Using an artificial horizon.

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Seadogg

.
Jun 16, 2004
8
Macgregor Venture 22-2 Michigan
Quick question:

When using an artificial horizon do you need to re-do your sextant's vertical and horizontal alignment?

I have set my sextant up to give me very minimal errors when sighting both a distant horizontal line and distant vertical line (as per the manual), but I was wondering if you need to do anything differently when using an artificial horizon as the "horizon" is so close and, of course, is NOT aligned with the previous setting.

Or do I just leave it be?

Thanks in advance!

Nick
 
Ross

Ross

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Jun 15, 2004
14,693
Islander/Wayfairer 30 sail number 25 Perryville,Md.
Just leave it properly adjusted .

But don't forget that you divide Hs by 2.
http://www.oceannavigator.com/ME2/Default.asp
 
S

Seadogg

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Jun 16, 2004
8
Macgregor Venture 22-2 Michigan
Thanks, Ross! Another question

I have noticed that when using my Davis artificial horizon and my sextant set at zero, I can't get both the reflected sun and the mirrored sun in my view finder at the same time. I CAN get both images to coincide when moving my index arm up to the appropriate angle.

Strangely, I CAN get both images when using the surface of our swimming pool as the artificial horizon and the sextant set at zero.

Is this due to the fact that the Davis unit is much narrower? Kinda weird.

Thanks,

Nick
 
Ross

Ross

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Jun 15, 2004
14,693
Islander/Wayfairer 30 sail number 25 Perryville,Md.
Nick if the sun is too high the arm won't swing far

enough to bring the the sun to the reflection. Try it later in the day or try it when the moon rides low.My almanac puts the dec sun at 9d45m I am about 39 north so Hs will be about 59d15m times 2 puts me off arc with an artificial horizon.
 
S

Seadogg

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Jun 16, 2004
8
Macgregor Venture 22-2 Michigan
Yep, got that, however,

I'm actually talking about when I first begin the sight and I've got the index at 0. All I'm doing is looking through the scope at the reflection of the sun in the artificial horizon.

If I do this looking at the reflection in the swimming pool, I get both the pool sun and it's image reflected by my sextant's mirror. No problem.

I don't get this when I use the artificial horizon. That's why I'm wondering if it's just cause the Davis AH is just too narrow. everything else is the same really; height above ground for example.

Not a big deal but it's kinda weird....
 
Ross

Ross

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Jun 15, 2004
14,693
Islander/Wayfairer 30 sail number 25 Perryville,Md.
You may be off angle horizontally. Walk a little left and

right while using the Davis or swing the sextant. I use a bird bath for an AH but you have to be very close to position.
 
S

Seadogg

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Jun 16, 2004
8
Macgregor Venture 22-2 Michigan
Understood. Here's the weird part

When sighting via the swimming pool (which is really only slightly larger than a wading pool) and with the sextant at 0 I see this

( | )
reflected sun mirrored image

I can swing through it with no discernible "jumps".

When doing the same thing with the Davis AH with the sextant at 0 I see this

( |
not even in the scope; it's quite low.
reflected sun mirror image

The Davis and the water surface of the pool are just about at the same height.

Any ideas?? As I mentioned before, my sextant is pretty well adjusted and, if it weren't, I would think I'd be getting the same issue using the swimming pool as the AH.

Thanks, again, Ross. I REALLY appreciate your help with this!
 
Ross

Ross

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Jun 15, 2004
14,693
Islander/Wayfairer 30 sail number 25 Perryville,Md.
Nick, At this distance all I can suggest is to keep

playing with it and see if you discover what you are missing. I am pretty sure that it is so plain and obvious that when you figure it out it will be a forehead slapping moment.
 
Sailgunner

Sailgunner

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Jun 4, 2004
1,087
Mainship Piliot 34 Punta Gorda
No use

I was going to get a sextant but figured I could never get my wife in it.
 
S

Seadogg

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Jun 16, 2004
8
Macgregor Venture 22-2 Michigan
Oh! That's BAD!

But I like it!

Ross, thanks for your help. I did two sights tonight. One using the pool and one using the artificial horizon. Breeze was calm enough to get a half-way decent sight. Both sights were almost identical, so I guess I'm good to go...

Also, after reduction, I was able to plot a position that was only twenty miles off. Not bad for a first-timer.

Cheers,

Nick

Dennis---where do you get those sextents?
 
Ross

Ross

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Jun 15, 2004
14,693
Islander/Wayfairer 30 sail number 25 Perryville,Md.
Nick , I figure that if I can determine if I am approaching the

Chesapeake bay or the Delaware bay I am close enough. When Harrison built his first chronometer the Admiralty was happy with 30 miles after a trip from England to the Azores.
 
S

Seadogg

.
Jun 16, 2004
8
Macgregor Venture 22-2 Michigan
Heh Heh

Very good, Ross.

Thanks again for your help. Have a great weekend.

Nick

s/v First Step
 
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