Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 15-01-2015, 13:58   #16
Senior Cruiser
 
StuM's Avatar

Cruisers Forum Supporter

Join Date: Nov 2013
Location: Port Moresby,Papua New Guinea
Boat: FP Belize Maestro 43
Posts: 6,713
Re: Planning a short journey to windward, with a backing wind

Quote:
Originally Posted by canyonbat View Post
We just spent a week in San Diego sailing with a professional racing helmsman. His advice was "always sail to the new wind". Following this advice, you will sail on the starboard tack until you reach a point where you can make your destination on a single port tack. If the wind switches early, you tack early, if it is delayed or doesn't switch at all, you tack later.
If you are talking about a sudden wind shift, there is merit in what you say. But if the the wind is expected to gradually back over time, not so.

In this case, how do you identify "where you can make your destination on a single port tack". As the OP implied, he can often make it from the start on a single port tack.
__________________

__________________
StuM is offline   Reply With Quote
Old 15-01-2015, 14:10   #17
Registered User

Join Date: Sep 2013
Location: Alert Bay, Vancouver Island
Boat: 35ft classic ketch/yawl.
Posts: 935
Images: 4
Send a message via Skype™ to roland stockham
Re: Planning a short journey to windward, with a backing wind

Two ideas that might be useful.
One, is there any current/tide. If so a guide is to 'lee bow it. So whichever way it is flowing make sure it is hitting your downwind bow. The tide then pushes you into wind and you store a shorter cause and stay closer to the straight line.
Second one is, draw a tacking cone on the chart. This is two straight line at about 45deg out from the destination giving you a defined sailing area. When you get to the line tack. It helps to stop you getting into a position where a wind shift puts you in a bad position. Tacks get shorter as you approach your destination.

The other thing I might think of which is not about the fastest way there is that in the morning I would be fresh and may enjoy a 'good beat' by the afternoon I want to relax and enjoy the reach. It may be a longer sail but would I enjoy it more!
__________________

__________________
roland stockham is offline   Reply With Quote
Old 15-01-2015, 14:15   #18
Registered User

Join Date: May 2013
Location: Mangareva, French Polynesia
Boat: Heritage West Indies 36
Posts: 513
Re: Planning a short journey to windward, with a backing wind

I think this will work............. but i've never tried doing it like this!

OK, you presumably know what your boat speed will be while beating, the angle you can make to the wind, the rate at which the wind angle will change and the time that you wish to be at your destination (bearing in mind that the wind direction is related to this).

For this example, let's say you can sail 50d to the wind and your boat speed will be 6 knots. On a chart, start from your destination and draw a line back towards your point of origin at an angle that is 50 degrees from the anticipated wind direction at that time (the time you want to be there!). Now, go 6 miles along that line. From that point, draw another line at 50 degrees to the new wind angle. Another 6 miles.....and another...... and another.....and another. Now, using a compass (not the magnetic kind - the kind with a spike and a pencil!) draw a curve that passes through each of the points where these lines cross. This will be your actual anticipated course that you will follow as the wind changes lifting you towards your destination. Continue this curve beyond the point that you anticipate you will have tacked at. Now, turn the compass around and place the pencil on your point of departure. Draw a curve from there that passes through the first curve you drew. They should intersect at about a 100d angle........ i think. This is the point at which you will tack. Finally, measure the total combined length of the two curves to determine the actual distance you will need to travel and work back from there to determine the time that you will have to leave your home port in order to make it to the destination at the time you originally intended. maybe add on an hour for safety :-)

Mind you, 35 miles isn't very far. By the time you've done all this and figured it all out you might as well have just set sail and figured it out on the way :-)

A simpler way to do it given the distance you're going (and what i usually do, because i'm lazy and figure that any extra time spent sailing is a bonus!) would be to just set off into a knocking breeze (on a starboard tack) and then tack about half an hour before the VMG on the new tack is better than the one you're currently on. That way you'll get lifted toward your destination, and if you get lazy and just leave the tack too late then you're easing the sheets as you go. Definitely start on a starboard tack though i'd say - there's nothing worse than getting knocked at the end of a trip, which you would be if you started on port and then tacked over at the end.
__________________
DefinitelyMe is offline   Reply With Quote
Old 15-01-2015, 14:32   #19
Registered User
 
Seasick Steve's Avatar

Join Date: Jan 2015
Location: England
Boat: Westerly Centaur, 26
Posts: 32
Re: Planning a short journey to windward, with a backing wind

Just one more point. Presumably you like sailing or you wouldn't be out there in the first place. So why do you want to get it over with as quickly as possible?

