For years I’ve wanted a solution that can provide real-time tracking for divers underwater, now we have a one. AIS is a marine radio positioning system that at is simplest, broadcasts a vessel’s GPS position for other to track. The system however can be leveraged to send the non-emergency position of other objects drifting in the ocean such as fishing nets, or in our case divers underwater. The signal is then received by the boat’s VHF radio and displayed on the chart plotter.
The conceptual solution is relatively simple; get a low cost Chinese fishing nets AIS beacon and attach it to an SMB that is deployable by divers drifting in the ocean. The problem until recently was putting this in a form factor that isn’t a burden to carry and/or use on deep technical dives. The issue we faced originally was finding a AIS electronics solution in the right form factor, most were large and didn’t suit small diameter pressure housing used underwater. Mounting the antenna in the vertical seam of the SMB was also presented problems (mostly reliability over time).
More recently, low cost and narrow form factor AIS beacons have appeared on the market. I recently took one of these, did some minor tweaks to the antenna, extending the wiring and folding it back on along the board to make it short. I knocked up a pressure rated housing and like magic you have an AIS enabled SMB.
Usage is simple…turn the unit on pre-dive, validate signal on boat plotter, seal canister and dive. Divers then launch the SMB from the bottom as per normal and when the SMB reaches the surface the GPS signal is sent to the boat. The advantage is that the boat gets an active position signal from divers that may have hours remaining to surface.
The solution isn’t perfect, with these issues:
- Range is yet to be tested and is likely compromised by the antenna being laid back against the battery and circuit board (versus sticking out the end on the OEM solution)
- Size of SMB seems to matter; I purposely used a small one for initial tests though I’m planning to upsize this. The smaller SMB too 6-9lbs of negative weight to get the SMB erect
- The AIS beacon I used doesn’t allow programming of MMSI and ping intervals
- The AIS beacon I used doesn’t seem to be available anymore online, though similar one is here and allows programming MMSI
For interest sake we also carry the Nautilus LifeLine and housing PLBs on deep drift deco dives, but both require the diver to surface which could be hours if initial traditional SMB are not sighted by the boat. We’ve done drift dives in up to 5kts of current which is problematic to say the least. The AIS SMB is simply another tool in the bag to ensure the boat reacquires divers promptly.
