JFD Fintan: 2013-16

The JFD prototype swimmer delivery vehicle Fintan was my primary task on joining the team at JFD. The vehicle had been built on a tight budget as part of a UK MOD contract. These vehicles are described as ‘wet’ as they are full of water when dived and at ambient water pressure. The crew all have to be divers with the depth limitation this creates. The plan was to provide an alternative to the American MK8 that was in service with both US and UK special forces. The MK8 was proving expensive to maintain and had limited capabilities and there was a desire to get away from the very expensive silver zinc battery cells that were only good for 5 charge cycles. The UK dry deck shelter that could be fitted to the back of the new class on nuclear submarines was bigger than the US counterpart, so a larger vehicle was also possible.

Fintan broke new ground in many respects. It had state of the art lithium batteries that had proven reliable and safe on the JFD rescue subs and it had an entirely composite shell. However, it had several significant issues which had proven difficult to fix. My task was to decide what exactly was wrong with it and plan a route through to improvement.

There were four primary issues. The first, lack of reliability was improved by fitting a new motor and importantly a new motor control unit that did not emit electromagnetic noise. Second, the control software was re-written by a sister company which removed the glitches and enabled proper data logging thought the test. Now the Sonardyne sonar worked spectacularly as well as the Lodestar navigation system.

The third issue that the builder was at a loss to explain was the poor range and performance. I introduced the concept of an efficiency matrix in which all the minor contributing efficiencies are multiplied together to get an overall efficiency. Then taking a stab at what I considered likely in each case, it was matched with the actual result. By calculating incremental improvements in each category an overall improvement could be predicted.

However, the defect that proved most serious was the complete lack of stability in the vertical plane, as well as to some extent, the horizontal plane. This made it painful on the ears of any diver attempting to pilot the vehicle. Unfortunately, without a complete re-design of the tail, this was not possible to fix within the time and budget constraints. An X plane tail as S351 and S104 would have been the answer.

The MOD funded several rounds of modification and trials before asking me to design a completely new next generation vehicle. Sadly, there has never been money to build it.