Life and death situation

First of all, if its a boat there'll be something called as an inflatable raft which you can use. Or else you can build a raft if you have the time and if you're driving the boat make sure you dont get yourself in such a situation...if you are not skilled enough just dont put everything you have at risk. Nobody wants to lose their loved ones thats why they have these safety measures in place. And if the distance between land and the boat can be covered by just swimming I think i would use a large piece of wood for one of them to float on and then tell the other whom i am swimming with to drag the board with the help of a rope, which is obviously available, as you were on a boat. This would surely mean less stress for you...and dont forget the life jackets which can help you to take few breaks in between.