We use one (large) ice eater positioned off the bow and tied with three lines to "angle" the unit to acheive water flow down the entire hull. 50ft Sailboat and we have no problems keeping ice free. Make minor adjustments to the center "angle" line once you turn unit on as the ice eater will move forward and up slightly while operating. Do not let it get too close to the surface - it's designed to bring warm water up from bottom of river/lake to unfreeze surface. Ours rides about 2 ft under and works really well all winter. Takes a little "adjustment" to keep the unit from twisting the lines when you turn it on, but you'll get the hang of it. Keeps the boat a lot warmer also.