Following call on Ch 65, watchkeeper located vessel with engine failure off Dawlish and advised HMCG of bearing etc. 3 POB. As requested by HMCG, asked vessel to communicate with HMCG on Ch 73. RIB Lunacy and MLI Thunder arrived on scene. Continued observation and listened in on communications between HMCG and rescue boats. Thunder towed casualty safely back to Exmouth.