bow, prow
舳 centers on the front part of a ship: the bow or prow, the leading edge that cuts through water.
舳 combines 舟 (boat) with 由, which likely contributes the sound. The character specifically denotes the bow or prow of a vessel.
The boat radical 舟 on the left and 由 on the right can be seen as the reason (由) a boat (舟) has a pointed front: to cut through water. Picture the bow as the boat's leading reason.
For ジク, imagine the bow of a ship jutting out like a jig: jig -> ジク, and the prow jigs forward through the waves.