Seven Days At Sea: Storm-Raiser Sail, A System-Agnostic Magic Item

Storm-Raiser Sail

Description:  Plain but well-made canvas sail, woven through with the sapphire-blue hairs of a marid.  Strangely difficult to measure but adjusts itself to fit whatever mast you care attempt to hang it on.  Magical detection is unneeded to tell these sails are enchanted, they throb with elemental power even a mundane can feel - which makes them difficult to disguise as something more innocuous.

Powers:  When a seagoing vessel is rigged with a Storm-Raiser Sail, it will never lack for wind but also draws storms and other foul weather upon itself and its surroundings.  In game terms, treat any locale within 5 miles of the equipped ship as having wind strength one step greater and weather conditions one step worse than normal.  

If your game system lacks fiddly meteorological mechanics (as most thankfully do) abstract these effects by rolling 1d6 at the start of any voyage the ship makes.  Expected travel time is reduced by the die result x10% (ie 10-60%) but the vessel will be confronted by hazardous weather (generally short but intense storms and squalls, but can include hurricanes, waterspouts, and similar extremes) a number of times during the journey equally to one half the die roll, rounding down (ie 0-3 times).  Dealing with these hazards requires appropriate nautical skill tests (or attribute checks, if your game lacks suitable skills or talents) as decided by the GM.  For example, navigating safely through a sudden storm might require an intelligence or navigation roll, shoring up leaks and pumping or bailing water during a hurricane calls for carpentry, shipbuilding, or strength checks, etc.  Generally speaking, the higher the d6 roll was, the more extreme weather will be encountered.  

Failed checks to deal with hazards can result in delays that more than offset the time savings granted by the sails.  Multiple or very severe failures can lead to capsizing, running aground, or sinking outright.

The sail's effect on the weather applies continuously as long as they're rigged on a sailing ship, even if furled or if the ship is docked or at anchor rather than travelling.  Taking the sails down completely will prevent this, but the effects take 1d3 days to wear off before weather returns to normal.

Possible Origins:  Storm-Raiser Sails are most often given as gifts or rewards to sailors who catch the attention of oceanic deities, marid nobility, or magic-using undersea civilizations.  Said "attention" may or may not be wholly positive for the recipient, as the sails bring both great rewards and great risks.  Legends tell of mortal, surface-dwelling mages who learned to craft these sails themselves by capturing marid princesses to harvest their hair.  These legends generally end with various strongholds, kingdoms and even entire land masses being devoured by the raging seas.

Complications:  Aside from the obvious dangers, these sails directly affect the weather in a large area and may distort the climate over a much larger region over time.  Many seafaring cultures have myths about Storm-Raiser Sails and will generally react extremely badly to ships rigged with one that attempt to enter their ports, use busy shipping lanes, or otherwise drag unpredictable and often destructive storms into their territory.  It's also nearly impossible to stay in formation with other ships when using these sails, so leading fleets or traveling in a convoys is right out.

This doesn't stop some people from using them anyway, and (with a good captain and crew) they serve well for high-speed courier work, smuggling, spying operations, and for transporting adventurers on desperate quests to save the world.  Particularly cruel seafarers may foist a set of the sails off on the inexperienced or unwary, and it's not unheard of to try to use such people as catspaws to (for example) unintentionally wreck a trade route or port by unknowingly calling storms to it.

Design Commentary:  Depending on one's ship-handling skills these items might even qualify as cursed rather than beneficial, although there's nothing stopping you from taking them down.  All you have to do is survive the d3 days of lingering aftereffects once you do so.