The correct answer is D) directly under the boom. For personnel transfers using a personnel basket, the vessel should be positioned directly under the boom to ensure the basket can be lowered and raised safely without the risk of the vessel drifting away or colliding with the boom. This positioning keeps the transfer path as short and vertical as possible, minimizing swing and improving control during the lift. The other options are incorrect because stopping the vessel dead in the water (A) or moving it away from the boom (B) would increase the risk of the basket swinging or missing the target, while tying it to the boom (C) could still allow undesirable vessel movement.