Captain Ron's

Sailing and Cruising Pages

Getting a little more from your GPS

By Ron Butler

Ok, I’ve ranted about the shortcomings of Garmin and other brands of GPSs so this time I thought I’d share some of the virtues. Of course, the greatest virtue of the GPS is that it has made child’s play of navigation; literally. It’s now like playing a video game. Color chart plotters and mapping software have made obsolete such nautical artifacts as the sextant, parallel rules, course computers and even LORAN. But please note that they haven’t yet displaced paper (or plastic) nautical charts anymore than digital books have replaced the paperback. This is not to suggest that you don’t need to know how to work a DR plot or use a hand bearing compass, on the contrary, the old techniques still work, it’s just that GPS has made it so very much easier.

I carry two Garmin GPSs on Kismet. One is attached to the binnacle and is used for steering and the other is anchored to the chart table at the nav station and interfaced to a laptop computer.

First the steering GPS. I think it is essential to have a late model DGPS within easy sight of the helmsman. The one I have, is one of the first DGPS units to hit he market and it is a chart plotter type with a 6” (vertical) black & white screen. It is a Garmin GPSMap 230 . There are a number of issues with this unit that I have discussed elsewhere but it does have a NEMA 0183 interface, which enables me to display navigation information on my Furuno Radar. This is a very handy feature. For one thing, the radar will display our GOTO waypoint as a target with a rhumb-line course from our position. This can be a confirmation of our plan vs. actual if the next waypoint happens to have a radar signature. A large buoy used as a waypoint, for example, would show up on radar. If the return from the buoy is not inside the target, there might be reason to investigate.

One night we were traversing the space between Three Rooker Bar and Anclote Key on Florida’s west coast. The waypoint I chose to use appeared on the radar screen as a target squarely on dry land. It had been years since we visited this area and shoaling had built an island where our old waypoint was located. Good thing for radar.

The integrated system also displays our heading, bearing, position, speed, etc on the radar display. I can see both the radar and the GPS displays from the steering station but because I have them interfaced, I can also see all of the nav information on the radar display from a nice cozy spot up under the dodger. This is because I have the radar mounted to a swinging arm that we swing into the main companionway when we are using the radar in the cockpit. This mounting position unclutters the helmsman’s view ahead and enables a nice sheltered watch-keeping spot under the dodger when making a passage in less than fun conditions. This swinging mount also means that I can see the radar from the nav station by simply swinging the radar screen into the cabin.

We also keep the track feature of the GPS turned on thus leaving our little trail of breadcrumbs should we need to find our way back the way we just came. More on this feature later.

Next, the nav station GPS. This unit is a small, inexpensive, handheld, Garmin GPS72 set into a mounting bracket on the nav desk. It is wired to ship’s power and interfaced to our laptop computer. When we are underway I usually keep our MapTech Ocean Navigator software up and running and displaying our current position from the GPS. This system constantly keeps our route, track and position displayed so if we need a quick look at exactly where we are, a peek down the main companionway at the laptop screen does it. Of course the software will also display all the nav info from the GPS as well. This system is used to plan our travels as well as provide an immediate route check. We usually plan our next day’s travels the evening before we depart using the laptop system and then manually transfer the waypoints to the steering computer. Time consuming, yes, but it is also a built in redundancy. In the Bahamas the planned route on the computer is an estimate using artificially spotted waypoints. The route I key into the steering plotter is usually pulled manually from the Explorer Chartbooks using their waypoints or waypoints that I have already entered into the GPSMAP 230. Generally our routes are less than 70 miles long since we prefer to stop overnight, mostly.

The redundancy comes in once I’ve keyed a route into the steering GPS. If the planned route was say 50 miles long and I key in a route that ends up 62 miles long then I have a cue to check things out. Likewise when we’re out sailing and our actual path ends up wildly different from the plan on the computer, it’s time for some do over or at least a reasonableness check.

I do not have either GPS interfaced to the autopilot, nor do I have them interfaced to each other. They are two independent displays. I think this is a reasonably good way to set things up. Sure I could interface one of them to the autopilot but I prefer to correct our course myself according to the steering GPS and compass while occasionally checking it against where the MapTech plot shows us. Also I think that navigation requires that you keep your head outside of the boat and thinking about what you see out there rather than playing the video game displayed on some LCD monitor. In the Bahamas especially, you must always be aware of the water color, the wind and wave set, the tidal flows and other boats. In the Bahamas, there are no channel markers nor should you need any. The water is so clear that the bottom is visible in 40 feet or more of water in most places. The water color marks your channel and while the Explorer charts that I have on paper and in my MapTech system are the most reliable there are, you still navigate passes and anchorages by sight. In addition, the visual cues such as the shape of a headland, an airplane taking off or landing, the channel wash, a radio tower or a stone monument offer confirmation of what the charts and GPS are telling you. Lesson #1 for cruising the islands, ”Keep your head out of the boat!”

