Question for the Cel Nav Pros - SailNet Community
 5Likes
Reply
 
LinkBack Thread Tools
post #1 of 11 Old 11-04-2019 Thread Starter
Senior Member
 
Join Date: Jul 2017
Posts: 112
Thanks: 10
Thanked 6 Times in 6 Posts
Rep Power: 3
 
Question for the Cel Nav Pros

Im teaching myself Celestial Navigation. I got a nice deal on a Astra III sextant on ebay and have been reading up on the subject. Anyway, I am currently land locked in Kentucky. I purchased a bubble horizon to practice with, since its pretty much impossible to get a good horizon line here.

I started taking some sun shots to get the feel for it and I wanted to make some LOPs for practice. Do I make "height of eye" corrections for my height off the ground (6 ft) or do I use my eye height above sea level (about 560 ft)? Seems like it should be from sea level. But then using the bubble I would get a different angle to the "real" horizon if I could actually see it compared to the bubble, wouldn't I? Confused.

Thanks in advance!

Last edited by CrispyCringle; 11-04-2019 at 04:04 PM.
CrispyCringle is online now  
Sponsored Links
Advertisement
 
post #2 of 11 Old 11-04-2019
Member
 
cascoamarillo's Avatar
 
Join Date: Aug 2013
Location: Cape Cod
Posts: 95
Thanks: 30
Thanked 5 Times in 5 Posts
Rep Power: 7
 
Re: Question for the Cel Nav Pros

I think since you are using the bubble, there is no DIP correction for your sextant altitude (Hs->Ha). Your "bubble horizon" just run parallel to the real horizon or sea horizon.
I have never taking sight with a bubble, maybe others can share their thoughts.

Best
cascoamarillo is offline  
The Following User Says Thank You to cascoamarillo For This Useful Post:
CrispyCringle (11-04-2019)
post #3 of 11 Old 11-04-2019
Senior Member
 
Arcb's Avatar
 
Join Date: Aug 2016
Posts: 3,681
Thanks: 212
Thanked 196 Times in 192 Posts
Rep Power: 4
 
Re: Question for the Cel Nav Pros

Your height of eye correction is height above sea level. Correction tables likely don't extend to 560 ft above sea level, so you will likely have to either extrspolate or accept the error since its just for learning purposes any way.
Arcb is offline  
The Following User Says Thank You to Arcb For This Useful Post:
CrispyCringle (11-04-2019)
 
post #4 of 11 Old 11-05-2019 Thread Starter
Senior Member
 
Join Date: Jul 2017
Posts: 112
Thanks: 10
Thanked 6 Times in 6 Posts
Rep Power: 3
 
Re: Question for the Cel Nav Pros

Well, I did a test shot and reduction. Since Im sort of on my own I use a pretty nice excel sight reduction calculator to check my work (free at Interactive Spreadsheets for Celestial Navigation ).

What it told me was I need to use height above sea level. I was about 3.1 miles off of actual GPS position using height above sea level dip correction, and about 17 nm off using height above ground. Ive just done it once tho. It could be that I was horribly off and just dumb luck that made the results work that way.
Arcb likes this.

Last edited by CrispyCringle; 11-05-2019 at 09:42 AM.
CrispyCringle is online now  
post #5 of 11 Old 11-05-2019
Senior Member
 
outbound's Avatar
 
Join Date: Dec 2012
Location: NE & Windwards
Posts: 6,392
Thanks: 137
Thanked 190 Times in 181 Posts
Rep Power: 8
 
Re: Question for the Cel Nav Pros

Love the elegance of celestial. Like you when starting out practiced on land. Being near the ocean didn’t need to use an artificial horizon.
Still I learned celestial to not take the time penalty on Marion Bermuda races. So practiced on the boat. Boy was that a huge wake up call. It’s so much harder to do on a boat. Even simple things like getting local noon or lower limb of the moon.
Really glad you’re learning this skill. But if you can practice on a boat. Even if it’s just on a big lake with a chop. See how you do getting both your sight done and recording the time.
Think the mechanics of a good sight is harder than the rest of it. Personally never got better than magnitude 1 stars, moon, planets and sun on the boat.

s/v Hippocampus
Outbound 46
outbound is offline  
post #6 of 11 Old 11-05-2019
Member
 
cascoamarillo's Avatar
 
Join Date: Aug 2013
Location: Cape Cod
Posts: 95
Thanks: 30
Thanked 5 Times in 5 Posts
Rep Power: 7
 
Re: Question for the Cel Nav Pros

Quote:
Originally Posted by CrispyCringle View Post
Well, I did a test shot and reduction. Since Im sort of on my own I use a pretty nice excel sight reduction calculator to check my work (free at Interactive Spreadsheets for Celestial Navigation ).

