Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 27-03-2015, 02:52   #436
Registered User
 
El Pinguino's Avatar

Join Date: Aug 2013
Location: Punta Arenas ahorra
Boat: 39' Westerly Sealord
Posts: 3,953
Re: Speed Through GPS Versus Old Fashioned Paddle Log

Quote:
Originally Posted by Dockhead View Post
Pitots . . . LOL . . . you crack me up

Actually, there are very few power boats on the Hamble -- the ratio is about 20:1. About 4000 sailboats. And the powerboaters are mostly extremely courteous and skillful. The whole problem here is blithely assuming that COG will do just fine if you don't feel like keeping up the paddlewheel -- good enough for government work, as they say . . . why do we need STW anyway? But in some cases, it is glaringly not.
Take care that you don't split clean in half ... you may downflood and sink...

I must admit that apart from a few days 20 odd years ago I haven't been afloat on the Hamble since '65..

However ... lookee here and enjoy the Vimeo
The Hamble in Full Spate - locally known as the Hamble Scramble - Cruising Anarchy - Sailing Anarchy Forums
__________________

El Pinguino is offline   Reply With Quote
Old 27-03-2015, 03:51   #437
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,750
Re: Speed Through GPS Versus Old Fashioned Paddle Log

Quote:
Originally Posted by El Pinguino View Post
Take care that you don't split clean in half ... you may downflood and sink...

I must admit that apart from a few days 20 odd years ago I haven't been afloat on the Hamble since '65..

However ... lookee here and enjoy the Vimeo
The Hamble in Full Spate - locally known as the Hamble Scramble - Cruising Anarchy - Sailing Anarchy Forums
No split -- I do not consider those powerboaters to be stupid just because of this mistake. They don't have any STW data, and then they see the speed limit -- what else are they supposed to do? Could happen to anyone. As we've seen from this thread, very few people actually "get it".

There are some gorgeous power boats on the Hamble -- a number of beautiful old motor yachts from the '30's, for example, like Bounty, Seafin, and others.

I like motor vessels -- especially full displacement, narrow beam ones. One of my best friends just bought a 60m former polar research vessel to use as a yacht -- what a magnificent vessel!! With a helo on the after deck. Surely the most extraordinary toy one could ever have. I was on board it a couple weeks ago in the Med with him. If I just didn't love to sail as passionately as I do, I would gladly go over to stinkpots. Hey, I even like cats

I haven't participated in the full-on "Hamble Scramble" in a while -- I migrated to the Eastern Baltic last summer and am preparing to do it again this summer. The harbormaster sublets my precious mooring, and I only get back a proportionate share of the nominal annual fee! If I were allowed to sublet it myself, it would pay for the whole summer's cruise! I spend fall and spring on the Hamble, and winter in Cowes, these last years, and summers out cruising somewhere.

Sorry to everyone for the rambly thread drift -- carry on.
__________________

__________________
Dockhead is online now   Reply With Quote
Old 27-03-2015, 05:42   #438
Registered User
 
Ericson38's Avatar

Join Date: Aug 2012
Location: Virginia
Boat: Taswell 49 Cutter
Posts: 187
Re: Speed Through GPS Versus Old Fashioned Paddle Log

Quote:
Originally Posted by Dockhead View Post
Very well reasoned and useful way to look at it

In other words, without STW, you are missing one key datum without which you cannot calculate a number of things which you want to know.

The only question I have is about paddlewheel logs -- do you really have one which works without power? I haven't seen one like that in decades. Mine, unfortunately, does not.
This is the one - Signet Marine SL11 Self-Powered Analog Marine Knot meter
__________________
Ericson38 is offline   Reply With Quote
Old 27-03-2015, 06:38   #439
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,750
Re: Speed Through GPS Versus Old Fashioned Paddle Log

Quote:
Originally Posted by Ericson38 View Post
Very cool! Never seen one of those before.
__________________
Dockhead is online now   Reply With Quote
Old 27-03-2015, 07:17   #440
Registered User

Join Date: Apr 2013
Posts: 4,877
Re: Speed Through GPS Versus Old Fashioned Paddle Log

