The 8000m dive went very well. Not an unqualified success, since the manip was balky and my push core sediment sample washed out on ascent because the sample door wouldn’t stow all the way, and because of the speed of the flow over the vehicle on ascent (5 knots average). But overall the vehicle performed like a champ. Plenty of power, and even though I lost one thruster, I still had 11 left, so the massive-redundancy approach worked. I never lost functionality. All lights and cameras worked. Sonar was balky… that’s going to need some work.
Bottom time close to 5 hours, range of exploration about 1.5 km horizontal, and about 300m vertical along the trench wall, which was like the Grand Canyon, vertical faces interspersed with angled scree slopes. Dramatic terrain.
The ponded sediment in the center of the trench was the finest I’ve ever seen. When the thrust-wash just barely kissed it, it formed silken veils undulating across the bottom, and then it would rise and hang in tendrils like ectoplasm. Not at all like the typical turbidite plains of abyssal depths. Where I dove the basin of ponded sediment was 1.5 km across, flat as a billiard table, and virtually featureless. It actually ended at a well-defined “beach” where the normal rocks and sediment commenced, terracing upward to the fault scarps. I explored up the scarps onto a plateau.
The small exposed rock faces had large communities of white anemones about 1 foot long. Hanging gardens. It was a completely distinct micro-habitat from the flat basin.
Out on the plain the dominant fauna were 1′ diameter jellies that would lie on the bottom or swim about 2 meters up. When disturbed they would fly off the bottom. There also were large numbers of amphipods in all sizes. The baited lander captured images of incredible aggregations, including individuals close to a foot long. I tried but was unable to rendezvous with the lander because the sonar was not cooperating. Normally the lander is a very bright target, and it should have been easy to find on that flat plan. But without sonar, nor accurate coordinates from the surface, it was a visual search, which is very limited. It might have been 50 meters to my left and I went right by it. I could have done an expanding-square search pattern, but I decided it wasn’t the best use of my power, when there was real exploring to do.
Actual deepest depth for the dive was 26,791′ (8221m). Initial descent speed was 4.5 knots, attenuating near the bottom to about 1.5 kt, before I trimmed neutral with a few small shot dumps totalling about 50lbs. I drove the final 100m down on thrust, very slowly (because I didn’t trust my altimeter yet… we’d just met and were only dating)… and parked on the bottom using about 10% downthrust.
Ascent speed was 5.7 knots slowing in the upper water column to 4.8. The soft ballast system functioned perfectly, giving the sub an additional 400kg of lift. The bag pops out automatically at about 200m depth and inflates slowly after the sub reaches the surface. It is an oil-over-gas system of our own design, which uses a spring-loaded poppet valve to open a bottle of nitrogen at 3500 psi when the external pressure balances on descent. The valve locks open, charging the bag, and a reservoir of silicon oil fills the tank so it doesn’t implode at depth. On ascent, the gas boils out of the silicon, filling the float bag in about 3 minutes after surfacing.
Surfacing at 4.8 knots is dramatic. I point the boom camera and the 1000w spotlight straight up. I can see the surface shimmering from about 100′ down. There’s a real sense of “ground rush” as the shimmering patch grows rapidly bigger, filling the “sky” above the sub. Then BWOOSH! an explosion of foam and bubbles, and the sub pogos back down about 5m, then rises again and comes to rest. I call it “Splash-up”… bastardizing a term from the 60′s space missions.