oar
檝 centers on a tool for propelling a boat: an oar. It is a specific implement for rowing.
檝 combines 木 (wood) with 戢, which likely contributes the sound. The character is a phono-semantic compound for a wooden oar.
The left side is wood 木, and the right side 戢 looks like a complex tool with a blade 戈 and a handle. Picture a wooden oar carved from a tree, ready to row.
For シュウ, imagine the sound of an oar slicing through water: "shoo" as it glides, then the wood creaks. "Shoo" cues シュウ, and the oar moves the boat.