Unlit Marks - nav techniques?

[severnseadog]

Chaps and chapesses.

What techniques do you folk use for finding unlit marks, as per the RYA advanced course? Obviously it depends a bit on the location of the mark/point to get to an what's available to use, but interested to find out what ideas people have.

I've observed a couple of advanced courses and done it myself some time ago, but it struck me that it was not something people are really taught to do until the day itself when they are asked to apply it.

Things I've seen:
- using 2(+) lit marks inline as a transit for one heading
- using other lit marks to get a 3 point fix with hand bearing compass
- travelling from a known position at a fixed speed on a fixed heading and using a stopwatch to determine distance travelled
- using directional lights that happen to change colours at the correct heading

What other techniques would people use? Any Advanced instructors out there - I welcome your input on what you have seen that works well.

[jlandells]

That's a great question! Since I'm currently preparing for my Advanced course, I'll be watching with interest to see what others suggest!

-John.

[hamster]

When I run advanced exams I'm looking to see that the candidate can demonstrate a range of different skills and knows which to apply and can implement them confidently.

When I did my advanced course years ago we were just taught to use speed, time and distance calculations and hope to land straight at the buoy assuming all went to plan. This is all well and good if you have a competent helm who can steer an exact course at an exact speed and nothing affects you like tide, waves, wind or other boats and you factor in things like time taken to accelerate to speed and then half the time they over anticipate the speed the conditions or their ability allows us to travel at and therefore all their time calculations are useless and a waste of time.
When I do exams I'd much rather the candidates use the log on the instruments or GPS to measure distance than faff about with stop watches etc in the dark.

Other techniques like back bearings, transits, clearing bearings are all useful if you know how to use them and reposition yourself when they don't put your self where you want to be. I've spent many hours sat in the back of boats while candidates look at the bearing they have written down and want to see on their compass and can't work out where to move the boat to in order to get nearer to where they want to be.
If you have bearings to locate the mark then the best thing you can do is pick up one of these position lines and drive along it using a back or forward bearing (not heading as this will be effected by tide and wind) and use one of the other bearings to tell you how far along this line to travel. The more perpendicular this is to your direction of travel the more accurate it is to pinpoint your position. This is much easier than having three bearings that are not what you want them to be and trying to work out where to drive to change all three. Get one bearing correct and then keep that constant to work on correcting the others.
Transits if you have them on your marks are much easier to use than a bearing as they give you an instant indication of your line. Again pick up the transit and drive along it and use a bearing off the beam to tell you how far along it to drive.

Another thing that's widely under used is the depth sounder. Usually the nearest point of reference for an easy indication of being in the correct place, or not, is directly below you.
Maybe you can follow a contour if the mark happens to lie on one. Again bearings to other visible things will help tell you when to stop traveling along the contour.
Often we can use the depth to tell us how far we have travel rather than time. Let's say your unlit mark lies on a 2m contour. Get to a know position nearby such as a lit mark that lies on another contour, say 10m. Note the depth here (which obviously includes tide) and drive in the direction of the unlit mark until your depth drops by 8m. Unless the seabed has changed a lot since the chart was produced you will be fairly close to the mark. This technique works best when the depth changes a lot. It's not so accurate when the depth is fairly constant as you can travel a long way with out the depth changing much. By using this method however you don't need to know the current height of tide as your only interested in a change of depth, not the actual depth, so there's no need to sit and spend ages working out the height of tide for every 10minutes around the two hours you think you might be looking for the buoy and want to guess the actual depth when you are there.

Having a variety of techniques is one thing, having the confidence and conviction to execute them when your out in the dark late at night and the pressure is on is another skill in itself. Believe in what you have written down on your plan. If you follow it and it doesn't work then you can start to rethink things. As I said previously I've sat in many boats with candidates getting flustered and not believing in what they have spent hours planning and writing down or not knowing how to get back on track when the boat ends up in a place they didn't expect and that's what most people fail on. If they end in the wrong place and can then use their plan to get back on track that shows a much better ability as a skipper than those that go nowhere or those that just drive around aimlessly not knowing where they should be pointing the boat.
Here are two examples of people who have done the later. Both ran the boat aground and subsequently failed the exam. I always record our track on Navionics on my phone so I can review with them later what we did and where we went with out any chance of a dispute



Get out and practice in the daytime first. Put a random dot on the chart and try and navigate to it. Note down the lat and long of it and when you think you have got there put it in the gps as a waypoint to check how far you are from it. You should be able to get within 50m of it easily and you can practice the same techniques you will use at night with out the stress of doing in the dark. Once your confident try it in the dark.

I often don't ask people to take me to unlit marks now. I use a random position on the chart. I don't like the idea of driving towards something big and metal at speed that they can not see and could easily hit. Also often with lots of back ground light or a full moon you can see the unlit mark from over 100m away so there is then no skill in navigating the boat to an exact position. I give the scenario that an object has been reported ok this position and we need to go retrieve it. The RYA are starting to encourage similar practice on advanced courses for the same reasons.


RYA Instructor, Trainer, Examiner and Skipper

[Doug Stormforce]

I echo most of Hamster's comments.

At this level i would avoid time/speed/distance. We are really looking for something more accurate. This is invariably driving along one position line (depth contour, back bearing, transit etc.) and picking up a 2nd position line that crosses the first one as close to 90 degrees as possible.

