The idea was that you would sail north cast spells until you level up, then stop, and move the boat 13 tiles, then repeat the spell. It genuinely worked for leveling up high eval.
The hash function was poorly chosen which had the effect that if you found a tile where you gained a skill point, there was a good chance the tile 8 steps to your North would let you gain another skill point.
So the algorithm became: 1. Run boat continuously trying the skill over and over 2. Stop when there is a skill gain 3. Move boat 8 steps north 4. Do skill again 5. Gain? Go to 3 6. Otherwise, go to 1
Generally people used the technique similar to leveling melee skills in towns but there was always a work-around to killing people in towns. In downs you would kill someone macroing by dropping like 5 explosion potions on the ground around them, then throwing 1 in and teleporting out while a friend would loot the body.
Magic on the boat involved walking in front of the mast to cancel the spell.
I used to own a house on that little pirate island with NPCs you could kill. My house was situated on some weird boundary line such I could fire spells at people outside while in the safety of my own home.