springboard

Diving off a springboard

A springboard or diving board is used for diving and is a board that is itself a spring, i.e. a linear flex-spring, of the cantilever type.

Springboards are commonly fixed by a hinge at one end (so they can be flipped up when not in use), and the other end usually hangs over a swimming pool, with a point midway between the hinge and the end resting on an adjustable fulcrum.

Springboard materials

Modern springboards are made out of a single-piece extrusion of aircraft-grade aluminum. The Maxiflex Model B, the board used in all major competitive diving events,^{[citation needed]} is made out of such aluminum, and is heat treated for a yield strength of 50,000 psi. The slip-resistant surface of the board is created using an epoxy resin, finished with a laminate of flint silica and alumina in between the top coats of resin. This thermal-cured resin is aqua-colored to match the water of a clean pool.^[1]

Adjustment of the spring constant

Adjusting Fulcrum with foot prior to a dive

The spring constant of a springboard is usually adjusted by way of a fulcrum that is located approximately mid way along the springboard. Springboards are usually operated in a linear regime where they approximately obey Hooke's law. When loaded with a diver, the combination of the diver's approximately constant mass, and the constant stiffness of the spring(board) result in a resonance frequency that is adjustable by way of the spring constant (set by the fulcrum position). Since the resulting system is in an approximately linear regime, it may be modeled fairly accurately by a second order differential equation. Typically the resonance frequency can be adjusted over a range of a 2:1 or 3:1 ratio.

Counter-intuitive user-interface

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The fulcrum usually travels over a range of approximately 0.75 metre (30 inches), and is set by way of a knob that is approximately 0.35 m (14 inches) in diameter. To stiffen the spring (as if tightening it), the knob is usually turned counter clockwise. This is counter intuitive, since usually things are tightened by turning clockwise. Additionally, if standing on the springboard, it is difficult to push the wheel with the foot, because the top of it needs to turn the other way from the way it moves. This is because the gearlike mechanism (usually a "soft gear" made of rubber) is on the board and not the base, so the wheel pivots against the board when rotated. Thus users often need to bend down and set the wheel, or come down from the board to set the wheel. Thus it would be much better if the gearing were on the base so that the wheel could be pushed with the foot, but tradition (consistency from board to board) dictactes maintaining a "backwards" convention.

• Note - Standing behind or in front of the knob, rather than directly above it, will give you better leverage to move the fulcrum. This is accomplished by holding on to the hand rails and leaning the body a few degrees, then placing your foot as low as possible on the knob. In this way, it is possible to move even the most difficult fulcrum.

Heights of springboards

Three and One Metre Springboards

Springboards are usually located either 1.0 metre or 3.0 metres above the water surface. It is very seldom that one is mounted at a height other than these two standard heights. In olympic competition, only the springboards of height 3.0 metres are used.

Historical heights of springboards

Some years ago, springboards, usually made of wood, were located at heights of either 10 feet (approximately 3m), or 20 feet (approx. 6m), above the water.

Home springboards

After an incident in Washington state in 1993, most US and other pool builders are reluctant to equip a residential swimming pool with a diving springboard so home diving pools are much less common these days. In the incident, 14-year-old Shawn Meneely made a "suicide dive" (his hands at his sides - so his head hit the bottom first) in a private swimming pool and was seriously injured (tetraplegic). Family lawyer Fred Zeder successfully sued the diving board manufacturer, the pool builder, and the National Spa and Pool Institute over the inappropriate depth of the pool.^[2] The NSPI had specified a minimum depth of 7 ft 6 in (2.55m) which proved to be insufficient in the above case. The pool into which Meneelly dived was not constructed to the published standards. The standards had changed after the diving board was installed on the non-compliant pool by the homeowner. But the courts held that the pool "was close enough" to the standards to hold NSPI liable. The multi-million dollar lawsuit was eventually settled in 2001 for $6,600,000USD ($US8,000,000 after interest was added) in favor of the plaintiff. ^[3] The NSPI was held to be liable, and was financially strained by the case. It filed twice for Chapter 11 bankruptcy protection and was successfully reorganized into a new swimming pool industry association.^[2]

References