Friday, October 09, 2009

Need Some Help

When I first started sailing the bay nine years ago, it seemed that every boat that came in front of my boat was on a collision course with me. It made me very nervous and unsure. Then one of my partners, Geoff, pointed out that by looking at the land behind the boat, you could determine if the other boat would pass in front or behind you. If the land is stationary, you are on a collision course. Once I learned this little trick my confidence soared. Can anyone tell me what this tool is called? If you have not tried it, give it a whirl. It makes a huge difference in navigating a busy sea way. Last question, is this phenomenon from the math discipline of geometry? Please leave a comment if you know the answer.

2 comments:

Mark said...

Ranging
http://en.wikipedia.org/wiki/Ranging

Craig Russell said...

From another sailor, Ray Tostado

"Frame of reference" would suit me. You are using a fixed object to determine YOUR position, then judging that anything transiting between your reference point and you is either going left or right. Then you must decide if this movement will in time become fixed in reference to your angle of sight to the land base. If this occurs then you are on a collision, or maybe just, a parallel course. Since in your example the other vessel is closer to the land base it's speed will be less, in order to appear in a constant position, than yours since it is traveling in a shorter arc from the land base than you are.

To determine any such collision course without a land based object one person on your vessel should determine what the angle is between your vessel's centerline, (course), and the angle to the other vessel. When this angle grows then you are going to pass ahead. When this angle diminishes, the other vessel will pass ahead.

When the angle remains fixed then a collision course is likely.

This becomes rather ineffective when you are doing 6 kts and the other vessel is doing 16kts. A sailing boat speed and a power boat speed make any collision judgments very subject to common sense. Just remember, " A POWER BOAT OPERATOR WILL ALWAYS MAKE A DELIBERATE EFFORT TO PASS IN FRONT OF A SAILBOAT." So you can expect that the power boat will increase it's speed in a manner to pass ahead of you.

Were I sailing on the Bay the tide/current velocity and direction would play an important role in my decision making.

It is common to be in a situation where both operators attempt to make anti collision adjustments to their course only to realize they are actually enhancing the situation. When you decide to yield make this gesture very obvious so as to inform the other vessel of your intentions. Especially when involved with commercial ships.

Just remember,: big is bad; Bigger is Bader; REAL BIG IS REAL BAD.

Cheers,

Ray