Waypoints and Sailboats

[MainlySteam]

I would be very interested in how people broadly manage their sailboat course (not how they work out where they are) under autopilot in pilotage and how frequently they use waypoints for this. By pilotage I do not mean in very restricted waters such as harbours and channels but the general coast crawling, for example, with some dangers which need to be allowed for.

Why I ask is because I never use waypoints as I find them inconvenient when sailing (extreme example is if the desired destination is directly to windward) and one day when talking with my marina neighbour I discovered he does not either, which surprised me considering all the references one sees to their use.

When under sail I almost always sail to the autopilot's windvane ie maintain a point of sail rather than to a strict course, but sometimes to a compass course if not sailing close to a flat run or close to the wind. I then tend to adjust things to suit current, desire to make ground to windward, wind direction change, etc as the voyage proceeds.

Under power, I always set the autopilot to a compass course, adjusting again as need be, but never waypoints.

The GPS then being relegated to a position fixing tool, plus the provider of other tactical information such as tide.

I am using "course" slightly loosely as being a direction to be made good over ground rather than the strict thru the water sense.

Any comments on your practices? Do they vary according to whether you are in frequently sailed waters or less so ones?

Thanks, John



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[MainlySteam]

Whoops, thought I was in YMS - still, I trust this is close enuff {Bad Navigation on my part!!!}.



<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by MainlySteam on 18/08/2003 12:07 (server time).</FONT></P>

 

[SlowlyButSurely]

I thought I was the only person in the world that still sailed this way!!! You have described the method we use precisely. We plot everything on the chart and just use the GPS for fixes.

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[AndrewB]

Allowing for tide.

Like most I suspect, I tend to steer to GPS waypoints unless my destination is actually in sight.

It can work badly if the course is one of several hours across a varying tide, e.g. Dover - Calais. Holding a heading on the waypoint might mean a straight line over the ground, but would result in a timewasting, constantly changing course. In that case I confess to still finding it easier to calculate the optimum compass course by traditional chartwork, than a good course based on the GPS.

Tips anyone?

 

[jleaworthy]

Provided I can lay the course ie no tacking involved, I use my GPS to drive the autopilot to the desired waypoint. Provided the autopilot can accept the nmea instruction and the autopilot has enough computing power to calculate necessary offsets - mine is a TP20 - it will take care of cross tidal streams and leeway.

Now I know this isn't the most efficient way to sail and will take slightly longer but it does mean that we stick to the track over the ground which I have made sure is free from hazards. Also on a long board all I have to do is adjust the sail from time to time while my wife plots our track on the yeoman - and we can keep a good lookout. Safe and Easy - but I'm sure someone will tell me I'm wrong!

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[jimi]

I don't use waypoints with the autopilot. I set the autopilot to a course which I've calculated.

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[qsiv]

Yep, me too, except when I'm using the pilot in wind mode.

When I ran a stinkpot 'twas different, but I really dont find that waypoints are of any real use when sailing.

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[freedom44]

I also do not use the waypoints to aim for on the autopilot. Beware someone changing the "go to" waypoint whilst you are not looking as happened once to me- luckily I intervened before the crash gybe!

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[Davy_S]

This is the way i do it. I have the gps set to true north, and my auto pilot is the poverty version it does not connect to gps. If on say a 12hour passage, one straight course, and a perfect world same windspeed and direction. I would work out the course allowing for leaway and tide, and put awaypoint about one mile uptide of destination plus another couple leading me into harbour. I would also put a waypoint in at roughly halfway (change of tidal direction) Then I steer one course and if my calcs are correct I will arrive near said waypoint. By placing waypoint halfway I can see how far or how near my course is and ajust if neccesarry. It really just gives me a way of checking my calculations out of curiosity. and if gps fails I will hopefully still arrive fairly accurately.

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[Peppermint]

Re: Rarely us em.

Thats because I hate my GPS, it's a Philips piece of dung, and by time I've made a sailplan for it I could be ten miles into the passage. I'm lucky and sail a lot of boat types with different gear. I think I might use more waypoints if I had a chart plotter, it's so easy to put them in place. Or probably if I had almost any other sort of GPS, I find Garmins the most intuitive to use and I like the way they use familiar controls on their whole range of products..

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[peterb]

If sailing free, then I do sometimes link the autopilot in to the GPS and leave it to look after tides, etc (though of course we keep tack of position on the chart.

