On a small boat there's really no significant benefit from picking up AIS signals at 30 miles versus at 15 miles. It is just more info to process. Any good display will have CPA/TCPA alarm
set, so you will be informed of anything that comes within your requirements of safety
. Class B are set at low power
, 2 watts, to avoid cluttering and overwhelming the system with excess info. More info does not correlate with more safety
- hence accident
descriptions as "Radar assisted grounding". The 2 watt output does mean that the Tx antenna needs to be good, or the antenna, coax, connector losses can be very significant. Using an antenna splitter with the main VHF antenna usually works well, but it does cause some small loss of low level VHF signals.
I mounted my VHF antenna on the pushpit rail for a few reasons. 1. I wanted a spare VHF antenna in place that was not connected to the mast. 2. I didn't want to tie it together with the main VHF via a splitter. 3. It was much easier to run the coax and and mount the antenna.
The receive distance is a quite a bit less than my previous splitter/mast head
system. Ships that show up at 15-20 miles on the low level antenna would have shown up at 20-30miles on the masthead. I don't have any specs on how far my 2watt is transmitting.
As noted above, by the time you buy an antenna and mount, you are at the same cost as a splitter.