Water-Oriented Frames of Reference

[Dockhead]

I was reading some German pilot resources, and came across this:

"Warnung vor den Tonnen! Fahrwassertonnen in Strömungsgewässern sind für ein Sportboot unglaublich gefähliche Hindernisse. Sie kommen wie von einem starken Motor getrieben mit rauschender Bugwelle auf das Boot zugefahren (jedenfalls sieht es so aus). Also gut Freihalten, mit Abstand passieren und die Gefahr eines Zusammenstoßes frühzeitig erkennen."


We have been talking about ground-referenced concepts (SOG, COG, rhumbline) versus water-referenced concepts (STW, heading, CTS) recently, and this struck me. It means:

"Warning about buoys! Channel buoys in tidal waters are unbelievably dangerous hazards for pleasure vessels. They come at your boat (or seem to) as if driven by a powerful motor, with a rushing bow wave. Therefore, keep well clear, pass them at distance, and recognize early the danger of a collision."


An excellent illustration of the water-referenced point of view, for those who find it difficult to visualize.

[ryon]

Not just channel buoys! I've noticed that drilling rigs can move surprisingly fast in a fog.

[monte]

so, if the buoy is making 6K STW and is off your starboard bow while you are sailing, which is the stand on vessel?

[msponer]

That’s an interesting way to look at it. Thank you.

I’m new to this thought, but aren’t there three common coordinate systems?

• Ground: SOG, COG
• Water
• Boat: CTS

In physics one changes the coordinate system to solve the problem.
In business we change the metaphor to control the argument.
And in storytelling we play with metaphor to make a thought compelling.

I feel like the German book is using the water frame for storytelling. So I wonder if the water reference frame is useful in a physics way -- where it makes it easier to think or solve a problem?

Now I want to read about navigation again. I’ve forgotten all the rules of thumb, about using your hands to measure angles to know how far from shore you are or how fast you are going, or correcting for current and leeway, and etc. Have you guys read any good books in that vein? Emergency Navigation has a few of these, but it's also ... grounded in a thought experiment that, while fun and instructive for learning the fundamentals, gets a bit boring for a second reading where I just want to brush up on the cute tricks and shortcuts to figure this out in your head. I also like to read the same idea from several people's perspective, if possible. Chapmans and Duttons, at least the ancient editions I have, are similarly a bit dense and focused on a context I don't care about (large ships, with the corresponding precision they need). Are the new editions of better?

[rhubstuff]

You might try Boater's Bowditch. Its out of print, and a bit out of date (Loran, anyone?) but maybe Amazon can find one. I'm the author.

[DeepFrz]

You might try "Boat Navigation for the Rest of Us" by Bill Brogdon. It was a free download but I don't know if it still is.

[dkroar]

Do you have a URL to where the book was a free download? I only found purchase prices on a Google search. Thanks

[Dockhead]

Originally Posted by rhubstuff

You might try Boater's Bowditch. Its out of print, and a bit out of date (Loran, anyone?) but maybe Amazon can find one. I'm the author.

Do you go into any water-referenced nav techniques, like CTS?

It's a black art because ship's don't need it -- due to their high speed relative to the speed of tidal currents. It's hardly touched by Bowditch; just a bit about set and drift and single-hour CTS.

The RYA teach you how to work up a multiple-hour CTS -- this is aimed at Channel crossings, which are basically impossible to do in a sailboat without this technique. But what they teach is very crude, and they don't go into the subtleties of the theories involved.

So there don't seem to be any good sources on this.

[FamilyVan]

Currents are one of my favourite topics of conversation! In my day job I skipper passenger ships in very strong currents, up to 10 knots with lots of airated water, standing waves and plentiful rocks. In a previous career i was a navigator on a large buoy tender (240') that operated most of the time in the strong currents of the St Lawrence River and tides of the Gulf of St Lawrence. In my opinion, the best resources on vessel operation in near shore currents aren't found in the sailing aisle, they are found in the paddling aisle. For canoes, kayaks, and rafts, strong currents and their interaction with boat hulls and propulsion systems is their bread and butter. An excellent resource for any water craft operating in strong currents is Bill Masons Path of the Paddle.

