Delta

Yes, thanks for that, it will/may be interesting to see what results I can get, as the laser beams form a circleof dots on the target and so some will fall on and some between any projections but should be esily visible around dusk. Realistically, I am only interested in how close to 35 or so feet it is, in the middle, so as to ascertain wehether or not there is any safety margin or whether the published height is actually given as the lowest point on the span which would be at the supports at each end. I have probably discounted attempting to travel with my masts fixed now but the question will not go away until I have had at least a good attempt at checking the height for myself. A single laser beam could be more accurate but I am not aware if there is a convenient source of such a calibrated item outside the military, scientific or surveying communities. It would not be likely to be affordable anyway.

45 degrees was an illustration not a practical proposition and my rudder would not be out of the water the 71& is not 71% shorter it would be 71% of the height of the mast but no matter. Anyway, I now have the use of a laser measure now so I just need a lift to get me under the bridge or I may have to get my old slalom kayak out again... or deflate the dinghy and launch nearby but it does not have a licence these days so no go.

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

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...

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.

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!

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...

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?

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.