SeaStu1
Well-Known Member
Can someone help and tell me when slack water occurs? I'm looking in particular at The Solent and Langstone Harbour. Is there a way of working it out and does it vary from location to location? Thanks.
Slack Water
- Thread starter SeaStu1
- Start date
Boomshanka
Well-Known Member
Admiralty tidal stream atlas (or there's a more basic one in Reeds Almanac)... work out HW and then you can visually see when slack water will be from the tidal stream:
http://www.force4.co.uk/4796/Admiralty-Tidal-Stream-Atlas---The-Solent---Adjacent-Waters.html
http://www.force4.co.uk/4796/Admiralty-Tidal-Stream-Atlas---The-Solent---Adjacent-Waters.html
sarabande
Well-Known Member
VicS
Well-Known Member
There is a period of slack water in the eastern Solent at about 2 hours before HW Portsmouth. Then the tide flows westwards until another period of slack water between 3 and 4 hours after HW Portsmouth before flowing eastwards again.
The tides turn a little later in the western Solent so that slack water periods are a little earlier than 1 hour before HW Portsmouth and again a little earlier than 5 hours after HW Portsmouth
These periods of slack water may be fairly brief.
I am rather curious as to why you should ask such a question. Surely if you are boating in the Solent you will have some tidal stream charts.
Not very clear but there are some chartlets HERE
Giblets
Well-Known Member
Are you referring to slack water through Langstone Harbour entrance?
SeaStu1
Well-Known Member
In particular the entrance to Langstone Harbour and just out of it. I'm planning a sail out of Langstone which will put me at the entrance 2 hrs before HW, having a couple of hours out in the Solent before returning to the entrance at around HW. Essentially i am trying to plan when the optimum time would be to leave the harbour so i'm not fighting the flooding tide and then to return around HW or just after, again not fighting against the tide running away.
I've just found the tidal stream charts on the back of my Imray chart.
l'escargot
Well-Known Member
The trouble is that when it is slack in the entrance you will find a tidal flow not far out. Slack water tends to be localised and doesn't generally last for long. Take somewhere like the Medina at Cowes, it can be slack water in the entrance by the floating bridge but 300 to 400 yards out in Cowes Roads you can have a couple of knots of tide pushing west.
Giblets
Well-Known Member
2 hours before HW you are looking at full flood, 3.4/1.7 knts. Slack is at HW & HW+6. HW +2 is full ebb, 3.1/1.5.
SeaStu1
Well-Known Member
Most useful - thanks Giblets.
SeaStu1
Well-Known Member
Just to add, l done my trip out of Langstone today. I was there 2 hrs before HW and was going along nicely with the sails but decided to start-up the outboard to give a bit more power as the tide was racing in - after twenty minutes the shear pin broke! I then carried on sailing out came back pushed in by the tide and using the sails. Never had a shear pin break, never thought about it, therefore never carried a spare - l will the next time.
Seajet
...
Truly slack water is very brief; the tide starts setting west in a determined way about 1.5 -2 hours before high water Portsmouth, outside the entrance.
Boomshanka
Well-Known Member
Are you sure there's not a spare shear pin (and split pin) somewhere under the outboard cover? Worth a check, sometimes held in a small rubber block.
oldharry
Well-Known Member
Trouble is, Solent slack water off Langstone will not be slack water in the Langstone entrance, as although the tide has changed direction in the Solent, the level continues to rise, so keeps flowing in through the narrows at speed. Slack water in the narrows will only occur when the water levels outside and in are the same, probably a short while after local high water. The same will happen at low water, the ebb will only go slack in the narrows when the rising Solent level equalises with the level inside the harbour. Local tidal flow chartlets are the only way of establishing exactly when slack water Langstone entrance occurs, and it may vary noticeably from that prediction according to the predicted height of the tide, and local weather conditions, barometric pressure and wind direction.
On spring tides, the period of actual slack when there is no flow in the channel may be very short, while a neap tide may give quite a long 'slot'.
On spring tides, the period of actual slack when there is no flow in the channel may be very short, while a neap tide may give quite a long 'slot'.
