After several hours of internet research I have been able to reduce the total material cost of the BoatDetect system from $37 to $24 ! The resources available online for developing a low-cost, low power Arduino data logger are just fantastic. This device may be my own design but it is certainly built on the shoulders of hackers across the internet that have shared their knowledge freely.

The most significant changes are:

• switch from a Arduino Nano to an Arduino Pro Mini 3.3V for reduced power consumption
• reduce micro SD card storage size from 4GB to 128MB for reduced cost and potential for reduced power consumption
• Tiny85 microcontroller no longer needed because of low operating current of Arduino Pro Mini
• reduce the number of 3400mAh 18650s needed from four to two and still be able to operate for four weeks
• removed 3D printed components to reduce cost and avoid need for access to a 3D printer