Tool for calculating course intercept

[YVRguy]

Where I sail there is a large amount commercial ship traffic in the form of large, fast moving ferries, ocean freighters and tugs (often towing). It's generally not a problem to stay out of their way but sometimes, particularly when traveling on a gradually converging course, it is hard to tell if and when our courses will intercept. Please understand I am familiar with collision avoidance regs and standard procedures. I monitor VHF channel 16 as well as the local traffic channel. With that said, I'm interested to know if there is a tool I can use that will estimate when my path will cross with another ship, based on the current speed and heading of both vessels. I use Shipfinder on my i-phone and cool little AIS app knows most of this info. Only problem is I am not broadcasting AIS - only receiving. I also use INAVX for navigation. Beyond my phone I have a basic Humminbird GPS chart plotter but no radar.

 

[Stu Jackson]

... I'm interested to know if there is a tool I can use that will estimate when my path will cross with another ship, based on the current speed and heading of both vessels.

KISS, use a stanchion. If the other boat is not moving against the background compared to lining it up to a stanchion, you ARE on a cc. Simple.

 

[SoSound]

Where we usually sail, there is very little dangerous traffic. But when we went up to the San Juans last summer, now THAT was a different story! Monitoring VT channel was a big help, and made us appreciate how much was actually going on that we didn't know about. Seattle vessel traffic was more than willing to hear from and continue communicating with pleasure craft near the traffic lanes.

On our new chart plotter, the system identifies "dangerous" traffic and will calculate closest point of approach and time based on your own course and speed (and that of the other vessel). I believe that the warning threshold is user settable. I haven't actually seen it working in real life yet (very little traffic near Olympia). My initial warning setting was a little annoying when we started moving on Lake Union in Seattle; literally set off an alarm for every commercial boat in the city!

If you haven't seen it already, Maine Sail had a great post recently about some of the things that AIS will not tell you, and why you don't want to let AIS lull you into neglecting to think about all of the other possibilities of a commercial vessel encounter… Just because you may know where it is and where it's going. Not to mention the non AIS vessels (such as yourself) who won't show up at all.

Keep your posts coming, you help to push my motivation and interest in traveling farther from home!

BTW; can anyone tell me why, on the list of vessels that I can see, there are a number of them listed with a "LOST" status?

Dave

 

[SoSound]

Before I get busted on this; It's not just the chart plotter. The VHF provides the AIS receive and is networked with the chart plotter. The VHF documentation indicates that it could be the sole source of AIS information, if it were connected to a GPS source… I'd rather have the level of information available on a chart plotter than try to figure out a tiny mono display on the radio...

 

[Roadking Larry]

Used to use the Navy version of these.
http://www.westmarine.com/plotting-tools/celestaire--maneuvering-board--2408169

 

[Ralph Johnstone]

KISS, use a stanchion.

Stu is 100% right. Practice alone will soon make you an expert on this.

One of the more formidable objects (at first sight) in Howe Sound is a BC Ferry. As a rule, if I'm under sail and can even SEE one of these on the horizon, I start to calculate where I want to be when it goes by at +22 knots. Mind you, they're very precise in their course and after seeing a few of them, you know exactly where they'll be as they pass you. They're wake at 22 knots is actually not bad .................. long and rolling.

However, that said, the deadliest objects in Howe Sound are drunken power boaters. I'm always on the defensive when these clowns are anywhere in sight and consider myself in the give way position, without exception. I've had too many close calls while under sail .

Practice is the best piece of equipment you can have out there for safety. After this summer, the above will bear notice but not panic.

 

[Stu Jackson]

On a recent RYA Theory course, a question was asked about a Skipper checking if another vessel was on a collision course. The answer given, was he should take bearings with a hand held compass or check the bearing against a stanchion. Should the bearing remain the same, a possible collision situation exists.

One of the other students, had been told by another instructor, that another method, was to take a suitable landmark & check the bearing of the other vessel against that. If it moved ahead, it was going faster & if it dropped back, it was going slower. This then confirmed that no collision is possible.

It's called BEARINGS or relative bearings.

Chapmans is your friend.

