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? > > -- > > 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" > > _______________________________________________ > http://mailman.xmission.com/cgi-bin/mailman/listinfo/montgomery_boats _______________________________________________ http://mailman.xmission.com/cgi-bin/mailman/listinfo/montgomery_boats