Yes - there is of course satisfaction in getting it done as efficiently as poss. But it's worth considering!
__________________
Seasick Steve is offline   Reply With Quote
Old 15-01-2015, 14:56   #20
Bailing as fast as I can.
 
GILow's Avatar

Join Date: Sep 2008
Location: Adelaide, South Australia
Boat: Swanson 42
Posts: 3,585
Re: Planning a short journey to windward, with a backing wind

Quote:
Originally Posted by DefinitelyMe View Post
I think this will work............. but i've never tried doing it like this!

OK, you presumably know what your boat speed will be while beating, the angle you can make to the wind, the rate at which the wind angle will change and the time that you wish to be at your destination (bearing in mind that the wind direction is related to this).

For this example, let's say you can sail 50d to the wind and your boat speed will be 6 knots. On a chart, start from your destination and draw a line back towards your point of origin at an angle that is 50 degrees from the anticipated wind direction at that time (the time you want to be there!). Now, go 6 miles along that line. From that point, draw another line at 50 degrees to the new wind angle. Another 6 miles.....and another...... and another.....and another. Now, using a compass (not the magnetic kind - the kind with a spike and a pencil!) draw a curve that passes through each of the points where these lines cross. This will be your actual anticipated course that you will follow as the wind changes lifting you towards your destination. Continue this curve beyond the point that you anticipate you will have tacked at. Now, turn the compass around and place the pencil on your point of departure. Draw a curve from there that passes through the first curve you drew. They should intersect at about a 100d angle........ i think. This is the point at which you will tack. Finally, measure the total combined length of the two curves to determine the actual distance you will need to travel and work back from there to determine the time that you will have to leave your home port in order to make it to the destination at the time you originally intended. maybe add on an hour for safety :-)
Well, with a few minor qualifications, you have basically just described my computational solution to this one. And I thought it was a pretty clever solution too!

I am coding something like this, but since clock cycles are cheap, I was doing it on one minute intervals, not one hour. Just having trouble with a few of the variables, and how to express them...

I tried to do it as a mathematical formula, but it's just been too many years since I last tried to express something this complex mathematically.

Matt
__________________
Very funny Scotty, now beam down my clothes.
http://www.swansonsailor.id.au
GILow is offline   Reply With Quote
Old 15-01-2015, 14:57   #21
Bailing as fast as I can.
 
GILow's Avatar

Join Date: Sep 2008
Location: Adelaide, South Australia
Boat: Swanson 42
Posts: 3,585
Re: Planning a short journey to windward, with a backing wind

Quote:
Originally Posted by Seasick Steve View Post
Just one more point. Presumably you like sailing or you wouldn't be out there in the first place. So why do you want to get it over with as quickly as possible?

Yes - there is of course satisfaction in getting it done as efficiently as poss. But it's worth considering!
Yes, fair point, but I am not joking when I say things close early over there.

Matt
__________________
Very funny Scotty, now beam down my clothes.
http://www.swansonsailor.id.au
GILow is offline   Reply With Quote
Old 15-01-2015, 15:05   #22
Bailing as fast as I can.
 
GILow's Avatar

Join Date: Sep 2008
Location: Adelaide, South Australia
Boat: Swanson 42
Posts: 3,585
Re: Planning a short journey to windward, with a backing wind

Quote:
Originally Posted by StuM View Post
If you are talking about a sudden wind shift, there is merit in what you say. But if the the wind is expected to gradually back over time, not so.

In this case, how do you identify "where you can make your destination on a single port tack". As the OP implied, he can often make it from the start on a single port tack.
Yes, for a given value of "sudden". I suppose the shift takes place over about an hour, following a classic sine wave. i.e. initial gradual shift, slowing accelerating in rate of change, before slowing down again to settle on the new direction.

