Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 16-05-2012, 19:00   #1
Registered User

Join Date: Jan 2009
Location: The Maritimes
Boat: 1980 CheoyLee35
Posts: 178
Best Location for an Autopilot Compass?

I'm in the process of installing my new Simrad autopilot and am trying to choose a good spot for the compass. The instructions say "not near motors, electrical cable, chunks of metal etc" but low and near the pivot point. My problem of course is finding such a place. My boat has an iron keel to complicate the issue. It seems that there are two reasonable choices: low on the centerline in the bilge but only a few inches above the iron keel or in the back of the chart table. The chart table is near the centerline and only about 30" above the waterline. It is fairly far from the engine and keel but may be subject to interference from a laptop or ipods. The bilge location would seem ideal except for the chunk of iron. I could also locate it about halfway between the keel and motor down low but then it is within a foot of 00 battery cables.
Any thoughts of best choice or should I just try one and see how it works and be prepared to move it?
This is turning into a bit of a project so I'm open to enlightenment to save a step or two.
Thanks,
Shoal
__________________

__________________
Shoalcove is offline   Reply With Quote
Old 16-05-2012, 19:16   #2
Moderator Emeritus
 
Ex-Calif's Avatar

Cruisers Forum Supporter

Join Date: May 2007
Location: Singapore
Boat: Maxi 77 - Relax Lah!
Posts: 11,514
Images: 4
Quote:
Originally Posted by Shoalcove
I'm in the process of installing my new Simrad autopilot and am trying to choose a good spot for the compass. The instructions say "not near motors, electrical cable, chunks of metal etc" but low and near the pivot point. My problem of course is finding such a place. My boat has an iron keel to complicate the issue. It seems that there are two reasonable choices: low on the centerline in the bilge but only a few inches above the iron keel or in the back of the chart table. The chart table is near the centerline and only about 30" above the waterline. It is fairly far from the engine and keel but may be subject to interference from a laptop or ipods. The bilge location would seem ideal except for the chunk of iron. I could also locate it about halfway between the keel and motor down low but then it is within a foot of 00 battery cables.
Any thoughts of best choice or should I just try one and see how it works and be prepared to move it?
This is turning into a bit of a project so I'm open to enlightenment to save a step or two.
Thanks,
Shoal
The location is to avoid pitching or yawing moments of the boat affecting the compass. The vertical, lateral and longitudinal "center" of the boat is ideal but I wouldn't stress about a few feet.

The caution to avoid metal and motors is obvious.

I'd get it close and logical and not sweat it too much. I'd avoid the masthead and tip of the bowsprit, for example - LOL
__________________

__________________
Relax Lah! is For Sale <--- Click
Click--> Custom CF Google Search or CF Rules
You're gonna need a bigger boat... - Martin Brody
Ex-Calif is offline   Reply With Quote
Old 16-05-2012, 19:31   #3
Registered User
 
Capt Phil's Avatar

Join Date: Jun 2010
Location: Stateline NV
Boat: Prior boats: Transpac 49; DeFever 54
Posts: 2,749
Re: Best location for an autopilot compass?

Amidships, low and easy to get to for service if necessary. One other caution, mount it away from SSB, VHF and radar installations by at least 4 feet. My buddy had his mounted by a marine technical installer who mounted the fluxgate less than 2 feet from his VHF under his chart table and couldn't understand why the boat went in circles everytime he engaged the autopilot. As a result, he didn't use the thing for about 2 years and was complaining to me about having to steer from Catalina Island back to San Diego.
It took about 5 minutes to figure it out, 15 minutes to rerun the wires and connect them up and 30 minutes to take the boat out and check the autopilots performance.
I think it was noted in the installation instructions to avoid electrical interference sources when mounting. Too bad the installer couldn't read... Capt Phil
__________________
Capt Phil is offline   Reply With Quote
Old 17-05-2012, 04:54   #4
Registered User

Join Date: Jan 2009
Location: The Maritimes
Boat: 1980 CheoyLee35
Posts: 178
Re: Best location for an autopilot compass?

Thanks for the feedback. The compass has about 18' of cable so that does limit my location choices somewhat. I am very concerned about having interference from electronics and electrical devices so may have to rethink a couple things. On the bright side, I don't have other simnet or NMEA2000 devices to consider so may be able to set up the system to optimize the compass location. Thanks again!
__________________
Shoalcove is offline   Reply With Quote
Old 17-05-2012, 05:17   #5
Moderator Emeritus
 
Pblais's Avatar

Join Date: Mar 2003
Location: Hayes, VA
Boat: Gozzard 36
Posts: 8,700
Images: 15
Send a message via Skype™ to Pblais
Re: Best location for an autopilot compass?

Quote:
Thanks for the feedback. The compass has about 18' of cable so that does limit my location choices somewhat
OK, so you put it some place and try it out. It's not uncommon for the "perfect" place not to work. Even though it is supposed to be a good spot it often is not. The compass will know if it is happy.

