How many floats do you need?

How many floats do you need to make a housing buoyant? My particular set up is...

5d mark 3

Ikelite housing

2 ikelite ds125 strobes

Focusing light

Video,light

4 8 inch ultralight strobe arms

Is there some formula or rule of thumb to determine how many floats to add?

The formula is you have to determine how negative buoyant you rig is and then calculate the number of floats you will need. in my experience you will need to fill the strobe arms with large stix floats and it will be close but I would also buy a pack of jumbo stix floats also as I don't think that the large will be enough to make it float. It also will depend on whether or not you have the new handles with the red rings on them. my rig has 11 large floats and two jumbo floats and it close to neutral. You can see it here http://uwcamerastuff.com/dyi_lift_handle.htm and the difference the new lighter weight handle makes is available here: http://uwcamerastuff.com/dyi_lift_handle.htm the old handle weighs 2lb 5oz and the new one weighs 1lb 12oz. I think you should experiment and adjust it to your liking but that should give you a starting point. Also be aware that the buoyancy in fresh water will be different than in salt water.

Which port Matt? A big dome will provide more flotation than a macro port, etc.

Steve

100mm and 50mm ports

I have some special, Italian floats on my D800 rig and i went with the try and error system to have the rig neutral.

As Steve said, there will be a difference between your dome and macromport so i found the - for me - practical solution

that i add approx 200 grams of lead on my handles when i use the mini dome port, 400 grams when i use the big dome port

and none when i use the macro port.
I fine tune my housing so perfect that i can just put it in front of me and it hovers there, this sometimes comes handy when

i need my hands free for something, but i use the rope from the handle to avoid that she floats away.
Chris

Just buy a bit more than you think you need..

Then simply just try it out!