Quote:
Originally Posted by OceanSeaSpray View Post
I think you precisely and entirely missed the point and the core of the discussion went exactly against what you just stated.
I am not going to once again repeat it in the thread, because you can just go back several pages and read why it is plainly wrong at long lengths.
Are you reading a different thread than the rest of us?
__________________
valhalla360 is offline   Reply With Quote
Old 27-03-2015, 13:01   #441
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Re: Speed Through GPS Versus Old Fashioned Paddle Log

Quote:
There you are - a multi-hour CTS, no reversing stream. Is it "dangerous", not to know your ground track? Hell, no. You can figure your ground track fairly easily, to the extent you need to (which you don't, much, since like most of these passages, there AREN'T any obstacles). Is it a "party trick"? Only if you think saving literally half the passage time is a "party trick".
We had this out before in the mega thread on CTS, about ground thread computation

The fact is unless you have access to a computer and reliable sub-hour tidal stream data, it is NOT easy to compute your ground track . short of working up a full one for you , or you doing it by hand yourself , will this aspect be clear.

quoting gulf streams etc, are all simplistic in effect continous non variable currents, rather like applying CTS to a river crossing

in reality , reality is nothing like you say why

(a) we often have poor tidal data
(b) we often have no data for the place we are, or maybe in a few hours as the data my be sparse and applies to another geographical position ( see tidal diamonds)
(c)In an area of complex tides and sparse data, without computerised aids, computing ground track on a single CTS is COMPLEX ( i.e. more complex then normal chart work is )

Have a look through Bowditch the quintessential tome on navigation, search for multi hour CTS !!.

Look at RYA exam papers to Yachtmaster level , including the instructors worked examples, at most you'll see 1-3 hour CTS over a fairly small physical area

PS I know all the differences between hourly , half hourly and multi hour CTS thanks, I used to teach this for years .

You have not answered my question, computing a say 12 hours single CTS vector, using complex tides and then sailing off on that heading , thats just nuts, outside of a few " clever" use scenarios. commuting a 1-3 hour CTS, that bring you back close to the rhumb line, and then recomputing is much safer and the approximate ground track and XTE can be estimated reasonably accuracy

( dead efficient is just that - dead)
dave
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 27-03-2015, 13:28   #442
Registered User
 
El Pinguino's Avatar

Join Date: Aug 2013
Location: Punta Arenas ahorra
Boat: 39' Westerly Sealord
Posts: 3,953
Re: Speed Through GPS Versus Old Fashioned Paddle Log

Quote:
Originally Posted by Dockhead View Post
Pitots . . . LOL . . .
A new dawn , another day.... etc

Not sure why that cracked you up..... pitot is the logical choice for anything but a displacement hull motor boat... lookee here Livorsi Marine, Inc. - Speedometers, Standard size, oversized
They were also the standard fit for merchant ships from about the mid 60's until they started fitting doppler logs in maybe the late 80's give or take. Electro/magnetic logs were/are a rarer bird...

edited to add...even WM sells em http://www.westmarine.com/buy/telefl...t-tube--288282
El Pinguino is offline   Reply With Quote
Old 27-03-2015, 13:54   #443
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,750
Re: Speed Through GPS Versus Old Fashioned Paddle Log

Quote:
Originally Posted by goboatingnow View Post
We had this out before in the mega thread on CTS, about ground thread computation

The fact is unless you have access to a computer and reliable sub-hour tidal stream data, it is NOT easy to compute your ground track . short of working up a full one for you , or you doing it by hand yourself , will this aspect be clear.

quoting gulf streams etc, are all simplistic in effect continous non variable currents, rather like applying CTS to a river crossing

in reality , reality is nothing like you say why

(a) we often have poor tidal data
(b) we often have no data for the place we are, or maybe in a few hours as the data my be sparse and applies to another geographical position ( see tidal diamonds)
(c)In an area of complex tides and sparse data, without computerised aids, computing ground track on a single CTS is COMPLEX ( i.e. more complex then normal chart work is )

Have a look through Bowditch the quintessential tome on navigation, search for multi hour CTS !!.

