Collision Avoidence test question ...

Peter-CA , the windscreen …
… is as clear as the air in front of you in your boat / kayak , (theory wise) … it represents your field of view relataive to your station .

If the windscreen / window / windshield wasn’t there , nothing would change in the technique .

Mintjulep gave the 100% book mark answer …

I too appreciate some of the other answers as they are good collision avoidence practices as well …

They need to include windshields
on all Tilley Hats as a safety feature.

Then you could simply turn your head a little to avoid a collision.



That’s good but…
Most boats I see when paddling open water are not on a steady heading.

Mostly I hope I’m seen.


Another way to explain it
Look at the shore line. If the other boat is staying under the same tree (or spot) on the shore than you will hit it. If the trees on the shore are moving from in front of the boat to the back of the boat then the boat will pass in front of you. If the trees are moving from the front of the boat to the back of the boat than you will pass in front of the other boat.

This also is a good way to see if another boat going the same direction is going faster or slower than you.

If the tree line is moving from the front of the boat towards the stern than the other boat is going faster. If trees are moving from the stern to the bow you are moving faster. If there is no movement than you going the same speed.

I use this all the time when racing my Hobie. It is the fastest way to see if your going to get in trouble.

When I race I do a port tack start most of the time . . .If the line is long enough. This give everyone else right of way over me so I need to be able to tell quickly if I need to duck under them or tack to avoid the problematic “T Bone” situation.


belles and others
That’s the greatest hazard I face from motorboats. The fishermen and tour boats generally know their stuff. But I’ve seen more than one yahoo towing someone, only person in the boat, and splitting their attention between their course and the rearview mirror. I’d like to see more oversight of water skiers and tubers to make sure there is more than one person in the tow boat, that one has their attention dedicated to the course.

Curiosity Question
The test question seems to assume a couple of things, not the least of which is that the vessel you are observing will hold its course. I can think of a number of situations I’ve been in recently, from paddling where lobster boats are pulling pots to coming into harbor on a friend’s sailboat where that was either not happening or at best questionable. In the latter case, tack changes were likely because of the narrowing bay and some fading wind, in the first the matching buoy colors were and the allover travel direction were a pretty reliable indication of where they’d go next.

Taking away the bit of testosterone flow around who was going to tack first that seems to come up when French-Canadian and US sailors are sharing a port, for the most part this seems to be a big-vessel kind of thing. So I’d hesitate to assume much of anything in places where there are no shipping lanes, which is where we prefer to paddle anyway.

As an example, two weekends ago my husband and friends came upon a boat that seemed to be sitting oddly on Lake George, a very pretty 30 mile long lake with mountains around it and very, very well-marked hazard buoys for all the rocks. The reasonably intelligent-seeming, nice guy who owned the boat had not noticed those hazard markers and run his cabin cruiser well up onto the rocks. When they got to him he was rocking back and forth between them with a dead engine of indeterminate damage and no propeller.

They were happy that they had not chosen that patch of rocks to stop in.

And before it starts, OBVIOUSLY this is one boater who made a bad choice among many more who were on the lake that day. So this is not a rant against motor boaters. It is a reason to be cautious about assuming that something so much bigger than a kayak is going to obey the rules you think they should.

No spotter required?
Waterskiiers here (and I assume other “pulled” people) must have a spotter in addition to the boat driver. That still means nothing, because I almost got mowed down by two people who were BOTH staring back at their towee. In effect, NOBODY was driving that boat. But it does provide some legal leverage.

"when used properly"
Unlike with a paddle boat, a jetskier who is not “using properly” is a hazard to others. The fact that some states have very low age requirements (12 years old, 14 years old, you get the idea) unleashes a lot of kids with poor judgment and NO driving experience on us. They should have to have a valid driver’s license first!

If you watch the background than it does not matter if they change course. You can still tell what will happen by watching the on shore objects. Granted when the other boat alters course things will change but just watch the objects on shore and you can tell if you need to alter your course because of his new course.

