Kathy's Reef Diary

Used with permission Day 1

We all set off to Chumbe island - a tiny, empty island with a lighthouse (which I’d used as a reference point for the programme where I was trying to navigate to a shipwreck).

The challenge is deliciously absurd - protect a bit of reef - a reef ‘burglar alarm’.

Specifically, Ellen and I had to place and make the buoy to support what ‘the boys’ were making. A suitably ‘female’ task!

We lined up a baseline on the beach, needing to locate a place out at sea 300 metres out. When we first went to the beach it was raining but it soon brightened and before long we were being burned to a crisp.

Next, we made up a lethal board with nails stuck in - to line up and find when the angle between the outer two flags was 19^o. We didn’t explain this to death - since I’d done it in the ‘shipwreck’ programme. The method may not have been accurate enough to locate a shipwreck - but it’s good enough for getting approx 300m from shore. (300m is the island’s defined exclusion zone - intended to protect the land + marine life).

We located the point in the boat - & could do nothing but muse upon how deep it might be.

So I’m to build the depth gauge, & Ellen will make the raft.

I started to play around with a tube & a balloon - trying to see if I could hear the balloon pop underwater. Basically - I need to make something that makes a noise when it hits the bottom - or release something that I can then see.

Used with permission

Day 2

Had a lot of hopeless nonsense with balloons today.

Tried to see if I could hear them pop underwater. NO.

So then tried to see if I could get them to pop out of a tube on impact with the seabed, intact. They were hopelessly unpredictable! I’d made a rocket-like tube - weighted with lead at one end and plastic water bottles at the other. This was just to get the thing to sink vertically - even when carrying its ‘payload’ of air in the balloon. I also tipped sand in - above the balloon, which was inflated and wedged in the bottom end of the tube.

The plan was - tube hits bottom, sand lands on balloon quite hard and pushes it out. Balloon rises to surface - so I see it after the landing.

It was hopeless - and funny. I kept trogging off into the sea, with heavy ridiculous looking rocket then dropping or hurling it at the sea bed, usually in water too deep for me.

Hopelessly unpredictable. The balloon usually burst, stayed in the tube. It occasionally escaped, but only after moments - that didn’t coincide with the impact, and varied in length randomly.

I had just half a day to come up with something else - AND take it out to sea and calibrate.

The pressure was on.

Ellen had been pretty sceptical about balloons from the start and suggested several bits of metal separated by floats.

When scuba-diving, you always use metal-on-metal to attract people’s attention when they’re not in reach.

I thought maybe I could use a plate of metal hanging from the bottom by some string - perpendicular to the tube’s length. Then have another piece of metal attached to the end of the tube - which would hit the first bit of metal just after the whole thing hit the bottom.

But I was worried that friction (‘water-resistance’) might push up the plate - so it was in contact with the bottom of the tube during the fall through the water. Then there would be no ‘bang’ when it hit the bottom.

I took my problem to lunch - and asked the whole team’s advice. (At these moments - often the camera or sound guys come up with the best ideas.) There were lots of ideas and suggestions - but eventually it was Jonathan who said “If you’re worried about the friction - put it at the top instead of the bottom”. Of course!!

And then beautifully - the whole team swooped to my rescue. I really was running out of time - and risking not being able to calibrate the depth gauge.

Jonathan helped get the metal bashing device sorted. The production team measured out lengths of rope - people brought us drinks.

Finally ready to go about 3. Took over an hour to get everyone together and ready on the boat … so only about 2 hours to take depths before it would get too dark.

But it worked! It was easy! It took about a second to fall a metre- seemed too ridiculously easy a ‘relationship’

Filming was not easy though. The boat swung round erratically – making it near impossible to film. Got really quite funny. We had a lovely, crazy time in the evening light.

Production team

Day 3

Had worked quite late last night - using stronger ropes and re-tying lots of bits & pieces.

Began early to get to Chumbe in good time.

A boat journey of over an hour - which was just a delight. Gorgeous sunny day and feeling unspeakably lucky to get to do this programme.

I drew up the graph I needed on the boat. Not ideal conditions for graph-drawing. Should have done it last night really - but it was full-on enough already.

Also at first I’d thought I would just estimate the depth from the time of fall of depth gauge. It seemed to be just a bit deeper in numbers of meters than the number of seconds it took the depth gauge to fall to the sea bottom.

In the night I thought “What kind of scientist are you? You have to draw a graph!”

With a body falling in a fluid - like my depth gauge in water, or like a parachutist falling through air - the body starts off accelerating due to gravity.

But the frictional forces increase as the body moves faster. Eventually the frictional forces balance the force due to gravity and the falling body reaches a steady speed (its ‘terminal velocity’).

So, if you draw a graph - of depth and time taken to fall - it will become a straight line once terminal velocity has been reached.

So I had to draw a graph - as any graph (especially when it gets linear at terminal velocity) will be more useful for estimating the depth than my guess-timate.

And wow! Was the graph straight. It looked too straight - given I could only really be accurate to ± 1 second and ± 0.5m - I’d have expected much more scatter.

It looked cheated. Only no-one would be daft enough to cheat so “well”. Chuffed to bits. It still worked out about a metre per second, but without the graph I’d have under-estimated the depth a bit.

Once at Chumbe I got us back to the point Ellen and I had sorted on the first day of the challenge.

So - it was time for the depth gauge. I was pretty apprehensive - I had only tested the gauge during calibration down to ~ 25m. If we were much deeper than that - would I hear the gauge hitting the bottom?

I did. It worked. 27 seconds to 27m and Kate announced it was 27.3. Chuffed to bits! She’d been smart enough to check the depth out at around the same point in the tides as we were going to be doing the test. Otherwise I would have been 2-3m out. We had to make the ropes longer than 27m for the buoys to cope with high tide.

Next was the ‘burglar alarm’ for the reef. It was crazily hard work getting it all up. And the current was so, so strong - ropes and waves kept breaking. Wouldn’t believe how many of us it took - or for how long - to get it all in place.

And even once it was in place - it didn’t work. By this time I was in the water. Realised the beautiful yellow flags were all wet - and often touching the wire - making the alarm go off. Mike and I tied up the aberrant flags.

Still - it wasn’t working - the alarm was constantly bleeping. Mike realised one of the loops of wire had cut through the insulation tape.

I swam to the boat and carried wire cutters above the water to the wire in question. I had to cut the wire - without it getting wet. It’s surprisingly hard to cut wire with small cutters when you’re in water and can’t touch the wire.

Managed finally to cut it (by holding the side that didn’t matter) - & the alarm stopped – we were ready!

Watching the boat approach the line of flags has to be the most tense moment of the series. We had all worked so hard. It had seemed impossible, even dangerous at times (Kate and Ellen in the water - being wedged between two boats). It had been such hard work we were all so tired anyway.

And now - was it going to work?

Even writing this (now about a week later) - I’m still getting goosebumps just thinking of it.

The boat approached … the tension mounted … it didn’t quite touch, then went into reverse … we began again … it nudged forwards, unbelievably slowly. We’d all stopped breathing. … and the alarm went off.

Crazily, crazily happy. An amazing moment - for us all!