yachtmaster

Re: Round N+1 with Gludy about the blind nav.

We agree its been done to death already /forums/images/graemlins/laugh.gif - we diagree on the safety - I just used it as an extreme example. /forums/images/graemlins/laugh.gif
There is no point in discussing it.
 
Re: Round N+1 with Gludy about the blind nav.

You can however, read bottom conditions from the chart, which is always a good starting point. Agree that local knowledge would help, but you can usually make do just by looking at chart and eyeballing local coastline. It's usually fairly clear when its sandy and moving, or rocky
 
Re: Round N+1 with Gludy about the blind nav.

Well we agree on that.

Local knowledge is best but you can make an educated guess if there is no local knowledge.

However, do you think that you can do an EP as accurate as a chart plotter just using depth and DR ?
 
10m viz

You are being a bit to picky/personal - or praps taking things a bit too personal, really? Not to worry tho

Back to the 10m viz. We want to be certain of our location. How about (for example) finding a solid wall by the contours/depth and approaching that wall and then nosing up to it. I'm talking about really realy slowly - it might take a30 minutes frinstance. No, not at five knots nor even at much more than 1 knot - at a speed that you knew it was 100-200 yds away but not quite sure. Then creep along that wall and so on. That wd work - you find the wall AND the positon. The same applies to long seaward pontoons or othjer more suitable thing to find. I don't think a buoy is suitable cos too metal and too crashabl with grp boat.
 
Re: Round N+1 with Gludy about the blind nav.

how long is a bit of string. ep just from dead reckoning and maths, would probably be a way off, unless you can take sightings. With depth thrown in, then it would make things a bit more accurate

Would take gps or chart plotter anytime.
 
Re: Round N+1 with Gludy about the blind nav.

There is a point in discussing it. You disagree as to the safety, and use it as an extreme example. I use it as a case of unless you've been in that situation, you won't know, and sea visibility was superb, waters flat, and was quite safe. If you haven't been out in those conditions, then you really can't comment on how safe it was
 
Re: Round N+1 with Gludy about the blind nav.

Over a couple of miles an EP derived from decent calculations and nice depth readings is, providing you or your autopilot can steer straight, very accurate. I can't say it is as accurate as a GPS and you know that already but you can certainly get it down to 25-50m over a 1 or 2nm leg, then you find the object you were looking for and the process starts again.
 
Re: Round N+1 with Gludy about the blind nav.

I think the point here should not be about whether GPS is more accurate or not. Over a long voyage out of sight of land, it should be. It's whether you can navigate by traditional methods if the electronics fail, and to do so confidently and accurately

I suspect my skills are diminishing as I haven't done a practical exam for some time, and don't practice as much as I used to, as the electronics become more reliable, and backup gps there as well
 
Re: Round N+1 with Gludy about the blind nav.

Of course, I was just answering Gludy's question.

I agree that it needs a bit of practice occasionally. Not necessarily because you get better with practice but because you just become more confident in your own ability, I think this is a key issue in blind nav because you can't do it reliably if if you're not decisive when the time comes.
 
Re: 10m viz

TCM
Maybe a bit picky ... I thought this thread was finished but maybe you were right, another two weeks! /forums/images/graemlins/laugh.gif
I also get fed up with assmumptions and being told go and do this and then ask. In my world I can ask sensible questions and expect to get sesnible answers - I am wary of those who cannot provide them.

The really slow creep is what you do in a marina when you know the wall is there - My worry would be knowing that you are close to the wall. Ok 100 yards out so keep up that creep for a few hundred yards, find wall and then try to find a feature to establish position.

As you say, would not do it to the buoys whilst trying to make way though. Unlike a wall they are only say 15 to 20 foot wide and you could never be sure where they are.
 
Re: Round N+1 with Gludy about the blind nav.

Moose then we are agreed it not as accurate as a GPS - that was the current point and you have agreed.

As regards finding this object in that vis and real life an error as stated by you of 25m to 50m is probably about right on a short straight leg but that leg would not be straight as you would be following contours and they by no means are not always straight.

