I was thinking about their navigation "system" and I can't figure out why they didn't have an onboard navigation device, something like this company makes:
https://www.movella.com/products/sen...s-mti-300-ahrs
Sure, it costs money, but it would save so much time. It should work, since you mount them inside your submersible. Seems bonkers not to buy this, considering the expense of all the other parts of the journey.