In general, these rules assume the PCs are the only sailors on the boat, though most rolls can be adapted to a full crew. Here's a slightly different version of a "saltbox".
I have not reread any of this, so enjoy typo-spotting...
Survival Fishing Rules
These are not general rules for fishing or rules to accurately simulate real-life fishing--these are just rules for Survival Fishing--you know: marooned in the middle of nowhere with nothing to eat for days, hallucinating fellow passengers looking like drumsticks and beef wellington, etc.
The purpose of these rules is to force the PCs to either:
-Rig up clever schemes they will be proud of in order to catch fish,
-Fall upon any passing boats or signs of civilization with fearsome fervor, famished eyes and steely knives, or
-Jump up and down, hug each other, and kiss their dice if they do actually catch anything
Chance To Catch Something:
-In these waters, base is 5% per day no matter how many fisherfolk
-Any passive modifiers PCs think of after you tell them this ("But my guy is a barbarian from a fishing village") are worth a max of 5% each. Commenters on this post are free to think up modifiers of 1-4% that might apply and post them.
-Any individual clever modifications to bait, tackle or tactics the PCs think up are worth 1-10% per modification. For example, if they go "Hey, we have a net! Let's use that!" that should be worth something.
If Something's Caught:
Roll d6--this represents all that they're going to catch all day. A result of 1-5 represents enough fish to feed the number rolled of humans for a day. Like roll a 4 and you've got 4 days food for one PC or 1 days food for 4 PCs or 2 days food for 2 PCs or whatever.
A roll of 6 indicates the PC has caught an unusual aquatic creature, roll d12 on this table, modify to taste:
1 Giant seasnake
3 Aquatic elf
4 Electric eel (can pulled up immediately but there's a danger of the PC geting shocked and falling over the edge)
5 Aquatic gelatinous cube or stranglekelp
6 Seamunculus (a toad-like aquatic humunculus on a mission for an evil wizard)
8 Leaping shark
9 Angry whale
10 Giant octopus or giant squid
11 Undead whale (no food)
12 Giant jellyfish or man-o-war
Strong creatures' first move will be to attempt to yank the fisherindividual into the water and/or tear any nets apart. Creatures are worth a number of days' food equal to their hit dice.
Rolling the same creature result 2 days in a row can indicate the PC has not caught a creature but has snagged his or her line on some unusual and adventure-hook-ish object afloat in the inhospitable brine.
Failed Control Rolls
This is for when the pilot fails his or her roll--usually in bad weather.
Taken from here:
1-Something caught in the rudder--someone needs to climb down there and get it.
2-You hit a whale carcass or something--the ship trails blood and there will be a corona of sharks surrounding the boat for the next 3 days.
3-Minor sail torn due to high wind or sudden beam swing--replace it or make future checks at -2/-10%.
4-Stray wave has smacked you sidewise and flung a volley of stinging jellyfish onto the deck, roll dex or reflex save for everybody up there to avoid having a random body part swollen beyond usefulness for d4 days--1 mouth, 2 eyes, 3 right hand, 4 left hand, 5 right foot, 6 left foot.
5 -- A freak wave has heeled the ship over, narrowly avoiding turning it turtle but shifting the ballast/cargo so that you now have a permanent list to (1-3) port or (4-6) starboard. Navigation and maneuverability is therefore badly compromised.
6--Some miscellaneous marine leviathan has crashed into the hull in its sleep, starting planks all along one side before plunging down into the depths in its startlement. The ship is leaking badly, gaining on the pumps by 2d6 inches per hour, and will eventually founder unless something is done to alleviate the situation.
7-Damn, you just had to kill the albatross, didn't you? Better pray for their beauty not doom, have a bless spell handy for them, and God's creatures too, otherwise the ship is stuck, day after day, no breath nor motion like a painted ship on a painted ocean, a terrible thirsting curse striking all aboard. And then... the visit by the Dark Ship, crewed by Death and She-Life-In-Death. Dice are cast for the fate of the crew...
8- The ship collides with a rocky outcrop just below the surface. The damage is not severe, but until the damage is repaired, at least one person must be on pump duty at all times, or the ship will take on too much water.
9- As above, but the rocky outcrop was the temple of some aquatic -- and now religiously offended -- species
10-Hole in the hull, must throw some (10%? x pounds?) cargo overboard to lift it above the waterline and sail light until it's repaired.
11-A sailor, bewildered and struggling, drops a tool from the rigging, a random person on deck takes 1d8 damage.