Look at RYA exam papers to Yachtmaster level , including the instructors worked examples, at most you'll see 1-3 hour CTS over a fairly small physical area

PS I know all the differences between hourly , half hourly and multi hour CTS thanks, I used to teach this for years .

You have not answered my question, computing a say 12 hours single CTS vector, using complex tides and then sailing off on that heading , thats just nuts, outside of a few " clever" use scenarios. commuting a 1-3 hour CTS, that bring you back close to the rhumb line, and then recomputing is much safer and the approximate ground track and XTE can be estimated reasonably accuracy

( dead efficient is just that - dead)
dave
Well, I'm not sure that anything new is being said here, or that it is interesting for anyone for us to keep repeating ourselves.

But briefly:

1. I already answered the question about Bowditch. Ships aren't interested in this because their speed relative to the speed of currents is high enough that they can use ground-oriented navigation successfully. You can be sure that if the average speed of ships was 6 to 8 knots, like ours, or if tides typically ran at 10 to 14 knots, Bowditch would be structured in a completely different way, and all navigators would know water-referenced navigation.

2. Yacht navigation is derived from the science which was developed for ships, which is why water-referenced nav is covered only superficially, and mostly for the benefit of Channel sailors (where you simply can't sail without it). But that does not mean that it does not have much wider application -- it does. You need it wherever (a) tides or currents reach a significant proportion of your speed; (b) and vary in speed or direction during your passage.

3. Yes, of course, efficiency is not everything. Just like you don't always insist on going in a straight line on land -- you may divert around dangerous places, for example -- you don't always insist on a straight line through water, if you have reasons not to. But that is not a reason to remain willfully ignorant of where that straight line is!!! That is a big, fat, logical fallacy.

4. I have already explain at some length that imprecision of tide data is no reason to abandon estimating a CTS, and sail off in intentionally the wrong direction. Up to a very large degree of uncertainty, a roughly estimated CTS will be much better than the rhumbline. When I have time, I will work up some examples to show it. Uncertainty of data is just a weak excuse not to bother to figure this out.

5. It is not hard to work up approximate ground tracks. One way to do it is with the old hand method for crossing the Channel -- and if you run several scenarios, you will immediately see the limits. Besies that, with modern plotters, it is a trivial matter to observe your ground track as it develops, something you should do all the time anyway. Your characterization of CTS nav as "dangerous" is highly exaggerated, and indeed, it's just an excuse not to do it. In 90% of cases, there are simply no obstacles, since currents don't run perpendicular to coasts. If there are, you just work up your ground track to whatever level of precision you need to. Very often you can do a quick check of the probable limits of your track by simply adding up the maximum set and drift of every hour -- simples, and that's a basic navigation technique. If there are some nasty hazards somewhere in your conceivable ground track, set intermediate waypoints and steer to those -- not so different from normal ground-referenced nav and, again, basic navigation.

6. Concerning short CTS's bringing you back to the rhumbline -- the shorter it is, the less sense it makes. If you need a high degree of certainty that you won't get to some particular ground position, set an intermediate waypoint that takes you approximately as far from the rhumbline as you need to be. You will be miles ahead.

7. Concerning the Gulf Stream, or crossing rivers -- those are quintessential CTS nav problems, which make really obvious several of the things I'm saying here, for example, the absence of any necessity to have precise speed or current data. You don't need to know how fast the Stream runs, or how fast you are going, to know immediately and instinctively that any course South of the rhumbline, is going to be better than the rhumbline, and a guess which is out even 10 degrees may still save you hours. It's a really obvious case, and really explains water-referenced nav very well.
__________________

__________________
Dockhead is online now   Reply With Quote
Reply

Tags
gps

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
Old Log will be moved to opencpn.log.log PHD1026 OpenCPN 26 19-05-2015 14:01
Log paddle wheel kit ancor Marine Electronics 4 19-10-2014 20:11
Speed Log Paddle Wheel Won't Spin in Water Reefmagnet Marine Electronics 11 12-09-2012 05:43
Log Speed vs GPS [SOG] Speed? Sandyh Navigation 57 07-06-2009 23:22
Any "old-fashioned" looking boats besides Tayana 37? coyotewrw Monohull Sailboats 30 07-08-2008 20:22



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 02:14.


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.