Down into the Deep: Dive Testing a U Boat Worx Submersible

I recently took part in the final client dive on a 1000m deep 7 seat submersible, designed by U Boat Worx, to the wishes of one of our clients at Superyacht Tenders & Toys. The client required it to be suitable for use on cruise ships to take 7 passengers 'into the deep’ and was looking for a sub with almost unmatched exploration capability, able to descend over 1000m.

The 7 seater submersibles are some of the largest in U Boat Worx's range, designed and manufactured in the Netherlands, costing upwards of 3 million euros. Initial inspection of the Cruise Sub shows a dual-ended sub with spherical viewing rooms on both ends. Unique rotating seating means no one has to compete over the best view; passengers experience the submarine world in 360 degrees.

Specifics will be witheld to protect the client's confidentiality but, to set the scene, we found ourselves on a large charter tug boat with a crane and suitable deck space for the submersible. The team was busy preparing the sub for the deep dive; this included around 1 hour of checks and tests to ensure everything was good to go. Keen to know more, Superyacht Tenders & Toys attended the Class inspection of the pre-dive checks and went through the checklist item by item — nothing is overlooked.

The 7 person Cruise Sub, Serie A, U Boat Worx, a similar submersible to the one Josh Richardson dived in, in a test for a Superyacht Tenders & Toys' client.  

Before embarking we had to be weighed (some took to this better than others!), as the sub must be ballasted to be ever so slightly positively buoyant in case of emergency; this ensures that it rises to the surface if it loses power or similar. We then dashed for a pee, knowing it would be a long time until we could go again! That said, this submersible even had a toilet. Whether you wish to share the moment with ‘friends’ is a question that might only be answered in an emergency; one hour plus to descend 1000m can be a long time to wait! Our dive actually lasted 4 ½ hours as we were having so much fun.

We were then briefed on all emergency scenarios, where various equipment was and what to do. Compared to other marine products, subs have backups upon backups and then some. There are 3 separate life support systems which work upon emergency with 96 hours of life support.

Following the sub launch, with the sub controlled via the remote controller from the launch boat, we embarked via a rib. When onboard we settled into our preferred seats and were then given briefing number 2. This covered all aspects of the sub, emergency breathing devices and more. We all nodded, and then the hatch was closed, readings to the surface were given and thrusters were engaged, the ballast tanks were vented and then further checks to the surface were given at 10m deep.

Inside the 7 seater Cruise Sub

The feeling as you descend is unlike anything I have ever experienced, off into the unknown. We remained enthralled as we continue to go deeper; the experience was mesmerising.

As we got below 10m, the ROV (remote operated vehicle) joined us with lights shining in from the darkness. This was our back up, with HD video and cutter arms, tethered to the mothership, filming every moment. For yacht subs this is not required but it has considerable advantages in the event of sub rescue, monitoring and surveillance. It also means crews can dive the sites before the sub goes down keeping up skills and ensuring that the crew are at the top of the game when on idle owner time. For a large sub like this there is a crew of 2 to pilot and maintain the submersible.

Lights turn on as darkness increases and thrusters are engaged to go down. In the dive location we found the water to have a lot of freshwater on the top and up until 30m deep it had a green hue. After 30m the transition to saltwater occurred and the darkness descended.

On board we took decibel readings of noise for the client and in quiet appreciation wondered what was coming next. There was a lot of sediment in the water, and we went through a small thermocline. We were moving down at 5m per minute, enjoying the tranquility.

Cruise Explorer 3 diving a coral reef in the Seychelles. Credit: U Boat Worx

From 160m down there were a lot of particles floating up and lots of small fish, however these decreased as we continued to descend. The light was simply terrific and one of those amazing life experiences.

At 250m down we made some readings to topside which covered everything to do with how the submersible was performing, state of charge, internal pressure, water temperature and much more. The sub pilot onboard made short and long readings at intervals to ensure the topside is fully informed of the sub’s progress and the state of all systems. We were then descending at around 25m per minute and making real progress towards the bottom! Any fish remaining were following us down, getting dragged with the sub. We were set onto a column of 345 degrees and working our way straight towards the bottom.