So yes, I can make it on a port tack... sometimes. It's when I get it wrong that I end up tacking back down to the South. And as Roland pointed out, tacking at the end of the day when you are tired is not so much fun. When I get it right it is a delightful, simple trip on the port tack.

I guess, being a maths type of person, I was hoping there would be some simple formula that told me which approach to use.

Something that related total distance, average speed, estimated time till the wind shift, angle of wind shift... That sort of thing. But I am starting to see from my own attempts to model it, even if you treat the wind shift as a single point in time, it's very difficult to express. At least, it is for me.

Matt
__________________
Very funny Scotty, now beam down my clothes.
http://www.swansonsailor.id.au
GILow is offline   Reply With Quote
Old 15-01-2015, 15:14   #23
Moderator
 
JPA Cate's Avatar

Join Date: Nov 2011
Location: aboard, cruising in Australia
Boat: Sayer 46' Solent rig sloop
Posts: 10,682
Re: Planning a short journey to windward, with a backing wind

Matt,

I think Mark J had a really good point, if your anticipated shift is a reliable sea breeze.

On the N. Qld. coast, where the prevailing synoptic flow is SE, and the sea breeze is NE, and will start between about 11 and 1, generally speaking, for a whole day's sail, we'd start out southbound, on stbd. tack, making more east than we really wanted, and then, when the shift was about time, tack a little before we could fetch the days destination, and use the lift after the shift was established. Any adjusting tacks taken at the end, if needed.

If you have a tidal stream where you are, definitely try and use it. It was not much of a factor where we were sailing. But we actually look at the currents a lot for coastal trip planning.

Ann
__________________
Ann, with Jim, aboard US s/v Insatiable II, in Oz, very long term cruisers
JPA Cate is offline   Reply With Quote
Old 15-01-2015, 16:06   #24
Registered User
 
Seasick Steve's Avatar

Join Date: Jan 2015
Location: England
Boat: Westerly Centaur, 26
Posts: 32
Re: Planning a short journey to windward, with a backing wind

I think any attempt to try and calculate precisely beforehand what you're going to do in a sailing boat is doomed to failure. There are so many variables, some partly predictable, most less so and they interact in so many ways, not all of them understood, that it's just too complicated.

If you do work out how to do it and can write the code, you could probably make money out of it. But I think I'll just go sailing
__________________
Seasick Steve is offline   Reply With Quote
Old 15-01-2015, 18:10   #25
Registered User

Join Date: Apr 2011
Location: Edmonds, WA
Boat: Wauquiez Amphitrite - 43' Ketch
Posts: 159
Re: Planning a short journey to windward, with a backing wind

I love that you are trying to write a program for this. Such a sailing geek.


Sent from my iPad using Cruisers Sailing Forum
__________________
ScottMeilicke is offline   Reply With Quote
Old 15-01-2015, 18:26   #26
Registered User
 
FamilyVan's Avatar

Join Date: Nov 2014
Posts: 1,779
Re: Planning a short journey to windward, with a backing wind

If I'm reading this correctly it sounds like your wind shift may be katabatic in nature? If so it should be more pronounced on warm sunny days and much diminished on cloudy days. So- as far as which tack to make- I'm not sure, I see good arguments for both. Advice I do have is I might expect less pronounced wind shifts on cloud covered days (expect more of your Westerly) on sunny hot days be prepared to get an earlier and more pronounced push from the south west.
__________________
FamilyVan is offline   Reply With Quote
Old 15-01-2015, 19:07   #27
Registered User

Join Date: Nov 2014
Location: Oregon
Posts: 209
Re: Planning a short journey to windward, with a backing wind

And if it's a slow cruising boat, you probably have a diesel to hurry you on if it gets late. Mac
__________________
Hard Rock Candy is offline   Reply With Quote
Old 15-01-2015, 19:44   #28
Registered User

Join Date: Apr 2006
Location: Western Med
Boat: 52' Crealock Farrington staysail schooner
Posts: 81
Re: Planning a short journey to windward, with a backing wind

