Range of lighthouse on Chanonry Point

Having noted that I could see lights on an oil rig that I worked out was 10 miles away, I wondered about the nominal range of this lighthouse as being 15 nautical miles. I've been trying to find out the power of an LED replacement bulb but that's hard because it is less electrical power for the same brightness as an old-fashioned bulb. I found a similar lighthouse that used to have a 250 Watt incandescent bulb. I was going to do an inverse square law calculation based on this power but the problem is that 250W of electrical energy in does not mean 250W of light energy out. It has taken me into territory about human perception of light that involves lumens. More research needed.

More measuring of distances at sea

I was wondering how far away the oil platform was moored off Cromaty when this cruise ship helpfully sailed in front of it. It was a Princess lines ship, most likely the Crown Princess, which claims to be 195 feet high. That is 63 metres high. It subtends about 0.25 of a degree as compared to my little finger or 0.0043 radians. Distance away = 63/0.0043 = 14.6km = 9 miles roughly. So maybe the best thing to say is that the rig was about 10 miles away. More on this later.

St Marys Harbour - 49 degrees and 55 minutes

The Scillies are the most southerly point in the UK and have made a thing out of the latitude. However, they are only 5 minutes off being 50 degrees north of the Equator. So how far is 5 minutes? The radius of the Earth is 6371km so circumference = 40030km. That's 360 degrees so 1 degree is 111.2km. 1 minute is 111.2/60 = 1.853km. 5 minutes is 9.266km which is comfortably enough to take in Tresco and St Martins meaning all of Scilly must be below 50 degrees.

What does 4000 square millimetres look like?

I'm always interested in units for measurement and was impressed to see a figure given in square millimetres. 1cm is 10mm so 1 square cm is 100 square mm. This means the area is 40 square cm. There are 1 million square mm in 1 square metre because it is 1000mm x 1000mm so the area is 0.004 square metres. It is circular so the diameter must be 40 = pi x diameter squared /4. Diameter = 7.1cm which is about right.

Data on my room for the night

We stayed in a shipping container. It had been beautifully done inside. I like the fact that there is data on the outside. The small panel has data called "Allowable stacking weight". Containers should be able to stacked up to at least 6 high. 192000/30480 = 6.3. This shows that the condition has been met even when the containers are fully loaded.

Safe working limit on the Scillonian

I'm always interested to see data in newtons. I had to look up S.W.L. It stands for "safe working limit". This is calculated by the maximum breaking load divided by some safety factor. 36kN is 36000N or just over 3.5 tonnes. I am still trying to find out what T.L. stands for in this context.

Bouyancy aid on the Meridian

I was interested to see that this life belt on Scilly is given a weight in Newtons. It is 100N but is suitable for people over 18kg. Such a person would have a weight of 180N so 100N must refer to the ring itself. It must have a mass of 10kg. I wonder whether the child having to be over 18kg is really about being big enough to grab the sides of the ring.