GPS and Compass show different headings - Page 2 - SailNet Community

   Search Sailnet:

 forums  store  


Quick Menu
Forums           
Articles          
Galleries        
Boat Reviews  
Classifieds     
Search SailNet 
Boat Search (new)

Shop the
SailNet Store
Anchor Locker
Boatbuilding & Repair
Charts
Clothing
Electrical
Electronics
Engine
Hatches and Portlights
Interior And Galley
Maintenance
Marine Electronics
Navigation
Other Items
Plumbing and Pumps
Rigging
Safety
Sailing Hardware
Trailer & Watersports
Clearance Items

Advertise Here






Go Back   SailNet Community > On Board > Gear & Maintenance > Electronics
 Not a Member? 
  #11  
Old 08-11-2010
davidpm's Avatar
Senior Member
 
Join Date: Oct 2007
Location: Madison
Posts: 3,818
Thanks: 206
Thanked 50 Times in 42 Posts
Rep Power: 8
davidpm is on a distinguished road
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.
Reply With Quote Quick reply to this message Share with Facebook
  #12  
Old 08-11-2010
BarryL's Avatar
Senior Member
 
Join Date: Aug 2003
Location: Long Island, NY
Posts: 1,671
Thanks: 3
Thanked 32 Times in 29 Posts
Rep Power: 12
BarryL is on a distinguished road
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.
Reply With Quote Quick reply to this message Share with Facebook
  #13  
Old 08-12-2010
montenido's Avatar
Senior Member
 
Join Date: May 2008
Location: Los Angeles area
Posts: 323
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 7
montenido is on a distinguished road
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
Reply With Quote Quick reply to this message Share with Facebook
  #14  
Old 08-12-2010
Maine Sail's Avatar
Senior Member
 
Join Date: Jan 2003
Location: Maine Coast
Posts: 5,539
Thanks: 13
Thanked 149 Times in 115 Posts
Rep Power: 15
Maine Sail is just really nice Maine Sail is just really nice Maine Sail is just really nice Maine Sail is just really nice
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.


Reply With Quote Quick reply to this message Share with Facebook
  #15  
Old 08-12-2010
jerryrlitton's Avatar
Senior Member
 
Join Date: Oct 2002
Location: Andaman Sea
Posts: 1,266
Thanks: 2
Thanked 6 Times in 6 Posts
Rep Power: 13
jerryrlitton will become famous soon enough
Send a message via ICQ to jerryrlitton Send a message via MSN to jerryrlitton Send a message via Yahoo to jerryrlitton Send a message via Skype™ to jerryrlitton
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.
__________________
"Duty, that grim demanding bitch, come to call with all her nagsome sisters, would never give a man a moment of his own."

A Kings Trade
Dewey Lamdin



Money canít buy you happiness.
But it buys you a big enough yacht to
sail you right up to it!
(Johnny Depp)







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.
Reply With Quote Quick reply to this message 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:

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

 
Posting Rules
You may post new threads
You may post replies
You may post attachments
You may edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On



All times are GMT -4. The time now is 03:55 AM.

Add to My Yahoo!         
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012

The SailNet.com store is owned and operated by a company independent of the SailNet.com forum. You are now leaving the SailNet forum. Click OK to continue or Cancel to return to the SailNet forum.