UPDATE: A different person has taken a deeper stab at 5e conversion system and it's worth looking at: https://www.reddit.com/r/spelljammer/comments/jphupm/5e_spelljammer_conversion/
Unfinished and abandoned per creator: https://www.reddit.com/user/Ubiquity4321
Reddit thread where /u/Ubiquity4321 turned over the document: https://www.reddit.com/r/spelljammer/comments/a85qpt/giving_the_spelljammer_doc_to_the_community/
GMBinder Source Code for a popular unfinished 5e conversion of Spelljammer: https://www.gmbinder.com/share/-LBaY4l6HcR4M-sItfl_
The list of to-dos before abandonment: https://www.gmbinder.com/share/-LE2no63kgklr7RoFN9N
List from to-do link:
Fix stations
Magic officer
Engineer
First Mate
Helmsman?
change size of images that the guy talked about on reddit
add in pets rules - crew benefits: morale booster, sanity/homesickness aid, and perception aid
lifejammer clarification
sequence helm clarification
designing ships
add in "A note about RPing or combat with NPC ships"
random NPC ship
put in other ships
add "flag raised" to ship page
teleporting between ships
repairing ships and tonnage
Remove Flyby, maybe make MO ability
Notes from the Treantmonk:
Balance and stuffs
ship repair
Use existing repair model from 5e DMG
add hit dice stat and divide by 4.5 to get hit dice for ships
airship - 66 hit dice, short rest/long rest rules
short rest - away from dock, long rest - at dock only
long rest only at civilized port, and able to recover hit dice
Ships
describe each ship in a paragraph or two
reach to the community and try to get someone to donate artwork, to keep creative commons/free art theme
Crew members
Change stats for the crew - make each one of them different
green crew is good, don't change
make trained crew stats better
give other proficiencies - proficency in the weapons and armor they're using
up the AC with better armor and give them proficency
make crack crew really good, maybe base stats off for a knight
give them expertise in vehicles
increase physical stats
better hit dice
even better armor, half-plate or something
a ship being repaired by crack crew, repair takes even less time
A lot of docks need guarding. Crew is kept busy when in dock. Maintenance and stuff - refilling the hit dice
standard practice is to keep an "away team"
Stations
90% the way it is
scale back first mate, give bonuses not blanket advantage
add in general actions anyone can take, little bonuses, feel like something is better than nothing
Phlogiston
Remove instantaneous double damage for fire spells, maybe just a +1 dice or something.
Maps
Hex vs square
Facing sorta needs to happen
Have "standard" be square, use alternate for hexes
With a square grid, your first facing is free and every other facing costs cost one speed point
Alternate rules for hex grids - Take out adding the 1 free movement for square grids - all hex facings changes cost one movement
Helms are insanely expensive - soften costs for helms - or - - material costs for create helm include the phrase "which the spell consumes" - have it use gold dust or diamond worth 1000gp or something similar - or both - - Helms - very rare - pg 135 dmg - like 25k gp or something similar - create helm - concentration up to a day - add costs for everything else
For 30 Hull Points worth of repair - With an unskilled peasant hitting wood with a hammer and jamming it in the boat with straw and tar, that's 30 days and 500gp. With a skilled laborer doing it herself out in the wilderness with tools and resources it's 30 hours and 750 gp of materials. With the same skilled laborer and a Mending cantrip - 15 hours and 750 gp of materials; With a 4th level Fabricate it's 10 hours and 750 gp of materials. At a port, it's 1500 gp and 30 hours, and you are free to do whatever you want in town cause the ship is being fixed by other people.
Include rules how to build a vessel as a second supplement
Pgs 128-129 has costs for a stronghold and making magic items
use ship stuff from http://dnd.wizards.com/articles/unearthed-arcana/ships-and-sea