Jonathan's Shipwrecked Diary

Production team

Started today with the beginning sequence of us arriving at the filming location by boat. This takes a little time but is great fun. Still, I am a little anxious to get started and to see what tools and bits and pieces they have provided for us.

Day 1

My part in the first programme is to be set the challenge of making an underwater camera. We will use this at sea to investigate the reef and so it needs to be able to navigate around the seafloor. The main challenge here is to make sure that no sea water gets into the equipment. In fact this was to be a recurring problem in all the programmes.

We have a very good selection of heavy duty plastic pipes that will do really well for waterproofing. We are also given a few battery powered hand drills and some model propellers. Finally a key ingredient is a surveillance type camera and TV screen – the sort of thing that you might use at home to monitor your front door for unwanted callers.

I intend to use the battery powered handrills for propulsion using the propellers in a design that will supply the power from the motors to the props, but keep the motors completely dry at the same time. There will be two motors driving two propellers and a camera to look at where we are going. We also need a system to make sure the movable camera is not too heavy, so that it just sinks, but also not too light that it won’t go under the water! So we need to make the whole thing neutrally buoyant but also provide some means to modify this so that we can make it go up and down when we want it to.

One idea is to use magnetism to provide a waterproof coupling between the motors and the prop. The motors will be fitted into the waterproof drainpipes and the power wires all sealed in. The motor drill chucks hold a wooden disc which has two strong magnets attached to it. When the motors are powered the disc goes round making the magnets rotate. These rotate up against the flat end of the drainpipe section.

Outside (on the other side of the flat drainpipe end) is another identical wooden disc which also has two magnets. This is attached to the shaft that goes to the propeller. When the inside disc spins there is a magnetic drag that forces the outside to follow. Thus the motor power can be transferred across the waterproof gap (the plastic drainpipe end) using the magnetism.

Production team

We found this worked best when the magnets were arranged so that they repelled each other across the gap, rather than attracted each other. When the motors are not moving, the pairs of magnets move as far as they can away from each other. One set of magnets might take up a 12 and 6 o'clock position while the other will fall into the 3 and 9 o’clock position. When the motor starts moving, one disc forces the other around keeping this relative separation.

This was fun to try out. There were problems though. Firstly there was friction between the discs and the plastic pipe end and the whole thing only worked well when the axles were precisely in a line. So we had to work hard to make sure both the motor and the prop shaft were positioned properly and didn’t move around.

I started to look into a mark II magnetic driving system that would move magnets around the curved part of the tub rather than the flat tube end. This I hoped would get rid of the frictional effect and because of the magnetic repulsion / attraction would be inclined to keep everything central. However time was running out and I decided to abandon this version.

Day 2

Took the camera and TV apart to see how they were wired as I needed to completely re-wire the equipment using the long cables we were given (these were household mains type cables and some odd TV aerial lead). All OK.

Make up a frame to hold the two magnetic driven propellers and the waterproofed motors. Start to think about the actual camera design. This obviously needs to be sea proof as well but with the added complication is that we need a window for the camera to look through. There is some transparent plastic sheet that we use for this.

Today was a long day. We got up at 6am and I was working flat out to try and get everything done for tomorrow’s test. It was all much harder than you might think, it took hours of experimentation. Ellen joined me to try and help solve these technical problems and we worked late into the night.

Production team

Day 3

By the end of yesterday we had what we hoped was a completely working underwater camera. We had two propellers driven by two magnetically coupled motors, a switching system that could control the direction of these motors independently so that we could go forward, backward, left and right. We had a waterproofed camera that showed black and white pictures. There were floats on the cables so that their weight would not interfere with the movement of the camera when it was in the water.

We also had a very simple system of weights that we could move around and remove to get the whole thing neutrally buoyant. Actually the system was made slightly heavy so that it sank a little. We fitted a bicycle inner tube on top of the equipment, via a tube, that could be inflated from above. This was used to control the buoyancy and so be able to make the whole contraption go up and down in the water. By the end of day 2 we had not had time to test out the equipment in the sea or for that matter even in a bath of water! So its first sea voyage was also to be its first test!

We got out into the boats early in the morning and set off, Kathy guiding us to where it might be a good place to set the camera in the sea. There was a swell but the waves were not too big. It took a while to set up the weights to make the camera suitably buoyant. Kate was in the water experimenting to get this just right. When we had done the best we could do on this first run we let the camera go and played around with the air in the tyre to make the camera go up and down. It worked - a little! We got pictures of the reef which was very exciting but it was very difficult to control and the propellers were perhaps too small to provide enough steerage for such a large weight. There was a delay between starting the motors and subsequent movement. However we got some lovely live pictures of the wonderful reefs of Zanzibar!