In light of the question on this months sail quiz I have this question. Are bridge clearances measured from the center span or at the ends where it drops off some two or three feet? I am quite certain that I'd not cut the passing under a bridge as close as they propose in the quiz given the large discrepancy between the actual and predicted tide swings here on the river....but it'd sure be nice to know if the difference in height from end-span to center-span was there for a safety measure. It is deceiving enough watching your rig pass under the 65' spans and KNOWING you have it clear.
Bridge Clearance Measurement ?
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I agree with you Dale...
Don't know the answer to your question, but I do agree that going under a bridge with only one foot of (supposed) clearance sounds to me like cutting it just a little too close for comfort. I'd be the guy heading out within an hour or two of low tide just to give myself a little 'breathing room'. It would be just my luck that as I'm directly under the bridge some guy in a powerboat screams by and his wake sticks my mast into a girder!
Don't know the answer to your question, but I do agree that going under a bridge with only one foot of (supposed) clearance sounds to me like cutting it just a little too close for comfort. I'd be the guy heading out within an hour or two of low tide just to give myself a little 'breathing room'. It would be just my luck that as I'm directly under the bridge some guy in a powerboat screams by and his wake sticks my mast into a girder!
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Len Mack
Bridge clearance
On the Illinois River, there are clearance numbers in feet painted on the bridge support piers. That way you don't have to worry about charted clearances or river heights due to high water. We do have to sail under some high-tension lines that the chart shows plenty of clearance, but it looks a lot closer when you're looking up at them and the masthead.
On the Illinois River, there are clearance numbers in feet painted on the bridge support piers. That way you don't have to worry about charted clearances or river heights due to high water. We do have to sail under some high-tension lines that the chart shows plenty of clearance, but it looks a lot closer when you're looking up at them and the masthead.
Len, ....my question still stands....
...We have the graduated height indicators on the bridges in Fla. as well...but is the clearance relevant to the center span or the end span? The Shands Bridge here on the St. Johns is listed as 46', (I think), and I have a stick somewhere around 46'-48', and if I could determine with a great degree of certainty that I wouldn't take out my antenna or tri-color on that bridge at low tide, it would open up at least another 40 miles of this gorgeous river to explore....its *real* close a lot of the time. I'd hate to think that if I were driving a WIDE loaded dredge or barge that was max'd out for height, that they would indicate only the highest point of clearance on a bridge....and the same thing goes for an 18-wheel trucker pulling an oversized load up the expressway looking for overhead clearance.
...We have the graduated height indicators on the bridges in Fla. as well...but is the clearance relevant to the center span or the end span? The Shands Bridge here on the St. Johns is listed as 46', (I think), and I have a stick somewhere around 46'-48', and if I could determine with a great degree of certainty that I wouldn't take out my antenna or tri-color on that bridge at low tide, it would open up at least another 40 miles of this gorgeous river to explore....its *real* close a lot of the time. I'd hate to think that if I were driving a WIDE loaded dredge or barge that was max'd out for height, that they would indicate only the highest point of clearance on a bridge....and the same thing goes for an 18-wheel trucker pulling an oversized load up the expressway looking for overhead clearance.
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Bill O'Donovan
Unrelated irony
Under the Coleman Bridge off Yorktown VA, someone the other day smashed into the "Danger" sign on the piling, crumpling it badly.
Under the Coleman Bridge off Yorktown VA, someone the other day smashed into the "Danger" sign on the piling, crumpling it badly.
