The treehouse that the Hemulen was building collapses, and so instead Snufkin takes him sailing in his boat, though the Hemulen realises that he gets sea-sick, and after the trip leaves to go home.
When the Hemulen's treehouse fell, he was taken sailing by Snufkin in his boat, but the Hemulen soon felt unwell at sea and subsequently chose to head back to his own abode.