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Old 09-24-2008, 02:20 PM   #21
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RE: GPS vs. Ship's Compass

But you see Marin, you've said you can only totally rely on your magnetic compass. Your example of entering Comox is a perfect example of where your magnetic compass will tend to lead you into trouble.

To chart your way into Comox with paper chart and magnetic compass what do you have to do? Draw a straight line from Point Here I Am to Point This is the Gap, parralell rule to the compass rose and get your heading to steer? No, not if you want to successfully navigate the channel. You instead check the state of the tide, you consult the Current tables, you do a little math to determine where you are in relation to what time you'll be at the gap. Then you calculate mag dev for the area, and hope all your numbers come together at the right time.

Or, you take off from Here I Am and steer the heading line on the chart plotter to the Gap. Then you sit back and watch the scenery. The GPS tells you where you are and where you're headed, automatically notifying you about set and drift when the bearing line is off.

Now, the knotheads who are running into things are not doing it because of any chart plotter. They are doing it in spite of what the chart plotter, radar and depth sounder are telling them. If those knotheads were calculating set and drift how much more attention would they be paying to looking out the window?

I'll bet that Marin used his chart plotter to know exactly where the gap was, going in to Comox. While he was following along with a paper chart, depth sounder and visual confirmation, he also looked at the technology to confirm what everything else told him. Most prudent mariners do.

My piloting is done with two chart plotters below and one above on the flybridge. If something doesn't look right, needs confirmation, or a failure occurs, I have paper charts, tide tables, current tables and plotting hardware a few steps away. It only takes a few minutes to calculate where I am and begin the more tedious process of paper charting my course. As I've mentioned before, I spend one day each vacation doing the paper chart. This keeps my skills at a level that I am comfortable with. Your level of comfort may vary and your history of paper charting may vary. In 1979 when I started in the San Juans and Gulf Islands Loran was out of my price range. Every trip was charted on paper and notes were made to make it easier next time.

Ken
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Old 09-24-2008, 06:23 PM   #22
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RE: GPS vs. Ship's Compass

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2bucks wrote:

But you see Marin, you've said you can only totally rely on your magnetic compass. Your example of entering Comox is a perfect example of where your magnetic compass will tend to lead you into trouble.

I'll bet that Marin used his chart plotter to know exactly where the gap was, going in to Comox. While he was following along with a paper chart, depth sounder and visual confirmation, he also looked at the technology to confirm what everything else told him. Most prudent mariners do.
The original question was assuming a properly swung compass, properly plotted course, etc., which would one trust the most to follow the magnetic course, the magnetic compass or the GPS magnetic heading indicator?* Assuming "trust" means which one is*least likely to crap out, the magnetic compass is the more reliable in my opinion.* So in that respect, it's the only instrument I feel I can totally rely on (not to fail).

However the magnetic compass won't help you compensate for changes in current that you might encounter as Ken has pointed out.* The plotter will, assuming you've entered a pair of waypoints to track between.* But if you're just using the GPS to hold a specific heading that you've plotted rather than track a course then it's not any more accurate or helpful*than the magnetic compass.

And yes, we most certainly did use every aid we had at hand negotiating the gap into Comox harbor for the first time.* We used both chart plotters zoomed in tight and the paper charts for the bigger picture.* And the depth sounder.**

But our primary instrument for finding and negotiating the gap*was neither electronic nor magnetic--- it was the*pair of binoculars we used*to monitor the ridiculously small range markers on*shore.* Had either or both of the chart plotters shown we were not accurately*tracking the gap, we would have ceased paying attention to them and continued concentrating on keeping the range markers lined up.

In our "order of dependability" list the electronics are at the bottom.* At the top are physical things like paper charts, binoculars, the lead line,*and navaids like buoys, range markers, etc.* Then come the magnetic compasses.* Then come the radar, GPS plotters, sounder, Loran, etc.

