Posted: 22nd July 2019 | Written by: Commander Sean O'Reilly
Let me refresh your memory …
Fishermen Alf and his son, Ben, have gone to sea for the day, expected to be home by 1600. But they aren’t. Three days of angst-ridden searching reveals nothing, until ominously evidential flotsam washes ashore. The vessel is later found on the seabed about 3 cables to seaward of its intended track, on its side in 55m of water off MG Point. There is no sign of either Ben or Alf.
Virtually the entire town turned out for the funeral. It was a beautifully crisp morning, rather reminiscent of the bracing day on which they had last sailed to ‘earn some victuals’, as Alf habitually characterised it. Ben and his Dad were carried into the Church by six RNLI pallbearers; their mates. Alf too had been a seagoing lifeboatman until he was deemed ‘too old’, and Ben had proudly inherited his oiled navy-blue seaman’s jersey.
Tough, gnarled men wept openly without any attempt at restraint... especially when ashen faced Demelza walked up the aisle alongside her boys’ coffins. The organist, he too digging stoically deep, let rip with ‘For Those in Peril on the Sea’. The hymn singing almost took the roof off.
So, let’s return to the rub of the matter; simply ‘why?’... what led to this catastrophe? Could it have been avoided; was it anyone’s fault; could anyone be blamed, or was it just one of those inexplicable turns of fate – simply bad luck, a case of wrong place, wrong time? Or might it not be a case that the difference between a gamble and a risk is similar to fate and luck in that both focus on more than mere serendipity.
Cannot risk and luck, to some extent, be managed? Or, to put it another way, can we learn from the wisdom of the great Gary Player, who anecdotally once chipped in straight out of a deep bunker, having seemingly miss-hit his blind shot. Reeling dramatically from amused shock and grabbing a rare opportunity to rib the great man, his astonished playing partner laughed, ‘that was a lucky shot!’ Unmoved, Player famously replied, ‘maybe, but the harder I practise, the luckier I get’.
How should the vessel have been navigated safely; ‘by the book’, as it were? Ask ten Master/command qualified mariners and you’ll get …. different answers (you fill in the blank). Books aplenty have been written to translate and interpret the implementation of the strictures of countless IMO edicts, SOLAS, STCW, MCA and local authority laws, bye-laws, rules, regulations and more. And Bowditch (US), Admiralty (UK) manuals galore and reams of commercial text books are wonderful tomes, but who reads them? Do you?
Thankfully for us all, MCA endorsed STCW syllabub driven courses reduce the mountainous plethora of ‘method’ to manageable chunks, so here’s what I reckon Alf probably ought to have done (massively compressed):
(AKA 'Wot I did on the course in Antibes')
IMO/MCA regulation demands a passage plan every time a (commercial) vessel goes to sea; it should be from berth-to-berth (in this case, a return trip from/to the fish quay jetty). On the largest scale, corrected (government issued) chart, hatch in the safe, navigable water to show No-Go Areas, or Limiting Danger Lines (LDL) as they are also known in naval parlance; to calculate the LDL add figures for draught, plus a desired under-keel clearance (UKC), and a worse case figure for squat.
Arguably, you can now factor in a deduction for tidal height, although if you don’t at least you are erring on the safe side (unless you are going under a bridge!) For example (for a relatively small vessel/ship):
Draught 2.3m + UKC 1.0m + Squat 0.5m = Safe Depth 3.8 metres
Draw the LDL outside the 3.8m soundings and hatch it in on the shallow/unsafe side. Bet you a pound to a pinch of sh*t that virtually all seasoned navigators would trace along the 5m contour, even on the largest scale harbour plan; makes sense, no? KISS*
Of course, the ECDIS process (provided you are fully compliant) is less laborious (Safety Depth/Safety Contour), but the principle is exactly the same.
Draw the intended track on the chart from the berth (observing Rule 9) to the outer limits of the harbour, and plan the detailed exit/entry – leading lights, headmarks, wheel over bearings, transits and, having established likely tidal streams, courses to steer on each leg. Pop in parallel index lines (remember ‘CARAFES’) and top the whole thing off by adding clearing bearings and ranges sensibly close to the limits of safe water; ie. how far you can stray off track without batting an eyelid.
You can now be happy in the knowledge – you KNOW, not HOPE - that you are SAFE whether you are on track or, for whatever reason, have drifted to port or starboard of your planned route (usually because a grockle’s sailing vessel is in the bloody way! It happens.)
Now we are out to sea, beyond harbour limits, so we can focus on the planned track along the coast a sensible distance offshore. Alf’s choice of about 5 cables is fine; but perhaps a mile could have given just a little more margin of safety; a few more seconds to react, and a wee bit more sea-room – at 10 knots, 5 cables is only three minutes which isn’t long if your attention is distracted, especially if the Master/OOW is also the sole lookout**.
Has anything crossed your mind along the lines of ‘Yeah, yeah, yeah’... if so, keep going; this article is written especially for you.
