| Sorry Nigel - being new at model boating myself I thought everyone knew the abreviations - yep it's a watertight compartment (pictured above) The front end cap is glued to the compartment, the rear one has a tray containing the RX, servos motor and stern tube etc glued to it then the whole thing slides into the WTC. and is fastened in. In this case it's by a threaded rod on the end of the tray which pokes through the front cap and is tightened up with a long threaded tube. On my two pictures you can see the propshaft sticking out of the rear and the long threaded nut sticking out of the front. Hope that's clear mate.
Ian |