Portsmouth Inner Swashway

Ruffles

Ruffles

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26 Feb 2004
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Boat: Portsmouth, Us: Stewkley
www.soulbury.demon.co.uk
Used it once - following a bigger boat - but seen people aground on it a couple of times. Usually use the Outer Swashway but always feel I'm being a bit timid, especially when the ferry cuts inside me!

If you're heading out how do you know there's enough water? The chart seems to show fairly consistent depth. Is there a tide gauge or a rule of thumb I should know about??
 
Re: Portsmouth Inner Swatchway

depends on your depth.... I only use it roughly 2 hours either side of HW.. normally have a quick glance at a tidal curve first then tend to line the three yellow racing cans up... we draw 2.1 metres
 
Just check your draft, the tidal height and the bearing that takes you through the deeper channel and you'll be fine.

Check you depth on the way over and if you are coming out of the deeper chanel you'll see the depth come up.

Beware of the drying areas just south of the post tha marks the inner swashway at low tides.

Good luck

Jim
 
Re: Portsmouth Inner Swatchway

We draw one and a half.

I tend to forget to check the book before setting off - and it's not the place to be calculating depths underway on a Saturday morning. The traffic can be scary!

Which was why I'm after a rule of thumb. I guess I could go for 3 hours either side of HW. Or even 3 hours before and 2 hours after to minimise the consequences of getting it wrong /forums/images/graemlins/wink.gif
 
Re: Portsmouth Inner Swatchway

we've used it a number of times this season, don't recall the tide heights though, but we do draw 6' ! I know we entered at around midnight on the night of the Cowes fireworks ... never had a depth problem .. also went back out around 10 the next morning....

The tides were:

Fri 10th
15:51 1.7m
22:49 4.1m

Sat 11th
04:18 1.4m
11:28 4.2m

So we went through at 1hr after HW on Fri night and back 2hr before HW on Sat.. ... more by accident than design!
 
My boat draws 1.5 metres and I use the Inner Swashway when the height of tide is 3 metres or above. Haven't run aground yet but I have probably wasted time going the long way round when I needn't have. However I seem to remember the chart is marked "Obstructions" in that area so I am not really tempted to reduce my safety margin without knowing what they are and where they are.
 
I used in the days when I moored in Portsmouth but with a draft less that half of yours my experiences are not really relevant. The hazard in those far off days were the IOW ferries using it around HW!

If I can make a practical suggestion, why not run through there one day when you are confident about it being Ok and keep an eye on the depth sounder. Make a note of the least depth you find (and the time) then at your leisure you can compare what you find with the predicted tidal height (maybe even comparing that with the heights recorded at Chimet or Bramblemet) That should then enable you to work out a minimum safe height of tide for your boat. All good evening class stuff.

Does the tide gauge show depth or tidal height. You need to know that.
 
[ QUOTE ]
Just noticed there's a tide gauge on one of the posts in the entrance. Must have been too busy avoiding other boats to notice it...



[/ QUOTE ]

I came in through the entrance just after lunch on the afternoon of Saturday September 1st. (LW 0805/0.63m, HW 1526/5.12m). I had plenty of opportunity to notice it that day, having spent a long time next to it!
 
Image1-1.jpg
 
A useful guide that I use is the platform that the harbour entrance mark sits on - the triangular mark on the shore closest to the new red pile off Dolphin. If it is just awash, there is about 2.5 metres of clearance in the inner swashway. I have sailed through at 2.01 metres draft with a good 50 cms showing and just made it through. You can then look up tides time to get your approximation of what works for you.

Just in case, no guarantees on this as it depends on which route you take through the inner swashway cause depths vary. I use it cause it works, but you'll need to exercise your own judgement on your depths and ability to stick to the channel.
 
As a rule of thumb (and from memory) Portsmouth Lowest Astronomical Tide is about 0.8m and of course a height this low is rare (although I don't have any tables to hand so may be proved wrong!). Therefore, using the chart provided by Aidy, turning right on leaving the entrance and keeping the racing marks in transit until you reach the first one you are going to be pretty unlucky to hit the mud unless, as usual, the world and his wife are going in and out of the harbour with massive wakes or you are bang on low water springs in October!
Notwithstanding the survey quality (look at the Source Data Diagram on any Admiralty chart - 1850's by Capt Cook and a leadline or 1970's onwards with sidescan sonar) the obstructions would be marked by a further sounding if significantly different to the surrounding seabed. They exist merely to deter the ill-advised anchorer.
 
[ QUOTE ]
As a rule of thumb (and from memory) Portsmouth Lowest Astronomical Tide is about 0.8m and of course a height this low is rare (although I don't have any tables to hand so may be proved wrong!).

[/ QUOTE ]

Well, by the chart in the Haslar marina brochure /forums/images/graemlins/wink.gif, the CD is around 0.5m. So with my draft of 1.5m I can easily make up the 20cm shortfall by taking a run at it. SWMBO has ploughed deeper furrows than that without noticing.

rb_stretch, that's very useful.

Please wave at me as you go by....
 
[ QUOTE ]
As a rule of thumb (and from memory) Portsmouth Lowest Astronomical Tide is about 0.8m and of course a height this low is rare (although I don't have any tables to hand so may be proved wrong!).

[/ QUOTE ] LAT portsmouth is in fact 0.15m. But the next time it goes that low is 21 march 2015. Consider your self proved wrong. /forums/images/graemlins/wink.gif (Never quote anything from memory or some smart arse will tell you how wrong you are)

See here
 
/forums/images/graemlins/confused.gif /forums/images/graemlins/grin.gif
oh well

/forums/images/graemlins/laugh.gif
 
Hi
There is a tide guage just off Dolphin. It is pretty well right for the inner swashway. The proper Admiralty chart for POmpey defines the transit for the swashway. When leaving the harbour pass between Dolphin and the red pole. Then head for midway between the first yellow buoy and the big spire at Ryde. Keep your sounder going to see what is going on. As soon as you leave the channel the bottom comes up fast.
 
[ QUOTE ]
Chart Datum and LAT - wildly (ish) different things!

[/ QUOTE ] I thought that Chart Datum was defined as LAT. At least for British Admiralty charts.

Or are you still using old "fathom charts" that used MLWS?
 
Rule of thumb I use is max of 2hrs either side of high water, might be a bit conservative but I would rather be safe than sorry and it does`nt add that much time to take the outer route.
 
[ QUOTE ]
A useful guide that I use is the platform that the harbour entrance mark sits on - the triangular mark on the shore closest to the new red pile off Dolphin. If it is just awash, there is about 2.5 metres of clearance in the inner swashway. I have sailed through at 2.01 metres draft with a good 50 cms showing and just made it through. You can then look up tides time to get your approximation of what works for you.

Just in case, no guarantees on this as it depends on which route you take through the inner swashway cause depths vary. I use it cause it works, but you'll need to exercise your own judgement on your depths and ability to stick to the channel.

[/ QUOTE ]

I use that shelf as a guide as well, we draw 1.8m and this can be well uncovered and we can still use the swatchway without problems.
hether we do or not rather depends on the conditions, if there is East in the wind or a swell then I am more cautious. IMHO the shallowest part of the swatchway is at the Gillkicker end
 
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