The correct answer is B) such that the vessels will be in step. When towing another vessel, the length of the towing line should be adjusted so that the two vessels are in sync with each other's motions. This helps to minimize the strain on the towing line and reduce the risk of the vessels colliding or becoming separated. Having the vessels "in step" means that their motions, such as rising and falling with the waves, are aligned, which is the optimal configuration for safe and stable towing. The other options are not correct because: A) keeping the vessels on different wave phases can lead to excessive strain on the towing line; C) an excessively long towing line can be difficult to control and increases the risk of the vessels drifting apart; and D) while a shorter towing line may be preferable in some circumstances, it is not an absolute requirement and does not ensure the vessels will be in step.