|
"DSK" wrote in message .. . One of the most frustrating things around here is that the tide tables are usually in error by at least half an hour. The tidal current in Snow's Cut (for example) is very strong, and so far I have yet to see it run on schedule. It's annoying after planning a departure at an inconvenient time so as to arrive at slack, only to find the current running like a champ with no sign of slacking. A couple of years ago we encountered a tide that seemed to be an hour early. Five boats set off from St Peter port for the trip to Cherbourg. The trip took us through the Alderney Race, where the stream can reach more than 10 kts! We had planned to catch the last of the tide .... in fact we caught the first of the next tide! Afterwards, we all checked our figures, and we concluded that the tide had definitetly turned earlier than forecast. I suspect that weather systems can have an effect. In future, I will always leave half an hour earlier!!! Regards Donal -- |
"Scott Vernon" wrote in message ...
"Joe" wrote Scotty Perhaps if you modified your vessel and made it float like this one: http://pao.cnmoc.navy.mil/pao/n_onli...photos/flip.jp g You would get a great current ride. This Navy ship has been in 80 foot seas! What the heck is that? and where is it? SV It was buildt to research ocean currents. Here is the story that went with the photo: AG3 `flips' for research vessel duty with Scripps Institute by AG3 Michael DeMauro It's not too often that one encounters a vessel with bulkheads and decks designed for use in both the vertical and horizontal position…including heads and showers! Late on the afternoon of Jan. 15, I arrived at the Scripps Nimitz Marine Facility in San Diego. Having never been to sea, I had no idea what lay ahead as I made my way down the pier looking for the R/P FLIP with TAD orders in hand. In the distance appeared the most bizarre vessel I had ever seen. "This has got to be it," I thought. FLIP, or Floating Instrument Platform, is a 355-foot long, spoon-shaped buoy. Built in 1962, FLIP is owned by the U.S. Navy but operated by the Scripps Institute of Oceanography, University of California San Diego. The FLIP has a series of ballast tanks along its submarine-like hull, which can be strategically flooded with seawater. As the tanks fill, the "top" end of the ship slowly lifts out of the water (i.e. Flips) until the entire vessel becomes vertical, with 300 feet below the waterline. The remaining 55 feet become a stable platform, ideal for performing a variety of marine research experiments—so stable, in fact, that although the vessel was designed to operate in 30-foot seas, it has weathered 80 footers on more than one occasion. The Office of Naval Research hoped for 20-foot seas for some of the data collection periods during the planned underway. The bulk of the research during this underway period focused on Air-Sea Interface experiments, but in the past, FLIP was used in a variety of experiments, ranging from communications to ambient noise to the development of vertical arrays for acoustic sensors. …and another step toward a mutually beneficial relationship between the research and METOC communities was solidified. On reporting aboard for the January trip, I became a bit disoriented, to say the least. It's not too often that one encounters a vessel with bulkheads and decks designed for use in both the vertical and horizontal position…including heads and showers! Simply finding one of the three berthing spaces entangled in the forward superstructure proved difficult. Once settled in, however, I got straight to work establishing communications with Naval Pacific Meteorology and Oceanography Detachment Pt. Mugu, my home duty station. The small crew and full agenda of the research platform didn't allow me a free ride, and I was put to work straight away with various tasks, including responsibility for taking salinity soundings on a nightly watch from 2000 to 0300. During one three-day period I was even pressed into duty as the ship's cook, with no apparent casualties. The Scripps research vessel began working with Pt. Mugu in September 1999 when AGAN James Ross embarked on a similar trip off the Southern California coast. Tom Golfinos, FLIP OIC, has enthusiastically folded Pt. Mugu sailors into the crew, making the trips interesting and educational for the Sailors as well as the remainder of the crew. Simultaneously, civilian and military forecasters at NPMOD Pt. Mugu earned the trust of the crew by providing the vessel with tailored and precise forecasts for the environmentally sensitive operations. During the January underway period, a risky personnel and supply transfer was planned for the middle of the trip, which involved lowering a scientist down a rope ladder and dropping him into a rubber dinghy over open ocean, a dangerous operation even under ideal conditions. A go/no-go decision on executing the operation was based entirely on the Pt. Mugu Forecast. CAPT (Ret) Bill Gaines, Assistant Director Marine Physical Laboratory, Scripps Institute of Oceanography, relied on the accurate sea height, wind, and visibility forecasts provided by the detachment to eventually proceed with this critical operation. Although the weather didn't do its part by providing the FLIP with prolonged periods of high winds and seas during the 17-day drift, a good portion of the required data was collected, the personnel transfer went without incident, and another step toward a mutually beneficial relationship between the research and METOC communities was solidified. For a first-time underway period, my experience on the FLIP proved to be a valuable learning experience and a rare opportunity to ride one of the truly remarkable research platforms in existence. Joe |
Thanks for the link and the story. That is an unusual and interesting
vessel. DSK Joe wrote: http://pao.cnmoc.navy.mil/pao/n_onli...hotos/flip.jpg What the heck is that? and where is it? It was buildt to research ocean currents. Here is the story that went with the photo: AG3 `flips' for research vessel duty with Scripps Institute by AG3 Michael DeMauro It's not too often that one encounters a vessel with bulkheads and decks designed for use in both the vertical and horizontal position…including heads and showers! |
No, not in the context of Dougs ideas about max stream lagging behind
height changes. Max stream is most often at the maximaum rate of change of height. Look it up. Cheers Scott Vernon wrote: Got that wrong Doug. Tidal stream is generally strongest at the time of the fastest rate of change of tide height. That is most often about halfway between high and low water. Look it up. Isn't 7/12s 'about halfway'? look it up. Scotty |
How do you think it related to the change in tide height that day?
