The Torch

My project to build a torch, like so many of my diving activities, grew out of a conversation held down the pub. Cleggy had brought his new Kowalski to the pub, and I was naturally green with envy. Slightly tipsy, and goaded on by Paul (at least that's my recollection) I vowed to build The Torch.

If I was going to build a torch, it was going to have to be done properly. Cleggy, Phil, Paul and myself spent the rest of the evening thinking about the best possible design for The Torch. Although there was plenty of thinking, there was also plenty of drinking, and so sadly no-one remembered any of the details the next day. Falling back on my physicist training, I went back to first principles to work out the crucial components of The Torch's design.

The first principle I had was that The Torch needed to be bright. I therefore decided to base the design around a halogen spotlight bulb, the MR16. These are often used in kitchens, but whereas kitchen bulbs are around 10W or 20W. I intended to use a 50W or 75W bulb to make my torch as bright as the Sun.

The second principle was that it had to look cool. I therefore opted for an umbilical design, as this would make me look cool, impress the ladies, and gain the respect and admiration of divers across the globe. Sadly experience has since taught me that it is in fact quite hard to look cool with a length of drainpipe stuck to your back.

The first part of The Torch I built was the lamphead. There's plenty of good advice on the internet, and "my internet friends" told me that a head of a D-cell Maglite would prove to be the perfect size for holding the bulb. I bought one from Ebay, and having removed the body of the Maglite, I needed to block up the other end of the lamphead with something. The first attempt used some sort of childs modelling clay. Unfortunately this, although waterproof, became crumbly and brittle. The second attempt used two-part epoxy resin, which is the dogs danglies for this type of job.

The other part of an umbilical torch is of course the battery box. My first attempt was an Otter box, which although waterproof, needed to be treated a little too gently to be of any real use as a battery container. My second attempt was a bit of drainpipe from B&Q. I used waste-water pipe, with push fit connectors. This has so far proved to be remarkably watertight, with only a very small leak, and has the advantage of coming in technical black, helping me maintain my diving cred.

Linking the two parts of The Torch is simplicity itself using these waterproof cable glands from Maplins. The cable is just regular 13A wiring.

Here comes the science bit- concentrate!

A 12V, 75W bulb, draws (75W / 12V) = 6.25A of current. I found a cheap source of 1.2V rechargeable NiMh AA batteries with a capacity of 1.80Ah. 10 AA batteries in series would give me 12V, but would only last for (1.80Ah / 6.25A) = 17 minutes. Using 40 AA cells in a series / parallel combination gives me a respectable burn time of over an hour.

Technical bit over now. For testing, I have been using disposable batteries, as I'm expecting leaks, and 40 NiMh batteries are expensive. 40 AA batteries cost only a few quid from www.7dayshop.com

The Torch has been tested in the pool, in Wraysbury, back in the pool, and now in the sea at Littlehampton. The less said about the Wraysbury attempt the better, as that test can be summarised with the simple phrase "abject failure". However the Littlehampton test was a partial success.

Twelve of us spent a day on the hardboat Voyager, a spacious catamaran with both tea and chocolate biscuits on board.

Cleggy (who was testing his Lobsteriser) and myself were the last pair in. Unfortunately, as The Torch did not have a switch, the only way I could turn it off and on was by plugging and unplugging the bulb. This is not easy to do in neoprene gloves, and consequently I dropped the lamphead, knocking out the lens and the sealing o-ring. I managed to refit these, but as soon as I was in the water it was obvious that I had not done things correctly. Water slowly entered the lighthead before we had even submerged, and sadly it wasn't really practical for us to get back on board and fix the problem.

Fortunately I had decided to follow Janos's First Law of DIY Diving, and had packed a backup torch. I therfore decided to ignore The Torch, fix the porblem later, and instead concentrate on having an enjoyable dive.

But The Torch shone on!

Because the MR16 bulb is such a snug fit in the lamphead, it managed to seal The Torch and prevent most of the seawater from reaching the electrics. In fact, The Torch worked fine for most of the dive, and only cut out finally when Cleggy and I were hanging around on our safety stop.

So? How did it do? I was using a 50W bulb for this test, which was bright, much brighter than my backup torch, a handheld SL6. It had good penetration, but was sadly not in the same league as Cleggy's Kowalski, which had a much broader and brighter beam. However, when I got home I also found a small leak in the battery box, which had shorted out 10% - 20% of my battery power. This would obviously have a large impact on the brightness of the bulb, and I am keen to see what a 75W bulb looks like at full power.

So where are we now? Well, currently The Torch is in bits in my inventing shed. I have bought a waterproof switch from Maplins, and I have wired this up with a relay. I have also sealed the lamphead with epoxy glue, and will be sealing the electronics with bathroom sealant. I also intend to and wrap the batteries in clingflim, which should allow the battery pack to be unaffected by minor leaks, or indeed sticky-backed plastic might be an option.

Subsequent tests over the winter have revealed more leaks in the housing, and I can't find out where they are coming from. I've applied Janos's Second Law of DIY Diving: “If at first you don't succeed, try, try, try again. Then quit, because life's too short.” and bought myself a reconditioned Kowalski.