 

[Gudenuph]

Here is an observation from the SSSS BB (Olympia, WA) I use to clarify converging courses. Quoting myself:
"We all know that if the compass bearing on a object doesn't change while we are moving, we are going to hit it sooner or later. If there is a distant and fixed feature beyond the object of concern there is a quicker way to make the determination. If you are on converging courses and the other boat is "making trees" i.e., continually covering the trees on the far shore, he will cross your bow. If trees are uncovering ahead of him you will cross his bow. If he continues to cover the same tree, you will soon be greeting each other. It works just the same if it is a point of land you are trying to fetch without having to tack. If the trees beyond the point aren't uncovering, you ain't gonna make it.
How about that?
George"

 

[YVRguy]

Before I get busted on this; It's not just the chart plotter. The VHF provides the AIS receive and is networked with the chart plotter. The VHF documentation indicates that it could be the sole source of AIS information, if it were connected to a GPS source… I'd rather have the level of information available on a chart plotter than try to figure out a tiny mono display on the radio...

SoSound,that's exactly the technology I was thinking of. Good to know the new plotters can use AIS in that way. BTW, love your signature!

 

[sailaway78]

Stu's post

This is the quickest, easiest and as sure as any way. Just line up the other vessel with something on your own boat. If it moves ahead of that point, it will pass in front, if it moves behind that point, it will pass behind. If it doesn't move from that point you are on a colision course.

 

[YVRguy]

On a recent RYA Theory course, a question was asked about a Skipper checking if another vessel was on a collision course. The answer given, was he should take bearings with a hand held compass or check the bearing against a stanchion. Should the bearing remain the same, a possible collision situation exists.

One of the other students, had been told by another instructor, that another method, was to take a suitable landmark & check the bearing of the other vessel against that. If it moved ahead, it was going faster & if it dropped back, it was going slower. This then confirmed that no collision is possible.

It's called BEARINGS or relative bearings.

Chapmans is your friend.

Sigh... So is your reference to Chapman's your version of RTFM?

Yes, I am familiar with the technique of measuring the other vessel's progress against a fixed point on your boat or by using a bearing compass. I guess I should have elaborated. There are many things that can and have been done manually that more recently technology can assist with. Given that I work in high tech, I am interested in solutions such as an AIS integrated chart plotter that provide some additional cues.

In the larger picture, I have been surprised by the actions of some of the freighters in English Bay recently and I've taken it upon myself to contact them on Vancouver Traffic and clarify their intentions. It is particularly tricky with a freighter at the far corner of the bay weighs anchor and heads for first narrows. In that case, both their course and speed are changing. I'm currently researching to see whether the Port of Vancouver has educational materials to better assist recreational boats to coexist with commercial traffic. The need for this was underscored for me the other day as I read the official account of the Washington State powerboat that was run under when they drove between a tug and a poorly lit barge.

So sorry I did't provide more detail for you. I was trying to Keep It Simple.... Stu

 

[Stu Jackson]

Doug, from "Simple Stu"

I laud your efforts to make things clearer for recreational vessels. That said, I do believe you may be overcompensating for an issue that may not even exist. We, too, sail here on SF Bay with a tremendous amount of commercial traffic, in both the "main" Bay with Alcatraz in the middle, the south Bay (anchorage 9 can handle at least a dozen major ships), the Oakland Inner & Outer Harbors (10-12 side tie berths for container-ships - I motor out and sail back right alongside 6 of these), the Coast Guard station on CG Island (right across the estuary from my marina), ferries - both single hull & high speed catamarans), cruise ships, and some idiot stinkpotters (although I have a few good friends with motorboats who I consider highly qualified and careful skippers, I have found that the majority are NOT, but we have this blessing of regular summer winds which keeps most of them in harbor - thank goodness!). So, I can relate to what you are saying, but am curious as to how because the skipper of a boat can be stupid enough to pass between a tug & a (its?) barge would trigger your concern. Perhaps you can explain a little bit more so I can better understand.

And, of course, there's that old adage about more recent technology not necessarily trumping good old "eyeball navigation 101."

Assuming the commercial craft have their AIS ON (I've heard VTS here caution certain ships to turn them on!), I am also puzzled by your: I am interested in solutions such as an AIS integrated chart plotter that provide some additional cues.

Not sure I get this one, since AIS superimposed on chartplotters has been "old hat" for a few years now. My friend sailed to Mexico from Vancouver in 2009 and had radar and AIS right on his Garmin chartplotter.

