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Old 14-01-2009, 06:58   #1
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Mast Height, Bridge Clearance, Tides.

Mast Height, Bridge Clearance, Tides.
We are looking at a 45 to 47 foot catamarans for our next boat. Mast height with some of these boats are too high for the ICWs and Im wanting to do this route plus where we are at in the Florida Keys we have a 65 bridge to get under to get to the ocean side. One of the boat we were looking at was 64.5 high. So my questions are..
When they say the clearance for the bridge is 65 is that at low tide?
Could we at 64.5 cruise the ICW?
Thanks!
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Old 14-01-2009, 07:06   #2
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David,

The NOAA charted bridge clearances are referenced to Mean High Water. If you traverse the bridge at low tide you gain some air draft. Charted Bridge Clearances
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Old 14-01-2009, 08:07   #3
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My answer would be a NO

The ICW was created some years ago. In Florida it's now up to the state to maintain it. Here on the east coast there hasn't been a maintenance dredging program in 20 years. The ICW is getting silted in , but only in some places. When the bridges were originally constructed, the clearance was as HUD3 mentioned, fixed at 65FT.

Today, you'd be fine in Florida in the rainy season, however in winter months when the ICW water level drops, you might be looking at 63.5 FT or 64 FT in some places.
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Old 14-01-2009, 08:31   #4
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I have a 43 ft Privileg catamaran with a 67 ft masthead height and I live in Miami. I can, under most weather conditions (and nearly always at low tide) pass under all the major bridges from the McArthur Causeway (I-395) south to Key West, including the new one at Jewfish Creek and the one on the 8-mile bridge just southwest of Marathon. (Note that the I-195 bridge on Julia Tuttle Causeway in North Biscayne Bay is only 55 ft.) However, clearance is often measured in inches as my VHF whip antenna typically hits the underside of most of the 65 footers, especially Card Sound Brige. The trick is to take it VERY SLOW and when there is no other boat traffic to cause wakes. Good luck.
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Old 14-01-2009, 08:35   #5
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Originally Posted by Tropic Cat View Post
My answer would be a NO

The ICW was created some years ago. In Florida it's now up to the state to maintain it. Here on the east coast there hasn't been a maintenance dredging program in 20 years. The ICW is getting silted in , but only in some places. When the bridges were originally constructed, the clearance was as HUD3 mentioned, fixed at 65FT.

Today, you'd be fine in Florida in the rainy season, however in winter months when the ICW water level drops, you might be looking at 63.5 FT or 64 FT in some places.

Rick,

1. Silting and dredging has nothing to do with bridge height clearance.
2. If the ICW water level drops, that would increase the bridge clearance, not decrease it.


David,

I think you'd be fine in most places. There's the Tuttle Bridge between FTL and MIA which you can't get under, and there are one or two others where the clearance at mean high water is a bit under 65', but you should be able to clear them with prudent navigation.

I'd be much more worried about depths, because as others have said the ICW hasn't been well maintained in recent years.

Bill
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Old 14-01-2009, 09:01   #6
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Rick,

1. Silting and dredging has nothing to do with bridge height clearance.
2. If the ICW water level drops, that would increase the bridge clearance, not decrease it.


David,

I think you'd be fine in most places. There's the Tuttle Bridge between FTL and MIA which you can't get under, and there are one or two others where the clearance at mean high water is a bit under 65', but you should be able to clear them with prudent navigation.

I'd be much more worried about depths, because as others have said the ICW hasn't been well maintained in recent years.

Bill

Bill,

The cats I am looking at draw 3 to 4 feet so I would think would be a plus for the skinny waters of the ICW..... it sure will be here in the Keys.

So mast height clearance on most bridges in the ICW would give me 65' as long as I play the tides right?
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Old 14-01-2009, 09:07   #7
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Yes, you should be fine.

The only bridge on the ICW which to my knowledge has a design height less than 65' is the Tuttle Bridge. How that one slipped by the regs has to be a good story :-)

There's one around Riviera Beach, I believe, which is tricky; I remember having to wait for the tide to drop before I felt safe passing with my 64.5' clearance.

There may be a couple of others. Someone with more recent experience and a high mast could advise.

No worries if you get up this way to Washington, DC. The old 50' clearance Wilson Bridge just below Alexandria, VA is gone. The new bridge has a measured clearance of 84 feet in the center!

Bill
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Old 14-01-2009, 09:09   #8
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Originally Posted by emcmia View Post
I have a 43 ft Privileg catamaran with a 67 ft masthead height and I live in Miami. I can, under most weather conditions (and nearly always at low tide) pass under all the major bridges from the McArthur Causeway (I-395) south to Key West, including the new one at Jewfish Creek and the one on the 8-mile bridge just southwest of Marathon. (Note that the I-195 bridge on Julia Tuttle Causeway in North Biscayne Bay is only 55 ft.) However, clearance is often measured in inches as my VHF whip antenna typically hits the underside of most of the 65 footers, especially Card Sound Brige. The trick is to take it VERY SLOW and when there is no other boat traffic to cause wakes. Good luck.
emcmia,

WOW! 67' , that is good news. And good news about the new Jewfish Creek Bridge. Is the old bridge completely gone now?
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Old 14-01-2009, 09:52   #9
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I passed through the Jewfish creek just after they completed the fixed span and the bascule bridge was still there. However, I have recently read that the old bridge is in the process of being removed.

As for Florida Keys ICW water depths, I draw 4ft and there are a few stretches between Marathon and Islamorada where I routinely stir up the bottom and/or the channel narrows causing one of the keels to bump.
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Old 14-01-2009, 10:18   #10
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Clearances under objects are measured from the highest astronomical tide (HAT). That is the theoretical highest tide possible, excluding the effects of storm surges et al. Dredging and water depth are irrelevant to overhead clearances as they're calculated from the chart datum.

Keep in mind that a 64.5' mast will have equipment mounted on top which needs to be considered.

Check your tide tables and go slow!!
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Old 14-01-2009, 10:41   #11
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Originally Posted by btrayfors View Post
Rick,

1. Silting and dredging has nothing to do with bridge height clearance.
2. If the ICW water level drops, that would increase the bridge clearance, not decrease it.




Bill


Yeah, what he said, I hope the bridges are not settling in the "silt"
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Old 14-01-2009, 11:45   #12
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one thing's for sure: you won't be able to lean the cat over like you can a mono to get under a bridge
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Old 14-01-2009, 12:10   #13
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you guys are spoiled 65ft bridge clearance

When i go on my local river,i have 2.2 meters thats about 8ft in old money,if i take my mast out of the crutch and support it on my shoulder,i can just squeeze under.
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Old 14-01-2009, 12:25   #14
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Clearances under objects are measured from the highest astronomical tide (HAT). That is the theoretical highest tide possible, excluding the effects of storm surges et al. Dredging and water depth are irrelevant to overhead clearances as they're calculated from the chart datum.

Keep in mind that a 64.5' mast will have equipment mounted on top which needs to be considered.

Check your tide tables and go slow!!

So is the Mean High Water (MHW) and highest astronomical tide (HAT) the same thing?
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Old 14-01-2009, 12:30   #15
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you guys are spoiled 65ft bridge clearance

When i go on my local river,i have 2.2 meters thats about 8ft in old money,if i take my mast out of the crutch and support it on my shoulder,i can just squeeze under.
You need to drain some of the water out of the pond!
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