Reply
 
Thread Tools Display Modes
 
Old 12-19-2012, 01:16 PM   #81
Art
Guru
 
Art's Avatar
 
City: SF Bay Area
Country: USA
Vessel Model: Tollycraft 34' Tri Cabin
Join Date: Feb 2011
Posts: 7,986
Quote:
Originally Posted by Baker View Post


Now....I got one for y'all??? Does cross current affect your SOG at all??? On the circular slide rule, it says it does not. But I disagree.
Exact 90 degree (any degree less or more will also somewhat alter SOG results) cross current affects "straight line" SOG (point A to point B) in that you must tack an extent (length and duration of tack depends on cross current speed) to stay on course to reach point B from point A. This means you traveled a somewhat (a little bit) further in total "over land" distance. Therefore the comparison of SOG calculated if traveling on a straight line from A to B would be faster than equivalent "straight line" SOG from point A to B when tacking due to cross current. All comparisons are figuring no wind whatsoever.
__________________
Advertisement

Art is offline   Reply With Quote
Old 12-19-2012, 01:18 PM   #82
TF Site Team
 
FlyWright's Avatar
 
City: California Delta and SF Bay
Country: Sacramento, CA, USA (boat in Vallejo)
Vessel Name: FlyWright
Vessel Model: Marshall Californian 34 LRC
Join Date: Apr 2008
Posts: 10,195
Quote:
Originally Posted by Baker View Post


Now....I got one for y'all??? Does cross current affect your SOG at all??? On the circular slide rule, it says it does not. But I disagree.
Whoooaaa! Now you're getting into a deep vector analysis with longitudinal and lateral components of speed vs. cross current. I questioned this in college after using the CR-3 and ran the numbers when my math skills (and some will argue thinking capacity) were honed like a razor sharp knife. The results were that the speed drop was so small as to be negligible. Surprised the heck out of me. That's not to say that the slower boat speeds and higher relative current speed wouldn't have a greater impact on your forward speed vector component. I'm not going to calculate it, though! ;-)

"Two pilots don't make a right."

Moonstruck, two wrongs don't make it right, but two wrights make it right!!
__________________

__________________
Al

Custom Google Trawler Forum Search
FlyWright is offline   Reply With Quote
Old 12-19-2012, 01:21 PM   #83
Enigma
 
RT Firefly's Avatar
 
City: Slicker?
Country: Bumpkin?
Join Date: Oct 2007
Posts: 9,997
Greetings,
Mr. FW. Shouldn't that be two Wrights make a pilot?
__________________
RTF
RT Firefly is offline   Reply With Quote
Old 12-19-2012, 01:41 PM   #84
Art
Guru
 
Art's Avatar
 
City: SF Bay Area
Country: USA
Vessel Model: Tollycraft 34' Tri Cabin
Join Date: Feb 2011
Posts: 7,986
Quote:
Originally Posted by RT Firefly View Post
Greetings,
Mr. FW. Shouldn't that be two Wrights make a pilot?
RT - Good One Liner! You're starting to sound more and more like the fine fellow on your avatar!!
Art is offline   Reply With Quote
Old 12-19-2012, 01:45 PM   #85
Enigma
 
RT Firefly's Avatar
 
City: Slicker?
Country: Bumpkin?
Join Date: Oct 2007
Posts: 9,997
Greetings,
Mr. Art. I RESEMBLE THAT REMARK!!!!!
__________________
RTF
RT Firefly is offline   Reply With Quote
Old 12-19-2012, 01:54 PM   #86
Senior Member
 
xfedex's Avatar
 
City: Seattle
Country: usa
Vessel Name: Fluke
Vessel Model: Krogen 42
Join Date: Apr 2010
Posts: 131
[QUOTE=RickB;120734]The authors of posts #41 and #42 need to do a rethink as do a few others.

