Verification of leading line into L'Aberwrach please

[dralex]

Verification of leading line into L\'Aberwrach please

I've been given a copy of The West France Cruising COmpanion for Christmas and see that on the chartlet on page 17 of the approaches to L'Aberwrach that the leading line for the Grand Chenal is given a bearing of 135T. In the text it says 100T. I don't have the charts for the area yet, so could someone just confirm the correct bearing for the leading line so I can ammend the chartlet while I remember. Just looking at it, 100T looks about right.

Thanks

 

[HenryB]

Re: Verification of leading line into L\'Aberwrach please

Dralex,
There are 2 ways into L'Aberwrach. The passage on 100T is the most straightforward but, for the brave or foolhardy, there is another on 135T - suggest that you wait until you get your charts, then you will see.

Regards,

Henry

 

[dralex]

Re: Verification of leading line into L\'Aberwrach please

Thanks- just wanted verification that the Grand Chenal is 100T.

Regards

Alex

 

[Talbot]

Re: Verification of leading line into L\'Aberwrach please

Just checked C-Map. The plotted line is def. 100 degrees

 

[Robin]

Re: Verification of leading line into L\'Aberwrach please

Alex

L'Aberwrac'h leading lines are very clear and obvious - when you are leaving! When entering the marks are difficult to pick up, often in haze (even fog) or into the sun early on etc, the marks are some distance from Libenter Buoy which marks the start point. It is a huge help IMO to plot some wpts along the leading line starting with one just offshore of Libenter, one on the line and abeam of the 1st port hand buoy (which is very close to the rocks) and another at the turn point to the next leg in the channel). These will get you set up pointing initially the right way to look for the leading marks and also will allow you to stick on the ground track to travel on the line because there are very strong cross tides, you may be pointing say 130degs to achieve 100degs for example and it is the COG here that is important rather than ship's head! Also note that the leading lines take you very close starboard of Le Petit Pot de Beurre beacon and that there is another channel joining here (Malouine) with it's own port and starboard buoys, I have seen people mistakenly head for these and pass the wrong side of the beacon, fortunately without mishap.

Leaving is much easier and you will wonder why you couldn't see the marks on the way in, they are big and clear. If you are headed east, the Malouine Channel is worth taking and saves quite some time, worth the effort to identify the marks to pass you between the rocks which are very close, there is plenty of water in the channel even at LWS though at LWS the rocks seem even closer. The leading marks (stern marks on exit) will keep you on track again in the cross tide, also usually a big swell.

Robin

 

[john_morris_uk]

Re: Verification of leading line into L\'Aberwrach please

I agree! When entering L'Aberach earlier this year (after a long channel crossing and at night) I started the entrance from Libenter bouy and identified the first lateral mark on the correct bearing (couldn't see the leading lights properly due to claggy weather/rain) and a few minutes later had to retrace our steps as we were in shoaling water with breaking water on rocks getting closer and closer.

Second time round it all worked according to plan, but the family still remind me of the incident!

 

[Robin]

Re: Verification of leading line into L\'Aberwrach please

At least nowadays GPS gets you to the start off Libenter Buoy correctly. I cannot understand why they have two buoys (Libenter and Le Petit Fourche), both west cardinals and only half a mile apart. Mistaking Le Petit Fourche for Libenter would be very dangerous indeed!

Seriously too this is a very good example of where modern technology can really help, with a ground track established between two/three wpts on the GPS (better still a plotter) you can see very quickly that the boat isn't going where it is pointing because of very strong cross tides. It is helpful too to have the GPS telling you which way to look for the leading lines and/or next mark. It might seem obvious (and I know you are very experienced so this is not aimed at you John!) but I have several friends who will only plot a wpt at a harbour entrance, it all stops there and goes to Mk 1 eyeball when in fact the GPS is still very useful!

 

[jimi]

Re: Verification of leading line into L\'Aberwrach please

I tend to plot a waymark on a leading mark and use the bearing to it to double check that I'm on the correct line

 

[john_morris_uk]

Re: Verification of leading line into L\'Aberwrach please

Agree totally - and you're never too old/experienced to learn. In fact the more experience I get the more I realise that!!

Your suggestion would have solved my problem straight away. Trouble is you get into habits of what aids to use where, and when I'm in pilotage mode I've got used to using the land/marks/lights/echo sounder.

The reason I was off track was that I cut inside Libenter a little early and then the hand bearing compass wasn't sufficiently accurate/stable in the heavy swell to show that I was off my bearing to the first lit bouy that I'd identified. The second time around I made sure I started from the right place and concentrated a bit harder on the bearing and it all fell into place.

I remember sailing into L'Aberach after a cross channel trip from Penzance without any electronic aids. Log, compass found the Isle Vierge light (ok I yielded to temptation and used what used to be called 'chat nav' and asked a passing ship to confirm my position 80 miles out across the channel. I was a mile or so off my plotted position which at the time I thought pretty good!) Anyway having found the Vierge light I couldn't identify Le Petit Pot du Beurre for the short cut in for love nor money and had to go the long way round down to Libenter.