When two object are moving you need to use a third stationary object as a guide to see if you are going run into each other


I suppose…
Having been at the wheel of a sailboat (our friends have maybe too much confidence) and paddled in and out of working harbors, I don’t recall that I’ve ever been notably wrong. And I have never paid much mind to how I am doing it - it works.

As to the point on shoreline, dumb point but it needs a shoreline or other fixed object(s). When you are out there a bit, it’s mostly a horizon except for buoys or islands that may be quite distant and spread well apart.

depends on the jurisdiction
I think mirrors are adequate in some places but rules are alway written such that it is a requirement to “maintain proper watch”. Granted that’s a judgement call but any booboo means that requirement wasn’t met. I find that the good skiers and wake boarders have good pilots and drive predictably whether they’ve just a driver or if there’s an additional spotter. It’s the tubers that get out there and shove their heads up their butts before pressing the throttle. They can have 10 people on the boat but dad driving will still be watching junior instead of his heading.

Something’s missing here.

– Last Updated: Sep-10-08 10:01 PM EST –

I can see how this would work if the objects on shore were extremely far away, sort of like how the moon does not change position as you "drive past it" at night, but seems to follow you. But objects on shore are not at such a distance.

Put yourself on a lake where the shore is off to the side of your direction of travel. Now imagine another boat between you and the shore going at similar speed and on a heading similar to yours but not exactly so, such that eventually their courses intersect. If the relative speeds are such that both boats arrive at the intersect point at the same time, you will be able to watch the other boat and see the background drifting past it from from bow to stern, right up until the moment of collision.

As another example, imagine two boats approaching a common point on courses that intersect at a 90-degree angle. In this situation, the operator of either boat will see the shoreline passing the other boat from bow to stern. In these situations and others I can think of, the original poster's method of anticipating a collison works, but yours does not. Your method would work IF objects on shore remained at a constant angle to your heading. This is true for the sun, stars and moon, but not objects on shore (otherwise the scenery would never change as you cruise along in a straight line!). If you are REALLY far from shore and the boat in question is VERY close to you, this method would be approximately correct, but in that case, why not observe the boat's angle off your bow and leave it at that?

It may not sound logical
But it will work 100% of the time. I have used this system when racing boats, so does everyone else I know.

try it for youself the next time your on the interstate. Watch the overpass as cars are approaching and passing over you. This way of testing is safer that using an intersection. You will see that it works.


I must be missing something

– Last Updated: Sep-10-08 10:32 PM EST –

A car on a crossing overpass which is on a "collison course" MOVES relative to the background. The closer the background objects are to that car (such as the guardrail on the other side of the highway from the car you are watching), the faster the relative motion between that background and the car. The greater the distance between that car and the background (such as trees on the other side of a half-mile-wide cornfield), the slower that motion, but the motion is still quite pronounced. Aligning that car with a "spot on the window" is a method that DOES work to anticipate a collision course. The background won't stay aligned with your chosen window speck (nor will it stay aligned with the car you are sighting) but the car that's on the collision course will. The ONLY "window speck" on your car that stays aligned with the background is a spot on the windshield directly in front of your face. All other points you choose on any window will show the background moving past (except for infinite-distance objects like the moon), so there is no way to keep a collision-course vehicle aligned with background points either, except "approximately" as described in my post above for a VERY nearby vehicle compared to a VERY far-away background.

Here's another way of explaining what I mean. If you draw two intersecting straight-line paths on paper, and plot the position of the two vehicles at discrete times, you can see that a line drawn between those two vechicles at EACH discrete moment in time is parallel to all other such lines. This is why in real situations, you will see that a bearing taken on a boat or car that's on a collision course with you never changes (because every line-of-sight is parallel to every other line-of-sight). Now, extend each of those parallel lines until they intersect with the background, and you will see that no two lines hit the same point. If you extend those lines across the floor and down the full lenghth of your house, those lines will be "pretty close" to intersecting the same background point since the actual distance between those points of intersection is hard to note at such distance, which is exactly why this method is a fair approximation when the background is MUCH farther away than the other vehicle. Us inland boaters won't ever face that situation, and this is also why this won't work in your freeway overpass example.

