Friday, February 7, 2014

Molasses – The Eatable Artificial Horizon

A plate of molasses as an artificial horizon for sextant sights. To get an optimum height, we use a box on the stool for coarse adjustment, and fine tune with some random book. The plate only has to be level enough to keep falling off the box.

 The nice thing about using a plate of molasses for an artificial horizon is if you spill some you can just lick it up.

After a week or so it firms up a bit more than you want, so just put a teaspoon of water on the surface and put it in the microwave for a minute, and you are good as new.  We have used the same plate of molasses for several years!

Molasses is thick enough that the surface is not affected by a light wind, which would render a water surface useless.  Some use thick dirty motor oil, but we have already pointed out why molasses is better than that.

We explain the nuances of taking sextant sights with an artificial horizon in our text How to Use Plastic Sextant – With applications to Metal Sextants and a Review of Sextant Piloting

This book is available as an ebook for $5.99. 

The title of that book, by the way, is a bit misleading.  It covers the best ways to take sights with all sextants, metal and plastic. It is just much more important to do it all right if you use a plastic one. Following the methods of that book, you will get usable and dependable sights from plastic sextants.  Following the same techniques with a metal sextant will reduce the scatter in your data and lead to optimum results possible from cel nav.


nemo said...

Dear David, I am a Junior Navigator with the United States Power Squadron. We determine position using the Altitude-Intercept method for determining LOPs.
We use local lakes and the dip short on the natural horizon to correct Hs to Ho.
If I were to use an artificial horizon, what do I need to anticipate; what preparations would I need to make, if any; and, how would I go about correcting for "dip short?"

David Burch said...

There is no dip short needed using artificial horizon. The short answer on sun procedure is overlap the two images (direct and reflected), then divide Hs by 2, and then sight reduce the sun as if it were a star. For more details, see our plastic sextant book. There are likely articles online as well. There are many experts on these matters that are active on the discussion group called NavLlist at Many specialize in artificial horizons and they have many options. For stars you need a good level mirror which is an active discussion there including many innovative design options. ( We have one of our own to add to that list at some point. )

heatherstreetsailing said...
This comment has been removed by the author.
Jim Revkin said...

The physics department at Williams College offered a winter study course in celestial navigation. There is no discernable horizon in the northwest corner of Massachusetts, so we used a bowl of maple syrup as an artificial horizon, as we stood on the roof of the physics building, to practice.

David Burch said...

Excellent. That should do the job as well or better. I hope you are using our textbook on cel nav! We offer all schools and colleges a good discount.