GPS and Compass show different headings - Page 2 - SailNet Community
Reply
 
LinkBack Thread Tools
post #11 of 15 Old 08-11-2010
Senior Member
 
davidpm's Avatar
 
Join Date: Oct 2007
Location: Madison
Posts: 4,422
Thanks: 345
Thanked 74 Times in 65 Posts
Rep Power: 10
 
The OP didn't mention how much the difference was and if the difference was the same in all directions.

Most of us on small boats find that a few degrees off is the best we are ever going to get.
I'm pretty happy personally with about 5 degrees.
davidpm is offline  
Quote Quick Reply Share with Facebook
Sponsored Links
Advertisement
 
post #12 of 15 Old 08-11-2010
Senior Member
 
BarryL's Avatar
 
Join Date: Aug 2003
Location: Long Island, NY
Posts: 1,975
Thanks: 4
Thanked 74 Times in 69 Posts
Rep Power: 14
 
Hello,

A real simple way to determine if your compass is close or not is to get another compass! I have a hand bearing compass on my boat, many people have a cheap hiking compass too. Spend $5 for a cheap one and if it is closer to your GPS than to your compass, the compass is wrong. If your new hand compass agrees with your mounted compass you have bigger problems.

Personally, I almost never use my mounted nav compass. Most of my navigation is line of site (sail towards that smoke stack) or by chart plotter heading.

Barry

Barry Lenoble
Deep Blue C, 2002 C&C 110
Mt. Sinai, NY

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
BarryL is offline  
Quote Quick Reply Share with Facebook
post #13 of 15 Old 08-12-2010 Thread Starter
Senior Member
 
montenido's Avatar
 
Join Date: May 2008
Location: Los Angeles area
Posts: 323
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 9
 
Thanks everybody for the great replies. My GPS is actually a multifunction display - Raymarine C80, not 60 (sorry, my mistake). The compass is made by Richie. All of the equipment is relatively modern and probably works as intended.

Good points made about the difference in a bearing on a compass and the COG on the GPS. I just thought that the bearing and heading should be close. I don't remember exactly, but I think they were 20+ degrees different.

The reason it came up is that I set a waypoint for my marina 25 miles away and made towards it using my chartplotter. Even though I tried to follow the most direct route shown, I ended up doing more of an arc than a straight line. This was with no wind or current, just motor sailing. Not a big deal, but I probably covered a few more miles than necessary.

Next week I am going to Catalina Island, a trip of about 60 NM. I thought I would plot a heading using my charts as well as using the chartplotter with waypoints. On a 60 mile trip I would rather not add any additional miles if I can help it.

Thanks again for the great input.

Bill

Odyssey, '79 CSY 44 Cutter
Channel Islands, CA


"There is no unhappiness like the misery of sighting land (and work) again after a cheerful, careless voyage."
Mark Twain
montenido is offline  
Quote Quick Reply Share with Facebook
post #14 of 15 Old 08-12-2010
Senior Member
 
Maine Sail's Avatar
 
Join Date: Jan 2003
Location: Maine Coast
Posts: 6,345
Thanks: 22
Thanked 296 Times in 229 Posts
Rep Power: 17
       
Find yourself a local compass adjuster and have them come out with you and professionally swing the compass. I do mine every two years or whenever I change anything near my helm. It runs about $125.00 here in Maine. You will steer cardinal positions then the inter-cardinal positions and they will adjust your compass as close as can be then make you a deviation card.

If you do not own a deviation card, set up specifically for your compass, there is no way you are getting accurate readings...

______
-Maine Sail / CS-36T


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




Images In Posts Property of Compass Marine Inc.


Maine Sail is offline  
Quote Quick Reply Share with Facebook
post #15 of 15 Old 08-12-2010
Senior Member
 
jerryrlitton's Avatar
 
Join Date: Oct 2002
Location: Phuket, Thailand
Posts: 1,727
Thanks: 9
Thanked 20 Times in 20 Posts
Rep Power: 15
 
Quote:
Originally Posted by montenido View Post
Thanks everybody for the great replies. My GPS is actually a multifunction display - Raymarine C80, not 60 (sorry, my mistake). The compass is made by Richie. All of the equipment is relatively modern and probably works as intended.

Good points made about the difference in a bearing on a compass and the COG on the GPS. I just thought that the bearing and heading should be close. I don't remember exactly, but I think they were 20+ degrees different.

The reason it came up is that I set a waypoint for my marina 25 miles away and made towards it using my chartplotter. Even though I tried to follow the most direct route shown, I ended up doing more of an arc than a straight line. This was with no wind or current, just motor sailing. Not a big deal, but I probably covered a few more miles than necessary.

Next week I am going to Catalina Island, a trip of about 60 NM. I thought I would plot a heading using my charts as well as using the chartplotter with waypoints. On a 60 mile trip I would rather not add any additional miles if I can help it.

Thanks again for the great input.

Bill
If your track described an arc then I would guess you put the bearing needle (or equivalent ) and kept it pointing at the bow of bow of the boat and a current indeed was present and you arced to the destination. Very common for pilots too. If your GPS also has a function to read lateral drift and you adjust course to zero (lateral drift) then your track will be a straight line.

Part time PADI instructor, part time sailor. Full time having a blast.


S/V TEMPTATION
Islander 44







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

Last edited by jerryrlitton; 08-12-2010 at 07:58 AM.
jerryrlitton is offline  
Quote Quick Reply Share with Facebook
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









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




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