Because a time charter party’s terms give the charterers control of the vessel’s commercial operations (i. e. her employment), whereas a voyage charter party’s terms do not.
Many charterers, e. g. oilfield operators or drilling contractors hiring offshore support vessels, require this higher degree of control of the vessel. A bulk carrier loading coal for several discharge ports might be time- chartered so that the charterers can direct the ship’s scheduling, routeing, etc. as they require.
