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Old 11-04-2012, 12:24   #16
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Re: Compasses

Moxy,
1) If you have a fiberglass hull / deck (which I believe you do), a decent compass (which you do), and mounted in a decent location (which I assume), there should be no problem getting your compass adjusted correctly....




2) At this point (apparently after struggling with getting things to work), my best advice is to contact a professional compass adjuster, pay them to come out to your boat and do a professional adjustment....
In your area (South Carolina), you have an excellent company to do this, Island Compass South, in Lake Wylie, SC...
http://www.islandcompass.com/repairAdjusting.htm
(They're a Ritchie service center as well)




3) On a side note, a few years back I hired a professional compass adjuster (here in S. Fla) to do my two Ritchie Navigator compasses.....it took him less than 90 minutes to do both (they were actually just about perfect before he started, but I wanted to be sure as I was heading across the Atlantic)....and we also checked/verified my Raymarine heading sensor (fluxgate).....
All 3 of my main compasses (my 2 Ritchie Navigators and my Raymarine Fluxgate), show the same headings.....now matter what direction I'm heading, they're all the same or within one degree.....

(Except for the binnacle lights themselves, I have no wiring/electronics within 2 feet of any of my compasses, and no heavy current wiring, no magnetic speakers, nor any ferrous metal at all anywhere near my compasses...)


And now, over 5 years and 12,000 offshore miles later, both of my Ritchie compasses (and my Raymarine fluxgate) are still just as accurate!!!
There is no reason that you shouldn't be able to have just as good results!!




When sitting at my dock, my boat sits at the heading of about 58* - 59* Magnetic (she moves around +/- a degree from the surges of wakes from passing boats).....
Although, the photo is at a bit of any angle, have a look at this picture.....(which shows one of my Ritchie Navigators and my fluxgate heading, displayed on my Raymarine ST-6002+ autopilot control head....)
http://www.c470.jerodisys.com/470pix/4713801.htm


I hope this helps...



Good luck and Fair Winds!!!


John
s/v Annie Laurie
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Old 11-04-2012, 12:33   #17
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Re: Compasses

You had your compasses adjusted by a pro and didnt end up with declination cards for them? That's amazing....
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Old 11-04-2012, 12:37   #18
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Re: Compasses

I just learned a lesson about this the expensive way.

My compass was off, and not in a consistent way. It was old, had a bubble, plastic dome was hazy, so I decided to spring for a new compass. Mounted the new one in the same location and ... you got it, it was whacko just like the old one. So I played around a bit and found that if I removed the VHF radio (which was about 2 feet away from the compass), the compass worked great. Moved the VHF to the other side of the boat and all is well.

The moral of this story: ANY electronics or metal in the vacinity of the compass screws with it. Check that first before you try to compensate.
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Old 11-04-2012, 13:03   #19
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Re: Compasses

When you think you have it right, and you are tied to a dock, try starting your engine and putting it in and out of gear.That sometimes make a big difference. Try turning the helm back and forth, and the mild steel sprocket that moves the chain,(which might also be mild steel) may have an effect. I used to have a steel boat, and learned to hate compasses. Just another 2 cents worth.____Grant.
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Old 11-04-2012, 13:28   #20
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Re: Compasses

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Originally Posted by Cheechako View Post
You had your compasses adjusted by a pro and didnt end up with declination cards for them? That's amazing....
Agreed.... so they match each other...that's easy...but to get them to be near the ACTUAL heading all the way around is the trick!
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Old 11-04-2012, 14:18   #21
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Re: Compasses

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I did several of our assistance towing boats that way in just minutes and the compaqsses are fine for finding home in an emergency.

most compasses don't need huge accuracy because between them and the helmsman...you can't be that accurate anyhow over very long distances.
There's a big difference between getting a towboat home and navigating a long passage. On a two-week passage, a two-degree error could mean missing a landfall by several hundred miles.
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Old 11-04-2012, 14:37   #22
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Re: Compasses

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There's a big difference between getting a towboat home and navigating a long passage. On a two-week passage, a two-degree error could mean missing a landfall by several hundred miles.
On most of the boat compasses I've seen you can hardly recognize 2 degrees...and yes I know it's all about averaging a steer....which MOST people couldn't do for more than several hundred miles anyway.
You steer for awhile and either have GPS or a sextant to keep you honest.

Yeah I know about long passages...been near the north and south poles long before GPS.

Plus if you know what you are doing...you don't necessarily miss landfall by several hundred miles...you miss your intended point of landfall by several hundred and adjust.
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Old 11-04-2012, 14:45   #23
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Re: Compasses

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I got into this a bit with one of my ASA instructors who knew a lot about sailing and nothing about compasses. I used to make field maps before
GPS, with just a map and a compass. I've used what was considered to be the gold standard of handheld compasses, and it had a margin of error of half a degree either direction in perfect conditions. My normal compass has a 2 degree margin, and it isn't cheap.

He was teaching that the cheap "look through" bearing compass he had, with 5 degree increments, was accurate to less than a degree. In the cockpit, moving around.

I grin when I see a giant plotter parked above a compass. My little plotter is up in the companionway and I can see the change when it's on. Good luck with that thing, even if it doesn't have magnets holding the chart card doors closed.

Here's something else I found out the hard way. I have a wheel pilot, and it would just randomly get lost sometimes. Took me a while to realize the iPhone in my pocket was jacking up the little flux gate. When I stand behind the helm, the pocket I normally keep the phone in is mere inches from the AP head. I imagine it's deflecting my binnacle compass as well.

JRM

Even my watch has a digital compass in it. Tracking barometer too. For under $100. It even tells time!

