The correct answer is B) reduce the swinging of the lifeboat as it is being lowered from the embarkation level. Frapping lines are fitted to lifeboat davits to minimize the swinging motion of the lifeboat during the lowering process. This helps to ensure a safe and controlled descent of the lifeboat from the ship. The frapping lines are tightened to restrict the lateral movement of the lifeboat, enhancing the stability and control during the launch. The other answer choices are incorrect because: A) holding the lifeboat to the ship's side is the purpose of the tricing lines, not the frapping lines; C) using the frapping lines as a safety line is not their primary function; and D) securing the lifeboat in the stowed position is the role of the lashings, not the frapping lines.