If beating, I may put a waypoint at the immediate destination, then pick two bearings as tacking lines. In a northerly wind, for instance, I might tack when the waypoint bears 340 or 020.

Near hazards, put a waypoint on the hazard and use distance off to keep safe.

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[seahorse]

But surely..

If U do all the pencil work on the chart, mark the course changes as waypoints which are entered into the GPS it's then quicker to fix your position on the chart via gps. The rolling road indicates how far off course you are & indicates time to the next course change. You have the best of both world!!

Placing a waypoint up wind on your course means that the GPS can indicate when to tack as you gradually "head up the cone" to the waypoint.

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[AndrewB]

Peter, what do you mean by 'leaving the GPS to look after the tides'. The GPS will just steer a straight course over the ground, won't it? Not as efficient as allowing for the tides so as to steer a constant compass course to the waypoint, surely: maybe 5% slower in exceptional cases. Or do you have some flash piece of tidal forecast software linked in, that makes the optimal adjustment to the GPS course?

Sorry if this seems a bit Luddite, but I haven't caught up with chartplotting yet; still navigating with a Breton plotter and a blunt Mk 1 brain.

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[jimi]

on a cross channel if you say put in a way point for Cherbourg and autopiloted to it from the Nab or the Needles, you'd be likely to travel at least 25% more than necessary through the water!

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[Birdseye]

Sailing in the Bristol channel, I rarely find that I can set a course direct from start to destination. Usually, there is some headland with overfalls, some sand bank or rock that requires me to sail a dog leg course. So I use waypoints for that - because I cannot be bothered to work out a "course to steer" even if the tidal data were really worth anything much. So I steer by comparing the track with the bearing of the waypoint and altering the autohelm accordingly (still Mk1 non linked type).

Yes,. I know that its not the pukka RYA approach, but it works.

Incidentally, how many of us really keep an effective log ie with notes at everycourse change etc.?

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[jleaworthy]

Nonsense! If you travel at 5 knots with a spring tide across your course it will cost you about 6% extra distance - say 3/4 hour on a twelve hour crossing. Try drawing it out on your chart.

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[jimi]

Really ... suggest you work it out properly! Applying hourly tidal offsets on an average spring tide from the Nab to Cherbourg will cause you to travel 69.45 miles on 60 miles or 16% more than you need to. working to second by second tidal offsets will cause you to travel even further.the assumption here is that tidal offsets are at right angles.

tide speed distance
1.8 5 5.31
2.8 5 5.73
3.2 5 5.94
2.6 5 5.64
1.6 5 5.25
1.6 5 5.25
3.7 5 6.22
4.2 5 6.53
5.4 5 7.36
3.7 5 6.22
0 5 5.00
0 5 5.00
60 69.45
1.16


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[peterb]

I agree with you on a long leg across the tide; tidal plotting is much shorter. But even there you can use plotting software and a GPS linked autopilot.

I have a piece of planning software which gives me the optimum time of departure for quickest passage, or lets me specify time of departure. It then shows me the ground track that will be followed. Pick waypoints along the route to tie in with the expected ground track and the autopilot can then follow that route.

But much of what I said in the previous post is used when coasting, and making short legs between or around hazards. With legs that only last an hour or so there is little advantage is making a proper tidal plot; straight line tracks between waypoints are just as good. As usual, its horses for courses, or should that be hacks for tracks?

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[charles_reed]

I don't use waypoints either - tho' for the first 2 years when I'd transferred from Decca to Gps I did.

Rather I use the course made good on my chartplotter which allows far better judgement of set when compared with the cmpass course.

Having seen the result of the light aircraft tyros habit of setting course from one radiobeacon to another in the '60s...

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[SydneyTim]

Like most people so far I lay out waypoints ahead in the GPS and manually alter the autopilot course based on what I anticipate from wind and tides in the coming hour. I also keep a proper deck log after a friend of mine got hit by lightning and lost the all the electronics.

However after thinking about this a bit, are we all falling foul of making a big assumption? ie that a waypoint is a fixed point in time and space. On a normal GPS changing the waypoint is a bit of a fiddle, but with a chart plotter you can move the waypoints around and add new ones on your route etc just by clicking and dragging. Theoretically you could set the autopilot to steer to waypoint and then move the waypoint around on the screen, add new ones etc to reflect where you actually want to go based on what you anticipate the tides and wind doing etc... The only "fixed" waypoints being the start and end points on the route.

This way you can lay out your tacking points to avoid dangers etc and set off the proximity alarm to warn you of an impending tack.

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