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Rough Science 5 Zanzibar: Jonathan Hare's diary: Lost at Sea

Updated Wednesday, 23rd February 2005

Jonathan Hare's diary about the challenge for the Lost at Sea programme, part of the fifth BBC/OU TV series Rough Science, based in Zanzibar

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We are all working together on making survival gear for someone (Kate) if they fell overboard. The idea is to make a life-jacket with various additions that might make it a really great bit of safety gear. We each have a part of the challenge and my part is to make some lights that can be powered from the sea.

Day 1

Show the possibility of making batteries from screws and pencil leads (or from carbon rods from old worn out batteries). The power from a battery is derived from chemical energy and we intend to use sea water (which technically is called the electrolyte). I demo a six cell battery made up from six screws, six carbon rods. I used an ice cube tray as this has a number of compartments that can be used to hold the six trays of sea water to form each cell separately.

I got some small LED lights from the radios and these will be used as the lights for the life-jacket. The screws and rods are fixed in pairs to a piece of wood, six of the ice cube trays are filled with sea water and the rod pairs are dipped in. These are then wired up, like a daisy chain (in series) to make a battery of six connected sea water cells.

Day 2

Six cells easily light an LED. However we want to light more LEDs and also if possible use the energy more effectively so that we get a bright flash. This will be much more noticeable out at sea.

The way to do this is to use a capacitor. These can be found in the radios. A capacitor is a device used to store electricity. It does not create electricity like a battery it simply stores it. If we take the example of household water pressure being like the electrical force in a battery, then the capacitor in this example is rather like a water tank – it stores water but does not create it.

What we do is charge up the capacitor (fill the tank) and use this stored energy to pulse across the lights. This way we make use of the batteries' ability to supply a constant low level power to the capacitor but also the capacitor's ability to supply short pulses of high power. We are not getting something for nothing because the overall power is the same, we just use the capacitor to allow us to deliver the power in a different way. I find a couple of 100 microfarad
 capacitors from the radios, which I add together - they look like they will be ideal.

Make up a ‘halo’ of 4–6 LEDs so that when the person is in the water a light can be viewed from any angle the rescuers may be coming from.



I make up a vibration switch so that the LEDs only get the power in bursts if the apparatus is moving (which it will do out on the open sea). This consisted of a metal spring surrounding, but not touching, a central wire. When there is movement the spring wobbles and makes contact briefly with the central wire. This was wired into the circuit so that the sea water battery’s charge-up the capacitors constantly and on movement this power is supplied briefly, by the vibration switch to the LEDs.

"I realised that my sea water battery idea had a design problem"

I realised that my sea water battery idea had a design problem. Simply dipping the apparatus into the sea won’t work because the sea water itself is a good conductor. If you dip the apparatus into the sea each cell will fill with water which is what we want, however each cell will also be short circuited by the conducting sea water, which is not what we want to happen. The way to get over this was to put some sponge into each cell. On immersion this soaks up water and keeps the cells wet even when the apparatus is pulled out of the sea, whatever the angle.

I tried this out in the sea and it worked!!

Finally put all the gear together onto a pole so that when Kate is in the water she can hold the lights above the water or fix the contraption to the life-jacket.

Day 3

Spend the day perfecting the final design and spending some time helping Ellen and Kathy seal up the rubber coated bags. This was a long job. Also help Mike make a detonator for the rockets out of a lighter. This idea works well but the lighter fails after a few tries. Have to go for an electronic ignition system with a hand drill battery, cables and thin wire.

We wait till it is dark and Kate goes out on the sea somewhere. The rocket / flare is launched and we follow the heading to see if we can find Kate in the water. Eventually after some time we can hear her but can’t see a thing then we see some little lights flashing ….

Kate looked very comfortable in the water in our Rough Science life-jacket.





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