Unless you arrive at your destination before the current changes direction you spend just as much time going one way as the other. The distance you move in that time changes but not the duration. If there are two boats traveling on reciprocal courses in the same mass of water they both spend the same amount of time in that mass.

I leave out hull speed, fuel use, and weather. What am I missing?

The round trip from A to B takes longer with a current is running in one direction than when there is no current at all.

John (Poster #41)
xfedex is offline   Reply With Quote
Old 12-19-2012, 02:11 PM   #87
Scraping Paint
 
City: -
Country: -
Join Date: Oct 2007
Posts: 13,748
Quote:
Originally Posted by Art View Post
BTW, Marin (regarding your post # 55) my post # 54 does not pose theory it states fact... just like this post!
Your SOG faster with the current, SOG slower against the current is indeed a fact. My dog instinctively knows this, too, as he has to put it into practice every time he retrieves something from the water and comes back in a cross-current.

My comment was on the notion (theory) of accurately calculating the current effects for a voyage up or down the Inside Passage. The data necessary for accurately doing this simply doesn't exist along much of that route. So all one has to work with are general current averages. That inaccuracy combined with the extremely variable local currents along the way in the maze of channels and passes one goes through make it pretty impossible to come up with a truly accurate prediction of time and fuel consumption.

In other locations--- SFO Bay perhaps--- where the current data is complete and the geography does not have the same extremely varied effect on local currents over such a huge distance, it is much easier to accurately predict time and fuel use for a cruise.

That's my only point.
Marin is offline   Reply With Quote
Old 12-19-2012, 02:22 PM   #88
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,724
Get a grip Marin your dog dosn't know s##t.

And John I though the end of this discussion was about 8 posts ago. Walt used to say that ... "end of discussion" when he'd get frustrated. Had about the same effect then as now. I don't see the discussion ending until the posts stop and unlike the tide that's not very predictable.
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 12-19-2012, 02:25 PM   #89
Scraping Paint
 
City: -
Country: -
Join Date: Oct 2007
Posts: 13,748
Quote:
Originally Posted by SomeSailor View Post
You need to update your chartplotter. Mine (Garmin) predicts the current flows and tides from the local stations and overlays those onto your display. It's handy to be able look ahead and realize you won't make it.

We've had that technology on the boat for years now on the Furuno and we also have it on the iPad and the Standard Horizon plotter on the Arima. Even all the lighted navaids flash with the actual sequence that's on the real navaid. Nice feature but it doesn't give you all the data you need to accurately calculate a trip up or down the Passage. In fact it doesn't give you the all the data you need to accurately calculate a trip through the San Juan and Gulf Islands. It gives currents in the more important passes and the average current for larger bodies of water like the Strait of Georgia, Haro Strait, etc.

But it doesn't give you any of the current variations across these bodies of water, just the mainstream average. It's not going to tell me what the south side current strength is in Mosquito Pass at such and such a time, for example, or what the difference is between the ebb current speed in the middle of Spieden Channel and the ebb current speed over against the San Juan Island shore of the channel. These speed differences can be pretty significant at times and have a significant effect on your SOG and the time it take to get somewhere. But there's no way to calculate this in advance because there are no numbers to do it with.

The only way to take advantage of those differences is local knowledge. We've learned over the years what side of the passes and channels to favor at what stages of the current flow in the passes and channels we use a lot. But there is no way to figure this out beforehand because there are no numbers to use.