Of course in practice we use all these things (except the lead line ).* But we operate the boat as though the electronics are supplementary, and we are ready to dismiss their information if it's not confirmed by what we physically see around us and what we see on the chart, assuming daylight and decent visibility.

If it's foggy we boat in the fog and so place much more dependence on the electronics.* But even then we have the charts out and basic courses plotted so if the electricicals stop holding hands we can still head for a safe haven with an acceptable chance of getting there.* Eventually
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Old 09-25-2008, 11:57 AM   #23
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RE: GPS vs. Ship's Compass

Whooooooo........ You had me worried when you tossed in the lead line. Thanks for clearing it up that you don't really use it.

Oh, and welcome back. I hope you saw some great things. Stretching boundaries and going new places is both fun and nerveracking.

Ken
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Old 09-25-2008, 01:57 PM   #24
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RE: GPS vs. Ship's Compass

The only time I've had reason to use the lead line (complete with the star-shaped tallow bowl in the bottom of the weight for bringing up "samples") is when we're at a dock in an extreme minus tide. There have been a few occasions when we wanted to know if we were sitting in the mud, or to confirm that we had enough clearance under the boat to start the engines without sucking stuff into the through-hulls. Other than that the line and its weight stay in the storage bag. But it's there if we need it.......

And yes, we saw lots of great things. This first trip was more of a runaround than we'd like, but we wanted to see a fair number of places to get an idea of the ones we'd like to spend more time in on later trips. Since you (Ken) know the area, we visited Ganges, Silva Bay, Pender Harbor, Grace Harbor, Prideaux Haven, Refuge Cove, Squirrel Cove, Von Donop, Herriot Bay, Rebecca Spit, Comox, Nanaimo, Telegraph Harbor, Port Browning and Prevost Harbor (Stuart Island). We'd been to some of the southern locations before, but everything above Nanaimo (including Silva Bay) was new to us.* We cleared customs by phone in both directions so did not have to go anywhere out of the way to clear in.

-- Edited by Marin at 14:59, 2008-09-25
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Old 09-26-2008, 05:23 AM   #25
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RE: GPS vs. Ship's Compass

Well thats the difference between Boeing and Douglas.

Chevvy VS Caddy.

The old DC 10s had ADG , air drag generators (if memory serves that was the designation) , that simply fell out when actuated that provided unlimited time on the emergency buss.

Probably cost too much for Boeing , on their cheapos.

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Old 09-26-2008, 12:02 PM   #26
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RE: GPS vs. Ship's Compass

That's a great loop that Marin took. I think we're headed to the Broughtons next year which will be a bit of a stretch for us. Although I don't think I'll ever stop going to some of the places, Victoria, Ganges, Nanaimo, Vancouver, and Pender Harbor, on our way up, we're starting to feel the need to see some of the more northwestern spots away from Desolation. According to some of the guidebooks a few of the places are starting to disappear as the owners get older and can't find someone to take over. Some of the places are getting bought up to become private and I imagine some will become Yacht Club outstations with no reciprocal.

It's never too early to start dreaming about next year.
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Old 09-26-2008, 01:15 PM   #27
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RE: GPS vs. Ship's Compass

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2bucks wrote: I think we're headed to the Broughtons next year which will be a bit of a stretch for us....According to some of the guidebooks a few of the places are starting to disappear as the owners get older and can't find someone to take over.
That whole area up there is really neat.* We've not taken the GB up there but we've trailered our 17' Arima up to Telegraph Cove and then gone halibut fishing and exploring out*in Blackfish Sound, Knight Inlet, etc.* And we've flown through the area a lot in the floatplane and stopped at Sullivan Bay and Minstrel Island (when it was still in operation).* And you're correct, some of the resorts and little marinas are starting to close down or are for sale.* Not that this makes the area any less desireable to visit, but it will mean that you may not be able to count on getting supplies as often, and you may have to anchor out more where you can now tie to a dock if you wish.* Fortunately, the distances between places are not that great once you're in the area, so places like Port McNeil, Echo Bay, and Sullivan Bay are always within easy reach.
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