Fin Buoyancy. How is it determined?

[Litefoot]

I dive Avanti Quattros which, if I'm not mistaken, are neutrally buoyant. This past weekend, on a freshwater dive, one side of a heel strap popped off when I jumped off the back of the boat. I didn't rush to go after the fin, instead opting to open the adjustments on my seconds (which I close down to prevent free flow when giant-striding into the water). When I looked up, the fin was gone. I found it at 33' on the bottom in some very low viz water. Thank goodness it was bright yellow. Are buoyancy characteristics of fins determined in salt water? The Avanti's sank pretty fast.

 

[iliketopetsharks]

Determining the buoyancy is relatively simple: Weight of the object vs weight of the displaced fluid.
If it sinks in fresh water, it might float in (heavier) salt water.
I'm not sure if fin producers put a lot of thought in the buoyancy of their products though...

 

[clownfishsydney]

Old Avanti Quattros sink in saltwater. Will certainly sink in freshwater.

 

[Truefin]

To determine buoyancy of fins in ocean water, typically mix aquarium salts with fresh water in a full garbage can to bring the specific gravity to 1.025, and measure the water salinity with a glass floating hydrometer, and then the fin is suspended with fishing line from a hook while weighing the fin in the salt water. This scale has a hook underneath it to weigh objects hanging from the scale hook. In this case the measurement taken was negative 0.485 ounces (Truefin, large, no heel strap).

 

[Nemrod]

Another way to do it. Fill an ice chest or tub (large enough to submerge the complete fin) to the brim with water and then place a pan under the tub to collect the over flow. Weigh the fin, weigh the displaced water. If the water weighs less, the fin is negative, if more then it is positive and if the same it is neutral. Yes, yes, some basic math can accommodate a calculation for the seawater difference due to salinity without pouring salt all over the place and making an even bigger mess..