I've studied ships and piracy for years and would like to leave some suggestions here
Yes, let "Hull health" be repaired by construction. Change "Boat Health" to "Water level" and add Bilge Pumps to the boats. That's much more realistic and less frustrating. Also do some research on types of ships. They shouldn't be called "[size] row/sail boat". Name them something real like sloops, cutters, frigates, brigs, galleons, triremes, longships, dhaos, etc.
But don't let any ships be smaller than a real sloop. Every ship with this skill should have sails. Otherwise, we could just use the Canoes from Woodcutting!
Look into the weapons used on real pirate ships, too. In the medieval times they used ballistae on upper decks of ships. There were many types of cannons used after the 1600s. Even catapults on ships with a wide deck.
The stations on the ship should be Helm/Rudder, Rigging, Oars, Hull, Bilge Pumps, Cannons/Ballista/Catapult, Nets. Helm, Rudder, and Rigging should be the only stations that require high Sailing skill to man. Oars and Bilge Pumps should require Strength, Hull should require Construction (as you repair holes with carpentry skills), Weapons should require Ranged, and Nets should require Fishing. When the sails get holes, rigging gets damaged, or nets get damaged, someone with high Crafting should be around to repair the stuff (Or, if the ship is equipped with ballistae, high Fletching.)
Anyone should be able to go on any ship to help out with grappled melees or even hang out or be transported... but you should only be able to work at a certain station if the specified skill is high enough for the boat type. For example, let's say Galleons are a level 80 ship. Anyone can get on the ship, but only level 80 sailors can working navigating stations and level 80 rangers can man the guns.
Your idea of a plank spawn and tar spawn could be exploited. How about just making cargo space in the ship and store stuff belowdecks?
I like your idea of island types
12-Aug-2015 00:28:48