>not be sea worthy

This, in my mind, would pretty much eliminate much of the market for these items. Both rivers can be swam with enough skill and the ferries themselves are both fast and cheap these days.

A major part of the draw for the ship system is the ability to travel to the islands freely.

>keep land in sight at all times when at sea

This would be very hard to use at sea if so because there are several stretches just between the islands where you cannot see any land at all. You'd be limited to sailing in circles around a single island and you could pretty much forget about ever sailing to the mainland in it.

I do love the idea for players making some sort of raft/canoe and have proposed it before in the past myself. But these days I can't really see a use for it. It was different when the ferries and stuff took longer, but these days it's pretty fast to travel around without any extra items or abilities.

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What are you worried about, a pool of black shadows might jump up and bite you?