How to Build a Bathtub Race Boat

Over the years many materials have been used to construct a racing bathtub. Early tub hulls were predominantly wood with a moulded fibreglass tub attached. There have also been some very innovative designs built of aluminum and other metals. As bathtub boat technology advanced, fibreglass has become the material of choice for almost all tubbers. With its ease of being formed into any shape, inherent strength, lightness and relatively low cost, it has dominated the scene when it come to building a competitive racing tub. With this in mind, here are a few ideas and hits that will get you on your way to ruling the waves on the outside of your bathtub.

Whenever building your own tub, read the rules over several times before, during and after your build to ensure you're conforming to the guidelines of the race.


Using an old bathtub, make a fibreglass copy by laying a combination of PVA release, E-glass mat material and E-glass cloth material to the inside of the tub. Be sure to wet out each layer with resin and use a roller to remove air bubbles and wrinkles. Reinforce critical areas such as the rear of the tub where the transom will attach and the rim where your hand will hold onto, with more glass material. After the resin has set, pull the copy out of the old tub. If it is hard to release, use compressed air or water to help loosen the fiberglass part. If you used the PVA release properly, it should come out with just little water to dissolve the PVA.



The tub hull can be made by several different methods. By far the easiest is to get on the phone and borrow one of the many molds lying in backyards around Nanaimo. For the more industrious individual, designing your own mold is the answer. Wood and filler are used to develop the shape. After you have the mold, laying up the hull uses the same materials and techniques as the tub itself. Remember to cover all corners and make sure no air bubbles are present to prevent weakness in the structure. After the mold is built or procured, the same layup process as the Tub portion ensues.



Transoms can be made out of wood, foam, aluminum or other materials. Wood and fibreglass are the easiest to work with. Engine heights vary between 15 and 25 inches, depending on propeller design, so remember it is easier to reduce the height than add it on later.
This is a very critical area. Be sure that it is well built and strong. Quarter-inch plywood uprights and two pieces of laminated half-inch plywood engine supports covered in mat fibreglass work well and are easy to build.


After making the tub and hull, join together using fibreglass strips, making sure it is well reinforced. Eighth inch door skin works well for side supports. Remember to leave six inches of the tub exposed. Alignment is critical for handling, so measure it, don't trust your eyes. Use at least three layers of mat when attaching the transom to the back of the tub. An engine 300 feet under water won't win races, not to mention the hole in the back of your craft. There must be enough floatation to support the complete craft in an upset: a minimum of three cubic feet. Most builders rely on attached foam or sealed air chambers. Use whichever suits your design, but be sure there is enough. Although fibreglass has been the mainstay of tub building for many years, the introduction of the 350 pound maximum weight rule has opened the way for the handyman carpenter or fabricator to get his or her feet wet in the great sport of bathtub racing again.



  • Fumes and dust are toxic and irritating so work in a well ventilated area and wear a dust mask when grinding.
  • Polyester resins are easier to work with and much cheaper.
  • Epoxy resins have low fumes and are much stronger, but also much more expensive.
  • All molds must be clean and smooth. Wax and PVA should be applied first to prevent fiberglass stick to molds.
  • Grind all attaching points and rough areas to facilitate pieces staying together and prevent cutting crew and/or driver when handling the tub.
  • Get a glass roller! You’ll be lost without it!
  • Acetone is used for cleaning. Make sure you have lots on hand for brushes, rollers and yourself. 
  • Using gelcoat before laying glass in molds prevents pinholes and adds to smoothness of finished pieces. Let it dry before applying glass. 
  • If in doubt, the friendly staff at Industrial Plastics in Nanaimo can always answer your fiberglass questions and supply all of the materials and tools.