Navigation Questions. Can you do them? - Page 3 - SailNet Community
Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.

Reply
 
LinkBack Thread Tools
post #21 of 122 Old 02-28-2010
Telstar 28
 
sailingdog's Avatar
 
Join Date: Mar 2006
Location: New England
Posts: 43,290
Thanks: 0
Thanked 15 Times in 12 Posts
Rep Power: 14
         
Last I checked, wouldn't that be 0˚T not 360˚T...

Sailingdog

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Telstar 28
New England

You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

If you're new to the Sailnet Forums... please read this
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
.

Still—DON'T READ THAT POST AGAIN.
sailingdog is offline  
Quote Quick Reply Share with Facebook
Sponsored Links
Advertisement
 
post #22 of 122 Old 02-28-2010
Senior Member
 
Join Date: Dec 2008
Posts: 711
Thanks: 1
Thanked 6 Times in 6 Posts
Rep Power: 7
 
Quote:
Originally Posted by TheBishop View Post
If the wind is reported as 360T, it's coming from the North. If the current (set) is reported as 360T, it's going to the North. Who decided this, and was it done just to torture me?
I also have the same question and just suppose that it's just convention. Much like a circuit diagram in EE where electrical current is shown going from the positive to the negative post whereas in reality the electrons flow from negative to postive. Not sure how all this "conventional wisdom" got started.
lancelot9898 is offline  
Quote Quick Reply Share with Facebook
post #23 of 122 Old 02-28-2010 Thread Starter
Senior Member
 
Boasun's Avatar
 
Join Date: Feb 2007
Location: New Orleans, LA
Posts: 3,070
Thanks: 1
Thanked 0 Times in 0 Posts
Rep Power: 10
   
The winds are named from where they are coming from because when you face into the wind you are looking in that direction. Thus the North wind is from the North because that is the direction you are facing.
About everything else is the direction they are going; Currents, Your Boat and so forth.
This is not that hard to understand... Not hard at all.

BTW: My post #13 here has not been answered yet... It is about figuring distance with a known chart scale.

1600 Ton Master, 2nd Mate Unlimited Tonnage

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Maritime Instructor
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

S/V Rapture

Last edited by Boasun; 02-28-2010 at 10:03 AM.
Boasun is offline  
Quote Quick Reply Share with Facebook
post #24 of 122 Old 02-28-2010
Senior Member
 
AdamLein's Avatar
 
Join Date: Nov 2007
Location: SF Bay area
Posts: 1,924
Thanks: 6
Thanked 7 Times in 6 Posts
Rep Power: 8
 
Quote:
Originally Posted by Boasun View Post
One other:
the scale of a chart is 1:80,000. What distance at sea does a distance of 3.5 inches on the chart represent? What distance on the chart represents an actual distance of 14.3 NM?
3.5 in at 1:80,000 = 3.84 nm
13.3 nm at 1:80,000 = 13.03 in

Quote:
Remember that a NM is 6076.11549 ft thought we use 6000 ft for practical purposes.
Okay,
3.5 in at 1:80,000 = 3.89 nm
14.3 nm at 1:80,000 = 12.87 in

s/v Laelia - 1978 Pearson 365 ketch
s/v Essorant - 1972 Catalina 27
AdamLein is offline  
Quote Quick Reply Share with Facebook
post #25 of 122 Old 02-28-2010
Senior Member
 
jackdale's Avatar
 
Join Date: Dec 2008
Location: Calgary, AB, Canada
Posts: 9,041
Thanks: 27
Thanked 59 Times in 56 Posts
Rep Power: 7
 
Quote:
Originally Posted by sailingdog View Post
Last I checked, wouldn't that be 0˚T not 360˚T...

You are closer than me.

Vol 5 of Canadian Tides and Currents uses 000 for currents flowing to True North.

I will have to fix that.

__________________
ISPA Yachtmaster Offshore Instructor Evaluator
Sail Canada Advanced Cruising Instructor
IYT Yachtmaster Coastal Instructor
ASA 201, 203, 204, 205, 206, 214
As I sail, I praise God, and care not. (Luke Foxe)
jackdale is offline  
Quote Quick Reply Share with Facebook
post #26 of 122 Old 02-28-2010
Senior Member
 
jackdale's Avatar
 
Join Date: Dec 2008
Location: Calgary, AB, Canada
Posts: 9,041
Thanks: 27
Thanked 59 Times in 56 Posts
Rep Power: 7
 
Boasun and others

Re: Chart scales.

