Hear! Hear! I would double underscore the **totally relaible** comment. Given a discrepancy between the GPS and the compass, I would go with the compass if I had no other indicators such as seeing the sun, north star, some known land point of reference... Dan John Fleming wrote:
Stephen,
I'm going to give it the old college try, to convince you why not only should you keep your compass, but that you should consider it to be one of your most valuable instruments and use it, in spite of the ready availability of GPS.
I have a M-17, and living in LA, I've prepped it for coastal cruising. That means I've also prepped myself in how to coastal cruise, which involves navigation to strange waters. And granted, I'm a traditionalist, so my arguments are colored in that direction. But I believe the arguments are correct in principle, it's just the relative emphasis is controlled by your sailing objectives. Also, I'm a pilot, so even though I'm a new sailor with very few cruising miles, pilots and sailors have very similar tasks and desires when it comes to navigation.
1. First, you are right, GPS gives you track and speed over ground. However, your track is the result of a number of factors: leeway, tidal currents, boat balance, wind direction and speed. Your speed over ground is also based on these factors. The question is, what ** heading ** should you steer to achieve a desired track? A sailor who is unaware of the tidal currents and the boat's performance is less likely to arrive on time to the intended destination, and has a higher risk of sailing into trouble.
A sailor who uses the compass for navigation is more aware of the effect of wind and tides, and is in better touch with the boat's performance, by constantly comparing the difference between the heading to steer, and the performance relative to the desired track.
2. Last month, I sailed to Catalina Island, 30 nm away. In all the last minute hubbub, I left behind the 12 volt connector to my GPS and the spare batteries (4 AA's for each 6 hours of operation). The GPS unit was showing that the batteries were about 40% of full. Not only that, but there was something weird going on with my house battery, and I was very concerned that the battery was also in deep discharge. When did I discover all this? Twenty minutes after I left port. And I was committed to making this trip that day. But, I have a bulkhead compass, and I know how to use it, and I've practiced steering to compass headings and staying on track. Through all the haze I couldn't even see my destination until I got within 5 nm. So what did I do? I steered compass headings, and every half hour or so, I turned on the GPS, checked to see whether I was still on track, and adjusted my heading, then turned off the GPS. Using basically compass, I was never more that 0.5 km off-track, and I arrived at Catalina with plenty of battery power to spare. And that was my first and longest cruise.
The moral: GPS only works as long as the electrons flow. And there's a zillion ways, especially in the corrosive saltwater environment, for the power to stop flowing. And when that day comes, if you don't know what compass heading to steer ...
3. GPS gives you speed over ground, but speed over water and apparent wind speed are more important to the sailor. I set my reefs and sail changes based on boat and wind speed and sea state. Speed over ground can be confused by tidal currents. Admittedly, in SoCal this is not important, but up in Puget Sound or SF Bay if you are not aware of the effect of these sizable currents, you could either be over-canvassed, or not getting best effort out of your boat. Either way, you have increased your risk of meeting with trouble before reaching your destination safely. Especially for a small boat like a Montgomery, where there is less than one knot difference between a happy boat (4.5 knots) and an over-stressed boat and crew (5.5 knots). Why? because with using only GPS, you are unaware of what the sea is doing to you.
4. Go into any plane, from the littlest Cessna putt-putt, to the biggest commercial jet, and you will find a magnetic compass prominently mounted for use by the pilots. Why, with all the fancy and expensive and ultra-reliable electronics, do they still have a compass? Because it is one of the few, if the only, instruments that, with proper installation and a modicum of maintenance, is ** totally ** reliable. The compass is used, on a regular basis (i.e. every flight, and several times per flight) to make sure that all those fancy electronics are working and telling truth. The compass is not an anachronistic carbuncle of a bygone era of flight, but is and will remain an essential instrument of flight. A compass is a flight-safety critical piece of equipment. Without it, you don't fly.
Remember that pilots and sailors have much the same problem: what heading to steer to achieve the desired track, and why is there a difference?
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For reasons like these, I'm convinced that boats should be steered primarily using the compass, the heading to steer should be calculated by the sailor, and GPS should be used as one of several means of navigation (DR, triangulation, LORAN, GPS, celestial), each of which is used to back up and cross-check the others. A sailor should be prepared and comfortable with all types of navigation methods, and the only way to be so is to do so, using each as available. So when you're sailing, make the effort to run a DR log, or do compass triangulation, and figure out what compass heading to steer to compensate for wind, tides, and currents.
You asked for it, you got my $0.02. Hope it helps.
John Fleming M-17: "Star Cross'd"
Stephen Martin wrote:
I suppose this will be considered nautical heresy, but here goes:
When my wife and I first started cruising about 5 years ago we were careful to calibrate (swing) the compas and make a deviation chart, etc. Mounted next to the compass was our GPS unit. After all that we had read about the importance of the compass it suprised us that in 4 years of cruising I don't think we ever looked at the compass once. We eventually quit taking the cover off. On the other hand, the GPS was used constantly.
Instead of heading, the GPS gives you your track, which is what you really want to know. Of course, some of the other benefits are that it gives you true speed (no need for a knot meter, which only gives you relative speed), position, tells you if you're on course, and tells you if your anchor is dragging.
I suppose one could argue that the compass is low tech, doesn't require batteries, and is more reliable. But I remember making the same argument for holding onto my slide rule. I still keep it stowed away somewhere in case the batteries die on my calculator.
Steve Martin, M15 "Cadenza"
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