How to Install a Boat Flotation

When building your own boat, you may consider adding flotation material to your watercraft. Flotation material in a boat is like a life jacket for a boat that suddenly has an unwanted hole in its hull. The water pouring through a breach -- every cubic foot weighs more than 60 pounds -- may overcome the boat's buoyancy. Flotation material compensates for this loss, filling voids with a light material that's securely filled with air; if the material takes up 1 cubic foot but weighs 4 pounds, it provides between 56 and 58 pounds of buoyant force.

Things You'll Need

  • Measuring tape
  • Urethane foam blocks
  • Handsaw
  • Construction saw
  • Razor knife
  • Drill
  • Plastic dropcloths
  • 1-inch hole saw
  • Gloves
  • Safety glasses
  • 4-pound density urethane foam kit
  • Clean containers
  • Paint-mixer drill attachment
  • Spackling compound
  • Thin-bladed putty knife
  • 220-grit sanding block
  • Clean cloth
  • Acetone
  • Denatured Alcohol
  • Lacquer thinner
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Instructions

  1. Solid Polyurethane Foam Blocks

    • 1

      Remove the interior paneling to expose the inside surface of the boat's side. Measure the thickness of the top of the boat's side -- the gunwale.

    • 2

      Measure the height of the sides of your boat's hull, using a measuring tape. Cut panels from blocks of urethane foam, using a handsaw, that are the height of the inside of the hull, the thickness of the gunwale and 1 foot in width.

    • 3

      Spread construction adhesive on one side of the foam panel. Press the foam panels onto the inside of the boat's hull. If necessary, use a razor knife to reduce the width of the panels to accommodate for curves in the side of the boat, such as the curve where the sides turn to meet at the front, or bow, of the boat.

    • 4

      Install the interior surface of the boat's sides over the flotation.

    Liquid Polyurethane Foam

    • 5

      Cut two 1-inch holes in the interior wall of the hull, between each of the boat's frames -- the "ribs" of the boat -- using a drill and a 1-inch holesaw. Drill the holes near the top of the wall. Turn off any air conditioning equipment. Ensure the ambient temperature is in excess of 75 degrees Fahrenheit. Turn on the engine room blower, if your boat is equipped with inboard or inboard-outboard propulsion.

    • 6

      Cover the floor of the work area with a plastic dropcloth. Tape a plastic dropcloth over the interior wall of the work area. Cut access holes in the dropcloth so you can pour the foam in through the 1-inch holes in the wall. Read the instructions on the urethane foam kit for mixing and mix the two parts of the foam into clean containers.

    • 7

      Don gloves and safety glasses. Have your assistant mix the foam vigorously for 25 seconds with a drill and paint-mixer attachment. Pick up the container and immediately pour the contents into one of the 1-inch hole; you have about 20 seconds to pour the foam before it begins to expand.

    • 8

      Wait five minutes for the foam to fully expand. If the foam does not fill up the wall, wait 20 minutes before pouring additional foam into the wall, to allow the foam that's already present to set fully.

    • 9

      Replace the 1-inch sections you cut from the interior wall, using construction adhesive. Spread spackling compound into the gap between the cutout and the wall, using a thin-bladed putty knife. Sand the spackling compound level with the surface of the wall, using a 220-grit sanding block.Finish the wall as desired.