Cruisers Forum

Join CruisersForum Today

Thread Tools Rate Thread Display Modes
Old 24-02-2010, 09:31   #16
Registered User

Join Date: Jul 2009
Location: Kitsap Penninsula, WA
Boat: C&C Mega 30
Posts: 85
Or dead reckoning and the use of visual landmarks, whether used to plot a specific point based on compass bearing, or just the old fashion "don't hit the island you see there".

The technology does exist, but from reading the articles I've seen regarding this nothing suggests that any short of a modern first world military has the abilities to jam or spoof a signal outside of their line of site. These signals don't go around the horizon, that's why they use satellites.

wannago is offline   Reply With Quote
Old 24-02-2010, 10:23   #17
Senior Cruiser
Captain Bill's Avatar

Cruisers Forum Supporter

Join Date: Apr 2008
Location: On the boat
Boat: Endeavourcat Sailcat 44
Posts: 2,099
The day that my GPS position jumped 11 miles probably due to local military activity was cloudy. I don't know how a sextant would have helped that day. If I had been threading my way through a narrow channel or some reefs the GPS error might have been an issue, but 11 miles was still closer to my actual position than I could have determined with a sextant on a cloudy day. Can any of the sextant experts tell me how to use a sextant to thread my way through a narrow winding channel? What's my backup for the sextant on cloudy days?

I don't worry about these things because I Know where I am, I know where I'm going, I know how I'm going to get there and I know roughly what external influences are affecting my boat. I'm confident that given a functional compass, I'm going to get pretty close to where I want to be even on a cloudy day. The GPS just helps make it a little easier. If the GPS suddenly jumps 10 miles or even a hundred, I'm not going to believe that I was magically teleported across the planet, I'll simply ignore it until it makes sense with what I know. If you have so little situational awareness that a GPS failure is a major crisis, perhaps you should take up another lifestyle.

Captain Bill is offline   Reply With Quote
Old 24-02-2010, 10:33   #18

Cruisers Forum Supporter

Join Date: Apr 2006
Posts: 12,077
"Can any of the sextant experts tell me how to use a sextant to thread my way through a narrow winding channel?" Used horizontally to measure angles, with a little trig it becomes a great piloting tool. And, if you lose the lead on your leadline, you can dip the bottom of the sextant in tallow and use it to sample the bottom.<G>

" What's my backup for the sextant on cloudy days? " Why, a Viking "sunstone" of course. (A large crystal of Icelandic spar, a natural polarizer, that will still give you a good idea of where the sun is behind the clouds.)
hellosailor is offline   Reply With Quote
Old 19-06-2010, 02:52   #19
Registered User

Join Date: May 2010
Posts: 20
GPS is also susceptible to the solar activity.
The Sun activity recorded on December 6th 2006 is a good example how systems may be affected. Many GPS receivers were getting inaccurate signals while others could not locate GPS signal at all.

CaptnPete is offline   Reply With Quote
Old 19-06-2010, 16:19   #20
Sponsoring Vendor
brak's Avatar

Community Sponsor
Cruisers Forum Supporter

Join Date: Jan 2009
Location: East of West
Posts: 252
Sextant is not "be all" of navigation. In fact, if I recall my in-shore/near shore navigation correctly it has absolutely nothing to do with sextants. It does have to do a lot with taking bearings of things and drawing LOPs on a chart.

You can do the same thing now, in fact it may very well be a good idea. It can even be done in software if software permits drawing LOPs or something similar. 3 bearings give you your position triangle. Not having to use paper or pen to do that - priceless.
Polar Navy - because life is too short to use ugly navigation software
brak is offline   Reply With Quote

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not 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 Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Sailboat Security Tigerlily Atlantic & the Caribbean 6 04-04-2015 06:44
WiFi Security nhschneider Marine Electronics 6 08-12-2009 17:43
Furuno GPS - 'GPS Week Number Rollover' bitman Navigation 0 25-11-2009 03:53
Autopilot/GPS Interface Issues nhschneider Navigation 3 15-02-2009 17:03

Our Communities

Our communities encompass many different hobbies and interests, but each one is built on friendly, intelligent membership.

» More about our Communities

Automotive Communities

Our Automotive communities encompass many different makes and models. From U.S. domestics to European Saloons.

» More about our Automotive Communities

Marine Communities

Our Marine websites focus on Cruising and Sailing Vessels, including forums and the largest cruising Wiki project on the web today.

» More about our Marine Communities

Copyright 2002-2015 Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 04:07.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.