Hi Matt et al,
I love this winter reading and the availablity of so much technical advise.
All brilliant and so now the village idiot chimes in and also with a 30 ton cruising beheamoth I wonder why you dont either change your boats home port, driving 20 miles for a sweet sail is way funner than beating to wind, to me anyway, or change your favorite anchorage destination, probably harder. I enjoy the sweet spot of our schooner but she always reminds me when she thinks Im going the wrong way and to bear off would be indeed pleasant, Fair winds as they say
__________________
barnaclejim is offline   Reply With Quote
Old 15-01-2015, 22:02   #29
Bailing as fast as I can.
 
GILow's Avatar

Join Date: Sep 2008
Location: Adelaide, South Australia
Boat: Swanson 42
Posts: 3,585
Re: Planning a short journey to windward, with a backing wind

In no particular order....

The sailing geek comment made me laugh. Yeah, a bit tragic, but I have to find SOMETHING to do with my maths degree and 20 years of writing code for a living. But I promise the boat is a techno-free zone.

Moving port? Er.. A bit extreme, but fair point. Sadly the only other port is the one I am sailing to. 30 odd miles by boat, 100 miles by road. I think I'll keep with the current arrangement. It's only ten minutes to the boat and there are no traffic lights on the journey.

Katabatic wind shift? I don't think so. We get the katabatic winds at night here, after 21:00 hrs usually, they are from the South East and they are truly heaven on earth. I think the afternoon wind shift is the land heating up. Someone picked it earlier in the thread.

Well, I am sort of relieved that there is not a consensus on this one. I can justify both approaches in my head, and there are some good explanations here that have furthered my understanding of each option. Thank you all.

Matt


Sent from my iPad using Cruisers Sailing Forum
__________________
Very funny Scotty, now beam down my clothes.
http://www.swansonsailor.id.au
GILow is offline   Reply With Quote
Old 16-01-2015, 06:23   #30
Registered User

Join Date: May 2013
Location: Mangareva, French Polynesia
Boat: Heritage West Indies 36
Posts: 513
Re: Planning a short journey to windward, with a backing wind

Quote:
Originally Posted by GILow View Post
Well, with a few minor qualifications, you have basically just described my computational solution to this one. And I thought it was a pretty clever solution too!

I am coding something like this, but since clock cycles are cheap, I was doing it on one minute intervals, not one hour. Just having trouble with a few of the variables, and how to express them...

I tried to do it as a mathematical formula, but it's just been too many years since I last tried to express something this complex mathematically.

Matt

Well, here's another completely un-tried and un-tested theory! The curve will be a y=x^2+mx+c function......... Maybe if you model it in vector form, then you could define limits when the vector angle to the destination is greater than 75d (the point where one tack becomes favoured over the other), and then have another x^2 function. Would that work?

I didn't realise when i wrote my first 'solution' that it isn't a gradual wind change but rather a shift that takes place over an hour or so. In that case most of your course will be a straight line and you just need a bit in the middle, at whatever time you expect the wind shift, to model that section. If it shifts in the manner you described then the rate of change follows a logistic curve. The maths for this has already been done - it's just the same as a tidal change but condensed into the period over which the shift takes place....... I seem to remember learning about finding optimum values when i was at school...... I think you define what your optimum value is and then integrate the function to figure out where it lies on the curve....... or something. It's been too long!
__________________

__________________
DefinitelyMe is offline   Reply With Quote
Reply

Tags
wind

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
Crew Available: Punta Gorda FL - Short Day or Short Trips Mediaguy Crew Archives 0 13-12-2014 16:41
Calamity! ICW Journey Log #1 Alexei Sailor Logs & Cruising Plans 2 08-06-2009 07:13
ICW Journey Alexei Sailor Logs & Cruising Plans 21 08-03-2009 17:11
East Med Journey swagman Europe & Mediterranean 8 18-02-2006 00:33
Already in the Caribbean: Journey of Makai sv_makai Sailor Logs & Cruising Plans 1 20-07-2005 02:09



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 01:28.


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.