Tolerance on Bridge Heights

[PEJ]

Can any one tell me are the quoted bridge heights a worst case scenario when the river is a bit full or the maximum when the river is low?

I am thinking about moving a boat that is quoted as 4.04m high (13ft 3in) to the Thames. Windsor Bridge is quoted at 13ft 2in.

Do you think I would get under it in normal conditions?

 

[LimL]

Probably not!

My experience is that the quoted bridge heights can't be relied on to the degree of accuracy that you mention. As well as this, the river levels seem to vary +/- 15 cm quite commonly, and aren't necessarily at their lowest level in low flow conditions.

If your boat can squeeze under Windsor, it won't be able to go under the footbridge above Cookham Lock, which is a lot lower, and one of two bridges on the river where I usually lower my mast.

Of course the shape of the bridge is a factor too. At Windsor (and Cookham Lock Cut) the bridge is rounded so your positioning is critical.

 

[TrueBlue]

It's not been unknown

for the lockies to open the taps a bit - unofficially, you understand - to drop the level a smidge.
That would actually work quite well at Romney as it's a girt big lock and if he raises the sluices fully on an empty lock in summer conditions, the reach above might drop a bit for a moment or two.

Seriously, the levels do go up and down quite a bit. There's the concept of "winter" and "summer" levels with a variation of 6 - 8 inches between the two.

F'rinstance going out in the middle of the recent dry patch, I noticed that in some reaches I could moor in places normally only accessible out of season. My unscientific assumption was that EA were holding back the waters as much as possible in case they ran out later - if you see what I mean..

There's some Art in managing the flow; OK EA have level monitors everywhere but moving the water around still relies on the lockkeepers winding the odd weir gate and "Ring and Brymer" (as I call them) on the Upper-Upper-Thames locks.

That's why a resident lockie is so important.

 

[ADLS]

Why I wonder don't the EA fit river level height boards to all the bridges as in Holland? Then we would know air draft clearance at any state of the flow.

 

[teddington_lock]

Bridge heights are all measured from headwater ( an imaginary mark , lets call it zero ) , typically locks run their reach a little above headwater to ensure there is enough water to satisfy demand ( abstraction , navigation , etc ) ...

For example at Teddington , we run ( in the summer ) at between 4 and 6 inches above headwater , so Teddington Lock Cut bridge that is quoted as having 18'6" clearance in actuality has about 18'2" to 18'0" clearance .

If you are in a lock where there is a low bridge after it , ask the lock keeper how much above headwater he is running and you will be able to work out if you will make it or not.

Good luck.

 

[oldgit]

Also helps.....

.......if the boat is full to the brim with fuel/water/junk and people.
We recently took to a Fairline Brava with radar arch in situ under Windsor Bridge with only a smudge of light blue paint on the arch to mark the transit.
Crept up to bridge and then just pulled the boat through manually.

 

[PEJ]

Thanks

Good advice, thanks everyone.

I did not realise that the water level was so much higher than you would expect.

So I guess you had better allow at least 8 inches on top of your air draught to be sure of getting under.

 

[ADLS]

A little trick shown me by a Dutchman is to have a cheap pole that's the airdraft height, suitable knotched for easy break fitted in the jackstaff socket. The pole will easly break if you happen to touch th bridge without causing damage to the boat.

 

[Andrew_Fanner]

You may want to be cautios at Old Windsor before worrying baout Windsor itself. If you creep under OW you still may not fit Windsor.