12- fire in the galley! someone neglected their duties and left hot coals in the stone stove. during the storm they fell out and started a fire in the front part of the ship. The party has to declare their actions in 1d8 simple sentences, otherwise:
1 - the fire damages the foremast, if another storm occurs, the mast will break
2 - the fire spreads to the cannon deck, chance of expolsion
3 - the fire damages the outer hull and the ship starts taking water
4 - the fire burns through the planks of the galley floor, damages the stem and cut water. the ship starts taking water and can only travel at 50% of it's speed
13- One of the sails was left hoisted too long in the storm (/ come up with other excuse). That mast has now snapped, and the ship suffers a 1/3rd reduction in speed. Maybe you can jury-rig a jury-righ, in which case only 1/4 reduction. Or a 1/2 reduction if you do poorly enough.
14-You took a large wave broadside instead of sailing into it. 1d6 crew are washed or thrown overboard, including anyone in the crow's nest. Hurry if you want to save them - they can't swim.
15-Horrendous brain fart results in you leaving topsails deployed on mainmast/foremast and/or mizzenmast (assuming ship has such). Wind has now snapped the masts, laving thesails, booms and top parts of the mast tangled in the ratlines and rigging. 60 man-hours (in good conditions) to carefully clean-up the mess, 6 if you don't mind the details/consequences (like cutting everything and shoving it into the sea). If a storm is still raging around you, double this. Navigation, propulsion, and even crossing the main decks become much more hazardous with swaying netting and giant-sized clubs swinging about in the wind.
16- You are so busy mismanaging the ship that you fail to notice the large iceberg you're about to run into. Ship takes 1d8 in hull damage per 10,000 gp weight of cargo (or equivalent for whatever system), half if a saving throw to pilot the ship again is successful.
17-You vigorously steer the ship this way and that to maintain control... a bit too vigorously. The pilot wheel breaks, ship can adjust speed but not heading until repaired.
18-Amid the ship's tossing and confusion on deck, someone slips over the rails. Man overboard! Determine who it is randomly.
19- You tell someone to do the exact opposite of what you wanted them to do, and as a result the next time you have a die roll for hull damage, losses, distance blown off course, etc, instead of rolling you simply take the worst possible result.
20-Carelessness has caused someone to get tangled in the riggings. The person must make an appropriate saving throw every round while caught or die; any round they succeed they can try to make a dex save on 2d12 to escape. Otherwise someone can cut them down, with a -1/-5% on future sailing rolls until repaired. If the person dies while stuck, all NPC crew will be at -1 for morale-type rolls for the remainder of the voyage.
Roll once per day/every 50 miles (assuming 6 mph water speed, sailing 8 hours a day--it'd be a lot more if you had a full crew since you could sail properly all night. Plus it probably means you have a bigger boat.). Or whatever floats your boat. Sorry. d8
1-Creature (Roll on creature table)
2-Bad weather--How bad? Roll d12--make that many control rolls
3-Passing ship--roll on Passing ship table
4-Dead calm sea (lose a day of movement)
5-Annoying weather. Make a control roll.
6-7 A quiet day at sea
8-Weird event (DM should always have two or three setting-appropriate Weird Sea Events locked and loaded. There are some ideas in the comments here.) or, if no ideas are forthcoming, roll twice (and keep rolling more events if you keep rolling 6s) or use this one:
Mirror Water: the ship sails over a patch of sea which is a portal to a mirror dimension. PCs reflections climb up and try to kill them. Sailing away will break the connection but the duplicates will still have to be dealt with.
As the PC in the crow's nest looks toward the horizon have him/her roll d4 for size:
1-Small and tugboatish unless that's inappropriate for the kind of vessel (merchant ship for instance), in which case it's medium-sized
2-3 Medium-sized for your era
Who's On That Passing Ship?
1-Fishing boat (probably lots of food on board).
2-Pirates (sucky) (d12 of level 1-4)
3-Pirates (scary) (d20 of d6+2 level)
4-15 Merchant ship. Look at the number you just rolled. That's many 1000's of gp are on board, it is also how many gp worth of other goods is on board, however it's also the level of the fighting men protecting it. There are 15 of them.
16-Ahab-esque sea-monster seeker (roll on creature table).
17-'Tis the sea-borne wedding flotilla of Bluebeard and Snow White, with their corona of 7 floating frigates, each manned by a piratical dwarf renowned for a specific trait.
18-Warship of some local power.
19-Warship of some foreign power.
20-Ghost ship--manned by skeletal pirates like in the DMG.
21-Rich merchant ship. 20,000 gp on board, 10,000 worth of goods, 5 10th level fighters and 10 6th level fighters guarding it
22-Vikings. d20 d8 level berserkers/barbarians.
23-Raided, empty ship. May be more seaworthy than PC's ship, though.
25-Floating pleasure palace of exotic monarch--also int he flotilla: a galley galley, a haremship and or templeship and d4 warships
26-Lizardman opera ship--sea turtle integrated
27-Lizardman plesiosaur-drawn sea chariot
28-Dead vessel, crew's bodies sodden with sentient algae.
