Colour blindness

I was moved by Richard Gatley’s letter (YM April 2007) about his
failure to pass colour perception tests.

In 1969 I was a candidate for Royal Marine Officer Training. I’d passed the Admiralty board and had only the medical to do. I was fit and had no worries that I would pass that, too. As expected, I sailed through everything until I came to the colour perception tests. I
showed a weakness on the initial lantern tests and was sent to rest with green eye shades on before taking the test again. I was then put through a limited Ishihara Card test before I was failed as having faulty colour perception. I was devastated, and it took me many months to recover from the blow.

Subsequently I went to Birmingham University to study archaeology and
volunteered my body for student teaching purposes (it earned me money!). I was recruited, through a brief medical history, to be a guinea pig for opthalmology students and, to cut a long story short, was put through batteries of colour perception tests on several occasions. I passed every one as non-colour blind. Indeed I caused some head scratching when I was able to perceive a set of tracks at the end of the Ishihara tests which were divided into two categories – those that could only be seen by colour-sighted subjects and those that could only be seen by colour-blind subjects. I could see them
both, although I’ve always had difficulty with the main body of that test. As I’ve advanced in years I’ve had my sight regularly tested and, whenever my colour vision has been tested, it has been found to be normal.

I do believe that the tests used for offical purposes are flawed and I’ve had one ex Naval doctor agree with me. I think the Ishihara test in particular is flawed on many levels.
My message to you Richard, is don’t give up.

Graham Houghton
Writer/Archaeologist
Aldgate, South Australia

Blind to reason?
I was sorry to read about Mr Richard Gatley´s problem with eye-colour test pertinent to his examination as a RYA Yachtmaster.
However, in aviation, even pilots can be colour blind, and I recommend that he have a talk with a doctor from this sector who could perhaps disclose why it is ok in the air but not at sea to see colours differently.
Many of the new navigation methods and instruments do not require the same colour sightedness as of 20 years or even five years ago. Lighthouses are being shut down all over the world and more and more navigation is done electronically.
As a pilot and sailor I can´t say that I understand the need today to see red as red as long as the differences are constant.
Lars Tell
Karlstad Sweden f

MEDITERRANEAN MISTRAL
I endorse Mr Bob Johnson’s statement (letters to the Editor YM May 2007) that the extremely dangerous conditions that yacht Rosa Fascia’ (YM March 2007, page 36) encountered during her crossing from Antibes to Corsica were not a rare local occurrence, as their weather router would have them believe. Also, that Cap Corse is certainly no place to be in strong Mistral winds.

The Mistral they encountered was well forecast, and I was in fact sitting it out near Toulon (further West) at the time of their crossing. We were encountering winds of Force 7 upwards, and, let us not forget, a force 7 or 8 Mistral means gusts of the equivalent of Force 9 or 10. Not the kind of conditions in which to undertake a crossing towards Corsica.

So why did experienced sailors like them get caught out? I would like, in all modesty, to offer some answers based on my own knowledge of the area and explain some local idiosyncrasies of the Mistral wind (I have regularly cruised an area stretching from the Balearic islands, the Costa Brava and French coast, to Corsica, Elba and the Maddalena Islands since 1972, logging up about 20,000 miles). I write in the hope that some sailors new to the Med may find my comments useful.

Firstly, it should be well understood that the Mistral is very frequent at any time of the year, and definitely not a rare occurrence. The Mistral is predominately an offshore nor’-westerly direction wind along most of the French coast, and although sea conditions may be slight inshore, they become rapidly dangerous, even to well-founded yachts when venturing out to sea. Mistral conditions occur when there is a steep pressure-gradient between, very approximately, the Gulf of Genoa and the mouth of the River Rhone, i.e, when a depression exists somewhere towards Genoa or Corsica with an area of high pressure filling in from the West. The steeper the pressure gradient the stronger the Mistral will blow. It is in fact quite an easy wind to forecast, and doesn’t just mysteriously “happen” as some would have us believe.

