Underwater Set Construction

Designers of underwater film sets draw on the skills of boat builders and marine engineers

When designing and building film sets or set pieces to be used underwater Set Designers and Construction Coordinators are aware of two very important qualities of water.

 1.      Water is the universal solvent.    Many set construction materials (i.e. glue, paints, etc) dissolve or breakdown in water. In addition there is electrolysis, oxidation (rust), and chemical reactions with common pool chemicals to consider.  

2.     Water is very dense.    Think of water density as the 'battle of bouyancy'. Fresh water weighs 62 lbs per cubic foot. If the set components are lighter than 62 lbs per cubic foot they will float. Objects with a density equal to water (62 lbs/cu ft) will be neutrally bouyant. Anything denser than 62 lbs per cubic foot will sink.  Bouyancy relates to weight and volume. Force is required to counteract the effects of bouyancy. That Styrofoam rock that looks so convincing on a typical set will look silly underwater if it needs three weight belts to keep it on the bottom of the pool.

Underwater sets are not usually intended to be underwater for more than a couple of days but that is more than enough time for the set to begin to come apart or leech chemicals into the water. Poorly built sets will come apart before filming is finished. Really bad sets will fail before the camera gets in the water. Choosing the wrong set construction materials, glues, and paints will have an impact on water quality and visibility. It could become very hard to get a good shot if the water is full of paint flecks from a disintegrating set. 

It is not only the set that could affect water quality. Special effects rigs of all kinds must also be made of materials that can handle the marine environment. Aluminum and lexan are preferable to steel and wood. Stainless steel or galvanized bolts are the way to go. All hydraulic hoses and rams must be completely leak-free and clean before going in the water.

Underwater set dressing must also follow the underwater rules. Fasten everything more solidly if it is going underwater. Hot glue guns should stay in your tool box, or even better on the store shelf! Use the proper glue for the material you are putting together. 

Use products intended for marine use if you want to be certain that the set will stay together. Marine-grade plywood will last longer than ordinary plywood. Screws will loose holding power the longer the wood is underwater. Use bolts as fasteners where strength is required. All iron or steel used underwater must either be galvanized or painted with marine-grade paint to protect it from rusting. Be sure to paint all steel including the inside walls of pipe or HSS square steel tubing.  Ordinary pool chemicals accelerate the formation of rust. Too much rust could  cloud the water and affect the shot. 

Marine-grade paints will not come off when they get wet. Paints intended for boat hulls or swimming pools are ideal. Allow plenty of time for all paints to properly cure before immersing the set in the water. Gelcoat on fiber-reinforced composite materials is inert underwater and will last indefinitely. 

Scaffolding used underwater must be powder-coated aluminum and/or galvanized steel. Galvanized perforated metal decks are the only type of scaffold decks to use underwater since wooden decks will float even before air bubbles from divers get trapped underneath. Scaffold castors should be as new as possible. Tape the rubber wheels with duct tape to prevent black rubber scuff marks on the pool bottom. Paint all shiny scaffold components with flat black marine paint to hide scaffold in background. Fasten black rubberized carpet to scaffold decks for actor barefoot safety. 

  Buoyancy is a big factor to consider in set design and construction. A set that looks great in the shop could become a disaster in the filming tank after the water is added. If made out of wood, the set must be either bolted to the floor or weighed down with concrete, iron or lead. Fake rocks should be made from fiberglass or gunnite or some other material that is not buoyant in the water. 

Cars are commonly filmed underwater as the classic 'car-overboard-people-trapped' scenes. Gas tanks, engines, batteries, cooling/heating systems, transmissions, differentials, and brake systems must be removed before vehicle is steam cleaned for underwater work. All traces of mechanical fluids, oils, and greases must be removed from the car. Securely fastened blocks of styrofoam strategically hidden throughout the car make it more manageable for the underwater grips. Doors and windshields need to be easily removable underwater. Seat belts must be cut off and held lightly together with velcro if talent are to be filmed trapped and struggling with their seat belt.

When lifting or hoisting large heavy items such as cars out of the water make sure you allow water to drain so you are not lifting too much unnecessary weight. Seats and other components could retain a lot of water so keep the extra weight in mind when calculating loading of the lifting rigs.  

Density of Common Materials

          Material                          Lbs per Cubic Foot

          Aluminum                        169

          Brick                               125 – 150  

          Bronze                              509

          Cedar, Western Red          23 - 27

          Cement                             193  

          Cement - Portland              94

          Coal                                  56

          Concrete                          137 - 150

          Douglas Fir                     30 - 38  

          Gasoline                           42

          Glass                                162

          Granite                            165 – 172  

          Gravel                              110

          Iron, cast gray                439 – 445

          Iron, wrought                  487 – 493

          Iron, slag                        168

          Lead                                687  

          Limestone                         165

          Oak                                 50

          Oil                                   58

          Paper                                58

          Paraffin                           54 – 57

          Phenolic plastic, cast         79 – 82

          Pine                                 25 - 34

          Plastic, styrene                66

          Plastic, vinyl                    87

          Polyethylene                    57  

          Rubber                            94

          Sand, dry                        100

          Stainless steel                 510  

          Steel                               490

          Stone, plain                      144

          Water                             62.5

          Zinc                                443

From "Backstage Handbook" by Paul Carter. ISBN 0-911747-39-7. Broadway Press. Louisville, Kentucky 1994