Welcome to the forum Bigjed. Those are keels on the bottom of your pontoons. They are welded to them to add strength and rigidity and to protect them. They are either solid or hollow like yours and are capable of holding the weight of your pontoon boat.Hello Bannerman. I have a question for you relating to you boat and flat board bunks. I have the option to put my boat on a lift with a set up just like yours. My boat is a Bennington 2575 RLX tritoon. My concern is this. On the bottom of my toons are aluminum "v's ". I'm concerned resting the toons with the v's on the flat board will be a problem. What is your set up like? Thoughts? Do you have these on the bottom of your toons? If so, any issues. Thanks for the help!