Yes, we've all gone on one of OSRS gold these earlier. But about a boat players can buy, sell and maintain indefinately that is not a quest related item? Note that this doesn't necessarily need to be a kind of transport ( But it might help if it had been ). Sail the seas to your hearts content.
Okay, transporting really isn't the main idea about this topic, but its sure to come up however. Here's another facet: Fighting. Ship Vs. Ship, massive market in cannon fire. What midevil ship could be complete without them? They'd serve as a defence for the ship and will contribute to your attack ability. Get aboard the ship you sink and grab all the loot, a superb way of making money to me, and do not let the ships become plain. Beautiful, magnificent emblems on sails, colours and everything.
Captains could cover to build their ships, (roughly 4 mil?) Complete with 10 whole cannons. It appears quite expensive for me personally, but these cannons dont need to cost 750k. Their ordinary, maybe just 80k to me. Build slots for cannons and expand in your boat's power. All kinds of cannons. Fair enough. Overall I think it's a wonderful idea. Pick the type of cheap RuneScape gold boat, pick the build, choose the arnament and everything.