Compass Location?

CAVU · Posted: Sun Nov 28, 2004 4:54 pm Post subject: Compass Location?

I bought my boat used and the previous owner had the compass mounted under the electronics shelf almost on center line. I would prefer to move it to the dash right in front of the helm. This would put it close to the wiper motor. Does anyone have their compass mounted near the wiper motor? Has it been a problem? I know I could check the area for interference with the wiper running, but I have already pickled the boat and removed the batteries for the winter. I am looking for little projects to complete during the lo-o-o-ng winter and thought moving the compass would be an easy one.

C-Bill · Posted: Sun Nov 28, 2004 5:32 pm Post subject:

CAVU

Mine is mounted in the recessed area behind the dash just to the left of the steering wheel and I'm concerned that I may be getting interference from the wiring or steering.

I have a Helmsman, made by Ritchie. Here are some excerpts from the mounting instructions. "To assure maximum performance and accuracy from any magnetic compass, a mounting area must be selected which is as free as possible from local magnetic influence, particularly of a moving nature, such as a steering wheel with a steel core. The effect of such a constantly moving, highly magnetic material is impossible to to overcome by compensation. All electrical components, such as wind indicators, meters, tachometers, gas detectors and particularly hailers and stereos, should be kept as far removed from the compass area as possible." It goes on to say "... a magnetic field can penetrate wood and fiberglass."

Bill

Sneaks · Posted: Sun Nov 28, 2004 7:16 pm Post subject:

Cavu

I ran some quick and dirty tests while locating my compass and yes, the wipers did affect the compass when I tried to put it in an open spot to the left of the display in the photo below. I was able to use the compensators effectively, but when I turned the wipers on, the deviation changed again. Plus there was a difference due to the Lowrance.

Ended up mounting it as shown. Any closer to the window latches required more compensation.

k3nlind · Posted: Mon Aug 15, 2005 1:07 pm Post subject:

The compass on Topkick is mounted right in front of the steering wheel... I have noticed that the electronics cause quite a bit of deviation... I plan to move the compass soon but I haven't yet decided on a good location.

tpbrady · Posted: Mon Aug 15, 2005 2:56 pm Post subject:

I am still working on locations and haven't found any that allow me see the compass head on and not have unacceptable interference from electronics and other metal objects. The last location was on the underside of the electronics shelf with no electronics mounted on it. Something is still causing unreliable performance since there are times it is 30 to 90 degrees out compared to the GPS magnetic track.

El and Bill · Posted: Mon Aug 15, 2005 6:24 pm Post subject:

Sorry to sound like a heretic -- and I know this could spark a rather heated discussion -- but why do you need to mount a magnetic compass? My chartplotter has one built in, more accurate than magnetic. My hand-held GPS has an excellent compass for backup. And then, I carry a little handheld sighting compass for backup or shooting sights (something the mounted magnetic compass has trouble doing, without swinging the boat). My binoculars also have a sighting compass. So, why mount that old-fashioned, next to worthless, probably not accurate, big ol' thing on your dash? ... unless you like that historic look on your boat?

rogerbum · Posted: Mon Aug 15, 2005 7:09 pm Post subject:

I have had the same attitude as Bill and El with regards to a fixed mount marine compass - I have a handheld boyscout style compass (a good one Brunton I think) and a fixed mount and handheld GPS. In the past 3 years, I haven't needed the compass. However, that being said, I just spent about 8 days fishing at Neah Bay and spent much of the time trolling and that changed my mind a little.

The problem with the "compass" built into my Garmin chartplotter and handheld is that it requires a little movement relative to the earth to provide directional information. Hence, at a slow troll in a current that is counter to the direction of travel (e.g. only making very slight forward progress), the directional indicator from the GPS is marginal and can be completely useless and swinging in all directions. In the fog under these conditions, it would have been handy to have a large, easily readable magnetic compass to keep the boat pointed in the right direction. This is especially the case when travelling slowly into the wind as it doesn't take long for the nose to swing around.

Maybe other chart plotters have other types of compasses built in - and my thoughts don't apply to Bill and El's situation, I don't know. Also, as long as I'm moving at >1-2kts' relative to earth, I don't really need any other compass. It's only when trolling against the current in the fog that the large format, fixed mount compass would be needed for me. I still might not bother with it since I have gotten by just fine without it and dash space (all space for that matter) is at a premium.

Roger on the SeaDNA

CAVU · Posted: Mon Aug 15, 2005 7:17 pm Post subject:

Tom: I just posted a picture in my album showing the location of my compass. I moved the windshield wiper to the top of the window to reduce the interference. I gave it a good workout on a recent fishing trip and all seems to work well. It still needs a little tweaking on the compensators which I will do soon. I need to launch in a lake on a nice calm day when I can use my GPS to tweak the headings.

Bill: I would have to disagree with you about the utility of the compass. You are correct that the GPS will give you a very accurate heading, however it will not give you a heading until you are moving and establish a track record. I use my compass to complement the GPS. If you try to follow a course in the fog on your GPS, the lag time in computing heading will have you constantly making S-turns and overcorrecting to course. The method I use is to put my waypoint in the GPS, observe the bearing to the point, and then turn to that heading on my compass and proceed. After a minute or so of following the compass the GPS will have computed my actual course relative to the required course and I can make steering correction to get on course. I agree you can get to your waypoint using only your chartplotter but it won't be pretty. Of course I know from looking at Halcyon's pictures you have radar which would also help. I don't have radar and have a very minimal GPS but with my compass I can navigate very precisely.

