Age of Sail rules for 5th ed D&D

So after a lot of work and a good bit of reading and stealing ideas from various places, I came up with a set of rules for Age of Sail combat (Ship v Ship, easily used for Ships v. Big Monsters). They're presented here. I finally ran a combat with them last night, my regular game having gotten around to going to sea after 6 levels of dungeonneering on land. I'll post a postmortem for our first playtest of the rules a bit later.

Age of Sail Rules: For 5th ed D&D. These rules should explain how a ship operates in combat against other ships or sea monsters, using a grid map. They’re intended to be used with the stats for ships and artillery in the 5th ed books, as well as the basic combat rules for things like actions, initiative, etc.

1. General
1. Ship Scale Map is 30 ft per square. Placed on the map will be wind speed and direction, and visibility.
2. A ship moves and takes actions on the initiative count of its Captain.
3. Visibility is dependent on weather, clear sky 10 miles away, overcast 5 miles, raining 1 mile and fog 100 to 300 feet.
4. All checks listed herein are base DC 10, subject to situational modifiers.
5. Ships require a minimum number of crew to move and fire guns. For every 30 HPs of damage a ship sustains, one randomly determined crew member will be removed from active duty. The Surgeon can return them to active duty.
6. People on a ship (crew, passengers, etc.) have 1/2 cover from ranged attacks from outside the ship.
2. Ship Actions & Movement
1. All checks to turn, board, accelerate, decelerate, etc. are made by the Captain using his Pilot skill. In the event the Captain takes no piloting actions, a ship moves on its bearing from its last turn at the same speed as last turn.
2. Pilot is both an Dex and a Cha skill. Dex is used if the ship has a crew requirement of 1 like a Keelboat, Cha is used if the ship has a crew requirement greater than 1.
3. All ships have a speed. Sailed ships go double speed with the wind but cannot move directly into the wind. Oarred ships go normal speed all the time.
4. A ship can move on its initiative as per speed, plus take a Dash (double move) or Turn Action (90 degrees max).
5. Ships can Accelerate or Decelerate in increments of 30, or less, per round. E.g. A ship with a max speed of 60 takes 2 turns to go from 0 to max speed or max speed to 0.  
6. A ship without its minimum crew complement, and a captain/helmsman cannot Turn, accelerate or decelerate.
7. A ship performs a Ram by moving at max speed straight into another ship or monster, thereby dealing Ram damage as per ship. A Ram automatically initiates a Board.
8. A ship performs a Board against another ship by ending its move next to that ship and performing a Grapple action. The Boarding Captain’s Pilot check opposed by the Boarded Captain’s pilot check. If attempting to Board an immobilized ship, the check is made with advantage. An immobilized ship cannot break free of a Board.
3. Ship Hit Points and Conditions
1. Ships have hit points and an AC like a creature, they take damage the same way. They typically have a damage threshold as well.
2. A ship automatically fails any dex save (e.g. against a fireball) and is immune to any damage that wouldn’t affect a ship (e.g. poison, psychic).
3. When a ship is between 100% and 50% hit points, it moves and functions as normal.
4. Between 50% and 25% hit points, a ship is immobilized. It can be repaired at sea to 100% HP using magic and/or conventional repairs. A ship regains mobility once repaired above 50% HP.
5. Between 25% and 0% hit points, a ship is immobilized and can be repaired to 50% +1 HP using magic and/or conventional means at sea. It cannot be further repaired unless put in dry dock. A ship regains mobility once repaired above 50% HP.
6. If reduced to 0 HP, a ship begins to sink. It will sink completely in 10 rounds. Damage dealt to a sinking ship speeds sinking by 1 round per 25 damage dealt. It can be repaired only using magical means. If repaired above 0 HP, a ship stops sinking. It can then be repaired as though it was between 25% and 0% HP, explained above.  
4. Cannons - This is specialized artillery. It is not the only type of available artillery.
1. A cannon takes 3 people 25 rounds to load and aim for firing. It cannot be made ready to fire with less than 3 people. See DMG for cannon  stats.
2. A cannon requires 100g worth of blackpowder and a shot worth 30g per firing.
3. Available shot types are: Ball - Deals 8D10 damage to target hit. Chainshot - Deals 10D10, Cannot reduce ship below 50% HP. Scattershot - Deals 8D10 damage, no ship damage but incapacitates one crew per 15 damage dealt.
5. Officers and Actions - To avoid standing around during ship combat, PC’s can take on Officer roles and have something to do.
1. Captain / Helmsman - One person can perform both roles, or two people can do each separately. The ship moves on the Captain’s initiative, and the Captain makes Pilot checks to have the ship Turn, Accelerate, Decelerate, Board, or negotiate other hazards. If two players perform these jobs separately, and both have proficiency in Pilot, they both add their proficiency bonus to the Captain’s Pilot checks.
2. Master of Artillery - One player can be a master of artillery. This player can do the following as an Action on his/her turn:
1. Order Broadside: All ready to fire artillery on a side of the ship (min 2) fire at once. If a target is within close range, make a single attack roll per 2 firing artillery with advantage. For each 2 firing artillery, target takes normal artillery damage on a hit and half artillery damage on a miss.
2. Hustle Crews: Make a DC 10 Cha check to speed up loading time. On a success, -5 rounds until artillery are ready to fire. Only crews that can see and hear the Master of Artillery can receive this benefit.
3. Spot Weakness: Make a DC 10 Wis check to spot a weakness on a target, giving one piece of artillery or attacking character advantage on one attack roll against that target this round. Attacker must be able to see and hear the Officer.
3. Crew Officer - These officers direct the crew sailing the vessel
1. Rally: Make a DC 10 Cha check to grant advantage to the Captain on one Pilot check made this turn. The Captain can only receive this bonus once per turn.
2. Brace for Impact: Order the crew to hunker down for one turn. Until this officer’s next turn, the crew has resistance to all damage other than psychic, and all Pilot checks made by the Captain have disadvantage.
4. Captain’s Officer - These officers assist the Captain.
1. Recon Target: Make a DC 10 Wis check to learn the current HP, flag, remaining crew, or other information about enemy ship. Requires a spyglass.
2. Signal Flag: Communicate a simple message to another ship that can see you using signal flags. DM should decide what can be communicated. E.g. “Follow us.” or “Surrender immediately”.
5. Surgeon - One player with either medicine prof or healing spells can act of ship’s surgeon, getting crew back on their feet during combat.
1. Triage: Make a DC 10 Medicine check or use a spell to return 1 crew member to active duty.