An important point (which may explain Rosa Fascia’s predicament) is that the Mistral wind, after flowing down the Rhone valley (and other gaps in the mountainous terrain) spews out into the Mediterranean in what seems to be a fan like configuration. The initial Northerly air flow curves towards the West offshore (in the area in question) and will, in the majority of cases, miss some coastal areas towards Cannes, Antibes and Nice completely. Out at sea however, or to the West of Cannes, it could be Gale or even Storm force.
I could well imagine that the crew of Rosa Fascia picked up the local inshore forecast (Bulletin de Metéo Côtière) for their area (Antibes) before setting out for Corsica. The inshore forecast for that area would, correctly, not forecast gale-force winds, but would generally mention if any BMS (Bulletin de Meteo Spécial, Force 7 and above) was in force and affecting offshore or other areas. Sailors should be aware of this and be sure to listen to, or study, the Offshore Sea Areas Forecast (Bulletin de Méteo pour les Zones du Large) prior to setting out on any major crossing in the Med. My personal preference for the Offshore forecast is Monaco Radio on 4363 kHz short wave (USB) also on VHF channel 20, I believe. (For coastal areas there are also excellent continuous forecasts transmitted on VHF, channels 79, 80 and some others, for the various areas from Spain to Corsica).

There is also a more positive side to the Mistral situation described above: should one have the misfortune to be caught in a Mistral when crossing back to the continent from, say, Corsica, by bearing away towards Nice or Antibes one could generally sail out of the main Mistral airflow into calmer conditions inshore.

Finally, the Mistral, of course, is not the only strong wind to be wary of in the Med. My personal hatred on the French coast, along with many other sailors, is strong Easterlies which churn up very nasty seas inshore, and inevitably bring bad weather as opposed to the lovely clear-blue Mistral skies.

Good sailing!
Tony Ringrose, Geneva.
(Name and address supplied)

Angel answers
Paul McNeill’s article ‘Do Angels Delight?’ about anchors (YM May) raised some questions for me and, I suspect, other readers. As a chartered engineer and Yachtmaster, I’ve done some sums to find the answers:
1) How much can you reduce the scope for the same anchoring performance?
2) How heavy should the angel be?
3) How much will the holding strength increase when adding an angel to an anchor chain without changing the scope?
4) What’s the best distance down the chain to attach it?
5) What’s their benefit used on anchor warps?
To find some answers to these questions I went back to my A level mechanics It had some useful ‘catenary’ analysis.
A few sums based on this helped me to determine the best way to use an angel. Most anchors work best with the chain horizontal and the shank touching the bottom or pulling horizontally. Once the chain becomes tight enough to lift it, the lifting or movement of the blade, levered by the shank, is what is likely to cause it to break out or fail to bed.
Therefore, I chose to calculate the tension at which, under the various conditions, the chain nearest the anchor will lift off the seabed, such that it is still just pulling the anchor shank horizontally and not lifting it. This is the maximum safe holding strength for each condition.
These compare well with Paul’s practical figures in his January article. Using his figures of anchor chain tension in high winds, this is likely to happen in about Force 7 on his boat with 8mm chain in 5m depth on a 5:1 scope without angel.
A very simple rule emerges! Reducing anchor chain scope by a length weighing equivalent to the angel will give the same holding tension before the last of the chain lifts off.
For example, 8mm chain in 5m depth with a typical 13kg angel would allow you to anchor with a 3:1 scope with the same holding strength. (10m of 8mm chain weighs around 13kg). In 10m you would need to use 4:1 scope to get the equivalent performance.
Stated more simply for the layman: When anchoring you can reduce your scope by a length of chain equivalent in weight to that of your angel without losing holding strength.
If you still use 5:1 scope, but add a 13kg angel,the horizontal holding tension needed to just lift the chain nearest the anchor will increase by virtually a factor of two from 83 kg to 165kg. This is equivalent to using a 7:1 scope in 5m or 6:1 in 10m depth.
The above assumes that the anchor will hold, if pulled horizontally. All the anchors that set in your December issue tests exceeded this figures by a good margin. If an anchor does drag under those conditions no amount of extra chain or angels will help!
To get the best greatest increase in holding power, it’s important the angle does not hang down much and far enough away to lift off the bottom easily. Attaching it around half the sea depth up the chain from the anchor would seem best.
However, to get better shock absorbing from a lightweight angel, it might be better midway down the anchor so that it is off the bottom more often. Paul’s very heavy long chain loop angel would give better shock absorbing as this will lift off the bottom progressively giving softer damping.
My kedge has 5m light chain then 1m heavy chain then warp. (I hardly ever bother with the bower now)
Peter Hebard, Yachtmaster, CEng, FIMechE (by mail)