Thin wall vs. thick wall lexan tubes

[chuck chesney]

I have been running my subs for years using thick wall (1/8 inch) lexan tubes for the various WTC compartments, but am interested in the real world strength of thin wall (1/16 inch) tubes . My boats rarely dive deeper than five or six feet, but I'm still not sure if the thin walled lexan is safe to use. They would be used primarily for the battery and ballast tank compartments.
After years of successful use, I am interested in repacing the RCAB-R system with a dispalcement ballast system similar to the SubTech/Mikes subworks types...low pressure, moderate speed bi-directional pump.
I know that all sub model drivers are, by nature, tinkerers, so I'll bet that a number of you folks have tried the 1/16 lexan. Your thoughts and experieces would be very much appreciated. Thanks in advance.

[Guest]

Re: Thin wall vs. thick wall lexan tubes

Lexan won't break at the thinner thicknesses- it's incredibly tough. Might get a bit squishy at larger diametere though.

If you're using a ballast system which pressurizes the cylinder (e.g. a piston tank) this will help the cylinder walls maintain ridigity. If not, you could pump in a few shots of air from bicycle pump. The end caps will have to be secured though for obvious reasons!

[chuck chesney]

Re: Thin wall vs. thick wall lexan tubes

Andy....Thank you, sir. The maximum size Lexan tube for the ballast tank would be about 3 Inch O.D., and with the vented, positive displacement ballast system, there would be very little pressure in the ballast tank...none when submerged. The battery holder tubes would be 1.25 I.D, just large enough to hold some "D" cell Nimh batteries in series.
Thanks again for your usual great input.
Chuck

[Guest]

Re: Thin wall vs. thick wall lexan tubes

3" diameter may be a little too large for 1/16" wall thickness, I was thinking maybe 2-2.5" maximum. But give it a go, it may be fine.

[stuartl]

Re: Thin wall vs. thick wall lexan tubes

If the pressures are being applied evenly then it won't wobble too much. If it's under pressure (compression or tension) it's going to prefer its natural circular cross section as the most even way of distributing that pressure. How about going for the thinner tube but cutting some ply struts to wrap around it or insert into it at intervals (maybe 2-3" apart)?

[chuck chesney]

Re: Thin wall vs. thick wall lexan tubes

Thanks guys. The notion of circular reinforcements in the ballast tank is a good one. They could serve a double purpose and be modified slightly to serve as slosh reducing baffles. Of course, the ballast tank can always be reduced to 2.5 inches and simply made a little longer...problem solved.
With the positive displacement pump type systems like the SubTech/Mikes Subworks, or a snort type, there is very little pressure on the tanks because the tank is essentialy empty when surfaced, maybe only an inch or so underwater, and filled entirely when submerged. The boat has to be at, or almost at, the surface to empty and fill the tank, with the air intake/outlet vent tube (ie. periscope) poking above the surface. They result in subs that are not true static divers, but are VERY close, with the added safety feature of being just slightly positive in terms of buoyancy in the event of power failure.
For the high cost stuff...the electronics and motor, I will continue to use the thick walled polycarbonate. I have a tendancy to build all of my boats, both subs and surface, more like locomotives than aircraft. Better safe than sorry.
Thanks to both of you, again.
Chuck