An apparatus and method for reinforcement of partially submerged structural elements such as piles, posts, pillars, and pipes are disclosed. The apparatus includes an upper unit which may be fixed to the structural element above the waterline and a lower unit which is suspended from the upper unit via cables or other support members. The apparatus enables a reinforcing sleeve structure to be constructed in multiple segmented layers from above the waterline which the sleeve structure is lowered beneath the waterline. The lower unit guides the lower end of the sleeve structure down around the submerged portion of the structural element and supports the weight of the sleeve structure until it is fixed in place and filled with concrete or another reinforcing core filler material.