How to Build a Boat Float

A boat float is a temporary, drive-on mooring that floats a boat out of the water. They're used for everything from personal watercraft to bass boats. While not intended to function as an automated boat lift for long-term storage, they serve many of the same functions temporarily. Commercial boat floats have angled rollers that allow the boat to be driven up onto the float. A DIY version of the same design, but without complex rollers, allows most boats to be driven or pulled onto the wetted surface of the float. An eight-foot float is sufficient for a 10-foot boat.

Things You'll Need

  • Tape measure
  • Straightedge
  • Framing square
  • Chalk line
  • 24-inch by 24-inch by 48-inch blocks of Styrofoam
  • Dovetail saw
  • 3/4-inch plywood
  • Paint rollers
  • Polyurethane adhesive
  • Utility knife
  • Power drill
  • 1/2-inch by 12-inch wood drill bit
  • 1/2-inch by 12-inch carriage bolts
  • 1/2-inch by 1-inch steel washers
  • 54-inch wide marine grade vinyl fabric
  • Vinyl-to-vinyl epoxy adhesive
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Instructions

    • 1

      Use a tape measure, straightedge and permanent marker to draw a pair of cut lines on the 24-inch flat side of a 24-inch by 24-inch by 48-inch block of Styrofoam. The lines should start in both corners and run toward the center of the block at a 45-degree angle, meeting the midpoint of the block 24 inches apart. Connect these midpoints with another, straight line. This will result in a flat, U-shaped channel to be cut through the body of the float.

    • 2

      Use a dovetail saw to cut out the trapezoidal shape defined by the cut lines. Repeat this entire process three more time, in three more 24-inch by 24-inch by 48-inch blocks of Styrofoam.

    • 3

      Lay the four cut blocks of Styrofoam cut side up and side-by-side on a 4-foot by 8-foot piece of 3/4-inch plywood. Inspect the upper, carved out surface of the four blocks and use the dovetail saw to correct any variations in the dimensions. The result should be a combined Styrofoam block unit that is 2 feet by 4 feet by 8 feet with a 12-inch angled trough cut along the center of its upper surface.

    • 4

      Use a paint roller to apply a liberal coat of polyurethane adhesive to the plywood board and to the bottom, uncut 24-inch by 48-inch surfaces of all the Styrofoam blocks. Lay the blocks on the plywood board and press them firmly into place. Allow the adhesive to dry for 24 hours.

    • 5

      Measure and mark four drill hole marks on the 24-inch by 24-inch cut-in, upper surface of all four of the Styrofoam blocks. Locate the marks four inches in from the outer, 24-inch dimension boundaries. Use a utility knife to carve out a 1-inch wide, 1-inch deep hole in the Styrofoam at each of these four points in each block.

    • 6

      Use a power drill with a 1/2-inch by 12-inch wood bit to drill the four holes in each of the Styrofoam blocks, through the Styrofoam and the plywood.

    • 7

      Turn the boat float assembly on its side. Bolt the four Styrofoam blocks to the plywood board with 1/2-inch by 12-inch bolts, inserted screw-end first down through the Styrofoam block and the plywood. Make sure that the bolt heads run through 1/2-inch by 1-inch washers and are inset inside the carved 1-inch holes in the Styrofoam. Wrench the bolts over lock washers.

    • 8

      Measure, mark and square-cut a 10-foot length of 54-inch marine grade vinyl fabric. Fold the piece lengthwise. Use a paint roller to apply polyurethane adhesive to all the upper surfaces of the boat float assembly. Lay the folded fabric down, folded edge first, along the inside center of the long axis of the Styrofoam blocks. Fold back the upper side and stretch it across the uncovered surface of the blocks. Use a clean pain roller to roll the fabric against the upper surface of the blocks, firmly attaching it.

    • 9

      Fold the ends of the fabric over the ends of the float assembly, apply more polyurethane adhesive to the ends of the float assembly and glue the folded ends of the fabric to the ends of the float assembly. Be sure to use a separate adhesive--vinyl-to-vinyl epoxy adhesive--when gluing the material to itself. Measure, cut and glue enough panels of the vinyl fabric to cover the sides and bottom of the assembly.