End on Launching and Launching Calculations

Abstract

In order to ensure a safe launch, calculations are carried out to confirm that:

• 1. The vessel will not tip bow up about the after end of the ways. This requires that, once G has passed the way end, the moment of buoyancy about the way end always exceeds the moment of weight about the way end (see Figs. 1 and 7).

• 2. The maximum loads on the fore poppet (cradle) are sustainable both by the poppet structure and by the hull. If necessary internal shoring/temporary structure may be used to strengthen the hull locally. Max poppet load occurs at the point of stern lift where the moment of buoyancy about the fore poppet has risen to equal the moment of weight about the fore poppet (see Figs. 6 and 7).

• 3. The fore poppet load drops to zero before the fore poppet passes the way end. This is to ensure that the bow does not forcibly drop off the way end, possibly resulting in the bow pitching down onto the river bed with consequent structural damage (see Fig. 7). The fore poppet load $F = W - B$.

• 4. The vessel must remain statically stable, despite the load on the fore poppet, for the whole travel after the point at which the stern lifts. The least stable position is at the point of stern lift.

• 5. The pressures between the sliding and ground ways should be sustainable by the lubricating grease (see Fig. 2). This implies limitations on both the average pressure over the whole of the contact area and on the peak pressure (occurring at one end of the contact area).

• 6. The speed achieved during the launch must be controlled, and drag chains must be chosen to stop the vessel within the limits of safe travel defined usually by the width of the river.