Reader Feedback: Lander Lab - Buoyancy
Thanks to the' Landereans' who replied to the article “BUOYANCY!”, in the May/June 2022 issue of MTR (Vol. 65, No. 4). There have been some very interesting follow-on conversations:
LIQUID SYNTACTIC
Kevin Ulmer, nU-Boats LLC:
“Enjoyed your article on buoyancy in the latest Marine Technology News. Your idea of glass micro balloons suspended in liquid exists as "pumpable buoyancy" from the Aubin Group. https://www.aubingroup.com/products/renewables/pumpable-buoyancy/
“I’m developing what I call “enhanced” liquid syntactics with different depth ratings, densities, simplified formulation and ability to cross-link in place. Aubin developed their “pumpable buoyancy” for a very specific application in the offshore oil & gas industry but there are many other applications for such material as you might well imagine.
“Keep up the great work!”
From Kevin Hardy:
I really like the idea of pumping positive buoyancy rather than negative buoyancy for trim. You probably recall the 1960's approach of pumping mercury ballast around. Yikes! Argo floats use the idea of variable displacement by pumping oil across a bulkhead to create buoyancy. The idea is that the displaced volume changes while the net mass remains the same, thereby changing density to some value greater or less than 1. It would take a smaller volume and less energy if the material were a "liquid syntactic” with a lower specific gravity, as you coin the term.
As one suggestion for your application, I use mineral oil (baby oil) for a number of p-comp applications. It has a specific gravity of 0.845-0.905, and is about as benign an oil as you can find.
From Kevin Ulmer:
“Yes, I think the version of Alvin I dove in back in the early 70’s used mercury as did Cousteau’s diving saucer.
“I’m very familiar with buoyancy engines and will be using those in my nU-Ray glider.
“3M offers a range of "glass bubbles" as they like to call them with different pressure ratings. One of the components you could vary in the liquid syntactic formulation.”
COMPRESSED AIR BUOYANCY SYSTEMS
From Capt. Charles MacVean (USN, retired):
Kevin, I read with interest your article on Buoyancy. I noticed that you spent a vast majority of the article on rigid or non-compressible buoyancy materials and systems, and little on compressible flotation systems. I know you have experience with both compressed gas compensation and flotation systems, and have amassed a body of work on these non-rigid systems. Perhaps you could use that scientific evidence and field experience to substantiate the attractiveness of compressed gas as a shallow water alternative to rigid flotation systems.
Your next article could be greatly enhanced if you included some pictures of the “soft systems”. Such an article would be a real hoot.
Keep up the good work,
Charlie
From Kevin Hardy:
Thanks for the comments, Charlie. Yes, I focused more on deep water than shallow, and skipped over the use of compressed gas systems for buoyancy. Ultimately, Boyle’s Law (P1V1 = P2V2) determines the useful depth of a compressed gas system for buoyancy. That said, the shelf break of the continental shelf is nominally 100-200m, where pressures are just 10-20 bar. The compressed systems developed for that zone could be shown in a dedicated column “BUOYANCY, Part 2. I read an interesting paper on a buoyancy engine that exploits the volume and pressure changes accompanying the reversible electrochemical interconversion of water to hydrogen and oxygen gases, providing soft VB displacement for subsea vehicles. That description also suggests it can supply breathing oxygen for a manned system as well. We’d have to look closely at the energy requirements of said system. Gaseous CO2 liquifies at a pressure of just 5.2 bar (74psi) between a temperature range of -56°C (-69°F) and 31°C (87°F), so that could be used near-surface from a pressurized liquid CO2 source. Also see RC Shipyard