Gone Outdoors

How to Build Your Own Pontoon Boat

by Jane Smith

Pontoon boats can be as simple as a floating raft held up by plastic barrels or as elaborate as a houseboat. Most consist of a platform with a convertible top and storage bench seating for six to eight. Some include pop-up dining tables and barbecue grills. Most have a low-powered trolling motor, providing just enough thrust to move slowly through the water, to avoid dipping the bow. They do not turn quickly and are not safe to use in high chop.

Section One: Deck Assembly

Sand all lumber using a disk and coarse, medium, fine and extra fine sanding disks in that order. If you do not have a disk sander, use a belt sander or sanding blocks. Use the carpenters' try square to check that all lumber has been cut at 90-degree angles and that the corners of all piece of lumber are square. If any are not, use the miter box and back saw to cut the edges and corners back into true 90-degree angles.

Set two of the 2-inch by 4-inch by 16-feet lengths of stock lumber on their 2-inch sides between the two 2-inch by 4-inch by 12-feet lengths of stock lumber. Use a try square to ensure that all four pieces meet at 90-degree angles. Space the remaining 16-feet lengths of stock evenly between the first two 16-feet lengths to make the deck frame, as shown in the diagram that accompanies this step.

Lay a spirit level on a board that is longer than the width of your deck. Check at the bow, stern and three points in between to ensure that the deck frame is level. If it is not, use a block plane to trim the beams until level is achieved.

Use a chalk line to mark the center line of each of the 16-feet-long stock lumber where they butt against the 12-feet long pieces. Drill two 1/4-inch-diameter pilot holes, spaced evenly apart, down the center line of each end of the 16-feet boards. Countersink all holes. Secure the 12-feet-long boards to the 16-feet-long boards using 4-inch-long galvanized wood screws.

Lay the 4-feet by 8-feet sheets of marine-grade plywood in the pattern shown in the diagram that accompanies this article. Snap a chalk line across the deck along the center line of each of the studs underneath the plywood deck. Lay your spirit level on a board that is longer than the width of your deck again. Check at the bow, stern and three points in between to ensure that the deck frame is level. If it is not, use shims to adjust the floor sheathing until everything is level.

Drill 1/4-inch pilot holes along the chalk lines, every 8 inches, beginning in one corner of the deck. Countersink all holes. Secure the plywood deck to the deck frame using 3-inch galvanized wood screws. Check level one last time, making any needed adjustments.

Section Two: Pontoon Cradle and Keel Assembly

Stand the five 1-inch by 12-inch by 16-feet lengths of stock lumber on their 1-inch edges, between the two 1-inch by 12-inch by 12-feet lengths of stock lumber to form a rectangle. Make sure the corners are flush and square with one another.

Place four barrels open topped barrels end to end an equal distance apart between every two 16-feet long boards in three rows, as shown in the diagram that accompanies this step.

Add ½-inch diameter bilge lines going from each barrel to a bilge pump. This will allow you to add or remove water from each of the barrels when you need to correct any listing of the boat later. Make sure that each barrel has the same arc as all the others, so that your barrels do not force their way up through the decking when the pontoon boat is underway. To do this, mark the place where the barrel meets the boards. Measure the arc on one barrel and then check all the other barrels. Reposition them until they all have the same arc. Screw all the barrels into place, using ½-inch diameter, 1 ¼-inch long marine grade bolts with acorn caps.

Place a 4-inch by 4-inch by 12-inch post at each corner of the pontoon cradle you are making, flush with the top edges of the keel boards. Drill three 1/4-inch diameter pilot holes down each outside face of each corner of the pontoon cradle, 1 inch from the top and bottom edges and one centered between the first two holes. Use 1/2-inch diameter, 41/2-inch long galvanized wood screws to secure the frame to the posts.

Lay the finished deck on top of the pontoon cradle. Use a carpenters' try square to make sure the edges are flush at each corner. Drill 1/4-inch diameter pilot holes every 4 inches, between the existing deck screws. Secure the deck to the pontoon cradle using 1/2-inch diameter, 8-inch long galvanized wood screws.

Attach 1-inch wide, 4-inch long galvanized metal brace plates across the line between deck and the pontoon cradle, along each keel board, using 2-inch long, 1/2-inch diameter wood screws.

Have a professional install your chosen propulsion system, bilge lines and bilge pump.

Items you will need
  • For pontoon cradle:
  • Carpenters' try square
  • Spirit level
  • Miter box and back saw
  • Power drill, 1/4-inch drill bit
  • Countersink bit
  • Five 1x12-inchx16-feet lengths of stock lumber
  • Two 1x12-inchx12-feet lengths of stock lumber
  • Four 4x4-x12-inch corner posts
  • Twenty four 4-1/2-inch long, 1/2-inch diameter galvanized wood screws
  • For buoyancy:
  • Eight empty, never-used 55-gallon plastic barrels
  • Sixteen 2-inch wide, 1/8-inch thick plastic straps
  • Thirty-two 1/2-inch diameter, 1/2-inch-long galvanized wood screws
  • Clear silicone adhesive
  • For the deck:
  • Two 2x4-inchx12-feet lengths of stock lumber
  • Seven 2x4-inchx16-feet lengths of stock lumber
  • Chalk line
  • Six sheets of 4x8-feetx1-inch marine grade plywood
  • Box of 3-inch galvanized wood screws
  • Box of 4-inch galvanized wood screws
  • Coarse, medium, fine and extra fine sanding disks or belts
  • Disk or belt sander
  • Marine-grade acrylic deck coating

Tip

  • Use three rows of barrels for added stability. Pump bilge water out of your barrels of the boat begins to list. Keep a fully-charged, battery-operated or crank-operated radio on board at all times. Keep a flare kit and distress flags on board at all times. Have a Coast Guard approved adult life vest available for every passenger. Children must wear a Coast Guard approved life vest at all times while aboard the boat, even while it is docked.

Warning

  • Do not operate a pontoon boat while under the influence of alcohol, prescription or over-the-counter medications, or any herbal or pharmaceutical substance that may impair your judgment or reactions. Do not operate a pontoon boat in choppy water. Come ashore if you see signs of approaching storms, including changes in wind speed, relative humidity, or rapid drop in air temperature. If you hear thunder, even if it is muted, dock the boat and go ashore immediately.