How did you get on with the dipping lights question?
If you scurried around the internet you would have possibly found different figures to use ranging from 1.92 to 2.095 depending on where you are on the planet.
What to use? The RYA teach us to use 2.0. In theory the multiplication factor should be 1.92 rather than 2, but in practice the distance to the horizon is slightly extended by atmospheric refraction, so 2 is a good approximation. (Tables are usually based on multiplication factors ranging from 2.03 to 2.095)
I can remember 2 and my maths can cope with the 2 x table easier than those other figures.
Using the formula 2 x √ height of Lt + 2 x √Height of eye = distance
Sanda Lt 2x√50 + 2x√3.8 = distance
2 x 7.07 + 2 x 1.95 = distance
14.14 + 3.9 = 18.04NM - if you had anywhere between 17.5NM and 18.5NM, well done.
Ailsa Craig Lt
2 x √18 + 2 x √3.8 = distance
2 x 4.24 + 2 x 1.95 = distance
8.49 + 3.9 = 12.38NM. - If you had anywhere between 11.75NM and 13.25NM, well done.
Sanda Lt 18 NM - just for interest it had a brg 315ºT
Ailsa Craig Lt 12.38NM -and for interest it had a brg of 017ºT
For interest, the instructor took radar ranges as follows
Radar range Ailsa Craig 12.13NM. 015T Corswell Pt 3.4NM 147T. RHE Sanda Isle 18.2NM 319T
The fix on the chart was just under 300 yards from the dipping fix - bearing in mind that it is a “we are where we expected to be ish”. So if GPS failed and we didn’t have radar it would be reasonable to say that until we have positive landmarks to navigate from we are safe and heading the right way - all in all a good result!
In the Almanac you might/should be carrying on board there will be a Geographical Range Table that will give you height of light on the left side in meters/feet and along the top the height of eye in whole metres/feet if your height of eye is not a whole number you will need to interpolate.
The table includes an allowance for atmospheric refraction (which is the bending of light rays as they pass through the atmosphere) Abnormal refraction may occur in unusual conditions of pressure, temperature and humidity. This can increase or decrease the range.
BTW - breakfast in Campbeltown was fab!
Hope you enjoyed the challenge, look out for the next one, have a great day.