How far should you back the trailer into the water until how much of the bunks or rollers are submerged?

When backing a trailer into the water, aim to submerge the bunks or rollers enough to support the boat without floating it off the trailer. Typically, this means submerging them by about one-third to half their height. This ensures the boat can slide on and off easily while still providing enough support when loading and unloading. Always consider the specific design of your trailer and boat, as well as water conditions.