Snowgoose-1
Well-known member
Easy to find live tide levels but can't find live tide speed.
Diamonds are ok but wondering if any folks know of any live sites.
TIA
Diamonds are ok but wondering if any folks know of any live sites.
TIA
Live Tidal Speed Stations UK
- Thread starter Snowgoose-1
- Start date
Chiara’s slave
Well-known member
‘Faster than I could swim with fins’ I can report, from just East of Yarmouth pier at 0800 on Saturday. I’d be fascinated by such data if it exists.
johnalison
Well-known member
Dunno about sites. I just bring it up on my plotter.
mjcoon
Well-known member
It's not a trivial thing to measure meaningfully. The further your sensor is from any fixed object, in order to be in clear and smooth flow, the more difficult it is to connect and ensure its safety!
Snowgoose-1
Well-known member
Can understand that.
The late John Goode of PBO berthing series , stated that one knot of tide is equal to a F4 wind. Not quite sure how one arrives at that figure but I believe him when trying to swim against the tide.
wonkywinch
Well-known member
Do the plotter based (almanac derived) streams take into effect coefficient? Keep meaning to check whether they are just based on mean or are biased by the coefficient.
johnalison
Well-known member
In practice, I find it rather clonky, but it gives a reasonable indication of direction and roughly what sort of strength. I haven’t checked but I imagine that the coefficient is taken into account. For critical situations I have always used the diamonds on Admiralty charts, often easier than tidal atlases. I’m sure that much more information is available nowadays, with less need for interpolation.
B27
Well-known member
I know someone who was involve with chucking buoys in the ocean and tracking them by satellite, also devices which sink to various depths to monitor currents, measure temperatures and amuse the fish.
There's various buoys around the UK you can get wave data from, but I can't find any live current speed/direction data.
Chiara’s slave
Well-known member
Normally I go in at LWS, slack tide, but still with a line to grab, tied to the boat. I’ll be doing it again soon, one of our XODs hit Harrys Rock, needs it’s keel looking at.
Stemar
Well-known member
Old Harry Rocks I know, but where is Harry's Rock? I'd hate to do the same as your XOD
ylop
Well-known member
It must depend on the cross section of your vessel (both above and below the water). Probably can be calculated by some fluid dynamics - but if your vessel is adrift, with zero wind with a 1 knot tidal stream the boat moves at 1 knot in the direction of the tide. John's rule of thumb implies that if there is no tide running but F4 wind and no sails up you will drift at 1 knot with the wind. Presumably if you find yourself with F4 wind against 1 knot tide, they effectively cancel each other out.
capnsensible
Well-known member
It's not the boat, it's the surface water movement.
ylop
Well-known member
am i being a bit dense - what is the surface water movement? is the suggestion the air blowing across the surface of the water at F4 creates drag on the water surface (which it will) moves the surface (how deep?) at 1 knot? Does a boat a drift in that sea then move faster than that (because it has its own cross section to catch the wind) or slower (because it has a keel below the surface creating a resistance to drift)? I don't recall John's article but he was generally quite pragmatic - so knowing the effect on the surface of the water, whilst interesting, seems less useful than knowing how a wind/current compare on a boat - particularly if trying to get it in a tight space.
srm
Well-known member
In order to give live tidal streams you need to deploy current meters with a live data feed. That's a lot of hardware to source and maintain to meet the OP's requirements. Tidal diamonds and other stream data were at best obtained by deploying a string of self recording instruments over a month. Observed stream would be correlated with the tidal coefficients. A lower level of accuracy could be obtained by anchoring a vessel and taking a profile of manual readings at 30 minute intervals for 25 hours. If we go back to before my training as a hydrographic surveyor a vertical spar would be released and the drift tracked for about 30 minutes, then returned to the release point and repeated. Predictions would be made from these readings on the assumption that stream was proportional to range at the time of recording.
While sailing I would look for the wake around marker buoys etc. to get an idea of the actual stream.
While sailing I would look for the wake around marker buoys etc. to get an idea of the actual stream.
Chiara’s slave
Well-known member
Obstruction to lower left. Its a big lump of concrete, marked with a small red and black unlit can. A serious hazard at low water, or even high water if you’ve got a big’un. Right in our race zone.
capnsensible
Well-known member
Surface water flow is generally accepted as the top layer that vessels operate in. There are various components to this and around the UK, the major cause is of course, tide. Tide streams are given as surface water flow. JG suggestio. Is that wind adds or subtracts to this with a vector depending on direction.
Imagine an inland lake on a windy day. The surface water will flow I the direction of the wind. On a grander scale, a avalook at how ocean currents are formed. Obviously this a very very basic view but gets one in the right direction....
One area I know that wind effect is tabulated is in the Gibraltar Straits. NP 629 published by the Hyrographic office gives a wind generated surface flow of water of 0.3 knots for a aF4 wind rising to 1.0 knots in a F10.
So who is right and does it matter? Well personally I take wind direction into account when estimating surface water flow but a bit more by experience and instinct rather than a defined rigid rule.
That's my interpretation of it anyway. And has been pointed out, learning to estimate rate and direction from a navigation mark, pot marker or similar is a great way understand water flow. And being downstream of it!
RunAgroundHard
Well-known member
Both Navionics and Lighthouse likely use coefficients based on my observation. The current velocity changes through the neaps to springs cycle. You can see this on Navionics if you select a tidal arrow and then scroll through dates. You will see the velocity change for each new day, for the same point in the high low cycle. I don't have Raymarine as an App, just on the boat plotter but it does the same. I have not compared to the tidal diamond at my area to see if the plotter and diamond correlate. That would be an interesting and simple exercise to do.
B27
Well-known member
There is a lot of hardware out there already, giving wave data and tidal heights..
Anemometers connected to the web are pretty common place..
I can only guess that the people paying for the hardware are not that interested in tidal stream data.
It's fascinating to the racing sailor, but most people don't need to know more than the big picture.
RunAgroundHard
Well-known member
I update my charts every winter, West Coast Of Scotland. There are always temporary tide measuring buoys and current measuring buoys deployed. Last year / this year, the area to the west of Islay, around the Stanton banks, has had a few buoys added to measure data.
The velocity will have been measured accurately for wind farm foundation loading and scouring management, so lots of data will have been collected, but real time, not aware of any beyond heights, as already stated by others.
The velocity will have been measured accurately for wind farm foundation loading and scouring management, so lots of data will have been collected, but real time, not aware of any beyond heights, as already stated by others.
srm
Well-known member
Yes, but I don't know how much finds its way to UKHO as there are also concerns about commercial confidentiality. The data belongs to the businesses that pay for it. However, its many years since I did any hydrographic work as I moved on into education and retired a while back.
Met data, wave and tidal heights are relatively easy to aquire, as all instruments are on the surface and can be left to run for long periods of time. Current measurement needs underwater sensors that adds another level of complication to keep them functioning over a similar time scale.
