Bembridge - why don't the move the channel?

[Angele]

http://heartburnentertainmentworldwide.com/international/isle-of-wight/isle-of-wight-stilt-walkers/

Out of interest, I was keeping an eye today on the tide reading on the Bembridge website and comparing that to the Bramblemet reading and the actual HW readings for Portsmouth from http://www.ntslf.org/data/realtime?port=Portsmouth:

The 13:45 (BST) reading at Portsmouth of 4.98m was in line with the prediction on the ntslf graph (but very slightly below the Easytide prediction of 5.10m at 13:23).

At 13:45 the Bramblemet reading was 4.75m and the Bembridge website showed 4.38m.

Whilst I'm sure Bembridge doesn't have a tape measure located precisely at the bar, and that rather (I assume) the height displayed on the website is derived from the height at the St Helen's tide gauge, this might give a useful guide for how the three values currently compare.

 

[prv]

I've been staggered how good Google maps are for finding the deep bit of muddy creeks.

In this case it was to look for uncharted landmarks to help distinguish between several barren headlands and find a tucked-away harbour mouth. In those waters the relative orientation of the land and the little boat on the plotter is unreliable, because some of the islands are known to be charted in incorrect positions from 19th century surveys. A windfarm that should have been an ideal landmark was shown by Navionics (them again!) in completely the wrong place...

Pete

 

[DJE]

Bembridge internet tide gauge agrees well with Easy Tide predictions for Bembridge Approaches with a drying height of 0.8m. I've crossed the bar twice this year when the gauge was showing 0.3m under keel and it was spot on.

 

[Garold]

The Bembridge fishermen and locals often seem to cut south of the fort.

Never had the confidence myself

Garold

 

[BelleSerene]

The 13:45 (BST) reading at Portsmouth of 4.98m was in line with the prediction on the ntslf graph (but very slightly below the Easytide prediction of 5.10m at 13:23).

At 13:45 the Bramblemet reading was 4.75m and the Bembridge website showed 4.38m.

Whilst I'm sure Bembridge doesn't have a tape measure located precisely at the bar, and that rather (I assume) the height displayed on the website is derived from the height at the St Helen's tide gauge, this might give a useful guide for how the three values currently compare.

I think you're accidentally comparing apples with pears there.

The Bembridge website predictions are for inside the harbour, beside the marina. They're cf chart datum. You'll find that location called 'Bembridge harbour' in an almanac.

But the heights you're talking about are outside the harbour! They're shown in an almanac as 'Bembridge approaches'. The two heights are not even close: today for example (at Springs) the difference between them was 2m at HW (Portsmouth +1.0m vs Portsmouth -1.0m) and 1.6m at LW (Pmth + 0.1m vs Pmth - 1.5m).

You're right that the height that's constantly updated on their website refers to the St Helens tidal gauge (ie for the harbour approaches). But that, just as the physical tidal gauge, shows the height of water over the bar, not over Chart Datum.

So to compare that gauge height with the CD height that you calculate from your boat, or which Bramblemet shows, is to confuse the height over the Bembridge bar with the same height over CD. And to compare it with the predictions for Bembridge harbour (from their website or from elsewhere) is to confuse the outside height over the bar with the inside height over CD. There's a big error, which changes with the height of tide, and it's easily enough to sink you!

 

[DJE]

So to compare that gauge height with the CD height that you calculate from your boat, or which Bramblemet shows, is to confuse the height over the Bembridge bar with the same height over CD. And to compare it with the predictions for Bembridge harbour (from their website or from elsewhere) is to confuse the outside height over the bar with the inside height over CD. There's a big error, which changes with the height of tide, and it's easily enough to sink you!

Also there is quite a marked difference in tidal range on the same day between East, Central and West Solent. A 4m range at Portsmouth is a 2m range at Yarmouth for example. So Bramblemet is of limited use for assessing Bembridge tides.

 

[Topcat47]

The Bembridge fishermen and locals often seem to cut south of the fort.

Never had the confidence myself

Garold

It all depends on the draft of your vessel and the height of the tide. Few Bembridge fishing boats draw much more than a couple of feet. Snark draws closer to six and even a Centaur draws more than three.

 

[VicS]

The Bembridge fishermen and locals often seem to cut south of the fort.

Never had the confidence myself

Garold

IIRC the entrance channel was to the east of the fort at one time.. It was shown like this on the first Solent chart I bought.

I dont know when it was changed. (Mid 1970s ??? but before my first visit in 1979 or thereabouts.)