I can remember at least one time where we were approaching Darby Cut from the east and saw a plane landing on the island ahead of us. We couldn’t see the pass but assumed it was behind a headland. I didn’t remember a landing strip near Black Point or Darby Cut. A quick chart check showed the nearest airplane patch to be Staniel Cay. We changed course and figured out what happened. I had fat-fingered the waypoint coordinates for Darby Cut. We were actually 3 miles north of where we thought we were. Of course, a quick look at the MapTech system showed our error. I suppose one could argue that having the steering GPS interfaced such that we could electronically transfer waypoints and routes would save this kind of error. Yes, it would and it would be much easier to boot especially if both systems could share the same library of routes and waypoints. The problem comes in from being unable to transfer data to and from the now old and obsolete GPSMap 230. The good news is that our position was in real time display down at the nav station so I didn’t have to waste time plotting it on a paper chart. By the way, we always keep the paper chart of our immediate navigation area in the cockpit for handy reference.

I would also relate the cautionary tale from last year, when a large motor-yacht ran onto a reef attempting to enter Little Harbor on Long Island. I’ve been in that wonderful little hole and we’ve always entered and exited based on the Explorer Charts using their waypoints and our own eyeballs with no issues. The power boat was following their RayMarine chartplotter and relying on it as their sole means of navigation. The RayMarine system does not use the Explorer Chart data and clearly shows an entrance to the lagoon that is barred by a barely submerged reef of stag horn coral. I’ve been diving on that reef and at low tide, it is right at the surface. The Explorer Charts clearly show the reef blocking the northern entrance to the lagoon. The motor-yacht ran right onto the reef. Just keeping their eyes out of the boat should have told them that their electronic chart was wrong. Later we found out that RayMarine is one company of several that have refused to pay Explorer Charts royalties to use their data and so make their own charts based on satellite or other sources. If you cruise the Bahamas, you need the Explorer Charts, period. No other charts are as frequently updated or as thoroughly researched. If you’re buying electronic charts for use in the Bahamas, make sure they are based on the Explorer Charts data. I have no interest in Explorer Charts, by the way, I am just a convinced customer; Nothing against RayMarine either just one more little item to keep in mind.

I mentioned our breadcrumbs. We always have the track feature turned on in both the MapTech system and the helm GPS. We record a track about every 2 boat lengths as we progress. This feature we find very useful at least once in a while even if it is a bit of overkill. More than once we have found ourselves in a position where we had to navigate a narrow channel in less than ideal visual conditions, sometimes even at night. Steering our way out of a risky passage at night for example, may only be possible because we have tracks that we can follow. Sure it takes some practice to learn to steer the boat so that it stays on ‘track’ but it can be done. We zoom our steering GPS map screen in to the ¼ mile display for this purpose. By the way, the track feature works whether or not you have a chart cartridge in the machine.

We have also used tracks to negotiate alternative anchorages. Some small cays and islands in the Bahamas offer anchoring protection from only one wind direction, usually east. This is fine so long as the wind doesn’t shift. Usually you get large wind shifts with the passing or approach of some major weather system feature such as a cold front. If we suspect that we may get such a wind shift sometime in the near future, we will scout out an alternative anchorage just in case we have to make a move. Usually you can count on the wind shifts to happen at night or other adverse condition. By scouting the alternative anchorage with our track feature on, we feel comfortable making the move even if we can’t see the water color all that well.

Tracks might also serve a safety function. If someone were to fall overboard, returning to the location would be easier if you can follow tracks. Thankfully we’ve never had to use that or the MOB feature of the GPS.

We also make extensive use of the route feature on the steering GPS and the MapTech software. We plan the route using MapTech and then enter the waypoints we want to use, manually to the steering GPS. While we do change course by pushing buttons on the autopilot or by hand if we are hand steering, having the route pre-entered to automatically announce the arrival at a waypoint and then change to the next waypoint, saves fumbling with the GOTO feature right when you’re busy changing trim or getting set-up for the new course.

Having the route and tracks displayed also allows you to see where and when you went off course. This I have found to be very helpful when doing post race analysis where the tracks will show you every lift and header. I have even used these features to call a tack when I see on the GPS that we’ve sailed into a favorable shift.

While I’m sure there is nothing new here to some cruisers, I hope I’ve managed to get you thinking about how you use your onboard GPS systems. Sure there are more sophisticated and expensive systems out there but this works for us. Thanks for reading; hope it was helpful.