deco bars

[lermontov]

im about to embark on making some deco bars using 1.8m wide PVC tubes and rope and looking at hanging on some surface buoys anyone been down this track ? what size buoys would you recommend

 

[Russjstewart]

I suppose the question is how negatively buoyant are the divers on the deco bar. A 30cm tear drop bouy / fender has a volume of 6.1 litres, giving about 6.25 kg of bouyancy

Boat Fenders - Polyform US

A 30 cm solid foam float has 15.2 kg of bouyancy
[URL='http://allfloatsaustralia.com.au/high_density_float.html']http://allfloatsaustralia.com.au/high_density_float.html[/URL]

Add in the weight you will need to keep the deco bar hanging down before the divers reach it, and you should be able to arrive at a figure.

 

[Edward3c]

Another question: Will PVC be negative enough in water to stay in position at the required depth?

 

[Russjstewart]

According to https://www.rinkerpipe.com/TechnicalInfo/files/InfoBriefs/IS402PipeBuoyancy.pdf. PVC has a specific gravity of 1.38 meaning it should sink in salt water, assuming it is open at both ends, but I have no idea how long it would take to get to the required depth, or how stable it would be. How rigid or strong the pipe would be is another question.

 

[Barnaby'sDad]

Another question: Will PVC be negative enough in water to stay in position at the required depth?

The PVC/bar position in the water column will vary based upon the buoyancy of the diver hanging off the bar. If the diver is positive...it’ll rise. Neutral...it’ll stay put. Negative...it’ll sink.

That being said...in the absence of a diver, if you have the buoy, weight, and bar rigged up properly the bar/PVC should maintain its depth. I have to admit that I was curious about this the first time I used a PVC “deco” bar, but in my case...it worked as expected.

 

[The Chairman]

Deco bars are usually hung from a boat, so the weight of the bar should be heavy enough to not float with the vagaries of current or surge.

 

[tbone1004]

im about to embark on making some deco bars using 1.8m wide PVC tubes and rope and looking at hanging on some surface buoys anyone been down this track ? what size buoys would you recommend

What are you making the deco bars for? Off of boats? Multiple depths or just the final stop?

Have you considered something like below where you don't have to deal with PVC and it's easier to stow?

 

[Edward3c]

Deco bars are usually hung from a boat, so the weight of the bar should be heavy enough to not float with the vagaries of current or surge.

In the UK they are normally attached to the shotline and unclipped to float free when all divers are present. I wouldn't want to be fighting a 4+knot current whilst doing deco (the Hespania comes to mind).

 

[cathal]

Metal/steel pipe (possibly aluminium?) is all I've ever seen used in salt water tbh. Its negative weight helps stabilise it in current and heave.

 

[The Chairman]

We do that all the time using SMBs. Deco bars are usually decorated with air or oxygen from topside.