| Title: | SAILING |
| Notice: | Please read Note 2.* before participating in this conference |
| Moderator: | UNIFIX::BERENS |
| Created: | Wed Jul 01 1992 |
| Last Modified: | Mon Jun 02 1997 |
| Last Successful Update: | Fri Jun 06 1997 |
| Number of topics: | 2299 |
| Total number of notes: | 20724 |
I picked up an artificial horizon (liqued type) at a yard sale cheap.
It's just a square dish with a couple of filters and some oil at
the bottom.
I thought this would be perfect for some practice sextant work.
Just put the artificial horizon up on the rail and shoot away.
I figured my LOPs would all cross at the right place because
(I hope) my house doesn't make that much leeway.
The problem is that there were no instructions with the artificial
horizon. Does anybody out there have any experience with one?
Would my height of eye adjustment be zero, or the height of my deck
above sea level? What do you actually use as the horizon? The
edge of the oil against the case? What should be the relationship
of your eye to the artificial horizon? Should you be even with
it? Above it? Does it matter? If the horizon is artificial, what
is reality?
Philosophical answers welcomed.
Encore
| T.R | Title | User | Personal Name | Date | Lines |
|---|---|---|---|---|---|
| 697.1 | 'tis easy | PULSAR::BERENS | Alan Berens | Mon Nov 16 1987 14:54 | 19 |
Sailing is reality, life at DEC is an illusion. Just point your sextant at the pan and look for the heavenly body. The angle you measure will be twice the angle you'd measure if you were using the real horizon. A large pan filled with water will also work nicely as an artificial horizon. (For more realism, have someone shake the pan to create waves.) If you snuggle right up to the pan, your eye height is at 'sea level'. But wait, you aren't at sea level. You're actually well above sea level, so perhaps your eye height is the altitude of your house (my navigation text didn't discuss this point). A geodetic survey map of your area will tell you your altitude. Have fun. By the way, do you have an el cheapo sextant? If so, I'd be interested in hearing how consistent your sights are. The sights with my Davis scatter quite a bit. Alan | |||||
| 697.2 | no dip | CLT::FANEUF | Mon Nov 16 1987 18:12 | 13 | |
Height of eye is zero with an artificial horizon; there is no dip
at all. When you take your sight, you are actually bringing the
body in congruence with itself rather than a horizon (you won't
see a horizon to bring the body to). If you draw the two rays entering
the sextant (the one directly from the body and the one reflected
off your horizon) you'll see that the angle you measure is constant
no matter how far you are from the artificial horizon. You could
substitute a carefully leveled mirror for the gadget; its important
property is that it has a reflecting surface which is dead level.
Ross Faneuf
| |||||
| 697.3 | I CAN find it with both hands! | CSSE::COUTURE | Abandon shore | Wed Feb 03 1988 08:56 | 32 |
My deck is at last consistent:
42 46N
71 26W
There was a lot of seismic activity in the beginning, shifting my
house up to 30 miles, but that seems to have settled down quite
a bit.
Even with an El Cheapo sextant I'm getting LOP's that match the
town survey as to where my house is located.
A few observations (forgive the pun) on using an artificial horizon.
1. When you take a sight of the sun or moon, place the lower limb
of the observed sun to the upper limb of the one reflected in the
artificial horizon. Then use the lower limb correction in the almanac.
2. Except for noon sights, don't bother trying to get an observation
any time around local meridian passage. These LOPs proved to be
the most unreliable. The best (most consistent) were morning and
late afternoon sights of the sun and east and west sights of the
moon.
3. I can pick up enough reflection in the artificial horizon to
shoot Venus and Jupiter pretty easily. Anything dimmer, including
magnitude 0 stars, is very doubtful unless there is no moon and
the power has gone off in your town.
I'm going to borrow a good sextant and see how my results match
up.
| |||||