… how can you tell for certain that your craft and another craft will collide or miss each other when converging (from any quadrant , in any convergence scenario) ??
hint : this is as basic as it gets and is a 100% accurate method , at any speed , any axial plane …
this is a helpful tool one can use and I post about because of that …
I won’t spoil this 
thanks salty , I knew you wouldn’t …
… but is worthwhile posting isn’t it , especially because of the paddler / power boat conflicts ??
wait and see NM
The airplane pilot’s answer
If another plane remains in the same spot on your windshield - and only gets bigger - you are on a collision course.
Works the same for boats, only kayakers have to imagine the windshield.
Other applications
I’ve heard it works for tornados, too…although by the time you figure it out, it might be too late for the avoidance part - yikes! =8-O
mintjulep , an A++ …
– Last Updated: Sep-09-08 8:51 PM EST –
...... perfect answer , exactly as expected .
You "can" put a dot on the windscreen (or side windows) but it's never done in real time except for practice of theory proof . The paddler , the pilot or any craft can use this collision avoidence technique to gauge the conflict as to a factor or non ..
I thought this technique would be a helpful "quick aid" to present for those not aware of it . Hope others will too .. thanks for the answer ..
ed: because of the very possible high speed closure rates in aircraft (easily in excess of 350 kts.for low powered aircraft), this technique becomes second nature in the visual scan pattern .
It is also a deadly trap if unaware , because the relative conflict craft (a pinpoint) never moves giving indication of it's position , only grows in size .
It’s called "Angle On The Bow"
If the angle doesn’t change, you are on a collision course. If the angle keeps getting smaller, the boat will pass in front of you and if it keeps getting bigger, it will pass behind you.
THIS IS BASIC NAVIGATION THAT EVERY PADDLER SHOULD KNOW before you paddle anywhere there is another vessel. I’m sure it would also be one of the first questions asked in a trial to determine liability.
Unless . . .
Unless it is a jetski. Those things have no angle, no heading, and really no class either. I hated worrying about running one over when I was driving a power boat. Now I just worry about them hitting me.
Sorry to sidetrack. Great tip. I knew the angle to bow bit, but never thought of the windshield. That’s great!
"CBDR"
Constant Bearing, Decreasing Range… if that’s the case, stand by for impact.
not quite perfect…
I don’t have a windscreen on my kayak. Haven’t seen too many with them. 
But the following posts that talked about angle on the bow did provide the response to make it applicable to kayaks…
relative movement
if the vessel does not appear to be moveing then it is on a collision course with you (unless of course it’s moored or anchored.)
The rule we use
If the angle of attack doesn’t change… you are going to hit.
David Burch
has several interesting pages about this subject in his book Fundamentals of Kayak Navigation. It’s an excellent book packed with very practical information
On the other hand…
It should work equally well if you WANT to hit something…
Except instead of a dot you imagine a gun site…
Jet ski’s are awesome!
May be the best lifesaving tool on the water!!!
Just a machine. Rode one to Alaska from Wa in 25 hrs!
Just for fun. Yeah, also paddled the route.
How about a motor boat
pulling someone on a tube, looking back at the tubber? He’s weaving about trying to throw the tubber, perhaps laughing his a$$ off, and not seeing me looking through my invisable windshield.
Splat
Abandon ship …
… quick and swim deep for as long as you can …
Avoid “splat” at all cost !!
Any speed , any quadrant …
– Last Updated: Sep-10-08 1:13 AM EST –
...... "Relative Movement" that's an A+ answer too ... (my test , I can give the grades , lol)
That would also includes one vessel at speed and the other at 0 speed . In this case you are on a collision course with it , "head on" .. unless you are doing a world record reverse , it's happened !!
The rule is , "see and avoid" , VFR in the air (Visual flight Rules) , works the same in a boat , a car etc. ..
Very Awesome …
… when used properly . And that from a guy who has never been on one !!