It's really easy to do. You will need to remove the mast caps. I don't have a Hobie but I suppose that the cap is secured with rivets. Drill the rivets out and remove the cap. You will need some silicone sealer. Seal around the edges of the cap and replace it onto the mast. Don't forget to do this to both ends. Seal around any other rivets, screws, et cetera, that are on the mast. The purpose is to make the mast watertight.