TyBoo · Posted: Mon Aug 15, 2005 8:04 pm Post subject:

CAVU · Posted: Mon Aug 15, 2005 9:30 pm Post subject:

Tyboo,
Your experience certainly shows that the compass can be a good thing to have aboard. A back-up handheld GPS and a little compass are good to have aboard, but when navigating in fog and the situation calls for a quick decision, it could take a while to put one of those in service. Something else you said about the visibility prompts me to post some thoughts. I want to put it in a different thread maybe to get some additional responses.

TyBoo · Posted: Mon Aug 15, 2005 9:37 pm Post subject:

Cool CAVU. Something you said on another thread fits here, too. Whatever you do, don't use Lenco screw jack tabs with a compass on board. Or a GPS. The motors ruin the compass, and the noise of the things makes it so you can't hear your GPS off course alarm beeping.

Just kidding - I think I have the exact same 12x12 tabs you are getting, and I wouldn't put them on B~C's new T~C, let alone a CD. But if you gotta have 'em, you gotta have 'em.

KenMcC · Posted: Mon Aug 15, 2005 9:47 pm Post subject:

I have a Garmin 176 C on the top of the dash, next to my Ritchie compass. I've never seen my compass deviate more than about 2º from the Garmin reading.

That's HUGE when you're heading for Tokyo. But not so bad when you just need to bail out for a couple of miles to avoid some hazard. Bill (Fiero) is right about having a hardwired main, and a handheld backup. But I sold my handheld when I got my 176 C, so my compass stays!

I've never compensated my compass, but have helped others do it. Some are pretty close, others can get you into trouble, especially in tight spots, or going long distances.
The nice thing about having a compass, and knowing how it deviates from your GPS, is that you can feel confident about your direction, as long as you remember the direction of the deviation. (Was that 3º East, or 3º West?). (Hmmmmmmm. Now I might be 6º off?)

P.S. If you have to go to the compass, it's a good idea to know where you are, and have the charts to get you back on dead reckoning.

Ken

SeaSpray · Posted: Tue Aug 16, 2005 12:15 am Post subject:

I recently mounted a Platimo Iris compass almost directly over the steering wheel. The Iris is a mountable or handheld compass with a nice sized card. You can buy additional mounts and use it in different places or boats.

I haven't had time to use it much but I am hoping it is far enough from stuff to not be bothered. If it is a problem I can take it down and get a reading from mid cabin.

Steve

rogerbum · Posted: Tue Aug 16, 2005 12:21 am Post subject:

Mike - as you can see from my post above, I'm coming around to a similar conclusion for similar reasons.

Even when the speed relative to earth is enough such that the GPS is pointing in the right direction, it can still be a little tough to hold a straight course in the fog. I found myself continually sensing that we were making a slow right turn even when the boat was going straight and that was reflected in a little bit of the s-shaped course that CAVU was describing. Two things helped that considerably though.

First on a reasonably long run in the fog (Neah Bay to Sekiu, visibility about 100-200 yds - speed 6-7 kts), it didn't take me long to discover that my instinct was just plain screwed up (my wife has known that all along!) - e.g. the LESS I touched the wheel, the straighter the course. Second, on a later day, I reaquainted myself with the route planning features of my Garmin and created waypoints along a route from Neah Bay to Blue Dot (25 miles out). Visibility was poor from Neah Bay to roughly Tatoosh but was good in the open ocean. With the Garmin "NAV" button set to follow the pre-created route, the "compass" window provides both a present compass heading and an orange arrow indicating the direction and angle of the required turn to point towards the next waypoint. This view allows one to more quickly see small deviations from the desired course and to steer a MUCH cleaner line. It's one of those features I played with three years ago when I bought the GPS, used on one trip and then quickly forgot about. If you haven't used it or don't use it, give it a try, you'll like it! Even with good visibility, I think I steer a better course when the route is pre-planned and I'm in NAV mode.

Roger on the SeaDNA

El and Bill · Posted: Wed Aug 17, 2005 12:06 am Post subject:

Roger --
Exactly!! Use the navigation ability of your chartplotter and you have a bearing to any waypoint. My display shows an arrow to the next waypoint, even if I'm stopped. So, in bad visibility when moving very slowly and the compass of the GPS is unreliable, peg a waypoint (or a series of waypoints) onto your chartplotter showing your intended course, and your GPS will point to your destination. The instrument takes a bearing, far more accurate than you can steer to a magnetic compass, and the GPS arrow indicates any off-course direction. You don't need a compass bearing relative to north -- what you really need are bearings for your intended route. In fact, my GPS will even show in a separate window how many degress (port or starboard) I need to turn to maintain a proper course to the next waypoint.
I find very little difficulty (barring strong cross-currents or fluky winds) cruising a straight course in fog -- I move at a crawl and follow the bearings on the GPS to the next waypoint (the radar will hopefully warn me of any traffic on my course).
A compass is not much help in a cross-current or wind in a fog. Yep, you're cruising north but, especially at slow speed, you are drifting way off from the bearing to your intended course.