Sounds like Cybele and Cyrus, aka the 'Stirling Craft', there's a picture of part of the framework in Ian Buxton's 'Diary of a Wartime Navy Constructor', but it doesn't really give you an impression of their overall structure. Goodall was very obviously not a fan of either them or Director of Torpedo and Mining.
"German pressure mines laid in shallow water were a threat that could not be countered with conventional minesweeping gear. The Stirling craft was developed in great secrecy as a counter, 360ft long, 60ft broad and 30ft deep. This lattice structure with buoyancy chambers was to be towed over suspected mines, which if detonated would dissipate much of their force through the open structure. Denny erected Cybele seen here at Dumbarton from material fabricated by Arrol and Motherwell Bridge, launching on 16 November 1943. She and her sister Cyrus from Swan Hunter were deployed in Seine Bay after the D-Day landings. (© National Maritime Museum, London G11240)
Buxton, Ian. Diary of a Wartime Naval Constructor: Sir Stanley Goodall (p. 156). Seaforth Publishing. Kindle Edition. "