Bridge height

[Roger Madison]

While looking at a chart the other day I saw a fixed bridge height of 40 feet. My question is: Is the 40 foot height measured from mean high tide, or is it measured from mean low tide?



rjmadison@juno.com

[Marc]

Hi Roger,
It's the minimum height, so it's always high tide.

Marc

While looking at a chart the other day I saw a fixed bridge height of 40 feet. My question is: Is the 40 foot height measured from mean high tide, or is it measured from mean low tide?

adrenaline@vif.com

[Bill Goldsmith]

Vertical Clearance under fixed structures such as bridges or power cables are charted at Mean High Water, to ensure that clearances and heights are normally greater than the charted values. The MHW is averaged over 19 years. If the height of the tide is above MHW then the clearance is less. Many bridges have clearance guages, but be sure to do your own calculations and compare them both for a reality check.

Bill Goldsmith
CD27#173
Second Chance

While looking at a chart the other day I saw a fixed bridge height of 40 feet. My question is: Is the 40 foot height measured from mean high tide, or is it measured from mean low tide?

goldy@bestweb.net

[Joe Mac Phee]

Roger,

Bridge clearance shown on the NOAA charts is measured from mean high water (MHW). It is not a guaranteed minimum clearance since high water on a given day may be higher than MHW. A check of the tide tables will reveal the actual clearance on a specific date and time.

Joe Mac Phee
S/V Iolanthe
CD-30/K
Bristol RI



jvmacpheeNOSPAM@aol.com

[Marc]

Roger,
Look on your chart all the measurements are explain in it.

I just want to add...Do'nt forget to add at the lenght of your mast the height of your sailboat over the water line.
I saw last summer a guy with is mast lock in the bridge of St-Jean-sur-Richelieu(Quebec,Canada) who forget to do that.

Vertical Clearance under fixed structures such as bridges or power cables are charted at Mean High Water, to ensure that clearances and heights are normally greater than the charted values. The MHW is averaged over 19 years. If the height of the tide is above MHW then the clearance is less. Many bridges have clearance guages, but be sure to do your own calculations and compare them both for a reality check.

Bill Goldsmith
CD27#173
Second Chance

While looking at a chart the other day I saw a fixed bridge height of 40 feet. My question is: Is the 40 foot height measured from mean high tide, or is it measured from mean low tide?

adrenaline@vif.com

[Neil Gordon]

>>Is the 40 foot height measured from mean high tide, or is it measured from mean low tide?<<

It's measured from mean high tide. Depending on where you sail, that may be significantly more clearance than you'll find. In Boston, for example, tides two feet higher than the mean are routine. Also, subtract some extra from wind/storm surges and wave/wake action. And don't forget that mast height is the mast plus the distance from the waterline to the mast step. Oh... and watch for lights, antenna, etc.

My mast is 40 feet from the water line, plus antenna. Just to be safe, I use a working height of 45 feet.


Regards, Neil
s/v LIQUIDITY
Cape Dory 28 #167



neil@nrgordon.com

[michael phillips]

As in the Destin pass bridge and Brooks bridge in Ft Walton Beach are both "charted" at 50 foot but don't even think about anything over 48 and half! At least the Mid Bay Bridge, built about 9 years ago, is 65 foot and the Hathaway bridge near Panama City is being rebuilt to 65 so that boats with unclipped masts will be able to enjoy Choctawhatchee Bay soon.

-michael
s/v KAYLA
CD28 #318
Bluewater Bay, FL



michael@bbsc.com