Chain Ferry

[Andy]

So, from the info above, what do I need to know or beware off ?
Obviously today the strength of the incoming and outgoing tides are stronger than 16th. This doesnt mean I shouldnt go out today, but would it be better for me to leave on an outgoing tide, or do I have more control on an incoming tide ? Or would it be better, today, for me to only go out and in between 11am and 4pm ?

I am trying to find some sort of general travel and safety logic I can apply at any harbour. Obviously depth at tide times at some places is relevant. I always buy a chart when I go to a new place, i am old school when it comes to paper

[Andy]

I would suggest you're best going through the harbour entrance when the tidal stream is at its slowest ie today that looks like between 10-12 when the line on the graph is flatest. Its less the depth you are worried out in the channel but more the rate at which the stream is following.
With experience it will be less of a problem. The concern is that if you had an engine failure and the tide was flowing at its fastest you would havd little time to react.
Well worth listening to harbour traffic on ch 14 as the ferry staff are excellent at communicating with local boats and harbour control if needed.
If you'd like to chat in person feel free to give Dom or I a call on 01202 901267.

[Sarah]

Just to throw one other consideration in.......wind over tide can have quite an impact in the Swash Channel (in strong winds).

[chris moody]

Great question @Andy .

I don’t know the actual tidal stream strength in the harbour entrance but I’d suspect it can get up to 6 to 8 kts on springs. With a displacement boat (like a sailing yacht) that could prevent you getting in or out if you were fighting the tide, but in a planing hull you can go much faster than 8 kts so it’s not an issue. Think of it like the moving pavements in airports, if you ran the wrong way down one you would make progress, albeit a bit slower than usual.

The bit you need to be aware of is that if you stop the boat in the water, you are still travelling at 6 to 8 kts (possibly straight towards the chain ferry). To actually stop you need to turn round so you are going the opposite way to the tide, and motor at the same speed as the tide is travelling. Then you are completely stationary (but travelling through the water at quite a speed).

Practicing holding the boat stationary in a strong tide (or wind) is a very useful skill to learn. It’s something you will learn how to do on a PB2 course.

A strong tidal flow would not stop me going though Poole harbour entrance in a powerboat, but it would make me more cautious, and make me keep further away from fixed stationary objects.

The thing that would make me not go through the entrance at Poole would be a strong tidal flow with a strong wind in the opposite direction (called wind over tide). This can create large waves. This is also covered on the PB2 course.

If you have any more questions just ask.

So, from the info above, what do I need to know or beware off ?
Obviously today the strength of the incoming and outgoing tides are stronger than 16th. This doesnt mean I shouldnt go out today, but would it be better for me to leave on an outgoing tide, or do I have more control on an incoming tide ? Or would it be better, today, for me to only go out and in between 11am and 4pm ?

I am trying to find some sort of general travel and safety logic I can apply at any harbour. Obviously depth at tide times at some places is relevant. I always buy a chart when I go to a new place, i am old school when it comes to paper

[Sarah]

Great answer Chris, completely agree ref types of boats etc. I have been there with a 2hp and no hope against the tide! Lots of get out options with some planning!
I go in and out the harbour in my RIB at any state of tide (although down the channel will depend on wind over tide) but I will have looked at the tide to know what effect it will have so I have a plan in mind if there were to be a problem with engine etc.
Andy the comments are just to help you think, not to put you off! Interesting question for us as Instructors to help understand the questions students may have as they venture out alone.
If you're local its worth going and sitting in the carpark by the ferry at Sandbanks and watching for a short while on a non boating day. You'll realise boats are going in and out all day. Just with a plan you'll be safer and enjoy it more.

[ChrisParish]

When I was a kid playing on boats with my family in Poole, we didn’t have a boat which would plane so if we were planning on leaving the harbour we would time it so that we didn’t have to go against the tide.
Last year I tired to get back through Christchurch harbour mouth when the tide was ebbing hard and I only just made it - I was at WOT on my 5hp engine. If I hadn’t been able to get through then I would have had to return to the beach and wait it out.
You are wise to be thinking about planning your journeys - I didn’t really realise how dangerous the situation could have been until afterwards.

[PeterM]

Nice comments from all …..

