I’m looking at your photo and suspect part of your performance issue relates to the signal gain of the antennas (or lack of).
On the BR1, if you open the device (this can be done in either InControl2 or locally on the device) and see what Signal Levels you are receiving. The advantage of using InControl2 is you can see historical data on this.
Also, why did you go an LTE instead of an LTE-A chipset, out on the water an LTE-A chipset will work better as it operates at the lower & newer radio bands used by mobile/cellular operators.
In Australia, we have successfully had customer deployments connecting with ample capacity to do live video streaming & video conferencing 30 plus km (over 16 Nautical Miles) out to sea.
There is a specific and specialist amount involved in correctly choosing an antenna system that will deliver the most suitable outcomes for your application.
Most wireless (be that cellular/mobile or Wi-Fi) antenna system for MIMO work best with an out of phase antenna array (+/- 45 Degrees of the vertical), meaning you can have a very tightly packed antenna with exceptional performance. The cabling system needs to be 50Ohm impedance (not 75Ohm as used for Terrestrial TV & most MATV systems). The quality of the cable system can make just as significant impact as the quality of the antenna; we run over 50-meter cable runs for some of our clients and get excellent results as we supply a professionally designed fit for purpose solution.
We suggest that you contact your local Authorised Peplink Partner for specialised assistance.
Your local Certified Peplink Partner can help you with a copy of the Antenna Selection Guide for Peplink Partners, this is a detailed guide and is only available to the Peplink Partners so to ensure that you get helped in working through it to get the most suitable antenna solution to your application.
Remember that the majority of these systems are MIMO (Multi-In, Multi-Out), so you must ensure you use antennas and cabling suitably designed for the application.
Happy to Help,