All about sailing!

The PC's in the campaign I'm DMing recently boarded a ship, which was my inspiration for all of this. I've left things open-ended for DM's to suit to their own tastes (ease of play, realism, etc.) I'd love some feedback.

Sailing
New Skill: Sailing
Ability: highest modifier (armor check penalties apply for strength, dexterity, and constitution checks)
After deciding where you can work most effectively, you get started on making sure the ship fares her best. The ship can sail faster, the crew can re-establish a correct course, or the ship can even be saved from sinking.
Sailing is a skill that is not possible to train, and does not get a bonus of one half a character’s level. Rather, skill in sailing comes from time spent on a ship, and the direct experiences gleaned from working on board. This time does not have to be consecutive and skill is never lost due to time off of a ship. (See table 1)
Time spent working on board a ship Skill in Sailing 1 day 1 1 week 2 1 month 3 2 months 4 4 months 5 8 months 6 1 year 7 2 years 8 3 years 9 Table 1
Rolling a Sailing check is used to recover from being seasick. Also, a party of characters assisting one another in Sailing checks can increase the capabilities of their ship. (See Table 2)
Task DC Recover from seasickness (one ally may assist) 10 Increase the ships’ speed (+1/2, does not stack) 15 Re-establish a correct course while at sea 20 Repair ship damage (minor damage) 25 Repair ship damage (moderate damage) 30 Repair ship damage (heavy damage/sinking) 35 Table 2

New Condition: Seasick
Each time a PC wakes up or ends an extended rest, he or she must make a standard d20 roll to see if he or she is seasick. On a roll lower than 10, the character is seasick, on a 10 or above, the character is not. Any character who is seasick may at this time make a Sailing check +con as a saving throw to recover from the effect. After the check, if any characters are still seasick, the DM rolls a d20 to see what effect the character suffers from. (see table 3) This effect persists until the character takes a short or extended rest, after which they may make another saving throw in the same manner. If the character does not recover, the DM rolls on table 3 again to determine the suffered effect (which takes the other effects place.)
D20 roll result Condition 1 to 6 Dazed 7 to 12 Weakened 13 to 18 Slowed 19 or 20 No effect Table 3

New item: Vial of Sailor’s Fortitude (Click for item’s card!)
Potion
Minor Action. Quaff 1 dose from the potion, and make an immediate saving throw against seasickness, if afflicted. Then, if not seasick, gain a +2 bonus to sailing checks until your next short or extended rest.
Cost: 30g

Complex, needless and harsh.

The chance of sea sickness goes down with time, keeping it at a flat 50% isn't realistic, fair or fun.

The seasick conditions are way too harsh. If a character wakes up to being dazed, weekend, or slowed then they just wait 5 minutes roll again and keep doing so until they succeeded. So all you've added is extra rolling for the sake of rolling because the players can try every short rest and they can take a short rest every 5 minutes. They will succeed its just how much rolling they've got to make until it happens. Unless of course they wake up to combat but if half the party is dazed and weekend and will spend the whole combat that way, no chance of save ending (outside a 30gp vial) then thats not fun either, then they get out of combat and spend as many short rests as needed to remove the condition, more rolling.

If the sailing skill is dependent on their highest attribute based off where they can work the most effectively why not let the players choose a skill an roleplay how it affects the functions of the ship and use a skill keyed of what they roleplay? Or even make getting down river or across the sea a skill challenge and be done with it instead of using a made up skill that advances at completely different rate, thats just more bookkeeping. If your adamant about having a skill for it just make it a regular skill that's keyed off of their highest and add one half levels, it still goes up with time as does your skill but already built into the system and doesn't need a separate workspace on the character sheet to tally up days at sea

As a player, why not just hire a few NPC sailors who already have a high sailing skill to take us there. Then we buy a couple of vials of sailor's fortitude (a gold tax because you gave them too much?) and hope no one is dazed if we get into morning time combat before spending the 10 - 15 minutes to un-seasick ourselves.

I agree with PoorHobo, my inclination would be to sketch out a variety of skill challenges {using Stalker0's Obsideon system} for events during the sailing portion of the adventure.

