raft
棑 centers on a raft: a flat floating structure made of logs or timber, used for transport on water.
棑 combines 木 (tree, wood) with 非, which likely contributes the sound. The character expresses a wooden raft.
The left side 木 is wood, and the right side 非 looks like two rows of logs tied together. Picture a raft made of wooden logs lashed side by side.
For ハイ, imagine a raft floating high on the water: high -> ハイ, and the wooden raft rides the waves.