Some time later the spoil from some dredging in the harbour was dumped roughly where the old channel had bee,n effectively closing it except to people with local knowledge

 

[derekgillard]

Am I missing something here ?
As a regular visitor to Bembridge I always used my own calculations
, however I now cross check with the height over the bar data from their web site and its in my opinion very accurate so if it says I have .5m clearance and that makes sense I go
It's the water over the bar I want to know once over I'm in and safe full and final

 

[Angele]

Am I missing something here ?

Yes, you are.

The OP was observing that, on the latest Navionics chart (which the Bembridge website links to), there appears to be an approach channel south of St Helen's Fort that is entirely below datum - i.e. at least 60cm (probably more like 80cm) more water than sticking to the buoyed channel.

It may well be a work of fiction.....

 

[Mark-1]

The OP was observing that, on the latest Navionics chart (which the Bembridge website links to), there appears to be an approach channel south of St Helen's Fort that is entirely below datum - i.e. at least 60cm (probably more like 80cm) more water than sticking to the buoyed channel.

In a nutshell.

It may well be a work of fiction.....

It might well be...

 

[dom]

In fact zoom right in and it would seem that keeping fairly close to the red buoy in that picture is indeed the optimal channel -- the only place where an intimate cooling experience exists close to equinoctial springs

 

[Mark-1]

In fact zoom right in and it would seem that keeping fairly close to the red buoy in that picture is indeed the optimal channel

Yeah, but I don't blame them for not completely rebouying the Channel to the South of the Fort for those few inches. Especially since most of their trade will come from North or East. I would have thought it *would* be tempting to re-bouy it to get an extra half a metre or perhaps nearly a metre, unless there were other factors in play which there obviously would be.

the only place where an intimate cooling experience exists close to equinoctial springs

I had to think about this for a scarily long time before I realized what you meant. You have invented the patent "scrotum thermo harbour bar depth gauge", congratulations.

 

[Boathook]

http://www.teamsurv.eu/Data/Display/tabid/75/language/en-GB/Default.aspx

Lots of data here about tracks and depths.

 

[Ruffles]

I'm most appreciative of the green and red reflective tape on the channel buoys. Off the entrance on a dark night you can shine a torch and pick the buoys out two or three gates in advance. Very reassuring when you're single handed on a falling tide!

 

[Angele]

http://www.teamsurv.eu/Data/Display/tabid/75/language/en-GB/Default.aspx

Lots of data here about tracks and depths.

Is that the data that Navionics uses to update its charts? Zooming right in, I can see that precisely none of them attempted to enter Bembridge from south of St Helen's Fort - so how would that be of any use in working out the depths there (and amending the chart accordingly)?

 

[dom]

Is that the data that Navionics uses to update its charts? Zooming right in, I can see that precisely none of them attempted to enter Bembridge from south of St Helen's Fort - so how would that be of any use in working out the depths there (and amending the chart accordingly)?

Navionics clearly need a new creative artist. After all fifteenth and sixteenth century explorers adorned areas of unexplained ship founderings with ornate and wonderful sea monsters ...perhaps one is currently living on the south side of St Helens Fort and that's why none of the locals enter?

As for the odd faux channel here and there -- that's nothing. When presented with embarrassingly large unexplored areas our early seaborne ancestors simply made up entire islands replete with towns, mountain ranges, bays, peninsulas, and little sub-islands! ...think of the mythical Atlantic island of Frisland.

I'd personally welcome a bit more va va voom on the oh-so-boring vector charts and as good a starting point as any would be the 'Crazed Wheelie-Bin Zombies' in Newport

 

[Angele]

I'd personally welcome a bit more va va voom on the oh-so-boring vector charts and as good a starting point as any would be the 'Crazed Wheelie-Bin Zombies' in Newport

If we ask him nicely enough, do you think our own Seajet could be persuaded to get a job at Navionics to spice up some of their chart corrections? No more boring drying patches or deep water channels, but properly useful information like that.

Google "Crazed Wheelie-bin zombies of Newport". First hit is a waste recycling page on Newport Council's website (apparently the words "crazed" and "zombies" are absent from that page), but the second hit is to this esteemed forum and a quote by our very own snail.

 

[Seajet]

Thanks for the thought !

Unlike Newport, I don't think there's much negative to say about Bembridge; though my elderly father injured himself quite badly falling at the deep unmarked step from the grass onto the road, just near the Duver - apparently the National Trust won't allow a white mark or something sensible...