What it told me was I need to use height above sea level. I was about 3.1 miles off of actual GPS position using height above sea level dip correction, and about 17 nm off using height above ground. Ive just done it once tho. It could be that I was horribly off and just dumb luck that made the results work that way.
Hi,

I have been thinking about it, and still I think there should be no Dip correction in your case using the bubble horizon. Let get practical; I heard about the excel sheet you mentioned. Looking into it, I don't see (check settings tab) the option of "bubble horizon", just artificial horizon (which is totally different). When I want to check my sights, I normally use two programs (free):
Celestial Tools by USP https://celestialtools.webs.com/
or
TeaCup Navigation Teacup Navigation Home

In both, they DO include the option of "bubble horizon". If you run Celestial Tools, when you click on bubble horizon, it remove the option of HE (height of eye).
Maybe you (we) need to ask the experts like in the forum NavList (NavList: for the Preservation and Practice of Celestial Navigation by Sextant), which I think is run by Frank Reed from RI. There is a couple of facebook sites about it too.

As outbound mentioned, one you get your sights on land (with whatever horizon) with accurate calculations, the real challenge is to do it on a boat.
cascoamarillo is offline  
The Following User Says Thank You to cascoamarillo For This Useful Post:
CrispyCringle (11-05-2019)
post #7 of 11 Old 11-05-2019 Thread Starter
Senior Member
 
Join Date: Jul 2017
Posts: 112
Thanks: 10
Thanked 6 Times in 6 Posts
Rep Power: 3
 
Re: Question for the Cel Nav Pros

Thanks for those links. Ill check them out!
CrispyCringle is online now  
post #8 of 11 Old 11-05-2019
Master Mariner
 
capta's Avatar
 
Join Date: Jun 2011
Location: somewhere south of civilization
Posts: 7,332
Thanks: 138
Thanked 396 Times in 384 Posts
Rep Power: 9
 
Re: Question for the Cel Nav Pros

First thing you are going to want to do, if you have a fine nautical sextant (not plastic) is to send your sextant to a nautical instruments technician for calibration. When I used a sextant as my only form of navigation (electronic navigation hadn't been invented for deep sea) I did this every year or when I reached a city large enough to have one of these shops. Sextants can get out of adjustment.
CVAT and CrispyCringle like this.

"Any idiot can make a boat go; it takes a sailor to stop one." Spike Africa aboard the schooner Wanderer in Sausalito, Ca. 1964.
“Believe me, my young friend, there is nothing - absolutely nothing - half so much worth doing as simply messing about in boats.” ― Kenneth Grahame, The Wind in the Willows

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

facebook.com/svskippingstone
capta is online now  
post #9 of 11 Old 11-05-2019 Thread Starter
Senior Member
 
Join Date: Jul 2017
Posts: 112
Thanks: 10
Thanked 6 Times in 6 Posts
Rep Power: 3
 
Re: Question for the Cel Nav Pros

Capta, you are right about the calibration. Ive calibrated it and it was pretty far off.

As for the debate of dip correction, I have answers. I was able to find and download the directions for this Bubble Horizon from the manufacturer. Turns out -drum roll- "A bubble horizon does not require a height of eye correction". Good and bad news for me. It means my first sight was total dog doo. But semi good news, I need to figure out a Bubble Correction which I did not factor in. It says the BC is normally less than 15 minutes of correction. The process looks like kind of a PITA but I dont have much choice.

EDIT: The Bubble Correction involves taking a few shots from a known position and averaging the error. Or, sighting the actual horizon, subtracting dip, and reading the index. Thats the Bubble Correction. I wish I had a real horizon :-(

Ill update later. Thanks all for the comments and links. And keep'em coming.
CVAT likes this.

Last edited by CrispyCringle; 11-06-2019 at 08:28 AM.
CrispyCringle is online now  
post #10 of 11 Old 11-05-2019
Senior Member
 
outbound's Avatar
 
Join Date: Dec 2012
Location: NE & Windwards
Posts: 6,392
Thanks: 137
Thanked 190 Times in 181 Posts
Rep Power: 8
 
Re: Question for the Cel Nav Pros

+1 on teacup

s/v Hippocampus
Outbound 46
outbound is offline  
Reply

Quick Reply
Message:
Options

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now



In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.


User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome