Investigations into problems with fuel systems on board the Navy's new $550 million fleet of Armidale class patrol boats are continuing.
Five of the six patrol boats have been docked in Darwin since the Maritime Commander announced the safety concern five days ago.
A Navy contractor in charge of implementing the fleet has been organizing the investigations.
According to a spokeman, there have been four unexplained engine failures.
The faulty engine parts arrived in Sydney today and engineers have only just started to examine them.