The creation of peril issue only arises in the lifeboat situation if there is an owner of the lifeboat. If the lifeboat owner allows others to board, then the owner voluntarily acts to assume responsibility for the safety of these fortunate guests. Therefore, if she determines that discarding one or more of her guests maximizes the chance of survival for the remainder of the lifeboat passengers, it does not matter, for if the owner ejects one or more guests in this situation, the owner has engaged in an act of aggression (specifically murder). Why is this an act of aggression? This is an act of aggression because the lifeboat owner knows that ejecting a passenger, who she has voluntarily assumed responsibility for the safety of, into the ocean clearly places the passenger in a perilous/dangerous/emergency situation (in fact near-certain death). Interestingly, this means the owner has an incentive to only permit a reasonable number of people to board the lifeboat in the first place.
Unowned lifeboats are a separate issue evaluated thoroughly, per usual, by Rothbard.