Camera Rig Buoyancy Fresh water vs. Salt Water ??

[Big Stig]

Buoyancy Question
My Rig is 5dmk2 in Ikelite housing with 2 ikeltie 161 strobes on ikelite arms. I have 4 of the buyoancy pucks added to the arms you can get from back scatter.
It still seems a bit to negative for me in fresh water whcih is all I have dove so far. (great lakes and quarries)
what impact should I expect in my first salt water dives in Cozumell shortly I dont want to waste the first few dives trying to get comfortable with the buoyancy.

thanks for any advise.
cheers SteveP

 

[Interceptor121]

You need to calculate the buoyancy of your set up in fresh water then add the physical weight this gives you the total lift
Multiply this for 1.027 and have the lift in salt water deduct the weight of the rig and that is the lift in salt water
Just physics
In short unless your set up is near to neutral 2.7% additional lift won't make any difference

 

[Kilili]

I find the following useful for making adjustments.

If your rig is already neutral or nearly so, you can simply weigh it all and multiply be 0.027.
That will give you the approximate additional lift going from fresh to salt water.

If your rig is negative, you can try estimating the perceived weight whilst underwater and subtract that from the actual weight. You can also attach to whole system to a fishing scale, and weigh it suspended in water. By also weighing it dry, you can derive buoyancy, and work from there.

My rig weighs more than 20 pounds so that's more than 8 extra ounces of lift.

Look at it this way, 20 pounds neutral means 20 pounds of lift. Multiply by 1.027 for salt water, and you have 20.54 pounds of lift. As actual weight does not change, that's 8+ more ounces of lift.

The small percentage can make a big difference, depending on the camera rig.

If you're fanatic like me, you can bring along some small fishing weights to adjust if the rig becomes slightly positive.

If someone thinks this is in error, I would certainly like to read a detailed explanation regarding such.

 

[Interceptor121]

You are saying the same thing I said except it is only valid if it is neutral which is never the case
Weight your rig in water with a luggage scale and you find out for sure with a small % error