poppet

A poppet is a vertical timber or post erected on the bilge ways of a ship launching slipway to support and guide the vessel as it moves down the incline toward the water. During construction and before launch, the ship rests on these wooden uprights; as the launch sequence begins, they hold the hull in position while being gradually withdrawn or allowed to fall away, permitting the vessel to slide freely into the sea.

Poppets are typically hewn from hardwood such as oak and positioned at intervals along both sides of the ways. Each poppet bears directly against the turn of the bilge, the curved section of the hull where the vertical side begins to angle inward toward the keel. They must be tall enough to support the dead weight of the partially built or fully laden ship, and strong enough to withstand the immense crushing forces involved. A large vessel may require dozens of poppets spaced several feet apart.

Mechanics of withdrawal

The removal or collapse of poppets follows a precise sequence during launch. Some designs use a hinged or pivoted base so the poppet can be knocked away or deliberately toppled as the ship begins its descent. Others are simply extracted by mechanical means or allowed to drop clear as the hull moves forward and upward relative to the fixed ways. Timing is critical: premature removal will cause the ship to slip uncontrollably, while delayed removal will jam the launching mechanism and damage both ship and infrastructure.

The term poppet derives from an older sense meaning a small doll or puppet, likely referring to the timber's upright, figure-like appearance. In other contexts within the trades, poppet also denotes a small moving valve in an engine or hydraulic system, though the shipyard usage predates this mechanical meaning by centuries. The word remains standard in shipyards wherever wooden launch systems are still employed, though modern steel and concrete launching facilities may use alternative support structures.