Coastal boulder deposits accumulate above high tide, emplaced by high-energy wave events. They include megagravel weighing >600 t close to sea level, 100 t up to about 12 m above high water, and 3 t boulders up to 51 m. How these clasts are transported, and how they are deposited to form imbricated, stacked boulder ridges, remain open questions. Field observations of the process are difficult because transport events are rare and unpredictable (plus they occur during dangerous storms). To complement numerical approaches being implemented by the Dias group here at UCD, we carried out scaled, force-balanced experiments at Queen's University Belfast, where we built a 1:100 model in a laboratory wave tank. The majority of boulder displacements were caused by a small subset of incident waves. Interestingly, the largest waves are not necessarily the most effective: instead, wave-front steepness just before cliff impact seems to determine whether a strong cross-platform flow will develop. The most powerful bores were generated by waves that approached the cliff unbroken, and had a front slope angle in the range 15°-25°. These waves moved very large boulders, with masses in excess of those predicted by existing hydrodynamic equations. This demonstrates that equations often used to analyze coastal boulder deposits in fact do not accurately hind-cast the wave conditions required for megagravel transport.