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Air Draft


Afishionado
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35 years of boating in Poole Harbour and I have never noticed if there is a hight (overhead clearance) gauge on Poole Bridge.

 

I have been going over the specs of the new boat and see that it has an air draft of 7' 6" (without a radar bridge or radio aerial sticking up). Having chortled in times past at motor cruisers gingerly approaching the closed bridge whilst I slid underneath in whatever I was in, I realise now that I will be in the same boat (no pun intended wink.gif )

When I had the big Romany in the 70's I had to wait untill the bridge opened because I had a mizzen mast and sail so I never looked for a gauge.

 

Does any one know? Or is it a phone the Harbour Masters office?

 

Mad Mike

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Mike, you need a couple of huge livebait tanks, and if you approach the bridge at high water, to fill them. Two cubic metres of sea water weighs a couple of ton, so imagine how much lower you would sit in the water!

 

Under the bridge at any time, no hassle!

 

Am just trying to work out how big a pair of tanks I might need....

 

Mike

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Mike, you need a couple of huge livebait tanks, and if you approach the bridge at high water, to fill them. Two cubic metres of sea water weighs a couple of ton, so imagine how much lower you would sit in the water!

 

Under the bridge at any time, no hassle!

 

Am just trying to work out how big a pair of tanks I might need....

 

Mike

Don't laugh, I had already thought up a scheme and was planning to patent it!! A sorta floodable space between a double skin and then an HP air system to blow it out.

 

Flood Q Dive off klaxon dive dive dive

 

Arooga! arooga! arooga!

 

Mad Mike

Edited by Afishionado
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A whole new discipline to apply then! sad.gif

 

 

So someone check that I have this right please.

If I was comeing back in and the tide chart showed a hight of say 1.5 meters at that time, I would add my air draft of 2.3 meters and get a total of 3.8 meters.

Then add together the bridge clearance of 2.1m and the HAT which I am guessing is 2.1 m as well, this gives me a total of 4.2 m. Therefore I will have an expected clearance of .4 Meter?

 

Mad Mike

 

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What you need Mike ,is the same device as Andy has. It's called a Jack [or Dad ].

 

You get it to stand on a side rail with the top of it's head at the same height as the GRP mast. [which is the highest point on the Arvor.

You then approach what appears to be the lowest point of the bridge,normally between the steel beams,at a good lick !!

If your Jack screams at the last minute,you don't have enough room.!.!.!..

 

Works for us.!.!...............jack laugh.gif

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i can hear the slintering of fiberglass aerials ohmy.gifohmy.gif

My long dead Uncle who was in HM Submarines during the war told a terrifing tale of when he was a sub lieutenant on his first tour. First I must explain that 'Q' is the emergency dive or rise chamber, flood 'Q' and you go down like a stone.

So there he is on his first patrol with a couple of look outs and the first officer all standing in the conning tower as the boat was on the surface running on diesels and charging the batteries.

Suddenly one of the lookout shouts "Aircraft bearing 150" or whatever and in a flash the first officer yells "Flood Q! Dive off klaxon" he punches a big red button and from below comes the sound of someone shouting "Dive Dive Dive" at the same time as the klaxon horn going off at full volume. Apparantly all of that took about 2 seconds and there was Uncle Barry on his own in the conning tower with the sub already awash and tilting down. He froze for a second then with water flooding in through the scuppers of the conning tower he jumped feet first down the hatch and as he was closing the hatch water was flooding in over him.

 

What a way to spend a war as they used to say.

 

Mad Mike

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I believe there is a gauge (white board) on the bridge pillar to the south when approaching upstream that shows clearance in metres. It looks as if it's had a bash so might be worth checking it's accuracy before relying on it. I presume this would be lowest clearance as you can squeeze between the girders and get another .5 metre or so.

Failing that you can call Port Control who should be able to tell you the air height under the bridge.

 

Rich.

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  • 2 weeks later...

I find it hard to believe that anyone would accelerate to pass under a bridge, on a cruise ship with a pilot onboard. but then again I would not have believed Freds incident if it were not on film.

 

imagine the incident report to the MCA

we just clipped the bridge ???

 

Charlie

 

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