Bob wants to go YARD next, and I agree. YARDs are meant to be green (and many are). Charriu, thoughts on YARD?
I'm not sold on DRAGON. They can be green, but are at least as likely to be red, black or gold. "Green DRAGON" does bring an image to mind, though, so I can see guessing this fourth...
Unless Bob, Amicalola, you want to switch to TRAIN? Trains are unambiguously a greener alternative to cars or planes.
SCUBA DIVERs need to control their buoyancy through a piece of equipment. There might be SEALs and valves involved? There's also a piece of equipment called a diving BELL used to move divers up and down from the surface.
The other kind of SEAL, the animal, uses blubber to stay buoyant.
There's a lot of buoyant PLASTIC trash out there in the ocean.
You can measure buoyancy by immersing an object attached to a spring SCALE.
I'd feel comfortable with SCUBA DIVER > SEAL > PLASTIC.
A SCUBA DIVER is Bouyant - they need weights to counteract this.
I believe a SEAL is also Bouyant because of their blubber.
PLASTIC pretty much always floats - and the volume of it doing so in the sea is a matter of current discussion.
I don't know if every NUT floats, but some (coconuts?) definitely can travel a long distance in the sea.
By contrast, I'd say a diving BELL is not bouyant, being something that sinks to the sea floor. However, the more I think about it, the more I think that at least some designs must be - again, don't they have releasable weights to counteract this. Hmm. I still feel that Thrawn is trying to avoid the link between DIVER and BELL with this clue.
SCUBA DIVER > SEAL > PLASTIC > NUT
It may have looked easy, but that is because it was done correctly - Brian Moore
SEAL and SCUBA DIVER seem pretty certain.
Many Bouys feature a BELL.
PLASTIC is usually buoyant, e.g. the great trash island in the Pacific.
Palm trees spread from island to island via their floating NUTs.
A SLIP is another name for a dock, which is frequently built on bouyant material.
Floating BOMBs can be used to attack ships in harbor?
Bouyant can also mean happy-go-lucky, but the connections there seem pretty forced: AUSTRALIAN because they're stereotypically happy chappies? Drag QUEENs?
Top choices, in order of preference: SEAL, SCUBA DIVER, BELL, PLASTIC.
Post spoilers: hmm, shallow_thought makes a good point about diving BELLs being the opposite of buoyant, although I still have the image in my mind of a bouy with a ringing BELL.
Reverse engineering: maybe Porthole would work for SEAL, SCUBA DIVER, PLASTIC, NUT? In addition to the animal, a SEAL is a US Navy special forces member, so they could easily be on a ship or submersible.
Train is interesting and a maybe, but I like yard better.