One quick dockside check is to locate the compass and have someone hold it unattached and slowly rotate it both clockwise and counter clockwise while you watch the reading at the control head. It should display in smooth increments watch the 90 degree boundaries too. This is just a quick way to tell if the spot really is perfect. One of the pro installers here made a remote control turn table so he could do this test without an assitant. It's a good way to avoid a hassle and have to move the compass. You can do it dockside too and save even more hassle and time.

In our last boat it was installed in the perfect place and ddin't work. We could find no metal or interference but there was some there any way. It loved the spot under the nav staion near the electrical panel. I'm not saying the electrical panel is a good spot but the compass was happy. Low and in the center is a good place to start looking.

The cable can be extended too it's just wires.
__________________
Paul Blais
s/v Bright Eyes Gozzard 36
37 15.7 N 76 28.9 W
Pblais is offline   Reply With Quote
Old 17-05-2012, 07:49   #6
Registered User
 
svHyLyte's Avatar

Join Date: Mar 2006
Location: Tampa Bay area, USA
Boat: Beneteau First 42
Posts: 3,434
Images: 25
Re: Best location for an autopilot compass?

The Fluxgate for our Simrad is mounted under the settee on the bulkhead between the salon and the forward cabin, about as far away from our engine, electronics et al as possible and yet closer to the center of roll, pitch and yaw than it would be farther forward and more remote from our Iron keel. (It is/would be very difficult to mount the thing entirely outside the influence of a big chunk of iron.)

Overall, our system works very well in terms of maintaining the yacht's heading once set although the fluxgate's indicated heading rarely comports with our actual (Compass) heading, erring moreso as one's heading has more east/west components. (As such, it would be difficult to safely interconnect one's autopilot to a plotting system to follow a route unless the plotting system's route headings were first filtered through a correction table calibrated to the Fluxgate.) In our case we have made up a correction card for the Fluxgate--just as one might for a Compass--and have had no difficulty.

FWIW...
__________________
"It is not so much for its beauty that the Sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."
svHyLyte is offline   Reply With Quote
Old 17-05-2012, 12:57   #7
Moderator Emeritus
 
Ex-Calif's Avatar

Cruisers Forum Supporter

Join Date: May 2007
Location: Singapore
Boat: Maxi 77 - Relax Lah!
Posts: 11,514
Images: 4
Quote:
Originally Posted by svHyLyte
The Fluxgate for our Simrad is mounted under the settee on the bulkhead between the salon and the forward cabin, about as far away from our engine, electronics et al as possible and yet closer to the center of roll, pitch and yaw than it would be farther forward and more remote from our Iron keel. (It is/would be very difficult to mount the thing entirely outside the influence of a big chunk of iron.)

Overall, our system works very well in terms of maintaining the yacht's heading once set although the fluxgate's indicated heading rarely comports with our actual (Compass) heading, erring moreso as one's heading has more east/west components. (As such, it would be difficult to safely interconnect one's autopilot to a plotting system to follow a route unless the plotting system's route headings were first filtered through a correction table calibrated to the Fluxgate.) In our case we have made up a correction card for the Fluxgate--just as one might for a Compass--and have had no difficulty.

FWIW...
How do your spirit and fluxgate compasses compare to gps heading?

Steering a plotter course, even with fluxgate error, is not a problem. Steering commands come from the gps to the autopilot not the fluxgate in track mode. The only time it is a factor is if the plotter course is 090 and you need to select, say 087, in heading mode to get the boat to drive 090 mag. In other words you arr compensating for a 3 degree mismatch in compass headings.

Of course in track mode with set the system would not know if it is being set by current and leeway or if the compasses disagreed. In heading mode I am usually steering way off the plotted course heading due to cross currents.

It is not uncommon for the numbers to all be a few degrees off from each other.
__________________
Relax Lah! is For Sale <--- Click
Click--> Custom CF Google Search or CF Rules
You're gonna need a bigger boat... - Martin Brody
Ex-Calif is offline   Reply With Quote
Old 17-05-2012, 17:50   #8
Registered User

Join Date: Jan 2009
Location: The Maritimes
Boat: 1980 CheoyLee35
Posts: 178
Re: Best Location for an Autopilot Compass?

Thanks for the advice everyone. I was out to the boat all day today getting ready for tomorrows launch so never got too far with the compass. I've been glassing in a platform for the drive unit and attempting (unsuccessfully so far) to drill my rudder shaft to pin my AP tiller. It is difficult to get enough force on the drill and it's resisting my good bits and cutting oil! I'll try the compass mounting tips and see how I make out. I figured someone here would have been through this.
Best regards,Shoal
__________________
Shoalcove is offline   Reply With Quote
Old 17-05-2012, 18:13   #9
Senior Cruiser
 
Cheechako's Avatar

Cruisers Forum Supporter

Join Date: Aug 2006
Location: Skagit City, WA
Posts: 19,365
Re: Best Location for an Autopilot Compass?

not in the bilge!
__________________
"I spent most of my money on Booze, Broads and Boats. The rest I wasted" - Elmore Leonard











Cheechako is offline   Reply With Quote
Old 17-05-2012, 20:31   #10
Registered User
 
xymotic's Avatar

Join Date: Dec 2007
Posts: 1,076
Re: Best Location for an Autopilot Compass?