Cheers Donal wrote: "DSK" wrote in message .. . One of the most frustrating things around here is that the tide tables are usually in error by at least half an hour. The tidal current in Snow's Cut (for example) is very strong, and so far I have yet to see it run on schedule. It's annoying after planning a departure at an inconvenient time so as to arrive at slack, only to find the current running like a champ with no sign of slacking. A couple of years ago we encountered a tide that seemed to be an hour early. Five boats set off from St Peter port for the trip to Cherbourg. The trip took us through the Alderney Race, where the stream can reach more than 10 kts! We had planned to catch the last of the tide .... in fact we caught the first of the next tide! Afterwards, we all checked our figures, and we concluded that the tide had definitetly turned earlier than forecast. I suspect that weather systems can have an effect. In future, I will always leave half an hour earlier!!! Regards Donal -- |
That sounds like an estimate based on an energy argument. However, I
don't think that case could be considered to be a closed system so such energy balance need not apply. Cheers Jeff Morris wrote: "Thom Stewart" wrote in message ... Scott, You've seem to have forgotten "The Gulf Stream Master" Jax. I'm sure he can help you ride the eddies:^) Maybe even find you a stray current heading south (g) Jax also insisted that the time of high water and slack current must be the same, to be otherwise would violate the laws of physics (on his planet). Now, for what's it worth. The Tide Flow is a sine wave. Us common folk understand that slack water is at the top and bottom of the wave. So slack is, roughly about a hour and it is roughly in the upper 30% counting the end of the rising tide and the beginning of the Ebb. 15% to the HW and 15% roughly to the Max Flow. That means about two hours to max flow, 8 hours of max flow and then another couple of hour of diminishing flow to LW. While the current flow in "simple harbors" may follow a sine curve, in cuts between two bodies of water the flow is different. The curve is more "squarish," that is, the flow ramps up quicker and stays high longer. The duration of slack is reduced. The best example is Hell Gate in New York. IIRC, the flow rate is proportional to the square root of the different of height of the two bodies. |
You should complain to the hydrographic offic. Tide tables are hardly
rocket science! Cheers DSK wrote: One of the most frustrating things around here is that the tide tables are usually in error by at least half an hour. The tidal current in Snow's Cut (for example) is very strong, and so far I have yet to see it run on schedule. It's annoying after planning a departure at an inconvenient time so as to arrive at slack, only to find the current running like a champ with no sign of slacking. Fresh Breezes- Doug King |
Then you're disagreeing with Bowditch:
"A slight departure from the sine form is exhibited by the reversing current in a strait, such as East River, New York, that connects two tidal basins. The tides at the two ends of a strait are seldom in phase or equal in range, and the current, called hydraulic current, is generated largely by the continuously changing difference in height of water at the two ends. The speed of a hydraulic current varies nearly as the square root of the difference in height. The speed reaches a maximum more quickly and remains at strength for a longer period than shown in Figure 914b, and the period of weak current near the time of slack is considerably shortened." "Nav" wrote in message ... That sounds like an estimate based on an energy argument. However, I don't think that case could be considered to be a closed system so such energy balance need not apply. Cheers Jeff Morris wrote: "Thom Stewart" wrote in message ... Scott, You've seem to have forgotten "The Gulf Stream Master" Jax. I'm sure he can help you ride the eddies:^) Maybe even find you a stray current heading south (g) Jax also insisted that the time of high water and slack current must be the same, to be otherwise would violate the laws of physics (on his planet). Now, for what's it worth. The Tide Flow is a sine wave. Us common folk understand that slack water is at the top and bottom of the wave. So slack is, roughly about a hour and it is roughly in the upper 30% counting the end of the rising tide and the beginning of the Ebb. 15% to the HW and 15% roughly to the Max Flow. That means about two hours to max flow, 8 hours of max flow and then another couple of hour of diminishing flow to LW. While the current flow in "simple harbors" may follow a sine curve, in cuts between two bodies of water the flow is different. The curve is more "squarish," that is, the flow ramps up quicker and stays high longer. The duration of slack is reduced. The best example is Hell Gate in New York. IIRC, the flow rate is proportional to the square root of the different of height of the two bodies. |
Jeff Morris wrote:
Then you're disagreeing with Bowditch Hmm... Navvie, Bowditch... Bowditch or Navvie... A tough call but I'd have to say Bowditch has the slightly greater weight of authority. I'd agree that Bowditch is nowhere near as pompous nor as self-seeking. DSK |
| All times are GMT +1. The time now is 03:25 PM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
Copyright ©2004 - 2014 BoatBanter.com