Depths at Bradwell Entrance

[Maxi Windsong]

We had a great sail down from Harwich on Sunday afternoon (5th May) and headed up the Blackwater and in to Bradwell. Arriving earlier than we expected we waited outside the entrance, with quite a few others, for the tide to rise sufficiently for us to go in through the entrance channel. The excellent ECP/ECS/CTE chartlet shows a least depth of 0.3 metres and being cautious we waited until around 17.40BST to head in. Our Belfield Tide Plotter software was showing that we would have around 2.25 metres of tide then, and as we draw a nominal 1.87 metres, so maybe 1.95 when loaded(?), I expected to have depth to spare.

In fact we ran gently aground opposite the second orange buoy in from the cardinal exactly where the chartlet shows the least depth, the depth below the keel having showed zero for at least 50 metres before we stopped. We were almost exactly in the middle of the channel between the buoys and withys (? spelling) and Mrs Maxi Windsong did point out that other boats seemed to be going closer to the withys. We waited a couple of minutes, mainly to let two boats coming out go past us, then put a bit more power on and slid forward into the "deeper" water - congratulating ourselves that we had in fact, by luck, timed our entry perfectly.

I would like to figure out why we got it wrong however. It seems to me that there are several possibilities. Either (1) the depth in the entrance is much less than when the chartlet was surveyed, but it seems unlikely that it is 0.5m less, or (2) the atmospheric pressure on Sunday was so high that it held the tide down - I did not check the barometer at the time (or at all on Sunday) but again a 0.5 metre effect seems unlikely, or (3) the Belfield software is inaccurate, or (4) most likely I read Belfield tide curve wrongly. Writing this now I realise that I should recheck that it does show BST automatically - I was "certain" that it did, but don't have it installed on this PC to check.

So why did I get it wrong? Is the depth going into Bradwell much less this year or can anyone point out an obvious mistake I have missed?

(PS: I know the chartlet shows deeper water to the East of the marked channel, but I just can't bring myself to try that out - and neither did anyone else who we saw going in or out)

 

[MoodySabre]

Four hours before HW is a bit optimistic with that draught. I draw 1.7m and 3hrs40 before has been my best effort without ploughing. That was by going outside the cans over by the white mooring buoys - hold your nerve and it works!

They have just finished dredging the marina and they pump the silt out over the island and the shallow bit in the creek is just the extension of that corner of the island. I don't think that they have dredged the creek this year yet (hopeful 'yet'). If you can make the third can in then all is well as you found out. The dredged bit in the creek was about 10ft inside the cans - it will be shallower by the withies.

I haven't had enough runs out lately to see if it is much different from previously.

Belfield is in BST. I think you did well getting in that early.

 

[Athene V30]

I tried to go into Bradwell on Saturday afternoon 1 hour after LW on a local LW of 1.4m (easytide data) - I need 1.4m so theoretically I should have had 0.3m spare but went aground gracefully in a similar spot. Yes pressure was high so this would have had an impact but not to the extent I experienced.

The channel has silted up and I don't think the deeper water that was to the east of the port hand buoys is there anymore. 2 local fishing boats passed me when I was sitting on mud over towards the witheys.

I got in about 2 hours after LW.

 

[tillergirl]

I'll maybe have a go at refreshing the data on Springs at the end of the month. Last time I was chatting about the entrance with the Marina people, there was a fear that the opening of the seawall just up the Blackwater and the partial removal of the baffle wall would lead to more silting and/or a change in the channel position. Before the baffle wall, all the old sketches of the Creek put the best water in the middle of the Creek just outside the line of white mooring buoys where my chart showed that marginally there was a little more water.

The advice to go close to the withies applied up to a couple of years ago but at the time of surveying for the chart was definitely out of date with the 'best' water (best being used in the most optimistic context you can imagine) being in the middle of the marked channel. It is certainly soft though and I have found more than a few times that I can power through it. I can see that being quite a useful thing for us to do!

 

[MoodySabre]

It is certainly soft though and I have found more than a few times that I can power through it. I can see that being quite a useful thing for us to do!

Particularly on the way out!

 

[tillergirl]

Yeah. We ought to all get there on the bottom of the ebb and go ploughing. Actually that's probably not as daft as it sounds.

 

[Lucky Duck]

We had a great sail down from Harwich on Sunday afternoon (5th May) and headed up the Blackwater and in to Bradwell. Arriving earlier than we expected we waited outside the entrance, with quite a few others, for the tide to rise sufficiently for us to go in through the entrance channel. The excellent ECP/ECS/CTE chartlet shows a least depth of 0.3 metres and being cautious we waited until around 17.40BST to head in. Our Belfield Tide Plotter software was showing that we would have around 2.25 metres of tide then, and as we draw a nominal 1.87 metres, so maybe 1.95 when loaded(?), I expected to have depth to spare.

