Help needed with a plotting question - SailNet Community

   Search Sailnet:

 forums  store  


Quick Menu
Forums           
Articles          
Galleries        
Boat Reviews  
Classifieds     
Search SailNet 
Boat Search (new)

Shop the
SailNet Store
Anchor Locker
Boatbuilding & Repair
Charts
Clothing
Electrical
Electronics
Engine
Hatches and Portlights
Interior And Galley
Maintenance
Marine Electronics
Navigation
Other Items
Plumbing and Pumps
Rigging
Safety
Sailing Hardware
Trailer & Watersports
Clearance Items

Advertise Here






Go Back   SailNet Community > General Interest > General Discussion (sailing related)
 Not a Member? 


Reply
 
LinkBack Thread Tools
  #1  
Old 04-10-2009
Member
 
Join Date: Jan 2007
Posts: 46
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
castoff is on a distinguished road
Help needed with a plotting question

When told to take a bearing on the light of a lighted buoy do you use the open circle at the base of the buoy or the open circle that (I think) represents the light on the top of the buoy?
Reply With Quote Share with Facebook
  #2  
Old 04-10-2009
sailingdog's Avatar
Telstar 28
 
Join Date: Mar 2006
Location: New England
Posts: 43,291
Thanks: 0
Thanked 9 Times in 9 Posts
Rep Power: 13
sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice
When taking a bearing on a buoy, you would put the line through the center of the open circle, which indicates the buoy's actual location. However, be aware that the actual, real world, position of the buoy can be significantly different from that on the chart as it is on a chain and has a swinging circle, much like an anchored boat, and the length of the chain and the depth will determine how large that swinging circle is. Also, buoys can be dragged out of position by ice, boats, storms, etc... so, you should generally take the position of a buoy as a general, rather than a specific point on a map.

A daybeacon or daymarker, which is fixed to the bottom, will be a more accurate way of locating your position, as they are not subject to the inaccuracies of a swinging circle.




I'd highly recommend you get Richard K. Hubbards's book, Boater's Bowditch, which is an abridged version of Bowditch specifically re-written for the small craft navigator. Or you can download Bowditch for free from HERE.
__________________
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.
Reply With Quote Share with Facebook
  #3  
Old 04-10-2009
Member
 
Join Date: Jan 2007
Posts: 46
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
castoff is on a distinguished road
Sailingdog, this buoy is the shape of an inverted cone with the top cut off and two open circles, one at the base and one on the top. In the question I am answering it asks me to take a bearing on the light of the specific buoy. I don't know which open circle to use.
Reply With Quote Share with Facebook
  #4  
Old 04-10-2009
Senior Member
 
Join Date: Jun 2001
Posts: 560
Thanks: 0
Thanked 2 Times in 2 Posts
Rep Power: 14
sailordave is on a distinguished road
well....

How accurate a reading can you get? Can you get less than 2 degrees error?
At a range of 1nm (6000') your 2 degrees error is going yield an error of about 200 feet. I highly doubt you're going to see a buoy move that much from it's charted position.

Less than a mile why are you even taking a sight? Just steer the boat.

GENERALLY baseball navigation works. (you're in the ballpark)
Reply With Quote Share with Facebook
  #5  
Old 04-10-2009
Member
 
Join Date: Oct 2008
Location: New Haven, Connecticut
Posts: 38
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
adru is on a distinguished road
Here is a link to the updated 2002 version of the American Practical Navigator.
Maritime Safety Information
Check out the "Menu Options" dropdown for add'l info you may find useful.
__________________
"Never pray for an easier life - pray to be a stronger person! Never pray for tasks equal to your power - pray for power equal to your tasks. Then doing your work will be no miracle - you will be the miracle." Phillips Brooks
Reply With Quote Share with Facebook
  #6  
Old 04-10-2009
sailingdog's Avatar
Telstar 28
 
Join Date: Mar 2006
Location: New England
Posts: 43,291
Thanks: 0
Thanked 9 Times in 9 Posts
Rep Power: 13
sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice
What kind of chart are you using. I've never seen symbols like the one you're describing. Can you post a photo of the chart in question??? The one at the bottom of the inverted cone is probably the correct one, since the base of the buoy should be its nominal position.



