Tides and slack water help please.

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bremar

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Hi,
I'm off to salcombe again today in our 18ft trailer sailer. "Motty". Just to try sleeping on board for 1 night.
Last time we had a drying out mooring at battson creek and always returned on the incoming tide on the engine. It had to be an incoming tide because we did not know what the boat and 4hp engine were capable of and We did not know how to assess tide speeds etc
I know the boat can only do approx 5 knots through the water because it's only 18ft long. So providing the engine can drive us at 5 knots we can motor against a say 4 knot tide and return slowly at 1 knot (I think this is right).
I have bought navionics for the Ipad and that gives data for the water speed? (Tidal stream??) in and out of salcombe harbour at various states of the tide. Varing from 0.2 knotts to 1.4 knotts. So I assume we shouldn't have a problem at any state of the tide getting in and out of Salcombe.
BUT someone reminded me that regardless of all that data Salcombe like all other harbours will have a "Slack water" time when there is reduced water movement that will not correspond with the change to either high or low water and suggested if you know when that is you can get into some harbours when you'd otherwise think you couldn't because of an ebb tide?
Does anyone have a view on this issue of Slack water and entering harbours or anything else I've mentioned above. And how do you find slack water for a particular harbour?

Thank you Bremar.
 
bremar said:
Hi,
I'm off to salcombe again today in our 18ft trailer sailer. "Motty". Just to try sleeping on board for 1 night.
Last time we had a drying out mooring at battson creek and always returned on the incoming tide on the engine. It had to be an incoming tide because we did not know what the boat and 4hp engine were capable of and We did not know how to assess tide speeds etc
I know the boat can only do approx 5 knots through the water because it's only 18ft long. So providing the engine can drive us at 5 knots we can motor against a say 4 knot tide and return slowly at 1 knot (I think this is right).
I have bought navionics for the Ipad and that gives data for the water speed? (Tidal stream??) in and out of salcombe harbour at various states of the tide. Varing from 0.2 knotts to 1.4 knotts. So I assume we shouldn't have a problem at any state of the tide getting in and out of Salcombe.
BUT someone reminded me that regardless of all that data Salcombe like all other harbours will have a "Slack water" time when there is reduced water movement that will not correspond with the change to either high or low water and suggested if you know when that is you can get into some harbours when you'd otherwise think you couldn't because of an ebb tide?
Does anyone have a view on this issue of Slack water and entering harbours or anything else I've mentioned above. And how do you find slack water for a particular harbour?

Thank you Bremar.
Click to expand...

Usually around HW & LW times, just when tide is highest/lowest for that day.
Will last for up to approx an hour either side of these times.
Tide flow fastest halfway between these times.
You might find it worthwhile going on a Dayskipper/navigation course.
 
There is a significant difference between slack water and high low water in many places but in most harbours and rivers this is not that significant. On much of the East coast of England for example slack water tends to be around 4 h before and 2 h after local high water with S bound tides over the high water period.
 
alant said:
Usually around HW & LW times, just when tide is highest/lowest for that day.
Will last for up to approx an hour either side of these times.
Tide flow fastest halfway between these times.
You might find it worthwhile going on a Dayskipper/navigation course.
Click to expand...
+1 for Theory Course, or at least buy a sailing manual. Tom Cunliffe's are excellent, as is Bob Bond's. But I do temper my remarks by saying that the course syllabus and the manuals do not actually impart the information on slack water in particular harbours as the OP requires. A Cruising Guide for the relevant area may help.
 
Slack water isn't a special magic time, it just means that the tidal stream is stationary (or very nearly so). In some places it doesn't exist at all as the water simply swirls around in different directions without ever stopping, in other places everything goes still for a significant time. The tidal stream will usually be least somewhere near high and low water, and strongest halfway up and halfway down, but it doesn't have to be. In parts of the Channel Islands it's completely the opposite - strong streams at high tide and weakest halfway up!

If your Navionics app is telling you that there's 0.2k of stream at a particular time and place, that's probably roughly slack water, or close enough to work with anyway.

For what it's worth, my preferred tide app is the Imray "Tide Planner" one, which shows pages from the Admiralty tidal stream atlas (the traditional paper books) but with the times all worked out for that day. See eg:

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Pete
 
Last time we were in Salcombe was in June; if you like to anchor I can recommend you go up river to the Salt Stone. We had a cracking night up there, very quiet and still. OK the rain was falling vertically at the time.

Try and work with nature; using the tide to come into harbour or go out. Having had to punch against a tide to get into the Exe last summer due to one of the crew being severely sea sick and I was quite sure he would not have lasted another eight hours at sea watching the Exmouth ice cream stall pass at 0.2 knots (SOG) was no fun at all.
 
Some good information on this thread. Would add that it's worth buying something like a Nautical Almanac. This will tell you the times of high / low water and also has tidal diagrams showing how strong the tide is at different times related to high water. Also on many charts you will find what is called a tidal diamond - on admiralty charts it's a maroon/purple coloured diamond with a letter inside it. You can look those up on the chart related to high water and find out what the tide will be doing at certain times. Then it's just a case of looking through the hours to find the times that the tide is doing what you want it to do.

As a rule of thumb - it's strongest 1/2 way between HW and LW and then weakens towards HW / LW but local areas may have specific anomalies that an almanac will tell you. Spring tides are also much stronger than Neaps. Speeds over 3 knots are very unusual and tend to be limited to a few specific locations at spring tides at the strongest times of the cycle. Such strong currents will usually be mentioned in almanacs. Practically over 12 hours that means you have about 6 hours of it going with you - about 2 hours of gently against you, 2 hours moderately against you and 2 hours belting out against you. As long as you avoid the strongest time against you or trying to beat against moderate / strong foul tides then your passage shouldn't be harmed too much
 
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