Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 08-08-2008, 15:30   #136
Moderator Emeritus
 
David M's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: San Francisco Bay
Boat: research vessel
Posts: 10,152
I had to know set and drift for my license and use vectors to renew my radar endorsement. I agree though, I think its good to practice the old stuff occasionally because of the what if's of boating.
__________________

__________________
David

Life begins where land ends.
David M is offline   Reply With Quote
Old 08-08-2008, 15:35   #137
Moderator Emeritus
 
David M's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: San Francisco Bay
Boat: research vessel
Posts: 10,152
Ok, I guess I am next.

Lets do a hypothetical question. If the Earth had no land and you started sailing a course of 080 degrees True from 10 north at any longitude, and stayed on that course for a long long time then where would you eventually end up?

If you dropped breadcrumbs along the way (remember this is hypothetical question so you cant say the gulls ate the breadcrumbs or some other smartalec answer) then what type of line would you leave across the Earth? What is this type of line called?

Pelagic....give someone else a chance to get this one because you probably already know it.
__________________

__________________
David

Life begins where land ends.
David M is offline   Reply With Quote
Old 08-08-2008, 17:35   #138
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Cruisers Forum Supporter

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: Van DeStat Super Dogger 31'
Posts: 7,336
Hypothetical answer: stuck in ice (or assuming global warming - north pole, spinning about the boat vertical axis).
The line should be called "a line of visual spiral pollution" and probably violates the vessel's garbage plan or whatever you guys call those MARPOL stickers.
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is offline   Reply With Quote
Old 08-08-2008, 17:40   #139
Senior Cruiser

Cruisers Forum Supporter

Join Date: Nov 2005
Location: Out there doin' it
Boat: 47' Olympic Adventure
Posts: 2,638
N pole; rhumb line
__________________
Lodesman is offline   Reply With Quote
Old 08-08-2008, 18:01   #140
Registered User
 
Hampus's Avatar

Join Date: May 2008
Location: Sweden
Boat: Between boats
Posts: 463
Images: 6
Send a message via MSN to Hampus
If you disregard the fact that the compass would point to the stars eventually, you'd end up going in very tight circles around the north pole. another question comes into mind... how many loafs of bread would you have to carry, if you used one every mile?

/Hampus
__________________
http://adventureswithsyingeborg.blogspot.com/
On the way back to Sweden.
Hampus is offline   Reply With Quote
Old 08-08-2008, 18:42   #141
Senior Cruiser

Cruisers Forum Supporter

Join Date: Nov 2005
Location: Out there doin' it
Boat: 47' Olympic Adventure
Posts: 2,638
The course is True, so the compass would still point to the Magnetic North Pole,while you spin about the True North Pole. As for the loaves of bread - the math is hurting my brain
__________________
Lodesman is offline   Reply With Quote
Old 08-08-2008, 18:57   #142
CF Adviser
 
Pelagic's Avatar

Cruisers Forum Supporter

Join Date: Oct 2007
Boat: Van Helleman Schooner 65ft StarGazer
Posts: 6,895
Quote:
Originally Posted by Kai Nui View Post
Yep. The real challenge is to see if anyone remembers how to calculate set and drift. Since GPS has become a standard, many of the traditional skills needed for navigation are being lost.
Ok David I will leave yours for others, but I think Kai Nui made an important point about remembering how to apply known current or estimated leeway to a navigation problem to get your “course to steer”

Here is an easy way to calculate using a Manoeuvring Board, (Plotting Sheet) which are pads of scaled paper that look like a Radar Display/compass rose. You can find these in any nautical store and they can be used for many things including plotting to avoid storms or intercept another vessel. I always have a pad on board.

For Known Current
1)…Use largest scale and draw line outward from centre in the currents true direction and a length equal to the currents speed in knots (for one hour)

2)…Label this Current vector A at the centre and B at the outward end

3)…From A at the centre draw a long line out in the true Course Line you want to make good to your destination.

4)…Set dividers at a spread equalling your vessel’s speed for one hour

5)…Put one point on B and swing so other point touches Course Line. Label that point C

6)…Connect points B and C.