Quote:
Originally Posted by castoff View Post
Sailingdog, this buoy is the shape of an inverted cone with the top cut off and two open circles, one at the base and one on the top. In the question I am answering it asks me to take a bearing on the light of the specific buoy. I don't know which open circle to use.
__________________
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.
Reply With Quote Share with Facebook
  #7  
Old 04-10-2009
Boasun's Avatar
Senior Member
 
Join Date: Feb 2007
Location: New Orleans, LA
Posts: 3,058
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 9
Boasun will become famous soon enough Boasun will become famous soon enough
You really don't want to use a buoy for bearings. Buoys are like a dog chained to the middle of your yard and moves around the plotted position of its anchor. Also I have seen buoys dragged off of its position so many times I have lost count. Nope won't use a buoy for plotting. But that is Me.
Day marks are on piles and don't move. Use the daymarks for bearings.
__________________
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
Reply With Quote Share with Facebook
  #8  
Old 04-10-2009
Senior Member
 
Join Date: Aug 2006
Location: Arlington, VA
Posts: 1,807
Thanks: 0
Thanked 4 Times in 4 Posts
Rep Power: 9
btrayfors will become famous soon enough btrayfors will become famous soon enough
dog, Bosun, et. al...

I think you missed his question. From it's phrasing, and from his response, I think he's taking some sort of course or exam.

Castoff,

3 assumptions:

1. you're using U.S. or Canadian charts;
2. you're asking about a question on an exam;
3. you still have your Valiant 37 and got it OK to Lake Ontario :-)

Most buoy locations are marked by a dot...like a thick period...at their base. A few, like private marker buoys, have a small circle at the base of a diamond to show their location. They are also generally in the shape of a diamond, not a triangle. The charted location of the buoy is indicated by the dot. Lighted buoys are indicated by circles or teardrops in color, generally purple/red. The colored circles are centered on the dots.

I know of no chart symbol with two circles. Sometimes, two items may be very close and if the scale of your chart isn't right -- particularly on electronic charts -- it may appear that one buoy has two circles.

When plotting a course directly to a buoy, you'd use the dot.

dog, Bosun, et. al are correct about not depending too heavily on buoy positions in the real world. They can move on their chains in deep water. They can be blown off course. They can be mis-plotted. They can have been moved, and your chart just doesn't show their new location yet.

Still, despite the caveats, in relatively shallow water I've found that buoy positions of U.S. buoys along the East Coast are generally dead smack balls-on accurate (an industry term). The Coast Guard takes great pains to ensure that they are, and they do a damned good job of it.

However, as ever, your mileage may vary :-)

Bill

Last edited by btrayfors; 04-10-2009 at 05:45 PM.
Reply With Quote Share with Facebook
  #9  
Old 04-10-2009
Senior Member
 
Join Date: Nov 2002
Location: New York
Posts: 5,401
Thanks: 0
Thanked 14 Times in 14 Posts
Rep Power: 14
bubb2 has a spectacular aura about bubb2 has a spectacular aura about bubb2 has a spectacular aura about
The only thing I can think of that the OP may be trying to describe is a sector light.
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Never Forgotten

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote Share with Facebook
  #10  
Old 04-10-2009
flyingwelshman's Avatar
Senior Member
 
Join Date: Aug 2007
Location: Ontario, Canada
Posts: 1,721
Thanks: 15
Thanked 17 Times in 14 Posts
Rep Power: 7
flyingwelshman will become famous soon enough
Could you mean the buoy on the right? (I think it's a North Cardinal Buoy - there's a different one in Canada)

If that's the case, the coordinates of the buoy should be taken at the open circle in the middle of the bottom horizontal line.




The marker on the right is an isolated danger marker. We do use the same one on Canadian Charts - I've just didn't remember it from my courses and I've never seen one.
__________________
1989 Hunter 30'
Southern Georgian Bay

The sea, once it casts its spell, holds one in its net of wonder forever. - Jacques Yves Cousteau

Last edited by flyingwelshman; 04-10-2009 at 06:33 PM. Reason: Found out what the marker is.
Reply With Quote Share with Facebook
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

 
Posting Rules
You may post new threads
You may post replies
You may post attachments
You may edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Keel/ballast Question?? Plus Extra Credit Question ;) stephenronning General Discussion (sailing related) 2 03-20-2009 07:25 AM
Anchoring question - what went right, what went wrong? josrulz Seamanship & Navigation 28 12-06-2008 10:01 PM
Plimsoll Mark question tomaz_423 General Discussion (sailing related) 4 11-09-2008 06:56 AM
Certification needed? gomer General Discussion (sailing related) 13 03-21-2008 04:41 AM
Question for sailmaker: Leech strength RichH Gear & Maintenance 0 09-18-2002 08:09 PM


All times are GMT -4. The time now is 08:07 AM.

Add to My Yahoo!         
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012

The SailNet.com store is owned and operated by a company independent of the SailNet.com forum. You are now leaving the SailNet forum. Click OK to continue or Cancel to return to the SailNet forum.