High & Low tides / visiting port solent

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johnchristie

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Hi all

I'm trying to get my head around the tide tables. Exactly how should i be planning my journeys around this?

For example, I want to visit Port Solent marina at some point this week which means navigating up towards the top of the harbour. I've looked at the tide tables and it says low tide is 10am and high tide is 5pm. I see the channel is dredged so I assume I should be able to visit anytime? but either way how do I use that information to plan my journey to port solent?

Thanks
John
 
The answer is Chart Datum but I would strongly recommend booking some time with Solitaire* of this Forum for the sake of your prop(s). Tides is the Solent are a little tricky and some of the sea-bed moves around a surprising amount so even understanding the charts may not give you everything you need.

In simple terms the depths on the chart are above chart datum so if the depth is shown as 1 metre you have 1 metre plus whatever the tide table shows for that time of day. For example, if the tide table says that low tide is 1.2 metres for the time you are there and the depth on the chart where you are is shown as 2.3 metres it's actually 3.5 metres.

There is a thing called the rule of twelths which says that the tide goes out 1/12 after high tide, 2/12's the second hour, 3/12's the third hour, 3/12's the fourth hour, 2/12's the fifth hour and 1/12 the sixth hour. After 6 hours the tide turns and comes in at the same rate. This rule doesn't work for much of the Solent unfortunately.

There's a few special rules for entering Portsmouth Harbour as well which I'm guessing you're aware of.

* I say Solitaire because he knows Portsmouth inside out and is regarded by all as a very, very good instructor. There's plenty of other good instructors around though obviously.
 
johnchristie said:
Hi all

I'm trying to get my head around the tide tables. Exactly how should i be planning my journeys around this?

For example, I want to visit Port Solent marina at some point this week which means navigating up towards the top of the harbour. I've looked at the tide tables and it says low tide is 10am and high tide is 5pm. I see the channel is dredged so I assume I should be able to visit anytime? but either way how do I use that information to plan my journey to port solent?

Thanks
John
Click to expand...

Port Solent is accessible at all tidal states - however you MUST keep to the buoyed channel. On low tide don't even try and cut any corners as you will soon find out why!

It's neaps next week with a low water of minimum 1.8 with 2.0 and 2.2 on Tue and Wed so you will have more than enough water even at low tide. You may have to wait around for the lock, but you will see the call up point as you make your way up the channel.
 
I took a quick trip up to port solent today and I see what you mean about the buoyed channel. I didn't have to wait for long to lock in but as I locked out there were at least 10 boats waiting in the channel to lock in including a huge fairline which pretty much took up most of the channel. Wouldn't fancy my chances on a low spring tide.

I was reading a post which advised not to enter bembridge other than +- 3hrs high water.

If I looked at the tidetable for bembridge and it lists high water at 16:00 it means I'm ok to visit between 13:00 > 19:00 or does that change depending on whether its a neap or spring tide?
 
I think you need a bit more than a quick answer, a bit of basic nav training would not go amiss here methinks. Plenty of renowned trainers available , some who populate this very forum. :D
 
As a general rule and pure common sense, if you have not visited a harbour before do it calm conditions on a flooding tide - so before HW. The reasons are obvious! At Bembridge, your best bet is to go in say an hour before HW so you have plenty of depth, pref follow someone who has been before. Bembridge is a twisty little channel to follow, but well bouyed (there are numbers on the bouys) and its simple once you get in.
 
johnchristie said:
I was reading a post which advised not to enter bembridge other than +- 3hrs high water.

If I looked at the tidetable for bembridge and it lists high water at 16:00 it means I'm ok to visit between 13:00 > 19:00 or does that change depending on whether its a neap or spring tide?
Click to expand...

The +- 3hrs is a rough guide. The actual time will depend upon your draught and the tide on the day concerned. In theory it will change between neaps and springs but being close to half tide the change will not be great

Look at your large scale chart of Bembridge entrance. Note the greatest drying height in the entrance . ( 1.1 m between St Helens Fort and the shore I think you will find)

Calculate the height of tide you will require to give you enough water over that drying height and add a little as safety margin.

From a Reeves-Foulkes Tidal atlas or using the tidal curve in say Reeds determine the period of time when the tide is above that minimum level.