You guys go at it…
What guideboatguy describes above sounds closest to what I am doing if I try to replicate how I look at it - as above in the more open sea situation I don’t see the roadway intersection thing being too helpful because the distances between moving and solid objects are so different when you are out there. More of a good approach for those working inland waterways.

But I’ll let others argue the fine points. For the moment I just need to avoid collisions, and thus far it seems I’ve done that OK.

The backgrouond method is best…
…IMHO, for kayaking. Why? The bow angle method requires that you maintain a straight course. That’s fine in calm water, but what about chop. Small variations in your bow angle translate into uncertainty. Also, the bow angle method requires a mental calculation, and/or that you look at your own boat to see where the bearing is.

With the background method you just look straight at the other vessel and the background right behind it – all in one quick view, with no mental gymnastics.

For the background method, you can use shore, if it’s behind the other boat, or clouds, or buoys, or even distant, relatively slow-moving vessels. It works for me 95% of the time or more. When there is no suitable background, then switch to the bow angle method.

I haven’t thought it out, but I think the background method works fine no matter how far away the background pattern or objects are.

My $00.002.

PS: I was once in a big group paused at a channel. Someone in the front of the group decided to go, and as I looked as a big sailboat going through the channel, it was steady against the background. Ooops! But the whole group followed the guy in front like sheep and, guess what, the sailboat luffed its sails and changed course. A bad mark for kayakers!

Probably okay for kayaking…

– Last Updated: Sep-11-08 10:37 AM EST –

...because your own speed is essentially zero. For all practical approximations, in comparison to the speed of a power boat, you are just a marker bouy out on the water, and a power boat must be aiming almost straight at you to be on a collision course. In that situation, the background method will work. In my posts above, I was arguing the geometric priniciples as to why it won't work for two vessels moving at similar speed, unless the background is extremely far away, far enough to make the method a reasonable approximation.

I won't talk about this any more unless someone askes something specific, except to ask any doubters to try one very simple test. Approach a four-way stop sign such that you arrive at about the same time as a cross-traffic vehicle (even though you are going to come to a stop, you can match the other driver's speed and distance from the intersection to simulate a collision course as you approach), and watch the nearby background, such as signposts or trees. The only way to keep that vehicle in-line with a particular point on the background will be to increase your speed substantially at an ever-increasing rate as you get closer to the intersection (and doing that would NOT be maintaining a collision course). Think about it: an extreme example of a nearby background is the shoulder of the road on the other side of the car. Looking at that background as you try this test will illustrate that the degree to which the background becomes useless with decreasing distance to that background is not a linear function, but an exponential one.

Breatholizers(sp?)…for everyone.

Try it
you will like it . . . It works.

Don’t know why. Can’t explain it on paper it just works

Already did, several times today.

– Last Updated: Sep-11-08 6:25 PM EST –

I drove about 120 miles during my workday, so I tried this out whenever I could. It doesn't work unless the background is a couple miles away, and even then it is not at all precise for observation times that last longer than 10 or 15 seconds. With a background a quarter mile away or so, it's a complete no-go, so you can totally forget about using backgrounds within couple hundred feet. If a background at any distance worked, you wouldn't see nearby objects sweeping by your car when traveling at highway speed while farther objects seem to slowly drift by (remember, this method is supposed to agree with the point-on-the-windowglass method provided by the original poster, so put your finger on your car window and watch what the background at various distances does as you drive down the highway, and compare that with the fact that a vehicle on a collision course with you would remain aligned with the same point on the glass the whole time). This is such basic geometry, there's really nothing more to say.