Am I missing something (again, wouldn't be the first time)? Are you asking how it is done?

PS - Doug, very nice Pr. Louisa trip writeup on your blog, great photos, too.

 

[Ralph Johnstone]

In the larger picture, I have been surprised by the actions of some of the freighters in English Bay recently

After sailing English Bay and Howe Sound for many years, I would say you're worrying the things which you shouldn't and ignoring the real hazards out there.

Yes, commercial vessels are big and unforgiving but at least they have skilled operators. They're sober and see you. They are also slow enough in English Bay to be outmaneuvered.

Forget the AIS, it's not going to help you with pleasure vessels and this is where the real hazards lie. In all the years of sailing in both areas, I cannot remember one incident involving a large commercial vessel which I would call "concerning" or a close call. I was always give way, got out of the way, and got on my way.

On the other hand, my number of near misses with pleasure craft is scary. And I'm always preparing to take evasive action. The closest call ever was with a Royal Van whacko who had his power boat on autopilot and everyone was below with martinis. This was way back in the day before I knew what was REALLY going on with other boaters in the area and figured I had the right of way under sail. That mistake almost cost me my boat and maybe my life. After sounding the horn repeatedly and hailing them on the radio, all we got was a salute from their martini glasses.

I can't begin to overemphasize that your best defence in the Vancouver area is personal experience. Forget the electronic assists and rely on yourself. It's MUCH safer that way.

 

[Stu Jackson]

Thanks, Ralph, very good points.

I would just add: a surefire technique to get "nailed" by powerboats is to set your waypoints as buoys or daybeacons. Those idiots all use them, too, so if visibility is reduced, either by exterior weather or the dolts drinking martinis down below (their own significantly reduced visibility!!! ), they are zooming from buoy to buoy.

The preferred choice is to offset your own waypoints to avoid the straight lines between the buoys.

Or, to have a little "fun" (like watching idiots try to anchor! ), hang out by one of the buoys and watch as the powerboats slam into the buoy. Boy, those GPS things are pretty darned accurate these days!

 

[YVRguy]

Uncle!!

Ok I concede the point. I understand now that the technology I was asking about is old hat and shouldn't be relied upon anyway.

Ralph: Our experiences are different. I haven't had any serious run-ins with pleasure craft. However I've had large ships blasting their ship's whistle at me when I thought I was getting out of their way and tugs cutting perilously close across my bow and leaving me to deal with their wake.

Stu, thanks for your kind comments on my blog.

 

[Stu Jackson]

Ok I concede the point. I understand now that the technology I was asking about is old hat and shouldn't be relied upon anyway.

You're very welcome, it was great.

Perhaps you misunderstood what I meant by "old hat." I just meant that it has been around for some time, NOT that it doesn't work. Indeed, it works VERY, VERY well. From my friend's 2009 report:

- new chartplotter with radar and AIS - large 8 inch screen on a bracket at the companionway. This is the perfect position for the instrument. Weekend sailing, you stand behind the wheel. Doing serious miles, you relax more comfortably in the cockpit and you can't see instruments behind the wheel. AIS is amazing. I thought it was poor mans radar, but it is much better than radar if you are trying to figure out what a vessel is up to (speed, direction, position, closest approach, vessel name and MMSI number right there for you). And best of all, the whole thing folds into the companionway so we don't worry about expensive electronics being left outside.

 

[Anonymous 121765]

YVR,

I gotta say, I like STU.

I use the stanchion method also.

Just keep a steady course/speed, pick a stanchion & take mark of the vessel you are watching. If the approaching vessel passes the stanchion to your stern, he will pass before your meeting/crossing.

If the vessel moves forward of the stanchion, you should pass in front of him & he should pass behind you. This only works with a steady course & speed between your boat & the oncoming vessel. So, make sure your course & speed stay the same.

And, I enjoy using this method.

CR

 

[Chris Patterson]

You could build a simple Peloris. I've had this in the back of my mind for future and time consuming projects myself..

 

[Stu Jackson]

If you have a flat compass card, like most mid-size boats with Ritchie compasses at the helm, you already have a Peloris.

 

[Benny17441]

And somebody asked on another thread what could we need a compass for?