As we worked deeper we saw lots of very odd creatures, some with long thin tails, others with lots of lights which reflected off us. After 26 minutes we were at 300m deep and the red lights came on inside. We viewed the ROV on the sonar a few hundred metres away.

We were soon at 400m and descending rapidly. Internal pressure was 1017 as per expected at surface and the water temperature outside was decreasing fast and was now at 7 degrees. Lying back in the leather chair, life was pretty sweet.

Topside were analysing readings including battery usage. We then found that beyond 430m there was less sediment and the ROV was more visible again. Needless to say, despite the depth, no one onboard experiences any change to their breathing.

A 3 person Super Yacht Sub by U Boat Worx diving a wreck in Malta. Credit: U Boat Worx

We descended to 500m. I was reminded that the acrylic dome is 21cm thick, designed to withstand considerably more pressure - up to 6 times more. I had attended all tests on the sphere with the manufacturer which gave me absolute confidence in its strength.

All was quiet and it was mesmerising watching the water going past. There were not a lot of fish, but the flow of the water was incredible into the darkness. At 45 minutes diving time we were at 750m deep.

Our sonar does not pick up depth until 200m from the bottom so we continued on. At 800m we still had 500m to go! The pressures at this depth are simply immense. The simple joys of this depth being no phone, no hassles, just enjoying the moment. The value of this magical isolation is priceless for our clients. 

Comfortable leather seats revolve to give passengers 360 views

At 870m the ROV joins, lights shining. At this depth we pump out water to ensure we have negative buoyancy, keeping the sub positively buoyant. This is noisy as the water goes out.

Pressure increased outside the sub to 100 bar as we got down towards 1000m deep. It was amazing being in total comfort, laughing and joking at 1000m deep. It was no different than being on the surface in terms of comfort levels. Batteries were still at 87% charge and we had plenty of time to play and check all systems for the client.

Now we were nearing maximum depth we performed all stability, emergency power and manoeuvrability tests. Every light, feature and piece of equipment was checked and signed off, even the stereo! Compared to the relative quiet descending it was quite noisy with thrusters working to their maximum. It was hard not to question every noise!

Having attended the pressure tests of the hull and spheres there was no question over the competence of the design and build team, with classification society also certifying the sub to 1.2 times the maximum depth. We spent over 45 minutes at the maximum depth then decided to go for an explore and tracked sideways to a rock wall, ascending and looking for life. As we rose we saw crabs, shrimp, starfish and other small creatures.

 From a personal perspective the best thing about this trip was the silence. It is rare in life you are so forced to slow down. Quite literally there is nothing to do apart from look out the windows, or play on the helm via the remote Manta controller (the joysticks used to control the sub can be given to the guests by the pilot). This controller is super simple to use, and is like having a go on a Playstation console!

To ascend we then blew out some air and decided to turn off all the lights. Even at 600m deep the phosphorescence from the hyper particles was incredible, mesmerising us all as it hit the top of the acrylic spheres and then drifted past. We were rising at 30m per minute. Needless to say, there was no decompression and we just went straight up. From 110m we started seeing some light from the surface and knew our peace and quiet was soon to be broken!

At 30m it got much lighter as we entered the green freshwater thermocline. At 10m we stopped, did comms checks to the surface and blew bubbles so the surface control knew where we were. As we came up to the surface we moved onto VHF comms and equalised the sub before getting collected by a rib and taken aboard the mothership.

Coming onboard the mothership everyone was bouncing off the walls with excitement, having just become some of very few people on earth to have descended more than 1000m in a submersible. To put that into perspective, modern nuclear SeaWolf submersibles go to 490m deep! It made for an experience that will live with me for the rest of my life. If any superyacht owner is wondering how it is, this comes highly recommended.