Looking at the circle of error, you have an object anywhere between 3 and 6 metres wide to find, you could easily miss it with a visibility 10 m and a 50m error yet when you do hunt back and forth to find it, you can easily get the DR all out and lose your position. If you do find it it is going to appear very near to you and you could easily hit it.

I am sure that you can be more accurate in following a contour and finding a buoy than say 25m to 30 m when the charted depths are good, the tidal change small - I bet you could almost get right up on it but then the variable would still be the time when you were there - following curved contours and logging speed/time cannot be very accurate. You would have to allow so much for the rror that you would in effect be proceeding at 1 - 2 knots all the time.

Also lets add a 2 knot tidal stream, say with you, for you to maintain sterrage you need say a 3 knot speed but that means your heading towards it at 5 knots when doing 3 knots.

Add together all the real world variables in the real world case and there are significant problems.

How accurate can the CG radio fix be? That seems to be the way to go.
 
Re: Round N+1 with Gludy about the blind nav.

"I think the point here should not be about whether GPS is more accurate or not. Over a long voyage out of sight of land, it should be. It's whether you can navigate by traditional methods if the electronics fail, and to do so confidently and accurately "

I think you should be able to navigate using tradtional methods but that is not the point under discussion. The current point under discussion is the claim that contour following can be more accurate than GPS in context of the bigger point which is the wisdom of trying to find buoys in 10m vis.
 
Re: Round N+1 with Gludy about the blind nav.

The calim was:-
"Well sure you would use radar. Not everyboat has it though!
GPS, yes but the time taken to transfer position to chart is too slow. Following a contour is safer and exact as long as you know its a safe contour.
Chart plotters, well they can be a way out, at least mine can. "

This was in defence os using DR/contour to fix position and it clearly dismissed the chart poltter in question as less accurate.

I then asked which chart plotter.
 
Re: Round N+1 with Gludy about the blind nav.

Mystique
Who says I do not do? I boat all year round and had no idea you knew what I do or do not do ........ I find it a little arrogant that you presume to know what i do.

I also find it a bit silly that because i ask a question, I do not do.

There are two ways of learning - agreed.

Doing - agreed.

Asking - agreed

So why not get answers to the asking?

Why do some people just escape the answers by making really ignorant statements like yours?

Why do you assume that those who ask questions do not do things?

Why should not people learn both ways?

The laws of physics apply to us all, no matter how much or little experience.

When I go boating I ask to find out tidal info, I ask to find out naviagational info --- mostly from books/charts .... I do all that then I do it. Once I have done it, I do not stop asking - others may have different views and may do it better or worse, so the asking and sharing of ideas is a good thing...... ifg that upsets some people ... tough!!!
 
Re: Round N+1 with Gludy about the blind nav.

Ah yes ...

but as already answered - it depends which electronic charts your using and ensuring your using the correct datum !! Not a problem for most of us ...
 
Re: Round N+1 with Gludy about the blind nav.

Agreed Fireball but then I think if you do not know how to ensure that you are using the correct datum etc, it is a lack of skill not the chart plotter that is to blame. No matter which way you slice this cake, the chart plotter is always more accurate than following contours with DR etc.


In practice following contours around the cost you meet very varying tidal currents around headlands etc, etc .... you are travelling slow and not even in a straight line ........ seems a no brainer that the chart plotter has it here game, set and match.
 
Re: Round N+1 with Gludy about the blind nav.

A little arrogant, granted and I apologise. I find your detailed dissection of rhetorical minutiae just a little wearing...my fault for getting involved.

However, you must have done 1000nm's-worth of asking on this topic. It would have been quicker for us all to meet in the Solent and actually try it.
 
Re: Round N+1 with Gludy about the blind nav.

But i would not go out in the Solent in 10m vis!!!!

You cannot escape the maths here.

Try it in the Bristol Channel with 2 and 3 knot currents that vary along your route and throughout time - so even when you are standing still in the current without any steerage, you can hit the bouy with a whack!!

All I have pointed out is the real world problems with the method and what I would do if caught out in it. Simply finding the buoy using contours is not an issue - they do it all the time on excercise.

Having a strategy to adopt in varying conditions is what i wanted to develop a discussion on in the htread ... that has proved impossible.
 
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