While Sarah & I get to boat in awesome locations in Poole & Christchurch they do have some challenges to think about.

I took some footage of a bouy at Peviril ledge on Sat - and as an exercise holding position into a tidal stream is really good fun.

[jimbo747]

"I am trying to find some sort of general travel and safety logic I can apply at any harbour."

Hopefully this is helpful, apologies if I've misunderstood and am teaching Grandma to suck eggs....

1. Easy Guideline - "Rule of Twelfths" (doesn't work for Poole, or other harbours with a double tide, so fails the "any harbour" test).

For the first hour after low (or high) tide, the depth increase is 1/12th of the total tide range
For the second hour after low (or high) tide, the depth increase is 2/12ths of the maximum
For the third hour, 3/12ths
For the fourth hour, 3/12th
For the fifth hour, 2/12ths
For the sixth hour, 1/12th
For a total of 12/12ths!

You can use this as a rough estimate on depth of water at a given time. For example, if you need to cross an exposed sand bar that is at sea level at low tide, and the tidal range is 12 feet then you can do so after an hour of incoming tide if your boat draws less than 1 foot, after 2 hours if your boat draws less than 3 feet, and after 2 hours if your boat draws less than 6 feet.

2. Using a chart.

http://www.visitmyharbour.com/harbours/ ... 2018-chart

Look just to the north of the entrance you'll see an "A" in a diamond shape. If you then look at the table at the bottom of the chart, you'll find that same "A" under which you'll find a table. For example, the top line is shown as 6 hours before low water Poole - and for A you will see:

192 1.0 0.5

This tells you that at this spot, 6 hours before low water Poole, the tidal direction is 192, with a speed of 1 knot at spring tides and a speed of 0.5 knots at neap tides. I don't know why they don't have a measurement in the entrance itself, but at least it's an indicator.

3. The Solent
Just be aware that there are a number of weird effects around the Solent down to Weymouth. Weymouth has a double low tide, but it's pretty irrelevant since the area is pretty benign especially if you are in a low draught boat. In Southampton Water you have an effect called a "young flood stand" which is particularly prevalent during spring tides. After low water the tide starts to come in for about 2 hours, then it kind of hesitates for two hours (meaning the currents slacken) for 2 hours, then it rushes in for the remainder. Again, shown on the tidal sections of charts and in tidal atlases, but can be useful if you are in an underpowered yacht. There is also a double high water, and because of this the ebb tide in the Solent only runs for about 3.5 hours every 12, not 6 as in other places. I think the theory used to be that all of this was caused by the Isle of Wight being where it is, but I think more accurately it is caused by the Solent being roughly the midpoint of the English Channel, and while the water sloshes up and down the channel twice each day, the movement is not uniform because of headlands, differing depths (eg the banks off Portland). And since the Solent is in the middle, it gets the chaos.

Maybe Sarah can explain the latter a bit better as she specialises in sea training - I did a Yachtmaster Offshore theory course ten years ago and have forgotten most of it - but I think the important thing is that for most ports you can use the rule of twelfths, but for safety's sake the tidal diamonds on a chart are a better indicator.

[jimbo747]

Hi
I have heard various explanations as to the double tide. Most often the Isle of Wight but like you Im more convinced by the bigger picture, the channel explanation and nodal points. Sorry I have no formal answer though. I will asm Dom to hop online as suspect he'll have a view too.

[Andy]

This is all good stuff, too much to take in, in one day, so ill have to go over it all again but with the chart out lol.

I suppose your right, if you have engine fail, at least you can try to make a decision on it all.

If your engine fails while going out, on a tide thats going out, surely this also makes steering difficult because no water is going round the prop ?

And obviously the reverse if coming in, so is the best cause of action, is to try to chuck the anchor out somewhere safe if possible ?
At some time an engine is going to fail on me, and I have tried to carry everything I feel I need. I am the sort of person that likes to know i have a plan for everything, I even have a personal sat alarm thingy if i am on my own and fall overboard. But its the unknown I am trying to find out about lol ! Hence why I need to chat about it all.

I must do my radio course, at least with one of them if I get into difficulties I can call for help, or notify the harbour master the shit is about to hit the fan !

Cheers all, I'm getting there !