Triton DV24 Acrylic 24-Passenger Tourist Submarine: 2017-2020

In the summer of 2017, I re-connected with Patrick Lahey and Bruce Jones of Triton when they visited the UK. I made it known I was up for a change, one that did not involve driving to Glasgow. They gave me the DV24 project for which they had taken an order from a sketch but no design work had been done so far. This 24-passenger tourist sub was to work in Vietnam and classified by DNV.

At the time Triton Submarines were entirely consumed by their full ocean depth project, the LF -Limiting Factor, so I had absolutely no resource available to me. As it happened, a number of good engineers were on the point of leaving JFD so with a slight push I was able to assemble a very good team.  Triton decided that the vehicle would be assembled in Spain, at their new facility in Sant Cugat near Barcelona.

The DV24 consisted of a series of acrylic cylinders between two spherical steel ends. The forward steel sphere had a large viewport for the pilot and a short acrylic cylinder forming the base of the conning tower directly above the pilot’s seat.  The aft sphere contained the main entry and exit hatch for the passengers. A very large amount of power was available from the two battery pods, but for economic reasons it was back to lead acid which worked very well in combination with the huge buoyancy from the acrylic cylinders.

A cylindrical acrylic submarine had been built before in the early ‘90s by Comex in Marseille, France. We adopted a different approach to the difficult problem caused by the large thermal movement between the acrylic and steel structures. The Comex solution was to take all of the longitudinal loads due to pressure into the deck structure and underframe, leaving the cylinders to ‘float’. As our vehicle had to be tested down to 125m this was not a practical option.

The total movement of the acrylic over the length due to the temperature variation expected by the Rules was around 35mm. Any steel structure directly exposed to this scale of strain would exceed its elastic limit and not return to zero. A hydraulic system was therefore devised whereby the 8 tie bars were kept under constant tension thought their entire travel. The aft sphere was firmly attached to the underframe and deck frame whilst the forward sphere including the forward deck and soft thanks were on slides.

The Steel parts were given to Metalcraft in Chatteris, Cambridgeshire and the acrylic was of course given to Heinz Fritz in Germany. The GRP was partly made in Florida and part in Devon UK. The longest lead items were the steel parts. In hindsight we should have split the order between several pressure vessel shops but parts started to turn up in the summer of 2019.

By then the fledgling Triton office in Barcelona, having come into being to support the LF project, had moved to Sant Cugat, about 14km north west of Barcelona city. They rented a section of workshop occupied by a very useful precision machining company, next door to an equally useful steel fabrication shop. Other than the pressure hull parts, GRP and the acrylic, everything else was made in Sant Cugat.

Life in Sant Cugat through 2019 and the first months of 2020 was very pleasant. In addition to the Spanish and UK engineers, a crew from Triton Florida joined us for the final build. A large part of the excitement was the open water pressure test, where we had to lower the unmanned hull down to 125m in the sea off Barcelona Harbour. A rehearsal in 20m did not go to plan, but fortunately the sub arrived back in harbour intact. We decided to wait until the LF support ship Pressure Drop was visiting with its more sophisticated A frame and winch.  This time it was 100% successful.

Harbour trials were set for early March 2020 to be witnessed by the DNV surveyor. As the date approached, Covid clouds were gathering. The electrical team had baled-out back to the UK a few days early with some brief parting instructions for us. Harbour trials went without major hitches and the DNV Surveyor signed us off and made a dash to the airport Saturday afternoon, 14th March. Spain locked down the next day whilst we sped to the airport but we managed to get a flight out in the early hours of Monday morning.

The Spanish crew were able to get the sub loaded aboard a ship during the lock down period and two American technicians met the sub in Vietnam. They formed a bubble with the Vietnamese crew and we able to proceed with the trials, troubleshooting and training thought the worst of the lock-down period in 2020 and 2021. The view from this vehicle is nothing short of spectacular with visibility from overhead to almost straight down, a real feeling of floating in space. The submarine is now fully operational and regularly taking passengers.