Other key points that come out are background lighting/light pollution, choice of light to navigate by (you don't loose sight of a contour in the dark), use of a hand held compass, briefing and taking charge of crew and identifying lights to name a few.

[captnjack]

Originally Posted by hamster

I often don't ask people to take me to unlit marks now. I use a random position on the chart. I don't like the idea of driving towards something big and metal at speed that they can not see and could easily hit. Also often with lots of back ground light or a full moon you can see the unlit mark from over 100m away so there is then no skill in navigating the boat to an exact position. I give the scenario that an object has been reported ok this position and we need to go retrieve it. The RYA are starting to encourage similar practice on advanced courses for the same reasons.

Agree with this wholeheartedly! Major marks/hazards are almost always illuminated and have sound here. So I can't imagine a situation where I want to find/ closely approach an unlit mark in the dark (or fog). I can imagine a situation where I want to go between 2 unlit marks (unlit channel) or avoid an unlit mark because the minor mark is itself the principle hazard in the dark/fog.

Obviously in these latter cases, you are using the other strategies to go or stay where you want to be. Locally a single line of position and a depth is good enough (it gets deep fast here) to know how far off you are. Then follow a heading to your next fix - between the unlit marks or X distance off the mark.

[severnseadog]

Great stuff. Thanks.

I've always been a bit wary of using soundings as a nav technique (don't know why) but I shall go out and try it in the daylight and see how I get on one day. Good new tool to have in the toolbox!

I think, like most things, there is no one-size-fits-all solution and it's all about having a variety of techniques to use depending on the position of the point you want to get to. The trick will be to have as many good tools at your disposal as possible, and picking the right ones!

[Doug Stormforce]

Originally Posted by captnjack

Agree with this wholeheartedly! Major marks/hazards are almost always illuminated and have sound here. So I can't imagine a situation where I want to find/ closely approach an unlit mark in the dark (or fog). I can imagine a situation where I want to go between 2 unlit marks (unlit channel) or avoid an unlit mark because the minor mark is itself the principle hazard in the dark/fog.

Obviously in these latter cases, you are using the other strategies to go or stay where you want to be. Locally a single line of position and a depth is good enough (it gets deep fast here) to know how far off you are. Then follow a heading to your next fix - between the unlit marks or X distance off the mark.

why do we ask candidates to find unlit marks on an exam?

It is not because we think they should be using them as way points, it's actually because they are often an easy way of testing pilotage techniques. Take for example my home waters, the Solent. if I have three exam candidates to test in one night and I ask each one of them to demonstrate entry into an unlit harbour we have to travel a fair few miles to find these harbours and on 6 occasions I am asking the candidates to put the boat in shallow water (in and out of each harbour). While this is something they should be able to handle I often choose to see if they can find an unlit mark in open water instead, they get to use the same techniques ( transit, back bearing, clearing bearing, depth contour, etc) without us having to travel miles to a harbour and without the risk of a week candidate grounding the boat.

Unlit marks are not the only way of testing pilotage techniques but they are one way, just as finding a cross on a chart or piloting into a harbour are.

However in the normal course of your navigation you would not dream of using unlit marks for a high speed powerboat.

[captnjack]

Originally Posted by Doug Stormforce

However in the normal course of your navigation you would not dream of using unlit marks for a high speed powerboat.

I'm a big fan of teaching/using/practicing what you use. If as you agree nobody in their normal boating would ever try approaching an unlit mark in the dark, then using it as a convenient test of pilotage isn't very true to life.

Perhaps you might test by having them avoid a series of unlit marks by X distance, their success could be measured on a GPS they aren't allowed to use for navigation (review the track afterwards with them). Or go between an unit mark and another landmark. Again how close they are to this artificial mid channel could be reviewed afterwards by the GPS track. Both scenarios seems more realistic and useful to me.

[Doug Stormforce]

Originally Posted by captnjack

I'm a big fan of teaching/using/practicing what you use. If as you agree nobody in their normal boating would ever try approaching an unlit mark in the dark, then using it as a convenient test of pilotage isn't very true to life.

Perhaps you might test by having them avoid a series of unlit marks by X distance, their success could be measured on a GPS they aren't allowed to use for navigation (review the track afterwards with them). Or go between an unit mark and another landmark. Again how close they are to this artificial mid channel could be reviewed afterwards by the GPS track. Both scenarios seems more realistic and useful to me.

I agree, keeping teaching true to life has immense value. There are of course skills we teach candidates to use that we would like them to adapt to different situations. The pilotage skills talked about in this thread are not unique to one single situation, they can be used in lots of situations. I think it's important to encourage their use in lots of scenarios.

Simulated fog navigation (candidate sits down below on a cruiser and we shut all the curtains and he/she relays up headings based on primarily depth readings) is not just about navigating in thick fog, it's about putting more tools in the tool box. In reality in restricted vis I would be using radar, plotter and everything I've got but the blind Nav excercise teaches students how useful depth can be for Nav.

Setting up an excercise that isolates a specific skills is very common in teaching.

When I took my padi Dive Master one of the excercise was for another candidate and I to sit on the bottom at 10m depth and exchange fins, BCD etc. while we would never do this in real life it was a very useful excercise, developing our confidence, breathing control, buoyancy control, communication etc.

In the same way finding a cross on a chart or an unlit mark develops skills that are used across our boating.