In fact we ran gently aground opposite the second orange buoy in from the cardinal exactly where the chartlet shows the least depth, the depth below the keel having showed zero for at least 50 metres before we stopped. We were almost exactly in the middle of the channel between the buoys and withys (? spelling) and Mrs Maxi Windsong did point out that other boats seemed to be going closer to the withys. We waited a couple of minutes, mainly to let two boats coming out go past us, then put a bit more power on and slid forward into the "deeper" water - congratulating ourselves that we had in fact, by luck, timed our entry perfectly.

I would like to figure out why we got it wrong however. It seems to me that there are several possibilities. Either (1) the depth in the entrance is much less than when the chartlet was surveyed, but it seems unlikely that it is 0.5m less, or (2) the atmospheric pressure on Sunday was so high that it held the tide down - I did not check the barometer at the time (or at all on Sunday) but again a 0.5 metre effect seems unlikely, or (3) the Belfield software is inaccurate, or (4) most likely I read Belfield tide curve wrongly. Writing this now I realise that I should recheck that it does show BST automatically - I was "certain" that it did, but don't have it installed on this PC to check.

So why did I get it wrong? Is the depth going into Bradwell much less this year or can anyone point out an obvious mistake I have missed?

(PS: I know the chartlet shows deeper water to the East of the marked channel, but I just can't bring myself to try that out - and neither did anyone else who we saw going in or out)

Intriguing - I came into Bradwell not long after you and don't recall having anything less than 0.6m under the keel, maybe one of us was lucky/unlucky with our approaches?

 

[tillergirl]

Maxi Windsong

I've had a look at the actual tide gauge data which shows that the recorded low water at Sheerness on 5th May was 1.274 instead of the predicted 1.7 (prediction from Meridian - not sure what Belfield shows for Sheerness). Doing a crude bit of extrapolation, the best height of tide you could expect would therefore have been 1.81m at 1740BST. OK that should have given you 2.1m of water over that low patch but I stress I have done a quick bit of mental sums rather than a precise calculation and it makes all sorts of assumptions such as the LW curve at Bradwell is nice and uniform - which personally I have some reservations about. In my early goes at collecting data I found it very hard to get some sense out of soundings taken towards low water.

But I would suggest that in fact there was significantly less water at the bottom of the tide than you might have expected through the predictions courtesy of that nice weather plus of course, the winter months may have silted up a little.

So you made no 'mistake' other than to avoid factoring in the barometric pressure - which, hey, didn't harm you.

Accuracy of Belfield? I have found differences of over half an hour between Belfield and other data sources at various places and variations in the predicted heights. I can find a source on the web that says low water at Sheerness was predicted at 1.3 rather than the 1.7 that Meridian is giving me. I think the lesson is that these are just predictions which is why my charts are always reduced to a datum based upon actual data.

 

[MoodySabre]

Yeah. We ought to all get there on the bottom of the ebb and go ploughing. Actually that's probably not as daft as it sounds.

The marina have a dredging rake for this job. Getting them to use it is not so easy! Or reinstate the depth gauge on the cardinal which has been in the workshop for the past year. We do have refurbished loos and showers though and only three years after they promised. One day..........

 

[tillergirl]

The trouble is they are supposed to get permission to use the rake from the EA or someone. I get the impression it gets all sorts of people down to the marina that they don't like (for one reason or another - just an impression)!

 

[Maxi Windsong]

tillergirl,

Thanks for cross checking the actual tide data - it is a great reminder that tide tables and curves are only predictions.

Simon14b's comments are intriguing, as he says, since I believe that we have identical boats (Maxi 1050), so it would seem that precise choice of route through the channel also made a difference.

Thanks for the responses - very interesting

 

[Ianqv]

Four hours before HW is a bit optimistic with that draught. I draw 1.7m and 3hrs40 before has been my best effort without ploughing. That was by going outside the cans over by the white mooring buoys - hold your nerve and it works!

They have just finished dredging the marina and they pump the silt out over the island and the shallow bit in the creek is just the extension of that corner of the island. I don't think that they have dredged the creek this year yet (hopeful 'yet'). If you can make the third can in then all is well as you found out. The dredged bit in the creek was about 10ft inside the cans - it will be shallower by the withies.

I haven't had enough runs out lately to see if it is much different from previously.

Belfield is in BST. I think you did well getting in that early.

Roger is bang on.... with that draft, 4 hours before is "hopeful" at best!!

If Bradwell won't fit the tide gauge back up, can we???
I don't mind spending some time painting it up. and then a dingy raid to "nail" it to the post!!

 

[meandraft]

We arrived at Bradwell just before 5.00pm on Sunday. As usual there was less water than predicted so we needed the keel halfway up to get in. Even going through the creek there were some shallow spots. Usual life at Bradwell I'm afriad.