Possibilitiess include:
- Storm at sea, the PCs have to join the crew in keeping the ship from being swamped
- Pirates! A pirate vessel is sighted in the distance and the PCs join the crew to speed the vessel to safety. Failure would result in fighting of a boarding party
- Doldrums, the ship hits calm waters and the sails go slack... what can the PCs do to keep the crew from starving or going mad?
- Lost.. land is sighted!.. but it doesn't look quite right {An island from the Feywild has temporarily materialized.. do you explore it, avoid it?}
- Mutiny! The crew is sick and tired and being told they are sick and tired. Which side do the PCs join.. and do they draw weapons?

There could be some minor mechanics added to flavour things as sea-going. In combat those without 'sea-legs' suffer a -2 to attacks and balance related checks. The deck is often awash and slippery.. {zones of difficult terrain move about the battle-field. Entering a zone requires a balance check}
Rocking waves and smashing sheets of water occasionially hit every on deck during combat, attack vs Fort with a push effect {don't get too close to that railing!}
And don't forget the tactical advantage of the crows nest and riggings!

After reading the responses I've been convinced that perhaps a whole new skill is a bit unnecessary. I didn't think it was too harsh , but in retrospects it does seem the consequences outway the gains, and I'll likely be scrapping it all and trade it for skill challenges. I particularly liked the ideas PrimitiveScrewhead provided. Thank lou!
I felt it would be cool to provide my low-level party with some show of progress while they're on a ship, since they've expressed an interest in ships and water themed adventures. So here is my new question: Since my party has expressed interest in staying on board for a little while, at least, what might be a more sensible solution to offer them progress other than experience through repetitive skill challenges and constant hack-and-slash encounters? Here is a little background of the quest they're on, and a few of my ideas at present:

The Quest:
The party is unaligned, a group of sell-swords. They've been hired to raid a merchant ship containing various valuable and magic items. They're reward is first pick at some of the cargo.

A couple ideas:
Let the party have some time on board the ship, and after the merchant ship is raided, have a whirlpool suck the ships into some part of Underdark. This would help me control what equipment the party could keep if they tried to take everything and go rogue on the mission.

Likewise, I could give them the same amount of time on the ship and then have the ship swamped in a storm and shipwrecked on a mysterious Feywild island (thanks PrimitiveScrewhead!)

Either route seems pretty good to me now that I think about it. My main story involves them returning to the city they came from, and since an NPC from the town is with them, they'll have to get back one way or another. But in the meantime, what can I do to involve the players in a fun way that highlights the ship setting without oo much repetitive combat or skill challenges?

Well, what is unique about the ship environment?
1. A ship is a small space, isolated from any possibility of help, resupply or escape. All fights are to the death.

2. A ship can go places. The characters have (at least the illusion of) freedom to travel in any direction.

3. Encounters on a ship tend to have certain characteristics:
a. They usually begin at sight range, often favoring ranged characters.
b. The terrain includes multiple vertical levels and many ways to move through those levels, favoring mobile and agile characters.
c. They can sometimes be influenced by skill rolls during combat, especially if characters take actions during the fight to control the ship, or fail to take such actions when they should (widening or narrowing distance, ramming, pitching the ship suddenly to try to shake someone off or holding it steady for secure footing).
d. Falls can result in exciting rescue/ drowning/ shark scenes, favoring lightly armored and athletic characters and possibly fatally penalizing plate armor wearers who can't swim. (Though RAW, plate armor only gives -2 to Athletics).
e. As the ship's residents, the players will know details about the environment that attackers would not be aware of; they may even set traps or improve the defenses ( Note that if they attack other ships the reverse is also true). This is different from most other encounters, where the players are usually venturing into unknown spaces held by others.

4. As a plot device, a ship makes the party available to take on various missions including merchanting, passenger or cargo transport, piracy or antipiracy, naval combat, or exploration. It can become a home base in the same way as a castle or a house, with some interesting differences. If the ship is unusually large, fast or powerful it may attract the attention of patrons or enemies. It can be improved over time, allowing something like lair treasures (ballistae, better sails, etc.)

None of this made any ideas jump out at me, but perhaps something here will resonate with your campaign. If not, then just adventure aboard until the novelty of all these traits has worn off, then land them one way or another.