In most cases when you are dealing with strong currents near shore, navigation isn't happening, what you are doing is pilotage, which is approached differently then open water navigation. It has more to do with ship handling techniques and maintaining spatial/situational awareness and reading the currents and less to do with the geometry associated with navigation.

Sent from my SGH-I547C using Cruisers Sailing Forum mobile app

[Roy M]

God, I love CF!

[Dockhead]

Originally Posted by FamilyVan

Currents are one of my favourite topics of conversation! In my day job I skipper passenger ships in very strong currents, up to 10 knots with lots of airated water, standing waves and plentiful rocks. In a previous career i was a navigator on a large buoy tender (240') that operated most of the time in the strong currents of the St Lawrence River and tides of the Gulf of St Lawrence. In my opinion, the best resources on vessel operation in near shore currents aren't found in the sailing aisle, they are found in the paddling aisle. For canoes, kayaks, and rafts, strong currents and their interaction with boat hulls and propulsion systems is their bread and butter. An excellent resource for any water craft operating in strong currents is Bill Masons Path of the Paddle.

In most cases when you are dealing with strong currents near shore, navigation isn't happening, what you are doing is pilotage, which is approached differently then open water navigation. It has more to do with ship handling techniques and maintaining spatial/situational awareness and reading the currents and less to do with the geometry associated with navigation.

Hot tip!!!

[Hoofsmit]

This 'sums it up'


"In most cases when you are dealing with strong currents near shore, navigation isn't happening, what you are doing is pilotage, which is approached differently then open water navigation. It has more to do with ship handling techniques and maintaining spatial/situational awareness and reading the currents and less to do with the geometry associated with navigation."

Brings us right back to the " lee bowing " thread , why plot a CTS in a piloting situation, use your eyes and judgment on the best course and vessels attitude.

The problem when discussing 'water referenced' is that you are aiming to get to a point on land not on water, the old table cloth theory is so far out as it says nothing to how your particular hull responds to different points of sail,never mind wave height and frequency the variables are incalculable, navigation at the chart table , after all is only ever a 'best guess'

Why look to confuse things?





Sent from my iPad.......i apologise for the auto corrects !!!

[hellosailor]

Ach, just like the Germans to complain about a few surplus self-propelled homing mines that got loose and went after sailboats. That's it, blame it on the buoys, don't say a word about who's been stockpiling naval mines again.

[IdoraKeeper]

This bouy behaved in an extremely aggressive fashion. It repeatedly attempted to collide with Idora over a period of several hours. The necessity of following certain headings to keep green water out of the cockpit made escape from this belligerent monster a challenge. I only had time to snap this shot when my position had advanced enough to get me out of the seven and eight foot breakers astern of me. In the end, Idora and I prevailed and nothing was broken.. Even the dink stayed upright. Beware large steel objects that defy physics!

[StuM]

Originally Posted by FamilyVan

Currents are one of my favourite topics of conversation! In my day job I skipper passenger ships in very strong currents, up to 10 knots with lots of airated water, standing waves and plentiful rocks. In a previous career i was a navigator on a large buoy tender (240') that operated most of the time in the strong currents of the St Lawrence River and tides of the Gulf of St Lawrence. In my opinion, the best resources on vessel operation in near shore currents aren't found in the sailing aisle, they are found in the paddling aisle. For canoes, kayaks, and rafts, strong currents and their interaction with boat hulls and propulsion systems is their bread and butter. An excellent resource for any water craft operating in strong currents is Bill Masons Path of the Paddle.

In most cases when you are dealing with strong currents near shore, navigation isn't happening, what you are doing is pilotage, which is approached differently then open water navigation. It has more to do with ship handling techniques and maintaining spatial/situational awareness and reading the currents and less to do with the geometry associated with navigation.

Sent from my SGH-I547C using Cruisers Sailing Forum mobile app

Excellent point!