And go halfway up the Passage and try to find accurate data for a route you may be following up some channel. It's often simply not there because the data for many of the channels up there has never been taken or if it has been it's not published anywhere you can use it..
Marin is offline   Reply With Quote
Old 12-19-2012, 02:30 PM   #90
Guru
 
SomeSailor's Avatar
 
City: Everett, WA
Vessel Name: Honey Badger
Vessel Model: 42' CHB Europa
Join Date: Oct 2011
Posts: 784
Quote:
Originally Posted by RT Firefly View Post
Greetings, Mr. SS. Newfoundlander would be the most polite term for your dog.
Actually no... He's a Newfoundland dog. We owners call them 'Newfys' or 'Newfs'

Quote:
Originally Posted by RT Firefly View Post
I think Newfy is considered a derogatory term according to my sources ...
That's unfortunate... He's doesn't seem to mind. That's all that really matters to me.
SomeSailor is offline   Reply With Quote
Old 12-19-2012, 02:35 PM   #91
Guru
 
SomeSailor's Avatar
 
City: Everett, WA
Vessel Name: Honey Badger
Vessel Model: 42' CHB Europa
Join Date: Oct 2011
Posts: 784
Quote:
Originally Posted by Marin View Post
In fact it doesn't give you the all the data you need to accurately calculate a trip through the San Juan and Gulf Islands.
Sure it does. I get predicted currents and actual observations from stations along the way. Those give me all the accuracy I need to plan my departures.

(This is where you say "No it does not...")
SomeSailor is offline   Reply With Quote
Old 12-19-2012, 02:46 PM   #92
Scraping Paint
 
City: -
Country: -
Join Date: Oct 2007
Posts: 13,748
Quote:
Originally Posted by SomeSailor View Post
Sure it does. I get predicted currents and actual observations from stations along the way. Those give me all the accuracy I need to plan my departures.

(This is where you say "No it does not...")
All you're getting is the data from the stations. There are not stations in every pass, every channel, in the middle of passes and on the edges of those same passes. All you're working with are averages if you consider the whole length and width of the channels, even those with tide or current stations.

Of course you can use it to figure out your best time of departure. You can use a current atlas and Washburn table for that just as accurately.

The current/tide station data is way better than nothing and it definitely will get you in the ballpark. But in terms of truly accurately calculating the time and fuel use for a trip, particularly a long one like the length of the Passage, "No, it does not."

And the ballpark data is fine. It's all we use with our boat. We don't try to calculate what will happen on every leg of a route. We don't really care, frankly.

But if you're really trying to nickel and dime your time, fuel consumption, and range, the data to do it accurately up the length of the Passage simply isn't there despite the scattering of tide and current stations along the way.
Marin is offline   Reply With Quote
Old 12-19-2012, 02:59 PM   #93
Art
Guru
 
Art's Avatar
 
City: SF Bay Area
Country: USA
Vessel Model: Tollycraft 34' Tri Cabin
Join Date: Feb 2011
Posts: 7,986
Quote:
Originally Posted by marin View Post
your sog faster with the current, sog slower against the current is indeed a fact. My dog instinctively knows this, too, as he has to put it into practice every time he retrieves something from the water and comes back in a cross-current.

My comment was on the notion (theory) of accurately calculating the current effects for a voyage up or down the inside passage. The data necessary for accurately doing this simply doesn't exist along much of that route. So all one has to work with are general current averages. That inaccuracy combined with the extremely variable local currents along the way in the maze of channels and passes one goes through make it pretty impossible to come up with a truly accurate prediction of time and fuel consumption.

In other locations--- sfo bay perhaps--- where the current data is complete and the geography does not have the same extremely varied effect on local currents over such a huge distance, it is much easier to accurately predict time and fuel use for a cruise.

That's my only point.
OK!
Art is offline   Reply With Quote
Old 12-19-2012, 03:00 PM   #94
Enigma
 
RT Firefly's Avatar
 
City: Slicker?
Country: Bumpkin?
Join Date: Oct 2007
Posts: 9,997
Greetings,
I stand corrected Mr. SS. Newfoundland dog it is.
__________________
RTF
RT Firefly is offline   Reply With Quote
Old 12-19-2012, 03:07 PM   #95
Guru
 
