A number of outlined (and system free) sea-going encounters and hazards to add to yuor ocean going adventures and charts.
Reefs- without caution a vessel can be driven onto a reef. Perhaps becoming trapped or even worse floundering and sinking. This will likely doom the crew to drowning or being battered against the reef if the seas are rough enough. Fishing will often be good near a reef.
Water Spout- a waterspout forms capable of sweeping sailors off deck and into the waters (those in rigging are almost certainly doomed). The sails are surely damaged and the vessel itself may be damaged.
Dolphin School- a dolphin school will follow the ships for hours or even days. Sailors who fall overboard may be rescued. Sharks will be driven off and encounters with other sea life may be mitigated.
Sudden Squall- sailors in rigging may be in danger. Strong chance of oncoming weather change.
Sandbar- usually only scrape bottom of boat but this can be a warning of a larger and more hazardous sandbar. May trap or flounder ship.
Giant Squid- will generally ignore ship but may snatch a few sailors from the decks before retreating. It will not stay to fight unless compelled by magical influences.
Sirens- will sing to draw sailors overboard or tempt the ship to be piloted into a nearby hazard.
Mermaids- a number of mermaids are sighted following the ship. With a good reaction they will defend the ship from sea monsters or warn about other hazards for a few days. on a bad reaction they may guide the ship to it's doom or tempt sailors to leap overboard to their doom.
War Canoes- savages or orcs attack the ship in a number of large primitive war canoes.
Sharks- sharks follow the ship for a few days. They will attack any sailors who fall overboard and may harass any small boats that launch while they follow. They will drive off schools of fish and may drive off other encounters.
Pirates- A ship or 2-4 longboats full of pirates. A ship may feign to be a merchant vessel prior to attack.
Raft- a raft with castaways. The cast aways are either survivors of a wreck, mutineers consigned to doom at sea or hapless victims of a pirate raid.
Raft, Ghoul- It will appear to be a raft of castaways but all onboard are dead (perhaps with a chest or other visible wealth to draw the greedy). Under the raft are a pack of ghouls ready to pounce.
Dragon Fly-by- A dragon flying high overhead. It may ignore vessel or possibly take a peek at the vessel in curiosity before moving on.
Hostile Squadron- 2-4 vessels of a hostile nation.
Patrol- 2-4 vessels of friendly nation patrolling the waters. They will be looking for pirates and smugglers.
Vortex- The ship is drawn to the exposed sea bed which will eventually close dooming those that can't escape.
Compass Malfunction- compass will be working improperly may throw the vessel off course for 2-7 days if navigation aided by compass.
Sea Snakes- little danger to the vessel unless it is becalmed unless one falls overboard or sailors are attempting to fish with nets.
Storm Damaged ship- a storm damaged ship is sighted limping along the sea. There will be a desperate captain and crew happy to be saved.
Rudder Comes Loose- the ship will be unable to maneuver quickly or well until repaired or replaced.
Rigging Fault- a sailor may fall from the rigging or people on deck may be harmed and possibly swept off deck.
Merchant Ship Approaching- A merchant ship is sighted and it is moving to match course and meet ship.
Merchant Ship Fleeing- A merchant ship is sighted and it is clearly avoiding the party vessel. Could be smugglers or simply cowards.
Ship Towing Another Vessel- a ship is sighted towing another ship. The second ship will either be clearly damaged or under-crewed. They could be pirates or buccaneers.
Plague Ship- a seemingly under-crewed vessel is sighted. It may have warning flags it may not. The ship is packed with dying victims of a plague that will surely spread to those that board it.
Ghost Ship- an odd vessel is sighted. It may appear recently abandoned or be
clearly crewed with undead.
Lost Ship- a strange ship from some exotic land (or time) any who stay on board for too long will be lost with the vessel and will either be displaced in time or vast distance.
Turtles- a school of sea turtles is spotted they are edible and may be trapped by nets.
School of Fish- a school of fish is sighted. Fishing will supply the crew with 1-3 days worth of food for each day the school can be followed and fished.
Flock of Sea Birds- a Flock of seabirds is seen. May be a harbinger for a weather change or a nearby school of fish.
Shore Birds- may be from a nearby rookery. They are often edible and a sure sign of a nearby island. If a rookery each hunter can gather 2-5 days of food per day. 10% chance of despoiling rookery each day.
Carrion Birds- land is nearby as is something they would be feeding on.
Whale Sighted- a lone whale is spotted in the distance. If followed it may lead the vessel to a school of whales.
Whale School- a school of whales is spotted. Some may attack vessel (or launches). Will drive off a school of fish, may be followed by sharks.
Water Supply Sours- something has polluted the ships water supply. It will only be possible to save 10-30% of the ships water supply.
Food Stores Spoiled- Rot, mold, weevils or rats spoil the ships food stores. Only 10-30% of the ships food supply can be saved if quick action is taken.
Grog Turns- the ships precious supply of grog turns, at best it is vinegar. A mutiny could follow if steps are not taken to correct.
Illness- an disease appears and quickly spreads among the crew (not likely if vessel hasn't been in port in past 3 weeks).
Scurvy- crew begins to sicken. Only possible if crew has been eating poorly.
Duel Between Sailors- two crewmen challenge each other to a formal duel.
Fight!- a number of sailors engage each other in a brawl. The brawl will last until one sailor is badly hurt, tossed overboard or killed if it isn't broken up. A loyalty check may keep the fight to little more then sour words.
Mutiny- a significant portion of the crew is unhappy with the captain and attempt to takeover the vessel.
Thief- there's a thief on board stealing from other sailors, the ships stores or the captain's cabin.
Stow-away- a stow-away is found. Could be a foolish youth, a beggar,a thief or possibly a family member or lover of one of the sailors.
Icing- a sudden cold snap coats the decks, ropes and sails in ice. The ship may be damaged and sailors are in jeopardy of falling from the rigging or overboard.
Becalmed- no wind or current of note for 1-6 days.
Contrary Winds- the winds are against the plotted course for 2-5 days.
Cross Current- an unexpected current draws the ship off course for 2-7 days.
Sargasso- calm waters overrun with troublesome sea plants. A sailed vessel will be slowed some but a rowed vessel will be drastically slowed for 2-7 days.
Flotsam- floating debris a possible sign of nearby island and or a shipwreck.
Lights- lights are sighted at night. Could be nothing a warning, cast-offs seeking rescue, wreckers or pirates seeking to lure a vessel to it's doom.