Can A Compass and GPS Be Used Together?

[sketchrbob]

This combines questions 6 & 7 on our compass question list. Why do we need a compass at all? If we do, how should we use it?

This gives an opportunity for those on each side of the question to state their case. I'll discuss any neglected points later.

Bob W

[digger]

The main time I use both together is to maintain a constant heading at very low speeds, and tough sea conditions. The bobbing and resultant swings of the boat make the GPS reading jump all over the place. Trying to keep gps reading fairly constant will wear you out. It is much easier to keep the boat online by glancing at both the compass and gps to maintain desired heading. Ron

[JamesTXSD]

Easier yet: set a course line with the GPS and follow that. Much like flying to a VOR or an NDB in an airplane, you will quickly see what correction you need to apply to maintain course (figuring set and drift). When our boat is bouncing all around, if I can get within 20º of a compass course, I am doing pretty good. The GPS/chartplotter is easier for me to follow to maintain a course, combined with a visual reference if available.

I do use the compass as a check with the GPS/chartplotter heading, and occasionally to get a reference bearing to a landmark. (some old habits stay with you)

Best wishes,
Jim B.

[Will-C]

Sure, but I like to look at Coastal Explorer on the laptop computer and use my wireless autopilot to put the boat icon on course from waypoint to waypoint. Then I write down compass heading on my paper chart with my speeds and record how long each leg took in between waypoints. Just kidding, I don't write down anything. Have IPAD with nav app as back up. Plus a back up GPS unit. But I do carry paper chart paralel rulers and a hand held compass. I have used compass roses but usually in the ocean to head directly for a wreck and used to mark down the resiprical down on a chart. I also have electric start on my car.
D.D.

[localboy]

The main issue I had to deal w/ was the compass had to be mounted >36" away from the Garmin 740S. I ended up mounting it on the port side of the V-berth entry/dash. Not convenient, but I can at least still use it if needed.

[1TUBERIDER]

I use my compass for a general heading when not moving or at slow speed and then switch to my gps mapping display for running at speed.

[El and Bill]

I have a hand-held compass aboard and the compass (and GPS) within my iPhone as a backup if there is a power failure to the chartplotter. I have not had a need for a compass as a primary navigation tool for many years.

[tpbrady]

The best way to swing a compass (adjust it for all the things that influence it where it is installed) is with a GPS. After that it`s the best way to verify it is still on. For those without an autopilot, it's the best way to attempt to steer a straight course with no visual reference (dark, fog, out of sight of land), especially in anything other than calm seas.

[Aurelia]

Like others, i use gps to get bearings to a point of reference and will use those bearings in poor visibility to steer a straighter course than i otherwise easily could by staring at the gps alone. I run dual chartplotters all the time but Love that compass in the fog. I do still monitor the radar of course and also my deviation from course. Actually getting quite good at it but still try to avoid night ops.

[damason]

I am from the old school of navigation. You need a compass and paper charts and know how to use them. They are one of the oldest sets of navigation tools in existence and are a very necessary backup.

Electronics do go on the fritz and when they do the compass will give you a heading to your port. If you are out in the Gulf of Mexico, the sky is overcast and your GPS (Chartplotter) goes belly up what do you do. With a compass you can always head North and find land. When you get close to land, hail another boat on you VHF and ask for directions to the nearest inlet.

I have a compass, paper chart books, and a Garmin 545-S and practice using all of them.

[Will-C]

In my experience I have never had a GPS or a Loran go belly up. I agree with having paper charts,parallel rulers, hand held bearing compass etc. But Having four different GPS devices each with their own antenna system two which can run off batteries. We have both a Garmin 4208 and a Lowrance multifunction chartplotters, a laptop running Coastal Explorer with its own USB type antenna,a IPAD that runs a nav app which one escapes me now. Old age setting in. Well actually five if you count my wifes Droid phone which has a nav app. I see the belly up thing to all of our devices has fairly remote chance of becoming an actual occurrence . If I lose all 12 vdc power the boat won't run so a compass won't save the day. I'll use a handheld battery powered VHS to summon assistance. Since I carry extra wire I pretty sure unless both batteries jump out the window I'll be able to rig something up. Now if something takes out all the satellites I'll probably stay in port and look for a bar with a nice tv and use cash to find out what happened to the satellites.
D.D.

[20dauntless]

I have a KVH Azimuth compass that feeds heading data to my Raymarine MFD. Since the info is repeated on the MFD, I rarely look at the compass. None the less, the data is useful, although now that I have an autopilot I think I'll use it less.

I also carry planning charts on paper for wherever I am. And I have a laptop with GPS puck, iPad, and iPhone, all with detailed charts of where I am, independent GPS antennas, and independent batteries. Additionally, I have another handheld GPS for when I'm ashore hiking and yet another in a ditch bag. That's six different GPS's! I do carry a small handheld compass, but with so many easier to use and more accurate navigation devices aboard I've never used it.

[sketchrbob]

Great Job Guys! I really do not have to add anything --but by now you know me well enough -- I have to get my 2 cents worth.

It should be emphasized that the GPS obtains a series of fixes on a boat's position. From these fixes it calculates direction and speed. However, the GPS needs to have an interval between fixes in order to have accuracy. Some of you may have noticed while fishing at a slow speed, that the GPS jumps around and is unreliable. Heading into a strong current or head-sea may do the same thing. This is where the compass comes in handy. The fact that you have six back-ups will not take the place of the compass. Some of you made reference to this use of the compass, but some may need reminding of it. That is why we recommended a 10 K speed for adjusting the compass.

Some of you also stated that you obtained a course or bearing from the GPS and then used that as a compass course -- particularly if you have your compass in a "line of sight" position. I like the molded mount for the compass on the new Marinaut for this reason.

Most all of you have had your boats long enough to have worked out a steering and navigating routine and are comfortable with it. That is fine. If any of you have your compass off-set like mounted in the center of the boat, you may want to look art my post "How to Make a Good Compass Better".

In a bad weather situation with low visibility - like thick fog there is nothing like slow speed yes even 5 or 6 knots. Windows open and ears tuned. Kids have better hearing than adults by the way. Don't let all your gadgets, Radar included, lull you into a false sense of security.

One other point. Back in 1956 my wife and I bought an 18' Old Town outboard boat right at the factory -- all set up with the biggest outboard made by Johnson at that time -- 35HP!! They launched us into the Penobscot River art Bangor at 5 p.m. -- all buttoned up with canvas as it was raining hard at the time. We had never been on the Penobscot River before, but with the use of the chart, we got down to the mouth of the river OK.

Now we just had a 10 mile trip across the bay to our home mooring. By this time the rain had let up and the fog had shut down -- thick! So it was dark and foggy and a strange boat. Good thing I had mounted an Airguide compass before we left, thinks I. Well, that compass would not hold a course. It just flopped from one side to the other and we were steering zig-zag with no idea what the right heading was.

Gradually it began to dawn on me that the fluctuations in the compass was related to the turning of the wheel. Then it came to me that the marine steering wheel had a steel core and this was the cause of the problem. We tried to steer with a minimum of wheel turning traveling a little faster and we made our mooring OK considering the handicap.

The Moral of the Story is don't always assume your wheel is stainless or non-magnetic -- check it out with your compass. No amount of adjusting will cure that problem. Change the wheel or move the compass. We moved the compass.

Next week we will combine the last two questions and wind up this compass business. See you then. Bob W