This Hot-Dipped Galvanized Roller Tongue bracket is very commonly seen mounted to the front of smaller boat trailers. This listing is just for (1) Side, so you would need to purchase (2) to complete both sides.
Essentially you would use two of these to mount on the front of the tongue, to hold a roller, which would contact the bow of your boat. See the picture to get the full effect, but using (2) 3/8 inch Trailer Bolts. Simpy measure the appropriate size you need for the width of your tongue material and select from zinc plated or stainless steel. Next you will need to choose the appropriate bow roller/ bow stop you would like to have between the brackets. It is important to remember that the length of roller or stop you need may be determined by the width of your tongue. Choose a roller that will accommodate a 5/8 diameter Boat Trailer Roller Shaft. Select the correct length shaft, then select 5/8 inch Zinc Plated Boat Trailer Roller Shaft Pal Nuts to mount to finish the assembly.