Mike's Lost At Sea Diary

Production team Day 1

For Programme 2, Kate wants me to make a flare that she can launch from a boat at sea. I'm going to love this, as it will involve making gunpowder. Hisdory, one of our drivers, and by now a good mate of mine, tells me that there's a bat cave at Mangapwani, a 25-minute drive north of Chuini. I've used bat droppings before as a source of potassium nitrate (nitre), one of the two chemicals I'll need for gunpowder. The other chemical is sugar, which I can easily extract from the sugar cane I've been given in the trunk at the top of the programme.

It's some time before a film crew and driver are available to go to the cave to film the collection of a few bucketfulls of bat droppings. It turns out that the cave is looked after by a Zanzibari called Ali Baba, and we have to take all manner of precautions to ensure that none of us inhales the dust that we kick up in the cave. A protective suit, a face-mask, rubber gloves - I look like a Ghostbuster. It's hot and humid in the cave too, and the place where the bats nest isn't that accessible. The crew and I have to crawl on all fours through narrow passages, and it's hard going. We all sweat buckets. The outside temperature (upper 30's Celsius) is uncomfortable enough at this time of day, but in the cave it's several degrees warmer, and a lot more humid.

The local villagers use the bat cave as a water source, despite the fact that it's dirty water, and probably contains all manner of dangerous organisms. It's heartbreaking to think that these people probably have to walk for miles and then descend into these hot and humid depths to get hold of something so essential to life. We take it for granted that our water comes at the turn of a tap, and that it's safe to drink. These people have to work so hard for theirs. I feel a strong sense of guilt, and a determination to do something about it when I get back to the UK. There are bodies like Water Aid that are tackling such problems. I'll get in touch.

By early afternoon, I'm back at Chuini, and the process of extracting the nitre from the bat poo begins. It involves dissolving as much of the poo up in boiling water, filtering off what won't dissolve, and reducing down the filtrate to get a concentrated solution of nitre (and other inorganic salts). It's going to take some time though, as we have a lot of poo to process. We shan't finish this till tomorrow lunchtime at the earliest.

For the other component of gunpowder, it's a simple matter of boiling the crushed sugar cane in water and reducing the resulting solution down to give crude, crystalline sugar. Again, however, it's a time-consuming process, and one that I shan't finish today.

Production team

Day 2

Processing all of the bat poo and sugar cane, as expected, takes all morning and some of the afternoon, during which time I start work on making the casings for the flares, which are essentially rockets. The casings have to be strong enough to contain the expanding hot gases produced by the burning gunpowder. They also have to be light enough to be carried through the air under the propulsive power of the rocket's exhaust - a small hole at one end of the casing, through which the hot gases can escape and produce the necessary thrust. They don't take long to make, and within an hour I have a dozen or so casings drying in the afternoon sunshine - thanks, Mike (Cartwright) and Peter (Taylor) for all your help and advice!

But how much, if any, potassium nitrate does the bat poo contain? It didn't look as if it had been lying around on the floor of the cave for very long, so have the microbes in it had enough time to do their work? There's one way to find out. A filter paper soaked in my reduced 'bat poo' solution and allowed to dry, should ignite readily and burn like a fuse - and it does, which is a sure sign that we have nitre. Carefully boiling off all of the water from this solution produces a solid that, when mixed with the sugar from the cane, will do the trick.

Day 3

“Can't be that many men who can claim to have given Kate a thrill using only bat poo and sugar cane!”

It looks like it's going to be a pretty easy day for me. All I have to do is pack the rocket casings and do a few test flights to check how much of a tail should be added to the rocket to make it fly with some kind of aerodynamic stability. I've got all day to do this too, as we'll be filming late into the evening tonight, to make the most of the darkness for my flare. To make more of a spectacle I pack some of the rockets with small pieces of aluminium from an old drinks can, and iron filings. These will help produce the 'twinkly linger' that Kate specifically asked me for. Can't be that many men who can claim to have given Kate a thrill using only bat poo and sugar cane.

Two hours after sunset, and my flare does the business, but it's difficult to catch the launch and flight on camera. The procedure is filmed from dry land as well as from a boat some hundreds of metres offshore in the dark. I'm not so sure that it'll look all that impressive in the final cut, but in reality, and close up, my flare's deemed a success.

As we don't actually finish filming till about 10pm, we're going to have a party on the roof terrace of the house in which Kate, Kathy and Ellen are staying. Conveniently, it's right next door to our workshop. We're halfway through the shoot at this stage, and, for the most part, I'm having a great time out here in Zanzibar.