MurrayM's Avatar
 
City: Kitimat, North Coast BC
Country: Canada
Vessel Name: Badger
Vessel Model: 30' Sundowner Tug
Join Date: Jul 2012
Posts: 3,330
And here's another wrinkle into all this navel gazing and futile attempts at precise navigation; bottom topography plays havoc with current speeds marked on the charts. Big issue here in BC, what with all our undulating channel bottoms and constricting of waterways. Just because it's marked as 2 knots here doesn't mean it can't be 4 knots there.
__________________
"The most interesting path between two points is not a straight line" Murray Minchin
MurrayM is offline   Reply With Quote
Old 12-19-2012, 03:11 PM   #96
Scraping Paint
 
City: -
Country: -
Join Date: Oct 2007
Posts: 13,748
Quote:
Originally Posted by MurrayM View Post
And here's another wrinkle into all this navel gazing and futile attempts at precise navigation; bottom topography plays havoc with current speeds marked on the charts. Big issue here in BC, what with all our undulating channel bottoms and constricting of waterways. Just because it's marked as 2 knots here doesn't mean it can't be 4 knots there.
See, at least one other person here gets it. Probably because he lives and boats in an area where all this local variation in currents directly affects him every time he takes his boat or kayak out. If one has any degree of observational skill at all, you can't help but notice it when you're out there in these waters.
Marin is offline   Reply With Quote
Old 12-19-2012, 03:15 PM   #97
Scraping Paint
 
City: -
Country: -
Join Date: Oct 2007
Posts: 13,748
Quote:
Originally Posted by manyboats View Post
Get a grip Marin your dog dosn't know s##t.

You'd think so, wouldn't you. But judging by the content of some of the posts in this thread I think our dog knows a hell of a lot more about being on the water than one would expect.
Marin is offline   Reply With Quote
Old 12-19-2012, 03:59 PM   #98
Scraping Paint
 
City: Fort Lauderdale
Vessel Model: CHB 48 Zodiac YL 4.2
Join Date: Oct 2007
Posts: 3,804
Quote:
Originally Posted by manyboats View Post
Rick your'e horney for anchors but you never had much or anything to say about anchors as I remember.
Thre is a good reason I never said anything, I could care less about anchors. They are just a heavy weight attached to a line or chain whose performance is measured by emotion and verbosity. My point is that this discussion is about as ridiculous as the one about anchors.

I wonder if the membership will be consumed by propeller slip or engine miles next ...
RickB is offline   Reply With Quote
Old 12-19-2012, 04:07 PM   #99
Guru
 
SomeSailor's Avatar
 
City: Everett, WA
Vessel Name: Honey Badger
Vessel Model: 42' CHB Europa
Join Date: Oct 2011
Posts: 784
Quote:
Originally Posted by RT Firefly View Post
I stand corrected Mr. SS. Newfoundland dog it is.
No worries. We call them 'Newfs' mostly because to call them Newfoundlands takes 5 minutes to explain the pronunciation.

He's more of a "Goof" than a "Newf" anyhow.
SomeSailor is offline   Reply With Quote
Old 12-19-2012, 04:14 PM   #100
Art
Guru
 
Art's Avatar
 
City: SF Bay Area
Country: USA
Vessel Model: Tollycraft 34' Tri Cabin
Join Date: Feb 2011
Posts: 7,986
Quote:
Originally Posted by RickB View Post
Thre is a good reason I never said anything, I could care less about anchors. They are just a heavy weight attached to a line or chain whose performance is measured by emotion and verbosity. My point is that this discussion is about as ridiculous as the one about anchors.

I wonder if the membership will be consumed by propeller slip or engine miles next ...
Rick, as we all have done and at times continue to do, you too sometimes make some pretty "of da wall" comments. This post contains more than one of em!

Only reason a boater could care less bout anchors/anchoring and think this thread's discussion regarding currents is ridiculous is because the person has not much experience with using anchors or traveling in currents. Just sayen!
__________________

Art is offline   Reply With Quote
Reply

Thread Tools
Display Modes

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





All times are GMT -5. The time now is 06:05 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012