INVESTIGATION

CASE 7
Damaged Butterfly Lets in Water
Narrative
A fisheries survey vessel sank while alongside
a marina berth. The vessel, a 17m long
aluminium catamaran, had two independent
engine rooms, each located in the port and
starboard side hulls. The vessel was unmanned
at the time of the accident.
When the vessel was salvaged it was noted that
there was water leaking into its port engine
room, through a ship side valve connected to
the port main engine exhaust system.
The vessel had undergone maintenance, carried
out by contractors in the week leading up to
the foundering. The crew had reported water
ingress and exhaust gas leaks in the port
side engine room. Contractors had attended
and had identified a defective section of
corrugated exhaust pipe connected to the port
main engine turbo charger. The decision was
taken to remove the defective section of pipe
(Figure 1) and to fabricate a new one at the
contractor’s workshop.
The vessel had a single butterfly ship side valve
that was connected to the exhaust piping by
a short section of rubber hose. The butterfly
valve was closed by the contractors and the
defective section of corrugated exhaust pipe
removed. The remaining exhaust pipe, still
connected to the butterfly valve by the rubber
hose, was secured by a rope that kept the open
end of the pipe above the waterline. There was
no water ingress at this time.
Crew from the vessel attended on the day
prior to the foundering and nothing amiss was
noted.
Clamped rubber coupling
Forward exhaust section: “T” piece
(removed for repair)
Mid-exhaust section
(secured by rope during repair)
Port main engine
Turbo chargers
Butterfly valve
Water level
Clamped rubber coupling
Hull
Figure 1: Port main engine exhaust
14
MAIB Safety Digest 1/2017