Postwick Tide Gauge

[Delta]

I am trying to find an image or photo of the tide gauge at the Poswtick viaduct (A47) near Norwich.  I know the clearance is 35 ft +/- tide and I need to get a 36 ft mast under it so this is for a bit of forward planning. If anyone can assist me with info it would be very helpful.

[quo vadis]

Try one of these 

[ranworthbreeze]

10 minutes ago, Delta said:

I am trying to find an image or photo of the tide gauge at the Poswtick viaduct (A47) near Norwich.  I know the clearance is 35 ft +/- tide and I need to get a 36 ft mast under it so this is for a bit of forward planning. If anyone can assist me with info it would be very helpful.

Hello Delta,

There is a variation of 18 inches to 2 foot  ( or I should say there is on the other bridges going into Norwich).

Regards

Alan

[quo vadis]

Then you will need one of these 

[Delta]

The clearance of 35 ft is at HW Springs so low water is 2-3 ft leeway and the only option but I would still like to see the gauge before I travel from Gt Yarmouth.  Arriving before LW Springs to avoid any confusion.  I could always climb up the mast and have a look to see just how close it would be, or mount a little camera (eBay <£10) but I would still like to know what the gauge looks like.  Apparently there is a boat club/moorings nearby that it can be seen from? Perhaps I will have to drive up there an do a recce?

Edited June 30, 2016 by Delta
typos

[quo vadis]

Or this 

[BroadScot]

17 minutes ago, quo vadis said:

Then you will need one of these 

Errr a bit drastic !

[JawsOrca]

 to the forum from me.  

You could message the yacht club and see if someone can kindly run over and grab a picture for you. It certainly sounds like it's going to be tight (Have you included any wind equipment, ariel etc in your calculations?).. the tides are obviously affected by weather and I believe at present the tides are higher than expected due to all the rain..it may be one that needs lowering  good luck  

[Poppy]

There isn't a Club close to the Viaduct, but there is Griffin Marine, also the BA engineering base nearby.

[grendel]

does it appear in Robins video of his trip up to Norwich recently?

[Delta]

Thankyou to you all.  I will share my images in case a similar question is asked in the future.  The images were taken this morning 1st July and the level shown is 33 feet. I got some useful local knowledge from the ferryman too.  The river is high right now of course following the rain.  The images I have attached are what I was looking for. It was a reasonable day out too watching the antics of day hirers and their minor collisions from the Wroxham Hotel coffee lounge...

[Vaughan]

23 hours ago, quo vadis said:

Try one of these 

 

Hello Delta and welcome to the forum. Excuse our sense of humour, but we find it helps!

Perhaps the above is a practical suggestion!

Beware that in the off season the rise and fall is a lot more. It can be well over 3ft on spring tides, and depends a lot on the weather in the North Sea.

[JennyMorgan]

Delta, don't forget the burgee. I know to the inch my mast height and worked out that I could sail under the bridge on the New Cut at St Olaves. Under I went, without a care in the world, down came the burgee, neatly snapped off above the truck!

[Delta]

Thanks for the advice and warnings. The purpose of the trip would be to visit a yard for certain repairs over the winter period.  Obviously if the weather leading up to the spring tide was wet it would not work and the mast would have to be stepped elsewhere.  I may revisit with a tale of success or woe - we shall have to measure the mast more accurately but it will be a close run thing if ever we try it.  The gauges are sited on both sides of the viaduct and the photo here is of the upstream one so we still have to locate the important one downstream.  Churchill said that any plan was likely to be altered to achieve the objective, often at the last minute but that the planning exercise that led to Plan A was a most worthwhile activity, having a Plan B ready to go was critical.  I can already feel a Plan B coming on!

[JanetAnne]

Come on chaps, surely this is still how its done?

 

[ExSurveyor]

How blooming clever is that 

[Delta]

JanetAnne thanks for a Plan C.... I wonder what was in those bags.  Not sure he gained as much as 20 ft but impressive anyway.  Off to do some trigonometry to find out if the river is wide nough to lower mast far enough for average tides.

[Delta]

Interesting, as the sine of the angle is equal to the opposite over the hypotenuse, we could assume say 45 degree tilt. Sin 45 = 0.85. Mast height of 9.4m x sin 45 = 7.99 giving an extra 10 feet to play with.  So just need to check how to get the weights on the mast to stay put over the side - if it was ever tried that is and to prevent a colliision if it was going awry.  Not sure if they were poled out or held in place with a line from somewhere.  Doh! I will now have to watch it again...

[Delta]

OK done that, winching the weights in rights the boat but they must have to be added while the boat is tilted over soemhow? Not sure how much preparation that required but it was a good film of a well executed plan and not giving away the full story. Good old YouTube.  Thanks JanetAnne

[RayandCarole]

Looks like standard water bags, we use them to load test equipment offshore, they usually have a quick release dump system so if all goes t*ts up you can dump the weight.

you would also need fairly accurate stability information for your boat and a careful stability calculation to get the right amount of weight into the bags or you could end up in trouble 

Ray

[Vaughan]

This would be called careening, but i have never seen it done on the move!

Be careful of where you suspend the weight in relation to the standing rigging. If you hang it all off the masthead you will snap the mast. for this reason it is normally done off the jib halyard.

The weight will also increase as the boat heels owing to the change in shape of the hull in the water, and of the "metacentric height".

I don't think I would risk it myself.

[ranworthbreeze]

I have seen that video clip before some time ago, very interesting solution to a problem, I bet a lot of calculations were done before attempting it.

Regards

Alan

[JanetAnne]

There are a number of other clips on YouTube if you have a browse. They may offer different information.

Look on the bright side, if you fail you have saved the cost of the chain saw as mentioned above 

[JennyMorgan]

All in all there is one factor that we, the boating public have no control over and that is the accuracy of the height gauges. The great imponderable! Perhaps a sextant is the answer?

 

[Vaughan]

2 hours ago, JennyMorgan said:

Perhaps a sextant is the answer?

Who invented that thing he is using? Sir Francis Drake? He wasn't even letting the plumb line hang vertical. Probably at least 5 degrees out.

As Peter says, this needs a sextant which gives you an angle correct in degrees, minutes and seconds.