Mine's mounted in underneath the dining table.
__________________
xymotic is offline   Reply With Quote
Old 17-05-2012, 21:04   #11
Registered User

Join Date: Nov 2010
Location: On boat Panama
Boat: Prout Snowgoose 37 Elite cat
Posts: 13
Re: Best Location for an Autopilot Compass?

On my cat. The absolute center is out of question, so in the nav station it lives, but it is easy to take a regular compass and check the deviation at the location with things off and on and I found my box of stainless clamps, non magnetic? Affected my flux gate.
__________________
macpowell is offline   Reply With Quote
Old 18-05-2012, 05:35   #12
Registered User

Join Date: Jan 2009
Location: The Maritimes
Boat: 1980 CheoyLee35
Posts: 178
Re: Best Location for an Autopilot Compass?

I have a couple locker areas that may work as long as I remember not to shove something beside it that is magnetic. I was worried about the effect of motion and therefore was keen to keep it low, but in re-reading the instructions I notice that they recommend mounting it on a mast 3 or 4 feet above the wheelhouse on a steel vessel. Free from interference seems to trump motion then. A nice dry locker does seem better than the bilge.
__________________
Shoalcove is offline   Reply With Quote
Old 18-05-2012, 07:13   #13
Registered User
 
svHyLyte's Avatar

Join Date: Mar 2006
Location: Tampa Bay area, USA
Boat: Beneteau First 42
Posts: 3,434
Images: 25
Re: Best Location for an Autopilot Compass?

Quote:
Originally Posted by Ex-Calif View Post
How do your spirit and fluxgate compasses compare to gps heading?
Our binnacle compass and our GPS bearings seem to agree quite well although our Compass is only graduated to 5 increments so it is difficult to make assessments. I do use GPS bearings to a mark data as a reference rather than heading as, depending upon tides/currents/leeway et al, one's heading/cog may have little to do with the direction one's bow/enter-line is pointing.


Quote:
Steering a plotter course, even with fluxgate error, is not a problem. Steering commands come from the gps to the autopilot not the fluxgate in track mode. The only time it is a factor is if the plotter course is 090 and you need to select, say 087, in heading mode to get the boat to drive 090 mag. In other words you are compensating for a 3 degree mismatch in compass headings.

Of course in track mode with set the system would not know if it is being set by current and leeway or if the compasses disagreed. In heading mode I am usually steering way off the plotted course heading due to cross currents.

It is not uncommon for the numbers to all be a few degrees off from each other.
Quite right. I was thinking of heading data being sent from the fluxgate but that is not how most systems work. In any case, aboard our yacht the plotting system and autopilot system are not integrated. Frankly, I don't like these systems talking to one another. One never knows what they might cook up on a long night watch. I prefer to set my AP courses manually and I do update my paper plot hourly which helps me to spot set and estimate drift reasonably early on during a passage.

FWIW...
__________________
"It is not so much for its beauty that the Sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."
svHyLyte is offline   Reply With Quote
Old 18-05-2012, 19:58   #14
Moderator Emeritus
 
Ex-Calif's Avatar

Cruisers Forum Supporter

Join Date: May 2007
Location: Singapore
Boat: Maxi 77 - Relax Lah!
Posts: 11,514
Images: 4
Quote:
Originally Posted by svHyLyte

Our binnacle compass and our GPS bearings seem to agree quite well although our Compass is only graduated to 5 increments so it is difficult to make assessments. I do use GPS bearings to a mark data as a reference rather than heading as, depending upon tides/currents/leeway et al, one's heading/cog may have little to do with the direction one's bow/enter-line is pointing.

Quite right. I was thinking of heading data being sent from the fluxgate but that is not how most systems work. In any case, aboard our yacht the plotting system and autopilot system are not integrated. Frankly, I don't like these systems talking to one another. One never knows what they might cook up on a long night watch. I prefer to set my AP courses manually and I do update my paper plot hourly which helps me to spot set and estimate drift reasonably early on during a passage.

FWIW...
+1. My auto steers exclusively in heading mode.

I read with interest reports of the autopilot going "haywire.". Mine has never done that but a charter boat I rented did. I found that the clutch on the wheel was no fully engaging, the clutch would slip and then the system would get confused. I let it steer a 360 to see how crazy it would get. Once I figured out the clutch thing it settled down for the next 3 days.

Weird those electrons are...
__________________
Relax Lah! is For Sale <--- Click
Click--> Custom CF Google Search or CF Rules
You're gonna need a bigger boat... - Martin Brody
Ex-Calif is offline   Reply With Quote
Old 18-05-2012, 20:47   #15
Registered User
 
Kijit's Avatar

Join Date: Jun 2010
Location: Virginia
Boat: Wauquiez Centurion 41
Posts: 53
Send a message via Skype™ to Kijit
Our compass is in a lower locker in the aft cabin. It works just fine there most of the time. When it doesn't, I just say "Honey, where did you put your purse?" She goes below and magically it starts working again!
__________________

__________________
Gerhard
S/V KIJIT
Wauquiez Centurion 41
Kijit is offline   Reply With Quote
Reply

Tags
autopilot, compass

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not 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 Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 02:33.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.