The company I work for builds the MiFi devices and the specs for transmit and receive are very similar to 3G. I would suspect that Verizon just doesn't have very good coverage with 4G, (which is LTE). Yachts and out on the water are NOT the primary demographic for any of the carriers. I would think the device would slip down to 3G... but I honestly don't know. I know it is a completely different chipset inside the device, but I would have thought it multi-mode.
I'll have to check with the digital guys.