Jackie Wu Ming-chuen has not actually found any sunken treasure, but he knows it is down there in the depths.
He has caught glimpses of artefacts that were just out of reach.
Mr Wu co-founded the Hong Kong Underwater Archaeological Association with Johny Lee in 2006.
After doing numerous diving courses, the Hong Kong duo realised that rather than frolicking with fish and sea turtles, they wanted to scour the ocean depths and unveil its secrets.
'We started out diving just for fun in Hong Kong, then later we went overseas and we wanted to go deeper,' says Mr Wu.
'The deepest we could go was about 40 metres, but we heard it was possible to deep-sea dive down to 55 metres, so we took lessons in Sipadan [in the Philippines].'
As they worked their way through a series of advanced training courses in deep diving, they found it requires very specific skills and equipment. Mr Wu says being aware of time is crucial, and divers should have very clear minds to make the right decisions - a wrong one could be fatal.
'We started doing underwater archaeological exploration in 2006 ... and that's when we set up our association.'
According to the two divers, the deeper you go the more equipment you have to use, such as tanks with different combinations of oxygen and helium to avoid decompression sickness when going back up to the surface.
Sunken boats are often deep in the sea, and very specific diving skills are needed.
Mr Wu says a detailed diving plan has to be made on a plastic note pad (right) and attached to his arm when they dive. The diving plan includes information such as when to make safety stops to release pressure when going up to the surface.
The plan is also useful for other reasons. 'After we started, we realised we had a lot to learn, such as how to record the location of a site,' Mr Wu says.
As a result, they invited underwater archaeological experts from Australia to come to Hong Kong to give them lessons so they can become more professional.
Mr Wu and Mr Lee say exploring sunken boats or sites that have never been discovered is exciting, but it has to be done responsibly to protect items of archaeological importance from being damaged. And hopefully, one day they will be able to reach the artefacts in the depths of the ocean.