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Onboard Plotters / GPS. True or Magnetic?


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One of our members has a signature which reads "Timid Virgins Make Dull Companions, add Whiskey :-)"

I find this sort of Rape Culture stuff extremely offensive. Wellington school boys have been suspended for Rape Culture this week. Real men stand up against Rape Culture.

 

http://captainawkward.com/2012/08/07/322-323-my-friend-group-has-a-case-of-the-creepy-dude-how-do-we-clear-that-up/

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Ok Kevin for you and those more easily offended, although I learned the one above many years ago in my coastal masters course (using true in place of timid), I also learned:

Variation east, compass least, variation West, compass best.

Is that more appropriate?

It still doesn't give TVMDC though.

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What part of the concept of Rape Culture don't you understand?

 

With all due respect, don't hijack my thread with this sh#t, please.

I'm learning lots and enjoying the different takes on navigation and don't need it to waiver off to some sh#t that has nothing to do with the thread I started.

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....this has been a good reminder to check my battery powered , hand held GPS and its spare batteries.

 

So, if you are down to one of these devices and need to steer....

(That would be in the case of a catastrophic power fail) 

Steering to a compass is not easy, but steering to a set of moving numbers or that tiny digital compass rose can be a lot harder..

I like to start by steering to the compass bearing with no regard for variation or deviation etc.. ....(check for a star if available)..and then after a minute or so check the hand held GPS for its bearing.

I then adjust my course until it is the bearing (true) on the GPS that I want.

It is then a simple matter of noting the compass bearing. This is now not a mathematically derived bearing but "real bearing".

It should be noted in the log along with the GPS bearing, just in case you run out of battery power. Remember this "difference" contains all leeway factors (current etc) which may change as your journey progresses....

You can now steer to the compass....and as IT quite rightly said , adjusting about every 15 min, a star if available.

 

Logging your lon and lat every 30 min and plotting it (sooner if in dangerous territory) allows you to turn the GPS off in between and save on battery power.

 

....and just for fun...you will find that people who are new to hand steering will often vary the  direction of the vessel in the direction they are looking....ie if they look to port they will bias to a small degree in that direction and visa versa  . :razz:

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....this has been a good reminder to check my battery powered , hand held GPS and its spare batteries.

 

So, if you are down to one of these devices and need to steer....

(That would be in the case of a catastrophic power fail) 

Steering to a compass is not easy, but steering to a set of moving numbers or that tiny digital compass rose can be a lot harder..

I like to start by steering to the compass bearing with no regard for variation or deviation etc.. ....(check for a star if available)..and then after a minute or so check the hand held GPS for its bearing.

I then adjust my course until it is the bearing (true) on the GPS that I want.

It is then a simple matter of noting the compass bearing. This is now not a mathematically derived bearing but "real bearing".

It should be noted in the log along with the GPS bearing, just in case you run out of battery power. Remember this "difference" contains all leeway factors (current etc) which may change as your journey progresses....

You can now steer to the compass....and as IT quite rightly said , adjusting about every 15 min, a star if available.

 

Logging your lon and lat every 30 min and plotting it (sooner if in dangerous territory) allows you to turn the GPS off in between and save on battery power.

 

....and just for fun...you will find that people who are new to hand steering will often vary the  direction of the vessel in the direction they are looking....ie if they look to port they will bias to a small degree in that direction and visa versa  . :razz:

 

 

So, if I am reading this right - you actually don't bother with deviation and variation to get the magnetic course to steer in the traditional sense....like what all the books and "yachmasters" teach, you just actually compare the true heading on the gps to heading on the compass , and that's your "magnetic compass course".....being aware you will need to keep an eye on it for leeway and tide and adjust as necessary so you don't drift into dangers.

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Ok Kevin for you and those more easily offended, although I learned the one above many years ago in my coastal masters course (using true in place of timid), I also learned:

Variation east, compass least, variation West, compass best.

Is that more appropriate?

It still doesn't give TVMDC though.

 

 

to go the other way

 

Cadbury Diary Milk Very Tasty

(compass - deviation- Magnetic - Variation - True)

 

CAdET  - Compass Add East = True

 

so if you are moving from Compass (Cadbury) to True (tasty) any deviation or variation that is East is added, if either is west it is subtracted, and its opposite if converting from True to Compass

 

Clear as mud?

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Yep..Zozza exactly .BUT..

It is super important to both remember and understand the fundamentals of traditional coastal nav. If for no other reason than to talk with other navigators and to keep all the facets of a sailing boats motion through the water clear in your head. Or to put it another way I can navigate in a traditional text book manner but usually chose what ever is the easiest, most reliable, and accurate method with what I have at my disposal.

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One of our members has a signature which reads "Timid Virgins Make Dull Companions, add Whiskey :-)"

I find this sort of Rape Culture stuff extremely offensive. Wellington school boys have been suspended for Rape Culture this week. Real men stand up against Rape Culture.

 

http://captainawkward.com/2012/08/07/322-323-my-friend-group-has-a-case-of-the-creepy-dude-how-do-we-clear-that-up/

Sorry Kevin, but I need to clarify, that is not a signature, it's a pneumonic to remember the conversion of true to magnetic bearings. Something I thought that was actually highly relevant to this thread.

I am ever so slightly offended that you take that as promoting rape culture, but each to their own. I can state with all honesty I do believe the consumption of whiskey does make a significant number of dull people more interesting. Some are beyond help though.

 

Thread drift over.

As you were.

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I think its worth remembering that magnetic Changes.....

True Does not....

Magnetic is location and date specific..

True is always true...

Charts are drawn true..and as such are the constant.

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Fair enough.scenarios for everything..

Personally I wouldn't cross a bar I don't know at night..and I wouldn't trust my compass regardless if it was so tight that I couldn't turn around.

Given what I have seen plenty of places I wouldn't trust paper or electronic charts for a first time night time bar crossing either

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Not often I agree with a man that sails a steel drum or a plywood box but today is that day

 

I'm always true North and north up on all devices, even paper charts

 

Your scenario re navigating with a compass bearing only works if you are exactly where you think you are, if your not then your compass bearings are all wrong

 

'Never trust less people than two forms of info'

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:lol:  :lol:  :lol:  :lol: ....I dont pretend too... but I would be curious how many times in x number of operational hours that they have had to resort to a compass ?...

...and the ramifications are ...lets say a little more dramatic if a failure occurs...

....and... I do have a compass on board......and...I would be very curious to know if commercial aircraft run on magnetic or true bearings...which was the point....

...and...what on earth makes you think that a non electronic compass dosnt fail ???

I got told by a very experienced old pilot ..."The reason why they use the new sh*t, is because it is more reliable and better than the old sh*t"...

I asked what did he mean...

He said "do you really think that a traditional compass dosnt stuff up ?,...Its why they have a couple more lying around " !!!  :lol:

 

 

PS they used to use a sextant to navigate to Lord Howe island in the flying boats too......

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