Q: How to calculate and choose the right floating arm without getting wet

[coralgirl]

Hi All,
I want to buy a set of floating arm for my Nauticam Sony Rx100 housing, I have 2x Sea&Sea D1 strobes, 1x Gopro, 1x Soloa photo light and 1x inon macro wetlens mounted on I-das S type tray. I would like to know which float arm I should buy. I am thinking to get a pair of Inon Mega float size S, it has Buoyancy of -390 g/-13.8 oz but I am afraid it is too much and it will float to the surface. I want to have the buoyancy of the rig on neutral or slight positive. How do I measure it? Should I weight everything and subtract it by (2 x -390g/-13.8 oz)?

I cannot try it on the pool, the store does not let you try it on.

 

[3D diver]

Here's a cheaper alternative to the commercial floats:

DIY Underwater Camera Floats & Strobe Arm Floats
DIVINYCELL FOAM PVC from Aircraft Spruce

Dry weight - buoyancy of float, neglecting buoyancy of your existing gear, will yield a buoyant rig...but that's more-or-less what I did when I made my floats. I made a pair of floats that I expected to be net negative and was surprised to find the rig just about neutral.

The first link above shows how to use a tub of water and scale to check the weight of your rig in water (the rubber maid method in step 1).

I document my float DIY in post 104 here:

http://www.scubaboard.com/forums/gopro-video/425784-my-gopro-3d-setup-11.html

 

[Interceptor121]

You can also buy separate floats as not in all countries sell the divynilcell to the public
Most of the items you mention have a declared buoyancy from the manufacturer
The nauticam with sony in is -170 grams
You can buy everyone and the weight it in your bathtub with a luggage scale and then calculate what you need
Sola are around 90 grams the tray and handle probably around 200 grams gopro another 100 negative etc