 

[Robin]

Re: Verification of leading line into L\'Aberwrach please

The swell off this NW corner is a hazard in it's own right isn't it, together with a propensity for sudden fog banks! The main channel entry used to be harder because the port hand buoy half way to the butter pots wasn't there and Adlard Coles pilot said don't attempt it in fog even with radar. I certainly wouldn't have tried it in fog back then even with Decca and 'actual' rather than theoretical wpts, the cross tides can be horrendous and the rocks over which the swell is continuosly breaking do not show on radar. However the simple addition of that half way port buoy has made a huge difference as a) you have a chance of seeing it soon enough b) it shows clearly on radar, unlike the rocks which are just submerged.

We had our systems tested to the limit in August 2003. We came up from Morgat and upwind through Le Four in crystal clear vis, actually having a bit of a friendly race with a Centurian 45 that we had kept pace with from the bottom. We had just tacked to go closer in to Le Four light for more tide as our Centurian pace boat was gaining in there when everything just disappeared in a monstrous fog bank. We went from eyeball to radar/plotter in rapid time as there were lots of boats about, many small without radar. In fact one yacht soon passed going the other way with a spinnaker flying and a combined closing speed with ours of around 14kts I guess since we were doing 7kts, at that time the radar had only just warmed up after switching on, L'Aberwrac'h entry was looking daunting! We have the advantage of a 10" plotter mounted below next to the radar and also can control the autopilot from there plus have a 2nd plotter in the cockpit. We dropped the main outside and sailed in with about half a genoa which both slowed us down and allowed us to listen as well as stare into the fog. The plotters were superb, we trusted the wpts because we had previously checked them several times in good vis and we also have differential GPS and the wpt off the port buoy was showing on the radar with a 'lollipop' from the link with the GPS/instruments. We passed 25m from Libenter and didn't see it! We did get to see the port buoy and the pots of butter but by then were being 'attacked' by seemingly hundreds (but probably 20!) cats from the local sailing school who had a race course set that crossed the channel - twice!

The Malouine short cut from the east by Le Vierge light seems easy when you are on the leading lines and terrifying when you are trying to find them and getting ever close to the breaking swells over the rocks! These days our route means we only need to use this channel on our way out for home, going south we never stop at L'Aberwrac'h just go straight on down to Camaret.

An interesting little corner with a deserved reputation as those of us old enough to remember the Amoco Cadiz going on the rocks here will understand, still marked on the charts as a reminder too.

Actually, going back to our original discussion about using GPS wpts for track pilotage, this is something we do from habit probably because our local playground for many years has been the Central Channel/Channel Islands area with it's very strong tides. Folks from gentler tidal stream areas might not immediately understand the huge differences of pilotage where the compass heading is largely meaningless and navigation is a land of transits or GPS tracks to stick on between the very hard rocks that are never far away

 

[Ships_Cat]

Re: Verification of leading line into L\'Aberwrach please

Hi Robin

I am not sure how you use the waypoints on entering port or navigating other restricted water in poor visibility unless, of course, you drive in on autopilot? Could you explain?

My usual practice is to just drive down the lead line (or my own planned course) on the electronic charting system, manual helming, and using whatever visual cues that are available as a rough double check.

In the days before we used electronic charts I still never used waypoints as firstly they were then a bother for us to set up, plus (without ever thinking much about it I have to say) I assumed best you could get from the GPS with waypoint was bearing and distance to waypoint which one would then have to plot to show one was still on the lead/course. I find it as easy to just plot Lat/Long directly off the GPS to do that so never really considered any other options using waypoints - perhaps there are some.

So, do you do it on autopilot, or drive down the lead on the plotter/ECS (in which case I am not clear as to why a waypoint adds value), or plot bearing/distance to waypoint, or something I have not thought of (which is quite likely as I have not really thought too much about other options /forums/images/graemlins/frown.gif )?

Regards

John

 

[Robin]

Re: Verification of leading line into L\'Aberwrach please

Hi John

Some harbours obviously are easy in that once you find the entrance the buoys are close together and your destination no far from there anyway. The awkward ones are where the entrance starts from some way offshore and the harbour itself is round two or more zigs or zags between the rocks and complicated as in this case with strong (up to 4kt) cross tides, frequently big Atlantic swells and frequent sudden fog banks often on a tide change as cold water gets thrown up from the depths.

I like to set waypoints along the track in. So in this instance I have a wpt just outside but clear to approach from any offshore direction. We could put just one wpt on the next turn point (there are 2 legs to this harbour entrance, 2 leading lines) to establish the ground track, but since there is a key port hand buoy at the riskiest point between 2 reefs halfway in we have a wpt there. This wpt is useful too because the wpt position is marked on our radar with a lollipop on the screen as the radar is interfaced to all the instruments/GPS. The next wpt (#4 in this case) establishes the ground track for leg 2, again on the leading line.