JRM, why were you surprised that the ASA instructor didn't know every single thing on Earth? Did you expect to get extended navigational instruction in a course focused on direct sailing skills? Did you also expect him to tear down the diesel engine and explain all its working parts?

He taught what was in the curriculum. He knows what he knows. you know what you know.

And, it IS possible to put the chart plotter over the compass if done correctly. In fact, using a chart plotter intelligently can increase one's abilities to navigate via other methods by providing valuable feedback regarding whether one's estimates are correct or not.

For instance, a chartplotter will reveal leeway very accurately if used intelligently. I always demonstrate to new sailors on my boat the advantages and disadvantages of the chart plotter and the paper chart. The chart plotter can zoom in and give details not included on the paper chart, but it's lousy at giving one the bigger picture.

Rather than deciding that old technology is somehow better than new technology, to me it makes more sense to learn to use the best of all of them.
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Old 11-04-2012, 19:53   #24
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Re: Compasses

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If you don't think that a differential/WAAS GPS can be used (of course correctly is the operative term) and ANY other method is better on a small boat attempted by one or two "unqualified" people then go ahead and spread the word...
Yeah I think you are agreeing with my correct post. The Richie instructions say bearing not heading, by the way. I will be best if the object is some miles away.
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Old 17-04-2012, 16:32   #25
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Re: Compasses

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JRM, why were you surprised that the ASA instructor didn't know every single thing on Earth? Did you expect to get extended navigational instruction in a course focused on direct sailing skills? Did you also expect him to tear down the diesel engine and explain all its working parts?

He taught what was in the curriculum. He knows what he knows. you know what you know.
What? Are you serious? Extended navigational instruction? I don't think the use of a hand compass as extended navigational instruction.

I don't expect him to know everything on earth, because that would make him my mother-in-law, and what a miserable class that would be. But to have absolutely no clue about the limitations of a safety device he is representing himself as an expert of, that is very poor form. If he wants to show how to set a GPS anchor alarm, or use shore based line ups to verify we aren't dragging anchor, that's good. If he wants to whip out his handy sighting compass and tell us that as long as it's always the same we're safe, that's bad. I didn't make him choose the latter, I just clued him in that the instrument he had chosen didn't have the accuracy to fulfill his requirements. If you want to always be within 1 degree of bearing to the same point, and the thing has a five degree accuracy, you'll appear to be dragging every sight. He asked me to shoot bearings every few minutes and verify they were within 1 degree of each other. I told him I couldn't do that with the tool he gave me, and we had a discussion from there. I think there are more bad feelings in your sarcastic post than the entire discussion we had aboard.

Would you rather I just made up the bearings and let it go? He asked me to do something impossible, and then insisted it was easy. The only reason it didn't end there is because it took a bit of convincing to change his mind from what he believed to what was accurate. Doesn't invalidate the theory, just that particular practice.

Believe it or not, it is possible for adults to disagree, and have a rational discussion to resolve that disagreement, in a calm manner. I should know, I'm wrong more often than not.

JRM
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Old 17-04-2012, 17:43   #26
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Quote:
Originally Posted by Bash

There's a big difference between getting a towboat home and navigating a long passage. On a two-week passage, a two-degree error could mean missing a landfall by several hundred miles.
What. That's not how you navigate on a two week passage. Cumulative error any way could be way over 2 percent. You don't need a compass any better then 5 degrees.

And yes gps can be used to swing a compass. It's not the best but it's better then most methods.

Dave
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Old 17-04-2012, 18:05   #27
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Re: Compasses

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What. That's not how you navigate on a two week passage. Cumulative error any way could be way over 2 percent. You don't need a compass any better then 5 degrees.

And yes gps can be used to swing a compass. It's not the best but it's better then most methods.

Dave
Thanks...
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Old 17-04-2012, 19:11   #28
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Re: Compasses

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You had your compasses adjusted by a pro and didnt end up with declination cards for them? That's amazing....
Declination? I think you meant deviation...

I've always used the Sun Az to check my compass for quick checks when on long tacks.(azimuth uncorrected to "C"ompass from "T"rue by the TVMDC "True Virgins Make Dull Companions" rule) You can quickly calculate Sun Az with a hand held calculator (I use an old HP-41cx). That pin standing up in the middle of your compass card is not ONLY for help in taking bearings.... It casts a nice sun shadow 180 degrees away from the sun (when the sun is low). This method gives you a really fast, accurate and confidence inspiring deviation check on your specific heading. It's easy in the morning and late afternoon, as the sun casts longer shadows on the compass pin at those times. Although you can get meaningful checks with a shadow line that is not that long too... Everyone should make a habit of this on longer passages. Just because you have a Dev Card made up doesn't mean that unbeknownst to the helms person the crew didn't stash their boom box speakers in the lazarette near the steering compass and you're happily steering a course ten degrees off!!

Also, this thread sent me digging through my storage lockers...and lo! I found it!!! There used to be a small device called the "Cape Cod Deviation Indicator"---and I found mine. It's a small square aluminum (non-magnetic) plate with rubber feet and a tall shadow pin in the middle and a degree scale printed on it. You simply place the Cape Cod Dev Indicator on a flat surface near your steering compass and set the card so the sun's shadow cast by it's central vertical pin casts a shadow on it's Dev Indicator's "sun line" then immediately turn the boat on a reciprocal compass heading and the Dev Indicator card will read your compass deviation by the sun on that heading. Sounds more complicated than it is but it's really simple to use and came with excellent directions. I tried a search on the Internet but didn't see this device mentioned anywhere. Maybe they aren't made anymore? ...or maybe it's called something else. This was made in Chatham, Mass and I bought it back in the mid 70's. If anyone can find it on the web please drop us a link. (Celestair didn't even have them) This is a VERY handy and easy to use device.
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