Having drawn the track on the chart, look carefully along and around it to check that NOTHING can bite you in the ass (ECDIS of course, clever-dick that it is, will draw your attention at this planning stage of APEM). A few of the symbols that should catch your eye:
Mindful that most ‘working’ vessels will have their ECS track plugged into the autopilot, on passage in the open sea it’s likely that you won’t feel rigidly constrained to keep the vessel on the planned track (coastal navigation is not pilotage per se). You’ll have decided an acceptable cross track error (XTE) to allow sensible scope to diverge from the track; for example, for COLREG collision avoidance, maintenance of the intended course made good, avoiding fishing floats, and perhaps scope to allow the OOW to keep CPAs outside a proscribed limit (1 mile?) to avoid frequently calling you (that’s what it says in your Masters Standing Orders, isn’t it?)
In the absence of a visual head mark, on a coastal passage the simplest real time method of knowing that the ship is ‘on track’ (and, most importantly, safe) is a parallel index line – no particular need for clearing ranges because you, the prudent mariner, have factored in safety margins off track by selecting a safe distance offshore (I reckon a mile would be sensible but many factors might draw you closer inshore).
So, the simple passage plan from harbour, around MG point and east to the lobster pots might look something like this: 'Minimal' Passage Plan.
Let me remind you that SKULLDUGGERY, like many other local vessels, was routinely observed to maintain a distance offshore of about 4-5 cables; her draught is 2.3m...
The MAIB directed that it was necessary to recover the wreck of SKULLDUGGEY, in part because of the sensitive but grim task of solving the mystery of Alf and Ben’s whereabouts, but mainly for forensic examination of the gash along the hull; the obvious cause of the almost immediate sinking. Recovering the vessel would also allow examination of the bridge/wheelhouse for anything that might throw light on what might have happened. To the horror of all concerned, when ‘SD’ was re-floated Alf and Ben were both found in the fish hold.
The key conclusions of the investigation were:
SD sank in less than a minute because her hull was catastrophically holed after grounding briefly on a rock 5’.124 miles west of MG Point, with a charted depth (sounding) of 3.8m.
The vessel’s speed was 10-12 knots
There was no evidence of a passage plan; no annotations of any description, including a planned track on the laminated, out of date and uncorrected chart, the datum of which was OSGB 36 (with a Horizontal Datum Shift from WGS 84 (ECS) of 85m.)
The ECS was functioning correctly; partially recovered track history indicated the vessel passed close to the rock which showed signs of recent impact.
A former employee of Alf confirmed that ‘eyeballing it’ was the apparent primary means of navigation; ‘Alf knew that area like the back of his hand; he’d done it thousands of times’.
There was no evidence of any bridge/wheelhouse records (eg position fixes, hourly pressure, wind etc.)
Alf and Ben were both free from any alcohol/psychotropic substances.
The Master/OOW was not on the bridge; it is possible that the bridge was unmanned at the moment of grounding and/or sinking.
Let’s now go back to some of the key clues in Part 1 that were there for the eagle eyed ‘salt’ to spot:
‘the unusually high berth’
‘the vernal equinox’
‘crisp, cool Atlantic still air ….’
‘refreshing breeze … generated by the boat’s speed …’
‘shadows created in the troughs of a typically long Atlantic swell’
‘the eddy tails on the buoys’
‘the sun just risen .. casting a wonderful light … across the unbroken sea …’
The ‘unusually high berth’ means that the deck of the vessel must have been unusually low; indeed, she was because it was low water, or close to it, and spring tides to boot – it being the vernal/spring equinox (when the greatest spring tides occur). There were no conspicuous eddy tails on the buoys; it was slack water which was the case for about 45 minutes either side of low water, so we don’t know for sure if it was just before and after LW; whether it was ebbing or flooding (and nor did Alf).
SD sailed south into ‘a typically long Atlantic swell’, evidence that some kind of significant meteorological event, maybe a thousand or more miles away centred around a mid-Atlantic depression, had caused it. The Atlantic swell must have been westerly; how else would a rising (eastern) sun create shadows in the troughs? By definition, you can only have an area of (relatively) low pressure if there’s a high anti-cyclone nearby(ish). And guess what ….. on that day the Azores High was indeed well north, and the barometric pressure an eye-catching 1045mB (or hectopascals if preferred, you pedant!)
Long swell, but with an unbroken sea; must have been very little wind, which is normal in anticyclonic conditions. It’s largely the wind that causes the waves to break in open water, so if the sea was ‘glassy’ (with no white water), there’s virtually no true wind. And we already know that because the (relative) ‘wind across the deck’ is caused ‘only by the boat’s speed’. So, the sky is virtually cloudless, it’s crisp and dry – it is the kind of weather that used to make me suck the air through my nostrils and joyously declare that ‘it’s good to be alive!’ A nice coffee, and a café crème cigarillo on the port bridge wing – what could be better?!
