Good morning does anyone have a recent height on the route 663 bridge in cape may? We are planning a trip and seem to be getting conflicting information. Any help is greatly appreciated!!
Cape may 663 bridge clearance
- Thread starter Cmp1110
- Start date
Not sure which bridge you are referencing, but Navionics says both fixed bridges are 55' clearance. That make it too close for comfort, I suppose. You can always go around.
Either way I have to go under at least one. There is some uncertainty at to the actual height some say 55 at high water some say 55 at low water.
I also use Navionics and spoke with uscg. Just checking for someone who has eyes on it or been thru this season.
I also use Navionics and spoke with uscg. Just checking for someone who has eyes on it or been thru this season.
We went under both bridges a couple of weeks ago at close to high tide. Our mast is 52' according to specs (haven't measured it) plus about 2.5' for the antenna and cleared with out touching.
How high is your mast?
How high is your mast?
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 23,341
The attached PDF has the Bridge Clearance Guide information from the USCG.
The convention is to give the minimum air gap. So Mean High Water is typically used.
Bridge heights, etc... from Bowditch:
335. Heights
The shoreline shown on charts is generally mean high
water. A light's height is usually reckoned from mean sea
level. The heights of overhanging obstructions (bridges,
power cables, etc.) are usually reckoned from mean high
water. A high water reference gives the mariner the minimum
clearance expected. Since heights are usually reckoned from high water
and depths from some form of low water, the reference levels
are seldom the same. Except where the range of tide is
very large, this is of little practical significance.
http://www.irbs.com/bowditch/pdf/chapt03.pdf
The convention is to give the minimum air gap. So Mean High Water is typically used.
Bridge heights, etc... from Bowditch:
335. Heights
The shoreline shown on charts is generally mean high
water. A light's height is usually reckoned from mean sea
level. The heights of overhanging obstructions (bridges,
power cables, etc.) are usually reckoned from mean high
water. A high water reference gives the mariner the minimum
clearance expected. Since heights are usually reckoned from high water
and depths from some form of low water, the reference levels
are seldom the same. Except where the range of tide is
very large, this is of little practical significance.
http://www.irbs.com/bowditch/pdf/chapt03.pdf
Specs say 52.5 w/o antenna. Do you recall what the boards read when you went thru?
Thanks for your reply
I went through there last week at close to high tide. I remember seeing the 52’ line on the board, and at least one tick mark below that. Unfortunately I can’t remember if it was more than one tick mark or just 1. I think at low tide you’d be ok though.
You will be fine going through at mid tide or lower. We're about the same height. The whip antenna is flexible, no harm if it touches.
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 23,341
Also known as a bridge feeler gauge alarm...
They make a painful sound
Metal-Impact-Hit-A1-www.fesliyanstudios.com.mp3
Why? The bridge hasn't moved in the 2 weeks since I went through it with a 52 foot mast.
Did you mean current or current? 
Just wondering if you meant current as in today or current as in how fast the water is flowing?
I'm not really understanding why the current bridge height would differ from the information on the charts. It's not like it has been re-constructed recently, has it? Sea level hasn't changed all that drastically has it?
Just wondering if you meant current as in today or current as in how fast the water is flowing? I'm not really understanding why the current bridge height would differ from the information on the charts. It's not like it has been re-constructed recently, has it? Sea level hasn't changed all that drastically has it?
When the bridges crossing the ICW were built some of the field engineering was off a little and the actual bridge height is not as it was supposed to be. Also, the height boards have been known to be off or so obscured with marine growth the height is not readable.Did you mean current or current?
I'm not really understanding why the current bridge height would differ from the information on the charts. It's not like it has been re-constructed recently, has it? Sea level hasn't changed all that drastically has it?
We went western bridge at 3:15 on June 10, 2022 and the eastern bridge a half hour later. On June 10 high tide was at 5:57 PM. So we know that the bridge clearance is at least 52' plus the height of a Metz whip antenna at mid tide. I would be anxious about trying to clear the bridges at high tide on a King Tide, but at mid tide or lower, not a problem.
Here's a link to my track if anyone feels the need to verify it.
So 52' plus antennae would seem to indicate that the chart listing at 55' vertical clearance seems to be a good reference. Saying that the field engineering was off is not an indication that the chart reference is inaccurate. I wonder what Navionics uses for their reference (aside from the mean high tide reference). If the "field engineering" is not accurate that may simply mean that the as-built doesn't exactly match the design (a common occurrence) but the as-built reference should be accurate (a more serious matter). Does Navionics use the as-built or do they have their own independent reference? (Surely they don't rely on the design calculation).
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 23,341
Not true Dave. You were correct for your experience.
What I intended to say was the boat owner must verify his own vertical air need. Verify it is 52 or 55 or 60 ft. What ever his boat actually is.
He should verify the tide level when he actually goes through the passage.
Your information is helpful information for others and accurate for your experience.
What I intended to say was the boat owner must verify his own vertical air need. Verify it is 52 or 55 or 60 ft. What ever his boat actually is.
He should verify the tide level when he actually goes through the passage.
Your information is helpful information for others and accurate for your experience.
Bridge heights on the chart are to the nearest foot at mean high water. The base data for all of the US charts are the NOAA charts, doesn't matter whether it is Navionics, C-Map, AquaMaps, they all use NOAA data. The different charts companies then add additional features or distractions, such as crowd sourced depth data, Active Captain, Waterway Guide and so on. Bridge clearances are measured at the lowest point on the bridge, known as "low steel." Spans that are arched will be higher in the middle.
@Scott T-Bird has better terminology, the bridges as designed are sometimes not the same as the bridges as built. Bridges on the ICW (Cape May's Bridges are not technically on the ICW) is 65 feet a MHW. A good example of a bridge that is not quite to spec is the Wilkerson Bridge over the Alligator-Pungo Canal, it is listed as 64 feet.
Adding to the error is changing sea levels and errors in placing the height boards. So, it is good to be concerned when the margin between the masthead and the bridge. We were the first time we went under the Cape May bridges.
The take home is when going under a bridge that is close to the boat's air draft, don't go at high tide, especially in a place where there is a significant tide. Cape May is around 4 feet.
@Scott T-Bird has better terminology, the bridges as designed are sometimes not the same as the bridges as built. Bridges on the ICW (Cape May's Bridges are not technically on the ICW) is 65 feet a MHW. A good example of a bridge that is not quite to spec is the Wilkerson Bridge over the Alligator-Pungo Canal, it is listed as 64 feet.
Adding to the error is changing sea levels and errors in placing the height boards. So, it is good to be concerned when the margin between the masthead and the bridge. We were the first time we went under the Cape May bridges.
The take home is when going under a bridge that is close to the boat's air draft, don't go at high tide, especially in a place where there is a significant tide. Cape May is around 4 feet.
