Thanks for the positive comments, my Dad is doing a fantastic job at the moment soldering the torpedo trough side bracket to a bolt to make it removeable!
Hi Derek
To answer your question I have drawn a diagram to explain how it works and keeps the water out.
The black lines indicate solid brass,
the yellow area is a solid brass rod,
the red line is the seal,
any blue area is solder,
the pinky purple areas are the rudder arms,
and the green dotted line is the slot out of the stern so imagine that the picture is looking forward toward the bows.
My Dad drilled a 4mm hole into the upper and lower brass plate and soldered a brass tube with a internal diameter of 4mm on to the lower plate. The brass tube was sealed with a thin piece of brass which was soldered and filed.
The lower rudder arm was soldered to the 4mm brass rod. Two short lengths of brass box were soldered to the lower brass plate. The upper rudder arm was soldered to a collet to allow for any adjustment when connecting up to the servo. The upper brass plate is clamped on to the brass box section with a silicon seal and held in place with four self tapping screws. The upper rudder arm with the collet is then attached to the the protruding 4mm rod which allows the movement of the lower rudder arm. The entire moving parts are sealed within ' a brass box'. The brass box is pushed into the stern bulkhead and sealed with superglue and more silicon. So no water can leak into the hull because the entire contraption is sealed.
Hope this helps.
Regards
Nick B