The winner of the 2014 Bay of Islands Bathtub Race will be invited to attend and compete at the World Championships in Nanaimo, Canada as part of the Nanaimo Marine Festival and World Championship Race from Friday 25th through Sunday 27th July 2014.
Some Tips on How to Build a Bathtub
Over the years many materials have been used to construct a racing bathtub. Early tub hulls were predominantly wood with a moulded fiberglass tub attached. There have also been some very innovative designs built of aluminium and other metals. As bathtub technology advanced it has been fiberglass, with its ease of being formed into any shape, inherent strength, lightness and relative low cost, which has dominated the scene when building a competitive racing tub. With this in mind, here are a few ideas and hints that will get you on your way to ruling the waves on the outside of your bathtub.
Construction of the Tub
Using an old bathtub, make a fiberglass copy by laying a combination of bubbles, mat and 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 hands will attach, with more glass material. After the resin has set, pull copy out of the old tub. If it is hard to release, use compressed air or water to help loosen the copy.
Construction of the Hull
The tub hull can be made by several different methods. By far the easiest is to get on the phone and borrow a mould from someone you know. Alternatively, you can contact Opua Marina Boatyard in Opua or Pacific Marine in Whitianga and have one made. For the more industrious individual, designing your own mould is the answer. Wood and filler are used to develop the shape. After you have the mould, 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.
Transoms can be made out of wood, foam, aluminium or other materials. Wood and fiberglass are the easiest to work with. Engine heights vary between 38-65 cm (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 fiberglass work well and are easy to build.
Gluing It All Together
After making the tub and hull, join together using fiberglass strips, making sure it is well reinforced. A 2cm (0.8 inch) door skin works well for side supports. Remember to leave 15 cm (6 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 90 metres (300 feet) underwater won’t win races, not to mention the hole in the back of your craft.
There must be enough flotation to support the complete craft in an upset: a minimum of one cubic metre (3 cubic feet). Most builders rely on attached foam or sealed air chambers. Use whichever suits your design, but be sure there is enough. Although fiberglass has been the mainstay of tub building for many years, the introduction of the140kg (350 lb) 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.
Some Helpful Hints When Handling Fibreglass
- 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.
- All moulds must be clean and smooth. Wax and PVA should be applied first to prevent fiberglass stick to moulds.
- 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 will 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 moulds prevents pinholes and adds to smoothness of finished pieces. Let it dry before applying glass.