How to Make a Kayak Trailer From a Boat Trailer

Cut the 2-by-4 lumber into 14 4-foot-long sections.

Mount the post base. Bolt a post retro-fit base in the middle of a 4-foot 2-by-4 lumber board. Use the 1/2-inch-by-2-inch bolts, flat washers, lock washers and nuts to secure the base.

Determine base board mounting. Place one base board 2 feet from the rear of the trailer. Place the front base board 4 feet forward of the rear board. Bolt each base board to the trailer frame with 3/8-inch-by-2-inch bolts, flat washers, lock washers and nuts. Trim the 2-by-4 to the width of your boat trailer.

Measure the vertical posts. Insert two 4-by-4 posts into the post retro-fit bases and measure according to the number of kayaks you plan to carry. You will need about 2 feet for each set of kayaks. For example: if you need to carry six kayaks each post should be about 6 feet long, depending on the design and size of your kayak.

Cut the vertical posts. Cut the 4-by-4 posts to the size you need. Secure them to the post retro-fit base with 1-1/2-inch 10d smooth shank nails.

Install vertical post braces. Cut four 2-foot long 2-by-4 braces with 45 degree ends. Nail the braces to the vertical post and the base board with 16d nails.

Cut the arm spacers. Cut four 3-1/2-inch long pieces of 2-by-4 lumber for each arm of the rack. If you will carry six kayaks, you will need 24 pieces.

Cut the bottom corners off each rack arm. With the 2-by-4 rack arm small edge facing up, measure 2 inches vertically down the end of the rack arm and 2 inches from the end horizontally on the bottom edge of the rack arm. Draw a cutting line between these two points so that the bottom corner of the 2-by-4 gets cut off at a 45 degree angle. Cut the corners from all 12 of the rack arms. The cut corner will face down, towards the ground.

Nail two arm spacers on each side of each vertical 4-by-4 post perpendicular to the axle. Place the cut ends facing up and down. These are the locations where the rack arms will be placed. Place the first arm as low as possible while still clearing the fenders of the boat trailer. Secure the spacers to the 4x4s with 16d nails.

Center two rack arms horizontally at the level of the spacer. The idea is to sandwich the post with the two rack arms. Nail the arms to the spacers at 90 degrees to the vertical post. Place a spacer at each end of the arms, just back from the cut corner. Place the cut ends facing up and down. Clamp and nail with 16d nails.

Bolt rack arms. Ensure the rack arm is squared with the vertical post and bore two 3/8-inch holes through the back arm, the post and the front arm on the other side. Place one hole at the top left and the other one at the bottom right of the arm post junction, so they are staggered. Secure each of the six rack arm sets with two 8-inch carriage bolts with the bolt head facing the tow car.

Screw an eye bolt lag screw to the front and rear of each of the vertical 4-by-4 posts for tie down attachment.

Install trailer eye bolts. Bolt a 3/8-inch eye bolt to the rear frame of the trailer inline with the vertical posts. Bolt a 3/8-inch eye bolt to the front of the trailer hitch post. Secure the bolts with 3/8-inch flat washers, lock washers and nuts.

Secure the vertical posts. Attach a tie down strap between the two eye bolt lag screws on the vertical posts. Attach a tie down between the front vertical post and the front trailer frame tie down. Attach a tie down between the rear vertical post and the rear trailer frame tie down.

Install the kayak eye bolts. For each kayak, screw a lag eye bolt to each 4-by-4 post and the end of each rack arm. These are used to secure each end of each kayak to the rack arm.

Weather-proof the trailer rack. Paint all the wood parts with oil-based exterior house primer and oil-based exterior house paint.