You can board from the deck by crossing a plank which gives 10 Agility. A rope is a good option to board 40 Agility. You can also get under the deck and use a rope to climb through a cannon area. This RS gold will result in 70 Agility. If you do board the enemies ship and die, you could be killed. You can now Melee the other players on the enemy ship.
If you kill all the players on the ship Enimies, NPC's cannot be attacked. You can also take their crew members and force them to work for you. They can also walk the plank...The stern of each boat has a forfeit button. This permits the boat and crew to be taken back to the mainland, along with their items. The loot will consist of the items on the boat as well as items the players drop when the lose their lives.
Redmonke suggested that the skill have a skillcape. I was thinking it should display a photo of a cape, with a boat and a sailor behind. The phrase could be: You try to get onto a mini-ship and then begin sailing across the sea. It's an easy concept and could be quite entertaining. Girfaniam recommended Fishing Boats. I'm adding his suggestion.
You can make an fishing boat as low as 20. The boat is a tiny wooden rowboat. As you get higher in your level, the fishing boat is able to get bigger. Your vessel will OSRS buy gold also allow you to travel on the port only (unless you have weapons implacments). You could fly fish or use regular fishing rods. You could also go fishing in this manner. If you're low on supplies for your crew,, you could just go fishing and offer the fish to them. Or you can just visit the nearest port.