Bridge squatting and the QE2

[dave1dpc]

I have moored my small flybridge upstream of the hamble river road bridge for over 20yrs. My boat just clears the arch if you keep to the middle on HWS which always seems to coincide with about noon on saturdays . Given there is a double stand at these times this can last a couple of hours. If you transit at dead low speed i only have less than 6 inches to spare but using a stab on two on the bow thruster i can keep the bow pointing forwards in the center of the arch. Should i FLOOR the throttles the instant SQUAT caused will result in an extra at least another foot of clearance, The extra wash produced is contained within the bridge structure but am mindful not to exceed the speed limit exiting the other side. I have only once lost a riding light but going by the marks under the concrete arch i was not the first or will be last to stray off center. I remember being told that the old Sealine brokerage that for many years was just up stream of the bridge [remember Jack's office in the old Howards Way ?] had sometimes to squat their largest boats at Low water neaps . It was due to this squatting effect that caused the QE2 to ground at speed in a chartered passage near Nantucket island of the east coast of the USA.

 

[jfm]

I think they are different things. The QE2's famous squat was a steady-state phenomenon arsing from the combination of high speed/a large flat bottom/ shallow water.

The squat that I think you're talking about is a dynamic state effect as you floor the throttle. In the steady-state a planing boat generally has negative squat (ie lift) as it planes, compared with when it's stopped, except in some boats right at the stern.

In your case, you could get up earlier and transit the bridge at 9am rather than noon

 

[benjenbav]

Every other Saturday you could still transit the bridge at noon…

 

[Seastoke]

As you get older and richer , you should have moved below the river bridge.

 

[dave1dpc]

As you get older and richer , you should have moved below the river bridge.

In the 25 years plus i have moored in a marina upstream of the bridge i have saved at least 20%. At today prices i pay about £500 per month i.e £6000 per year. £1200. Could buy quite a few riding lights for that.

 

[jointventureII]

High air pressure and full tanks will make a difference too

 

[ylop]

on HWS which always seems to coincide with about noon on saturdays .

I have only once lost a riding light

I think I might know your problem!

Many, many years ago I was on a narrow boat which loaded dozens of jerry cans full of water in order to make it under some bridges. I don't recall why it was taller than other boats designed for the canal but I do remember my task as young teenager was to carry the jerry cans from the tap where they were being filled to the boat.

 

[Alicatt]

I think I might know your problem!

Many, many years ago I was on a narrow boat which loaded dozens of jerry cans full of water in order to make it under some bridges. I don't recall why it was taller than other boats designed for the canal but I do remember my task as young teenager was to carry the jerry cans from the tap where they were being filled to the boat.

There is a video on Youtube of someone doing that at a bridge on a canal in England, loaded up the boat with quite a few 45gallon drums and then started filling them with water to get under the bridge