Hi all, I want to start doing blackwater diving in my hometown, we have the proper boat and the lights, but I'm not sure how to organize the lights line. We are planning to go to a site almost 100 metres depth and place a line with a big buoy on top, 25 meters long line with weights on the other end, and with an arm 75 cm long with a powerful light on each end every 5 meters. Our plan is to leave the line in the sea for a while and dive with the boat skipper following us close enough to take care of ourselves. Do you think is the right way ? or am I missing something ? It's our first time doing blackwater diving

Depth is a relative and non-essential factor; instead, you need to study the seafloor topography of the area where you plan to dive. The 75 cm arm is unnecessary. Dive lights must be securely fastened to the buoy line, using one of the many available solutions. Furthermore, for your safety, it is crucial to check the currents at the dive site: it is easy to get lost if there is a current, especially when you are focused on taking photos after finding a subject. The buoy must be highly visible, even if a skipper is following you. Always carry backup lights with you. Overly powerful lights are not necessarily important: 5000-7000 lumens are more than enough. Finally, make sure the battery life is sufficient to last the entire dive.

Yes, totally agree with studying seafloor topography.
Also, one way to prepare for BW it is to go during the day and look for current-lines on the surface - scout an area with interesting topography, and go check it out during the day, looking for areas that concentrate plankton - clear surface current lines and debris agglomerations can be a good indicator, even during the day.
Always take GPS points (Navionics or similar app for instance) so you can return to points.

Once you find a place that looks promising can then go in with a mask and snorkel and see how it looks, or even do a bluewater dive to scout it. There can be lots of interesting subjects during the day, just more difficult to spot and shoot.

On the downline, read this article if you haven't: https://codelift-managed.xray-mag.com/content/getting-blackwater
It has a clear illustration of Mike Bartick's downline assembly:




I've recently returned from an assignement assisting a Japanese blackwater photographer in the Maldives. Technically, we scouted offshore locations during the day, and did bluewater dives to confirm, and dived the most promising ones at night.

The downline didn't have a pumpkin, but a smaller fishing buoy, into which a 2m flagpole with a flag was inserted. It was well balanced so the flagpole stayed upright, and we had a small coloured flasher light on the the flag to help the boat follow it at night.
This buoy + mast unit was attached to a secondary white fishing buoy about a little smaller than a football (volleyball size?) to which the downline was connected

Be careful with the size of the buoy you use for the downline - a bigger buoy is more visible but can drift faster as it catches wind and acts like a sail - you don't want it to drift faster than the divers. The flagpole helped minimize buoy size while staying visible even if it's a little choppy.
You also don't need a lot of weight on the line either, we used two kg or so and it was fine.

Our line didn't use powerful lights, but they were setup as twin sets. We also had pairs of flashers (strong flashing lights, 3000 lm each) near the surface and on the line itself for visibility.
On bluewater dives we ony used the pairs of 3000 lm flashers on the line (be careful, it's more easy to lose sight of the line on a bluewater dive than blackwater).
We also tied small flasher lights on the tank valves at night for visibility, and used our strong narrow beam spotting lights to shoot a line signal in the sky on surface for pickups.

At the end of the dive, it's nice to mark the GPS location so you can check how much you've drifted and in what general direction (can be complex) - for us it ranged from a 300m to 8km drift on a single dive.

hope this helps!

cheers

Edited 34 minutes ago34 min by bghazzal