7)…Line B-C represents the course to be steered with given current to achieve the course you wish to make good.

8)…If you measure distance A-C that will give you the speed made good in that current

You can do the same for leeway
__________________
Pelagic is offline   Reply With Quote
Old 08-08-2008, 19:26   #143
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Cruisers Forum Supporter

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: Van DeStat Super Dogger 31'
Posts: 7,336
Quote:
Originally Posted by Lodesman View Post
N pole; rhumb line
Quote:
Originally Posted by Hampus View Post
If you disregard the fact that the compass would point to the stars eventually, you'd end up going in very tight circles around the north pole. another question comes into mind... how many loafs of bread would you have to carry, if you used one every mile?

/Hampus
Quote:
Originally Posted by Lodesman View Post
The course is True, so the compass would still point to the Magnetic North Pole,while you spin about the True North Pole. As for the loaves of bread - the math is hurting my brain
Guys,
How are you planning to sail through the ice?

David M has stipulated we have a long long time and there is no land but as there were no other exemptions, we have assume all other conditions are normal including the ice cap (unless you are taking global warming as normal , as I did).
Do I get more points for a smartalec answer (or lose points).
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is offline   Reply With Quote
Old 08-08-2008, 21:22   #144
Moderator Emeritus
 
David M's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: San Francisco Bay
Boat: research vessel
Posts: 10,152
Quote:
Originally Posted by Pelagic View Post
Ok David I will leave yours for others, but I think Kai Nui made an important point about remembering how to apply known current or estimated leeway to a navigation problem to get your “course to steer”

Here is an easy way to calculate using a Manoeuvring Board, (Plotting Sheet) which are pads of scaled paper that look like a Radar Display/compass rose. You can find these in any nautical store and they can be used for many things including plotting to avoid storms or intercept another vessel. I always have a pad on board.

For Known Current
1)…Use largest scale and draw line outward from centre in the currents true direction and a length equal to the currents speed in knots (for one hour)

2)…Label this Current vector A at the centre and B at the outward end

3)…From A at the centre draw a long line out in the true Course Line you want to make good to your destination.

4)…Set dividers at a spread equalling your vessel’s speed for one hour

5)…Put one point on B and swing so other point touches Course Line. Label that point C

6)…Connect points B and C.

7)…Line B-C represents the course to be steered with given current to achieve the course you wish to make good.

8)…If you measure distance A-C that will give you the speed made good in that current

You can do the same for leeway
Kai Nui did indeed make an excellent point of illustrating the importance of knowing how to do vectors. I just needed one more piece information in order to do one. I was given the boats speed vector. I needed a second vector for the boats leeway and/or current in order to come up with a third vector which would have been the heading to steer by in order to make good the correct COG.
__________________
David

Life begins where land ends.
David M is offline   Reply With Quote
Old 08-08-2008, 21:25   #145
Moderator Emeritus
 
David M's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: San Francisco Bay
Boat: research vessel
Posts: 10,152
Wotname gets credit for answering the first question...congrats!

The second question though is still unanswered. Do you know the answer Pelagic?
__________________
David

Life begins where land ends.
David M is offline   Reply With Quote
Old 08-08-2008, 22:04   #146
CF Adviser
 
Pelagic's Avatar

Cruisers Forum Supporter

Join Date: Oct 2007
Boat: Van Helleman Schooner 65ft StarGazer
Posts: 6,895
Yes! I think so.
Guys Google “Gnomonic Charts” to get on the right track…also read David’s question carefully… he doesn’t say anything about 080M (magnetic). Unless otherwise stated assume all courses to be True courses.
__________________
Pelagic is offline   Reply With Quote
Old 08-08-2008, 22:22   #147
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Cruisers Forum Supporter

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: Van DeStat Super Dogger 31'
Posts: 7,336
Quote:
Originally Posted by Lodesman View Post
N pole; rhumb line
Quote:
Originally Posted by David M View Post
...The second question though is still unanswered. Do you know the answer Pelagic?
Quote:
Originally Posted by Pelagic View Post
....…also read David’s question carefully… he doesn’t say anything about 080M (magnetic). Unless otherwise stated assume all courses to be True courses.[/SIZE][/FONT]
Hmm... I thought Lodesman was correct with "rhumb line", perhaps you are looking for the more formal "loxodrome".