Having set the wpts (and we check/adjust them by visiting them exactly at the 1st opportunity in good conditions) we have in effect drawn the lines on the chart which we need to follow over the ground. We can then follow the ground tracks by several means:-

1) Initially and starting from wpt 1, head on the BTW shown on the GPS for wpt 2 (in good vis this should point your eyes to where the next mark might be) but watch the off-track error and then steer to keep this on zero (or if off err only on the 'safe' side). We did this on the cockpit GPS repeater before we had an electronic chart plotter.

2) With a plotter in the cockpit the method is just the same but now you have continuous visual confirmation of your position as well. Our plotters are set up to show COG with a short line and the ships head is also shown.

3) We also have a 10" plotter at the Nav table and this is right next to the radar screen. The radar is interfaced to all the instruments and GPS and the next wpt is overlaid on the screen with a line from the centre spot to a circle round the wpt. In this instance because we have the extra wpt on the leading line just off the port hand buoy, we can see this marked on the radar screen and should then be able to confirm the target return from the nearby buoy. (it being difficult to otherwise differentiate between a buoy and any other small target). The problem in cross tides is that you still expect the next mark to be where you are pointing, or on the heading mark on the radar, but in fact it will be considerably offset to one side, now it is usefully illustrated with the lollipop on the radar screen.

In all cases I think it helps to use the autopilot as it is very easy IMO for a helmsman to become momentarily disorientated. So in our case with just the two of us on board I do the driving from below using the plotter, the radar and steering by the 2nd autopilot control head mounted there. SWMBO gets to stay up on deck by the wheel and stare into the murk, but she has the cockpit plotter as well so can also see where we are. If needed she can immediately disengage the pilot and steer manually.

We do also have our autopilot interfaced with the GPS so it can be set to follow the ground tracks between wpts and it is spookily efficient at doing this. The Chenal De Four which is the route south from L'Aberwac'h is a good example where this can be used, again having strong and variable cross tides. In good visibility you can almost go straight through, cutting inside some marks but I wouldn't do it at night or in fog. Our wpts therefore are set on the leading lights, straight down the white sectors of the lights and wherever possible the wpts themselves will be between the buoys or abeam of a mark to aid radar ident. We have driven trhrough here several times in clear vis on the track control just to check it works, which helps confidence if we were to need to do it in fog.

I'm not sure if that babble is understandable or if it is even any different from what you do!

Regards

Robin

 

[Ships_Cat]

Re: Verification of leading line into L\'Aberwrach please

No, thanks, that is great Robin and perfectly understandable.

Apart from us not having radar I think we actually do it pretty much the same. Except instead of me using waypoints I just drive with the ECS's look ahead vector (with its time increments on it) down the middle of the channel, or across the transit, or whatever for each sector of the zig zag.

If I found it necessary to have a line on the electronic chart to follow (but haven't to date) I would click out a route (effectively creating waypoints at each change of direction) but again just drive keeping the look ahead vector down the current sector of the route line on the chart.

Obviously, without radar we would not enter confined waters in thick fog if possibility of meeting another vessel with no room or warning time to manoeuvre clear - but such fog conditions are very rare in this part of the world /forums/images/graemlins/smile.gif.

Regards

John

 

[Robin]

Re: Verification of leading line into L\'Aberwrach please

Hi again John

Yes in our case any entrances with potentially difficult or confusing approaches are set up with waypoints even inside the entrance channels. These are then available immediately to make a route or indeed are set up as a memorised route where we use them regularly. We did this before we had C-Map chart plotters, actually using a Yeoman paper chart plotter where there were large enough scale harbour charts or insets available. Once we had C-Map however, very large scale charts are just a zoom click away and it is much easier to select and pop a waypoint in place.

For a new place and a first visit it is helpful to have these internal wpts set up so that the instruments (GPS repeater or plotter) tell us which way to point to find the next mark in the chain. In any entry or departure at night again it does the same and saves a lot of confusion taking hand bearings and counting numbers of flashes etc not to mention probably against a background of shore lights. All in the interests of stress free navigation!

Some of the harbours in our cruising areas like this one at L'Aberwrac'h have long and/or complicated approaches and the whole of this area also has huge tides (big ranges and strong flow rates). Sometimes in places the gaps between hazards are very narrow as in L'Aberwrac'h, where it is only perhaps 75m-100m at its narrowest between two reefs where the swell is clearly seen (or heard in fog) breaking over the rocks on either side. In these cases it is essential to follow the ground track very closely and the GPS does this pretty well, probably to better than +/-10m, and more accurate IMO than the BTW/COG/DTW comparison.

We could maybe send you some fog to practice in if you want, we wouldn't miss it!/forums/images/graemlins/smile.gif

Regards

Robin

 

[Ships_Cat]

Re: Verification of leading line into L\'Aberwrach please

We could maybe send you some fog to practice in if you want

Maybe we could do an exchange for some rain /forums/images/graemlins/smile.gif.

Actually, just had the coldest December for 60 years or something and is supposed to be summer - bring back global warming.

John

 

[Robin]

Re: Verification of leading line into L\'Aberwrach please

We have had a mostly warm December here in the sunny south UK! I played golf several times in short sleeves albeit with a sleeveless wind top as well, temps as high as 15degs C (12degs yesterday and sunny). It will no doubt go tits up later this month when we lift out for a month....