Notwithstanding the Hercule Poirot sleuth-like examination of the facts, and the clever dick description of what should (‘by the book’) have happened, let’s have a shot at sensible, pragmatic bridgemanship. The navigation and shiphandling procedure and process described in the preceding paragraphs is sometimes described as ‘best practice’, arguably a polite euphemism equating to ‘bullshit that I haven’t got time for’. Somehow, in the minds of a few, that standard of bridgemanship applies to other sectors of the shipping industry – Cunard, P&O, Maersk, ‘grey funnel’ Navies … but surely a line on the chart is not asking too much, is it? A PI and an occasional fix (which would take about 30 seconds for the practised watchkeeper to plot: surely, two radar ranges and the GPS lat & long isn’t asking too much, is it?)
We know already that Alf (just like many other mariners routinely operating in exactly the same areas) did not plan a passage every time; indeed, he didn’t plan one at all; he knew the area, and was almost certainly well aware of the 3.8m rock off MG Point, but didn’t factor that in because, well, he been near (or over) it thousands of times; in fact 12000 times in his career at sea (30 years x approx. 400 times per year).
Let’s dig into some of those obscure reference books*** and have a look at just a few of those clues:
Chart datum is coincident with the predicted lowest astronomical tide (LAT), which usually occurs around the equinox. Tidal height predictions can be incorrect; they can and occasionally do vary from the algorithm derived height.
‘Moderate’ swell is 2-4 m; a 2 metre swell has an amplitude either side of Mean Sea Level (MSL) of 1m (or at LAT, 1m below chart datum...) The ‘average’ length (aka wavelength) of oceanic swell is 100-200m (not immediately discernible in a small ship).
Pressure systems in temperate zones (approx. 30-60 degrees latitude) routinely oscillate between extremes of 970 and 1045 mB, a difference of 75mB. The weight of the air in a high pressure anticyclone can depress the height of the sea by at least 0.5m, perhaps even a full metre depending on the seabed topography.
Let’s apply these figures to SKULLDUGGERY, with a draught of 2.3m, a desired UKC of 1.0m, and a squat figure of 0.5m, giving a safe (charted) depth of – surprise, surprise - 3.8 metres.
What are the chances (ie. the probability) that SKULLDUGGERY was in the vicinity of the ‘perfectly safe’ rock charted at 3.8m at precisely the time when:
It was low water springs, at the equinox, hence 0.0m height of tide.
There was a long Atlantic 2m swell, the trough being 1 m below CD/LAT
An anticyclonic system of 1045mB depressed MSL by about 0.5m.
Take a look at this Levels Diagram for SKULLDUGGERY.
SD’s draught was 2.3m. The depth of water over the 3.8m charted wreck was also 2.3m. Was Alf unlucky? NO, he was not. Need any more be said?
For illustrative purposes only, the conservative (wet finger in the air) probability of these unlikely factors occurring concurrently just as SD passed over the rock at about 0600, as it had on 12000 previous occasions, is approximately:
LAT (+/- 0.5m) 1/90
LW +/- 1 HR 4/24 (semi-diurnal tides, 2 x LW/day)
2m Atlantic swell 1/30 (once a month)
1045mB Anticylcone 1/50 (late summer, ITCZ north)
Probability 1/810000 …. but if you keep doing it
The number crunchers amongst you will have calculated that the probability of the four factors combining is about 1 in a million (810,000 plus or minus a bit) which you might consider risk-worthy odds, but when you consider SD chanced it on 12000 occasions, there is about a 1% chance of gloom (0.0067 for the crunchers).
Would you risk your family’s wellbeing if there was a 1% chance of a fatal incident? Alf did.
A senior MAIB official ‘oppo’ and former naval shipmate of mine told me an interesting statistic: every day a vessel somewhere on the planet goes aground because of GPS; they follow it slavishly as the ONLY means of positional information and it actually drives them aground despite the evidence all around them, especially out of the windows. And in this ditty we haven’t even considered the routine errors that are in GNSS/GPS systems all the time. What keeps users afloat is being inside the 95% of a normal distribution curve (aka ‘no more than mere probability’ which, forgive me, is not ‘luck’, which you can shape. No, it’s nothing more than a gamble.
The Mariner’s Handbook (NP100) also tells us there is a 1-5% risk that raw GPS might be inaccurate by up to about 120m, sometimes more. The calculated risk/probability of this happening is spookily close to the number of users at sea; 1 in ten million – every day somebody, somewhere goes aground; they are that ‘1’.
Whilst I am confident that you practise at sea what you have been taught by your previous captains, what you learned in the classroom and described verbally in your Masters’ Oral exam (to a Class1 Master Mariner with no experience whatsoever in commercial yachting – and he’s never heard of Club 55), there are a few, just a few, who reckon they know better. It is an active decision to make sure that person is not YOU.
People’s lives depend on how you conduct bridgemanship. Navigate properly.
* Keep it simple, stupid
** See MGN 315
*** See NP100 ‘Requirement for the Carriage of Charts and Publications’ (the minimum requirement to enable compliance with COLREG 5 (Lookout); ‘all available means … to make a full appraisal of the situation …’).