When in the Volcano the player has all the speed modifiers the boat they entered it with had. Should be very easily reproduce this to noticeable effect by just equipping an Iron Wind to a boat and entering the Volcano with it. Also If this wasn't problematic enough, the speed boosts can be carried into other worlds using the Seaworthy or Skyworthy, so yeah theres room for great abuse here.
Steps to Reproduce
1. Equip a speedy sail like the Iron Wind to your boat. 2. Enter Volcano. 3. Notice jarring speed increase.
This issue has not been confirmed by a developer yet.