Pelagic, I think David M made it quite clear that the course was true in his challenge so assumptions weren't needed in this instance but I take your point, courses are assumed to be true unless otherwise stated.
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is offline   Reply With Quote
Old 08-08-2008, 23:44   #148
CF Adviser
 
Pelagic's Avatar

Cruisers Forum Supporter

Join Date: Oct 2007
Boat: Van Helleman Schooner 65ft StarGazer
Posts: 6,895
Quote:
Originally Posted by Lodesman View Post
The course is True, so the compass would still point to the Magnetic North Pole,while you spin about the True North Pole. As for the loaves of bread - the math is hurting my brain
That might have put some off track
__________________
Pelagic is offline   Reply With Quote
Old 09-08-2008, 02:03   #149
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Cruisers Forum Supporter

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: Van DeStat Super Dogger 31'
Posts: 7,336
Next ?

I am not sure if I should be posting a new challenge yet as we don't have a formal position on the answers to part 2 of DM's challenge; but not knowing the right thing to do as never stopped me in the past, so here goes - apologies in advance if I am out of line .

The background: Its summer (January) and a 30 ft yacht with total crew on three has made its first coastal cruise to a tropical cay (with lagoon) about 250 nm north of Brisbane, Queensland, Australia. After 10 days of soaking up the pleasures of living aboard anchored in the lagoon, its time to return home.

The crew: Skipper - first coastal cruise of more than 2 nights at sea; first mate, first coastal cruise but a lifetime of racing dinghies and son of a commerical fisherman, lastly someone who has never been on any boat in her life before.

Navigation: pre GPS days, we are navigating by DR, coastal bearings, chart, compass, log, sounder and eyeball.

The situation: Its the second night of the return trip, the barrier reef has been cleared and the boat is about 15 to 20 miles off shore in deep water (>100 fathoms), running south rolling gently before a 10 to 12 kt northerly breeze. The distant loom of a lighthouse had been passed abeam confirming the position. It is a new moon and the sailing is very pleasant with the stars shinning brightly. The sails are wing and wing with a preventer on the main and the genny poled out. The are no dangers ahead and the next lighthouse should be picked up before dawn. The course is taking the boat ever so slighly further off shore.

The newbie crew member has proved to be a reasonable sailor and quick to learn so the skipper decides to give her a solo night watch.

The instructions are: Hand steer to the wind direction, not the compass; Keep a sharp eye out for lights of shipping (none seeen so far); Wake the skipper if any of the following occurs - If you get tired, if the average heading changes by more than 15 degrees for more than 10 minutes; you see any shipping; if you feel unsure about ANYTHING or uncomfortable about anything and especially if ANYTHING changes.

The skipper and mate turn in about 10 pm. About 3 hours later, the crew on watch wakes the skipper with the message " Sorry but although there is nothing wrong, the boat wont sail properly". The skipper doesn't engage in any further conversation but is on deck in a flash. He has a quick look around and can't see anything except the boat slowly drifting around in a calm on an low oilyswell.

What would you do next and why?

There may be two answers.
1. What I did.
2. Perhaps something else I never thought off. I would be happy to learn how to do it better even if its 25 years later.
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is offline   Reply With Quote
Old 09-08-2008, 06:16   #150
Registered User

Join Date: Feb 2007
Boat: 1973 Morgan 36T
Posts: 808
Images: 17
I would start the engine and then grab a spot light.
__________________

__________________
Morgan Paul is offline   Reply With Quote
Reply

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
Jester Challenge - 'Would You Allow this...?' Thread Follow-Up conachair General Sailing Forum 27 22-05-2010 13:39
Solar Panel Conversion Challenge Keegan Electrical: Batteries, Generators & Solar 10 21-06-2007 00:28
Rolex Transatlantic Challenge GordMay Monohull Sailboats 2 22-04-2005 20:36



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 00:50.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.