I choseand , the standard spells that you see nearly everyone that isn't Jungler/Support using, but substituting for can prove useful for catching up in lane, while your mobility is still slower than most.

PROS

Massive Crits mid/late game
Decent CC clear
Quick boost to AS and mobility for Escapes/Chases
Global Ult to help your team secure kills.

CONS

Easily focused out in team fights.
No natural escapes
Can be heavily CC'd if Remove Scurvy is on cooldown.

I chose AD Marks for an early advantage over your opponent in lane. Flat armor and scaling MR will assure that you have more than enough protection from both AD and AP champs, as you will need both early game to protect yourself from a wide range of champions. AD Quints can be interchanged with scaling AD Quints, depending on play style, much like how the AD marks can be swapped for Armor Penetration Marks.

I chose Fury/Sorcery for a boost on the already fast AS you have as Gangplank, as well as a good way to trim down the time needed for your Parrrley to refresh. take any Offensive masteries that would boost your AD and Armor Penetration, and finish it off with Frenzy and Executioner to achieve more Critical damage on your opponents.

Choosing what to use the remaining 9 points on is really completely up to the player's own digression, but I placed them in masteries that would give me an added MR/ Hp Regen, as well as More health for a great early game.

Following my Tier succession list will guarantee that your Parrrley with nearly ALWAYS decimate your enemy's mid/ADC. Most tops you face may laugh at your attempts to dent their health, once they're past level 2, but you will definitely be able to exchange hits with them, once you get Statikk Shiv.

With this build procession, you will pretty much always be in a good position against your opponents, as you will have steadily raising AD, Crit. Chance, and Armor. Your Scaling MR will see to you getting decent protection against any AP champs as the game progresses.

Once you have completed the Phage in your Trinity Force, consider getting the Boots of Mobility early in order to chase/escape team fights without breaking a sweat.