your warlock spell save DC or be restrained by ropes for 1 minute. A restrained creature can use its action to make a Strength check against your warlock spell save DC, freeing itself and destroying the ropes on a success.
Stolen Sails. You manifest the tattered masts of the ghostly ship, which drain the wind out of your enemies' sails. Your speed increases by 10 feet for 1 minute, and each creatures of your choice within 30 feet of you must make a Wisdom saving throw against your warlock spell save DC. On a failed save, its speed is reduced by 10 feet for 1 minute.

Learn From Our Mistakes.

At 1st level, the crewmen of the Ghost Ship pass some of their nautical knowledge on to you. You gain proficiency with navigator's tools and vehicles (water). Additionally, you can determine whether or not an item is cursed by spending 1 minute examining it.

Level 6 Feature:

Bosun's Lash.

Beginning at 6th level, you can conjure a ghastly officer as a bonus action on your turn, who cracks a spectral whip at a willing creature of your choice within 15 feet of you before vanishing. The creature takes 1d4 force damage and gains a bonus equal to the damage taken to the next attack roll or ability check it makes before the start of your next turn.
This die becomes a larger one as you level up, 1d6 at 9th level, 1d8 at 12th level, 1d10 at 15th level, and finally 1d12 at 18th level.

Level 10 Feature:

Eternal Sailor.

Starting at 10th level, you gain some traits of the vessel's ghostly crew. You gain the following benefits:
-You are immune to poison and disease.
-You no longer need to breathe.
-You can sink in water at a rate of 60 feet per round, moving at the start of your turn.
-You suffer no penalties to your movement or attacks from being underwater.

Level 14 Feature:

Skeleton Crew.

At 14th level, you gain the ability to summon the entire crew to fight at your side. As an action, you can manifest a skeleton crew in an unoccupied space that you can see within 60 feet of you. The crew is friendly to you and follow your commands. Roll initiative for the crew, which has its own turn.
The skeleton crew disappears after 1 hour, when it drops to 0 hit points, or if you lose your concentration (as if you were concentrating on a spell). The skeleton crew can use your warlock spell attack bonus and spell save DC in place of its own attack bonuses or save DCs.
Once you use this feature, you can't use it again until you finish a long rest.