I think you will find that the tide gauge outside Bembridge shows the actual depth in the shallowest part of the channel ... but check that is the case and that it does not show the actual height of tide like the one at Chichester.
 
johnchristie said:
thanks Jokerboat

I am due to do my PB2 course later this week but I was trying to get a basic understanding before hand.
Click to expand...

Didn't mean to be so short but was on my phone which limits my typing abilities somewhat :rolleyes:

A good start would be to buy an almanac. You then get some tidal graphs which help plot the tidal height for ports against HW / LW. Usually an explanation is also given as to how to do this. Minor (secondary) ports are a bit more tricky, but not beyond the wit of man :)
 
Ripster said:
pref follow someone who has been before.
Click to expand...
Good advice - if you've got someone to team up with - but whatever you do -
DON'T JUST FOLLOW A YACHT IN - even if they're quite large - it could be that they've got a lift keel and can float in a puddle ... so unless you know them or have asked them their draft assume they've got no keel ...
 
fireball said:
Good advice - if you've got someone to team up with - but whatever you do -
DON'T JUST FOLLOW A YACHT IN - even if they're quite large - it could be that they've got a lift keel and can float in a puddle ... so unless you know them or have asked them their draft assume they've got no keel ...
Click to expand...

That is why I said go in a 1hr before HW in the bouyed channel. I would not have advocated just following someone you dont know anywhere on any tide state.
 
Ripster said:
That is why I said go in a 1hr before HW in the bouyed channel. I would not have advocated just following someone you dont know anywhere on any tide state.
Click to expand...

I know ... but I thought it best just to clarify ...
If I hit the ground I scuff the bottom of my keel .... if a mobo hits the ground it can be expensive props on the menu ... :o
 
fireball said:
I know ... but I thought it best just to clarify ...
If I hit the ground I scuff the bottom of my keel .... if a mobo hits the ground it can be expensive props on the menu ... :o
Click to expand...

Fair point... I suppose the best advice to the OP is get some training, which he is doing I understand.
 
To set aside all the waffle I have worked through an example.

Look at the chart at http://www.visitmyharbour.com/viewchart.asp?chart=50B10B0D65F757823 and you will see a drying height of 1.1metres marked adjacent to the buoyed channel inshore of St Helens Fort

Suppose you have decided the minimum safe depth of water for your boat is 1.5 metres. 1.1+ 1.5 = 2.6. you will therefore need a minimum height of tide (ie above chart datum) of 2.6 m

Now look at the tidal curve for today, 22 Aug, (cut here from the UKHO Easy Tide website)

Tidalcalc.jpg


Draw a line across the curve at 2.6m. You will see that it intersects the curve just before 1300 hours and a little after 2000 hours ( GMT)

You will have more than 1.5 m depth over the shallow bit between those times.

HW time is 16:16 so that corresponds to a little earlier than 3 hours before HW to a little later than 3¾ hours after HW.

Obviously rework for the day you are interested in and for your boat's draught.
Allow a bit extra safety margin if the barometer is high or in rough weather
 
VicS said:
To set aside all the waffle I have worked through an example.

Look at the chart at http://www.visitmyharbour.com/viewchart.asp?chart=50B10B0D65F757823 and you will see a drying height of 1.1metres marked adjacent to the buoyed channel inshore of St Helens Fort

Suppose you have decided the minimum safe depth of water for your boat is 1.5 metres. 1.1+ 1.5 = 2.6. you will therefore need a minimum height of tide (ie above chart datum) of 2.6 m

Now look at the tidal curve for today, 22 Aug, (cut here from the UKHO Easy Tide website)

Tidalcalc.jpg


Draw a line across the curve at 2.6m. You will see that it intersects the curve just before 1300 hours and a little after 2000 hours ( GMT)

You will have more than 1.5 m depth over the shallow bit between those times.

HW time is 16:16 so that corresponds to a little earlier than 3 hours before HW to a little later than 3¾ hours after HW.

Obviously rework for the day you are interested in and for your boat's draught.
Allow a bit extra safety margin if the barometer is high or in rough weather
Click to expand...

thats easy to understand...much appreciated. My boat has a 1m draught with the drive down so I can adapt this accordingly.
 
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