Strategy description:

1. Lord Haart should finish 112 capturing Inferno.

2. Roll Levitation in GM4 so it will be possible to go from Inferno to obelisk in one day without a boat.

3. Ciele take XP in Treasure Chest to get Advanced Water so she can cast Advanced Summon Boat on 111. Basic Summon Boat doesn't work because there are no boats on the map.

4. Hire Gem to get Summon Boat spell if it doesn't roll in GM.

5. Coronius (Scholar) will teach Ciele with Summon Boat spell.

6. Kyrre will capture mines.

7. On 112 Ciele swim south and give vision on an island.

8. Hire Fiona (Advanced Scouting) to get vision of the sea route.

9. Hire hero with Advanced Wisdom (Mirlanda/Astral/Jeddite) to cast Levitation and fight blue hero. After fight it's important to get Logistics, otherwise hero can't reach obelisk on 112. Unbelieveable, but without Logistics hero has 191 movepoints for last 2 moves (need 200). This part of the run requires MUCH re-rolls because these heroes have very low chance to get Logistics (2-3%).

P.S. There is a very-very small chance that Lord Haart gets Basic and Advanced Wisdom after Inferno fight. So you can finish the whole mission using only Lord Haart (he can cast Levitation and has enough movepoints to reach obelisk). But this requires a lot of re-plays. In my runs even if he got Wisdom, on next level he always tried to upgrade Estates or Leadership.

P.P.S. There is also a way to play without Ciele and a boat. For that you should re-roll until Lord Haart gets Spyglass or Speculum. Then take XP Treasure Chest by Fiona/Deemer to get Expert Scouting. And finally buy some boats and summon boats (Basic Summon Boat) to a certain place and put Scout hero on a boat.

P.P.P.S. Thanks to @N1kotin to the idea with Levitation!