I use Canadian Chart 3462 in my navigation class; it is 1:80,000 chart. However, the 1:80,000 is measured at 49˚ 30'N which is not on the chart. The top of the chart is 48˚ 54'N. As this is a Mercator projection, it seems to me that converting distances measured using the scale would not be exact.

In you view, would this be a correct interpretation?

__________________
ISPA Yachtmaster Offshore Instructor Evaluator
Sail Canada Advanced Cruising Instructor
IYT Yachtmaster Coastal Instructor
ASA 201, 203, 204, 205, 206, 214
As I sail, I praise God, and care not. (Luke Foxe)
jackdale is offline  
Quote Quick Reply Share with Facebook
post #27 of 122 Old 02-28-2010 Thread Starter
Senior Member
 
Boasun's Avatar
 
Join Date: Feb 2007
Location: New Orleans, LA
Posts: 3,070
Thanks: 1
Thanked 0 Times in 0 Posts
Rep Power: 10
   
If the chart is 1:80,000 that means that you have 80,000 square inches representing land & water area squeezed into 1 square inch of the chart.

But when using the latitude scale on the chart for measuring distances, I have found that there can be a slight difference from near the bottom of the chart compared to the top of the chart.

1600 Ton Master, 2nd Mate Unlimited Tonnage

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Maritime Instructor
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

S/V Rapture
Boasun is offline  
Quote Quick Reply Share with Facebook
post #28 of 122 Old 02-28-2010 Thread Starter
Senior Member
 
Boasun's Avatar
 
Join Date: Feb 2007
Location: New Orleans, LA
Posts: 3,070
Thanks: 1
Thanked 0 Times in 0 Posts
Rep Power: 10
   
How far will a vessel traveling at 16.5 knots travel in 34 minutes? In 2h 24m?

How long will it take a ship traveling at 14 knots to go 0.8 miles? To go 69 miles?

1600 Ton Master, 2nd Mate Unlimited Tonnage

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Maritime Instructor
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

S/V Rapture
Boasun is offline  
Quote Quick Reply Share with Facebook
post #29 of 122 Old 02-28-2010
Telstar 28
 
sailingdog's Avatar
 
Join Date: Mar 2006
Location: New England
Posts: 43,290
Thanks: 0
Thanked 15 Times in 12 Posts
Rep Power: 14
         
Answers in bold
Quote:
Originally Posted by Boasun View Post
How far will a vessel traveling at 16.5 knots travel in 34 minutes? 9.35nm In 2h 24m? 39.6nm

How long will it take a ship traveling at 14 knots to go 0.8 miles? 2.98 minutes To go 69 miles? 4.29 hours.

Sailingdog

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Telstar 28
New England

You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

If you're new to the Sailnet Forums... please read this
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
.

Still—DON'T READ THAT POST AGAIN.
sailingdog is offline  
Quote Quick Reply Share with Facebook
post #30 of 122 Old 02-28-2010
Senior Member
 
tomaz_423's Avatar
 
Join Date: Feb 2006
Location: Slovenia
Posts: 415
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 10
 
Quote:
Originally Posted by Boasun View Post
If the chart is 1:80,000 that means that you have 80,000 square inches representing land & water area squeezed into 1 square inch of the chart.

But when using the latitude scale on the chart for measuring distances, I have found that there can be a slight difference from near the bottom of the chart compared to the top of the chart.
Jacdale's post was spot on.
Boasun, you probably teach others this:
Chart is a flat paper representing a sphare. It is impossible to make it an accurate presentation.
Your statement is only true around one (reference) latitude. at any other latitude it is either less or more - but wrong.
Nautical charts are pretty accurate in representing angles, but not so good in representing surface areas. That is why we read distances at the closest left of right edge of the chart at about the same latitude as the distance was taken.
If we would only measure that distance and multiply it we could not get a very accurate result.
The error is neglectable for charts representing small areas, but can be significant in a general charts like Ca4700 or US13003.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Beneteau Oceanis 473

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

finished cruising after two years.
tomaz_423 is offline  
Quote Quick Reply Share with Facebook
Reply

Quick Reply
Message:
Options

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now



In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.


User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Similar Threads
Thread Thread Starter Forum Replies Last Post
Working With the Stars—Celestial Navigation Jim Sexton Seamanship Articles 0 05-06-2003 08:00 PM
Working With the Stars—Celestial Navigation Jim Sexton Her Sailnet Articles 0 05-06-2003 08:00 PM
Navigation Basics Jim Sexton Learning to Sail Articles 0 01-04-2002 07:00 PM
Navigation Basics Jim Sexton Seamanship Articles 0 01-04-2002 07:00 PM
Navigation Basics Jim Sexton Her Sailnet Articles 0 01-04-2002 07:00 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome