Just a thought, provoked by this thread, but didn't the first new Upholder boat have a problem with the bow and rear door interlocks at first? We all said weÂ´d not be too impresed going to sea in them!
The Thetis clip, always called that whatever Pusser had to say about it consisted of a simple screw bolt with a large eye nut on the end. See any current display O Boat, all have them fitted. After the test cock and reamer had been used and the main rear door clip opened the Thetis clip was unscrewed after a certain distance which would have allowed any flooding water to enter if present the screw bolt was swung up allowing the rear door to be opened. If the tube was flooded it was a simple job to insert an iron bar into the eye nut and screw it closed and shut the rear door.
These were not fitted until after this accident and specifically to prevent it happening ever again.
I hope that makes sense to the readers who do not understand what the clip actually did.
The 'Test Cock and Locking Bolt' is the correct terminology fella's and what you are referring to as the 'Thetis' clip was actually called the Safety Swing Bolt.
The test cock was pulled half way up and the reamer was used. If tested dry you would pull it all the way and the locking bolt will move out of the way of the tube locking ring. You would then open the tube by turning the ring. The safety swing bolt would be loosened but could not swing aside as there was a collar on the bolt which meant you couldn't fully open the door until you had cracked the seal. If ,of course, the tube was flooded you would know by now and shut the rear door. 8)