I don’t usually do reviews on this site, but in this case I’m moved to rant about the right load of tripe the usually wonderful BBC is wasting our licence fees on.
Episode 3 featured a “Marie Celeste” type incident where a small boat was found deserted of its crew of 3. One was found – wetsuit clad – in the water next to it. The episode had a diving theme, but sooooo much of it was just WRONG. I may get nerdy in some places. Sorry. It’s my ranty blog and I need to rant.
And in program which is supposedly aimed at the forensic scientific stuff, you just wonder how much science has been made up to fit a lazy scriptwriter’s plot.
[Since I wrote this I’ve had more things niggling, so I’ve edited. Edits in Blue]
“You’ve got 5 minutes of air left”
This was “radioed” down to a diver from the boat.
Divers know how much air they’ve got. They carry a gauge attached to their tank. The boat won’t know how much gas they’ve used.
And – usually – it’s bottom time that constrains your dive; the nitrogen loading dictates when you need to start your ascent. If you’re down to your last 5 mins of gas, then you didn’t take enough with you.
“300 Feet”
This was where I realised that they hadn’t run the script past someone who’d done any serious diving. And particularly not in the UK. And it wasn’t just a throwaway line, either. The “300 feet” thing kept on coming up. Now there was an equally sloppy episode of CSI:NY where they kept talking about 300ft (asa “really deep”), so maybe TBF’s writer just used that for his “research” …
On this side of the Atlantic, divers are trained to work in metres, not feet. The maths are easier (10 metres = 1 atmosphere of pressure). The depths on marine charts are in metres. And you’d have to look quite hard to find a depth gauge that displays “feet” (although most computers are configurable).
Actually, the plot would have held up much better if the depth had been 30 or 40 metres. That’s still significant in the North Sea.
But things get tricky when you get past 30m. For starters, you’re liable to get Nitrogen narcosis – at least on an air mix. It can be a bit like being drunk. The deeper you get, the less able you are to perform tasks – such as retrieving a flask full of euro notes.
Secondly, the oxygen in air actually starts to get toxic at around 55m. A diver who had done commercial diving all over the world – and the diving characters’ backstory involved them working on North Sea rigs – would know this was something to be managed. This can be done by mixing a (carefully calculated) proportion of helium into the mix. Nowadays, most dives of this depth would probably be undertaken on a rebreather (but that would mess up the plot).
Thirdly, diving to 100m would give a lengthy decompression schedule – quite possibly an hour or more (I’m – literally – out of my depth on this). So again “You’ve got 5 minutes of air” is another way of saying “you’re going to die”.
But that wouldn’t matter because he was diving in a wetsuit – something that was mildly important for one of the forensic McGuffins. Now, the deeper you get, the more the neoprene in a wetsuit compresses. After 30m you start to get very cold because the neoprene – which is your insulation – gets very thin. So at 100m in the North Sea (or wherever they were), he’d have checked out from hypothermia anyway.
And finally on this, the amount of gas you consume increases with depth. So for a dive to 100m, you would need much more than would fit into the teeny ickle tank on the actor’s back.
The Equipment
The dive kit on display might be what you’d take on a potter round the reefs in the Red Sea. It’s what I’d wear in clear, warm water.
But it really doesn’t fit the bill for the UK, especially for a 300 feet dive.
Top of the list would be a backup air source. Even 3ltr tank might be enough to get you up from 30m. But you’d probably need five tanks to do 300 feet. Something like this. And that piddly little Cressi jacket wouldn’t have enough lift to get them off the deck – you’d probably dive with a wing.
But – as I say – nowadays, you’d probably use a rebreather.
The Spooky Facemask
Most divers don’t bother with a full facemask. It’s more tricky to equalise, and you tend to use more air. But, OK, let’s say a commercial diver would use one – they normally would in hazardous environments with chemical danger. And there are now in-water comm systems – although they don’t come cheap. No, really, they don’t. Not the sort of thing a fairly broke dive boat skipper would have just lying around.
But they don’t have a very long range (perhaps 500m under ideal conditions). Sea water attenuates radio waves. And they are mated to a similar unit on the surface. So the idea that one of the characters – apparently in a different county – could just chat with a kid with a ship-to-shore is just ludicrous.
There wasn’t actually any sign of the unit on the face mask. So the guy walking around trying to use the air feed as an aerial was one of the comedy highlights. Mind, he doesn’t always take his meds.
Normally, the comms would be fed through a hard-line umbilical. But that’s a lot of line to have waving above you in open water current when you’re at 300 feet.
And most importantly it would be inconvenient to let the laws of physics get in the way of a heart-warming subplot.
The Big Fight
OK so it turns out the reason for the whole nonsense was that Patsy was worried that oil development would mean all the fish would be scared away. Or something like that. I’d lost the plot a bit by then …
Well, there ain’t a lot of fish in the North Sea anyway now – they were all scooped up 20 years ago. Most of the boats pot for shellfish and crustaceans now.
And of course, if there was oil, that’d mean property values would go through the roof. Take the money and run, girl.
Dive Procedures
We didn’t see a lot of them. But for a dive to 300 feet – and even considerably less than that – the skipper would drop in a shot line for diver descent. Or the current would probably blow the diver off his target on descent, and he wouldn’t stand a chance of finding it in 15m visibility. But … no sign of a shot, or a winch to drop it, or a buoy to mark it.
There were some nets and an anchor lying around however (for – as it turns out -Patsy to fall on). On the boats I’ve been on, anything not being used gets stowed away. That’s why it’s called “shipshape”. OK, I may be nitpicking on this, but kitted up divers aren’t too stable (and neither are small boats), so they don’t need more things to get tangled up in.
Similarly, when the divers ascend, they would ascend the shot or find some other way for the skipper to be able to find them if they drift off.
As I said above, a professional diver (and most experienced hobbyists) would plan to dive – even to 30m – with a tank of redundant gas – usually referred to as a “bailout”. This isn’t a big deal. It’s just something you’d do automatically, when you rig your kit. There’s a very good reason for this in the UK – visibility can be less than a metre, so you’re more likely to lose your buddy than on a tropical reef. But following this basic safety procedure, ingrained into most “green water” divers from their first sea dive, would make it more difficult to run out of gas (yes – that’s why you do it, of course !) – and again, that would get in the way of the plot.
Bureaucracy and the Legal System
I forgot to mention that there are some established procedures when a diver is found. These involve taking him – with his kit – away for some real experts to investigate how the accident occurred. These people actually understand the impacts of physiology on divers, and know what to look for – rather than taking guesses at it as they stumble on strange anomalies. They’d also know to check the diver’s computer to establish the profile. And yes, you’d normally have a dive ‘puter – especially if you were going to 300 feet.
Getting off the subject of scuba diving, I was a bit surprised at the final scene, at which point the evidence (and Lily Allen’s scary dad) had convinced the guilty to confess, and had even plea-bargained their sentences (I thought that was the CPS’ job …). But apparently this wasn’t enough for our unwieldy legal system, which still needed a jury to give carefully considered verdicts of “Guilty”.
But it did give us the opportunity for a more dramatic “It’ll be different when I get out” speech…