Final answer:
The new helmsman needs to know the course and speed of the ship when relieving the helm. This helps them steer the ship in the right direction and maintain a consistent speed.
Step-by-step explanation:
The new helmsman should find it handy to know the course and speed when relieving the helm. Knowing the course and speed of the ship helps the helmsman steer the ship in the right direction and maintain a consistent speed. For example, if the ship is on a course heading due north at 7.00 m/s and there is a local ocean current of 1.50 m/s in a direction 40.0° north of east, the helmsman needs to take into account both the ship's velocity relative to the water and the velocity of the current relative to the Earth to steer the ship effectively.