29-Seatemple (foreign god)
32-Weird pirates (as 2-sucky) but accompanied by exotic nonhumans or wizards
33-Weird pirates (as 3-scary) but accompanied by exotic nonhumans or wizards.
34-Goblin raiders employing toothed, gas spore-like floating bombs
35-Mariel-boatlift-esque asylum ship. No navigational equipment, rudders, wheel, or sails. Full of lunatics.
36-"Zooship" delivering exotic beasts
38-Lone maiden and several swine. Secretly, she is a witch and has transformed all of the crew, her harpy allies are currently off seeking land but will return soon.
39-Fishing boat again. Captain has valuable information.
40-Nephilidian Spidership--the amphibious vampires of Nephilidia cannot sail but protect their watery frontiers via spiderships--hollowed-out enemy vessels that are packed stem-to-stern with small, venomous, carnivorous seaspiders. They are manned by spider-stuffer manikins imitating real sailors and fly false flags.
41-Lone eccentric out for a quiet sail.
44-Refugees (from some disaster).
45-Scientific mission-oceanographers, biologists, etc.
46-Evasive weirdoes. Keep the PCs guessing until you can think of something.
47-Pirates in the act of piracy (roll again for victim ship)
48-2 Warships fighting
51-3-8 adventurers not unlike yourselves.
53-Ship full of creepy sea-going clerics excommunicated by their church and doing weird religious research who haven't touched land in years.
54-Prisoners being transferred
55-Spice merchants--not a lot of money but lots of spices
56-Explorers from the Exotic East. Possessed of magnificent maps of lands not known.
57-Clever general and his men, returning from a great war after much tribulation
58-Adventurer seeking metallic hide of mythical beast
59-Great big clipper ship going from this land into that. Crew is all nodding on black lotus powder.
60-70 Mixed group of passengers and merchant cargo.
71- Pilgrims heading to pilgrimage site.
72- Passengers heading away from PCs native land. One is a PCs mother. What the hell?
73- Pirates. Captain of the pirates is a former ally of a PC. Will be nice to the PCs as soon as s/he realizes it but his/her pirate crew is secretly scheming mutiny.
74- A learned zoological scholar, his hold bulging with taxidermized specimens, eager to hire adventurers to collect specimens of rare sea creatures.
75- It is not actually a ship. It is something else. Tell your PCs you have to go to the fridge and think fast.
76- White elves sailing far out to sea for a royal funeral. The monarch is slain and his most beautiful slaves are thrown--live and with limbs bound--into the sea.
77- Goblin grubship. Stuffed to the gills with baby grub carrion crawlers--which they cultivate and worship.
78- Red eyed sea wizard. Quite mad.
79- Sentient rabbit, sentient but narcoleptic doormouse, maker of hats and insane princess drinking tea.
80- An entirely peculiar vessel. Inside it looks like a cross between a model railroad and Schwitters' Merzbau. It's actually a floating city of tiny people, with tiny horses and elephants.
81- A fishwife sailing the seas, seeking a husband.
82- Tomb ship. This is how an ancient culture buries its dead. The inhabitants are not undead. Unless, of course...
83- A monarch in disguise, with retinue in disguise as merchants, searching all the world for a queen.
84- Passenger ship--most of the travelers are horribly diseased.
85- Mixed cargo/passenger ship--the passengers are a troupe of Somberists--anti-clowns who perform depressing dramas on street corners to inspire religious fervor and contemplation,
86- Dwarven sea raiders with stubwolves in spiked collars
87- Rum merchants, victims of recent storm, in need of aid.
88- Merchants unknowingly transporting a naga, succubus, demon, etc.
89- Young royal bastards, ages 4-13, marooned sea with so that they'll be unable to claim the throne.
90- Cargo vessel with passengers: mostly idiotic minstrels who insist on being called "bards" and that their music has magical powers.
91- Government-in-exile of nation in the throes of revolution.
92- Fishing boat wrestling with fearsome sea beast.
93- Gunpowder-filled merchant-ship.
94- This was once a merchant freighter overtaken by a a gang of pirates but they all died. It is now inhabited entirely by their pet macaws and monkeys, who subsist on the foodstuffs in the hold.
95- Warship delivering urgent diplomatic dispatch to foreign government.
96- Insane wizard has placed the minds of one group of travelers inside the bodies of the other. Roll twice.
97- Alleged merchant ship which is actually cover for an assassin on assignment sent to kill an eminent member of a foreign power.
98- Seems like an ordinary merchant ship with a few passengers but, during the day, the windows show night ans vice versa. The ship is cursed.
99-Merchant ship mostly filled with alchemical ingredients. Could be useful for making potions.
00-Slaves who've successfully escaped and taken over a slave ship.
...I am opening the Who Is On That Passing Ship table up to Gygaxian Democracy...