An alarm set to a CPA distance might be fine in the open ocean ... but
some fine tuning would make it also useful in a bay or close quarters
(when there are many other many boats within 1 nm), to alarm when the
danger is very real, rather then someone just being in my proximity

For example #1, if the software could determine if there is a real
collision potential. If a freighter is on a direct collision course
with me, and we are head on, I would want the alarm to go off at a
greater distance then if we are at right angles. It could take me
several minutes for me satisfatorylly (to my wife) get out of the way
if a freighter is coming right at me, vs at a right angle 30 seconds is
all I would need (I could just stop and wait)

For example #2, if the software could determine how rapidly another
boat and I are closing to each other, or a "time duration until
collision (TDUC) - i made this up" then it could allow another sailboat
my speed running behind me and won't catch up for 20 minutes to get
much closer then a 40mph speedboat five times as far away but will
reach me in 2 minutes. By setting TDUC = 120 seconds, it would alarm on
the speedboat. If I can easily change TDUC based on being at the helm
already, or longer when I step away from the wheel, that would be
useful ... or have two different settings for TDUC (autopilot = on or
off) that would be useful too, but I would still want to easily adjust
based on what I think my reaction time is, and how much traffic is
around me.

This is not a complete thought, I see I have to go and cannot finish
this now, if there is an interest let me know and I will ...




If, in addition to setting a value for CPA (and the value would be set
small, say 0.1 nm), be able to set an alarm value for "seconds until
target enters CPA", which for example might be set a 2 minutes.

But in shipping areas it wouldn't be nearly as helpful as being able to
set an alarm value based on minutes or seconds (given each boats course
and speed) until collision.