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Chris Burti
Here is the answer on gauges
The relevent portions of the Federal Code section follow. In summary, the gauge will show the low point clearance of the portion of the span over the navigation channel. Presumably' this also applies to fixed spans as that is the required information on the construction/alteration permit application(last section). I could not readily find the marking regs for fixed spans. Permitting requirment of CFR Sction 66; 3) The plans will show in figures the least clear height of the lowest part of the superstructure over navigation openings, with reference to the planes of mean high water and mean low water if the bridge is to cross tidal water. If the waters are nontidal, the least clear height will be shown with reference to the planes of extreme high water and mean low water. If records of river heights are available, the plane above which flood waters have not remained more than 2 percent of the time will be indicated. Reference will also be made to other datum planes if appropriate for the waterway in question. CHAPTER I--COAST GUARD, DEPARTMENT OF HOMELAND SECURITY PART 118--BRIDGE LIGHTING AND OTHER SIGNALS— Table of Contents Sec. 118.160 Vertical clearance gauges. (a) When necessary for reasons of safety of navigation, the District Commander may require or authorize the installation of clearance gauges. Except as specified in Sec. 117.47(b) of this chapter for certain drawbridges, clearance gauges must meet the requirements of this section. (b) Clearance gauges must indicate the vertical distance between ``low steel'' of the bridge channel span and the level of the water, measured to the bottom of the foot marks, read from top to bottom. Each gauge must be installed on the end of the right channel pier or pier protection structure facing approaching vessels and extend to a reasonable height above high water so as to be meaningful to the viewer. Other or additional locations may be prescribed by the District Commander if particular conditions or circumstances warrant. (c) Construction. Each gauge must be permanently fixed to the bridge pier or [[Page 639]] pier protection structure and made of a durable material of sufficient strength to provide resistance to weather, tide, and current. Gauges may be painted directly on the bridge channel pier or pier protection structure if the surface is suitable and has sufficient width to accommodate the foot marks (graduations) and numerals. (e) Maintenance. The owner or operator of the bridge shall maintain each gauge in good repair and legible condition. The bridge owner or operator is responsible for the accuracy of the gauge and shall remeasure the vertical distance of the numerals and foot marks below ``low steel'' of the bridge whenever the gauge is repainted or the structure is repaired. [CGD 84-022, 51 FR 16314, May 2, 1986]
The relevent portions of the Federal Code section follow. In summary, the gauge will show the low point clearance of the portion of the span over the navigation channel. Presumably' this also applies to fixed spans as that is the required information on the construction/alteration permit application(last section). I could not readily find the marking regs for fixed spans. Permitting requirment of CFR Sction 66; 3) The plans will show in figures the least clear height of the lowest part of the superstructure over navigation openings, with reference to the planes of mean high water and mean low water if the bridge is to cross tidal water. If the waters are nontidal, the least clear height will be shown with reference to the planes of extreme high water and mean low water. If records of river heights are available, the plane above which flood waters have not remained more than 2 percent of the time will be indicated. Reference will also be made to other datum planes if appropriate for the waterway in question. CHAPTER I--COAST GUARD, DEPARTMENT OF HOMELAND SECURITY PART 118--BRIDGE LIGHTING AND OTHER SIGNALS— Table of Contents Sec. 118.160 Vertical clearance gauges. (a) When necessary for reasons of safety of navigation, the District Commander may require or authorize the installation of clearance gauges. Except as specified in Sec. 117.47(b) of this chapter for certain drawbridges, clearance gauges must meet the requirements of this section. (b) Clearance gauges must indicate the vertical distance between ``low steel'' of the bridge channel span and the level of the water, measured to the bottom of the foot marks, read from top to bottom. Each gauge must be installed on the end of the right channel pier or pier protection structure facing approaching vessels and extend to a reasonable height above high water so as to be meaningful to the viewer. Other or additional locations may be prescribed by the District Commander if particular conditions or circumstances warrant. (c) Construction. Each gauge must be permanently fixed to the bridge pier or [[Page 639]] pier protection structure and made of a durable material of sufficient strength to provide resistance to weather, tide, and current. Gauges may be painted directly on the bridge channel pier or pier protection structure if the surface is suitable and has sufficient width to accommodate the foot marks (graduations) and numerals. (e) Maintenance. The owner or operator of the bridge shall maintain each gauge in good repair and legible condition. The bridge owner or operator is responsible for the accuracy of the gauge and shall remeasure the vertical distance of the numerals and foot marks below ``low steel'' of the bridge whenever the gauge is repainted or the structure is repaired. [CGD 84-022, 51 FR 16314, May 2, 1986]
Thanks Chris
So it would seem from that bit of verbage that they use the worst-case scenario...and so I'll have just have to ride the mast head and sweep some cobwebs from the underside if clearance proves adequate... Thanks again... (P.s. How do guys FIND this stuff anyway?)
So it would seem from that bit of verbage that they use the worst-case scenario...and so I'll have just have to ride the mast head and sweep some cobwebs from the underside if clearance proves adequate... Thanks again... (P.s. How do guys FIND this stuff anyway?)
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Chris Burti
It is the nature of my job.
I have to know the correct answer and can not rely on what someone, no matter how knowledgeable, has said it was. Thus, you might say that I have, in a sense, become somewhat of a professional researcher. The web is a tremendous boon to my efficiency I have numerous research links saved and have become fairly adept at using them.
I have to know the correct answer and can not rely on what someone, no matter how knowledgeable, has said it was. Thus, you might say that I have, in a sense, become somewhat of a professional researcher. The web is a tremendous boon to my efficiency I have numerous research links saved and have become fairly adept at using them.
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Chris Burti
Heheheh....
You shouldn't have to ride or sweep as long as you know how high the top of your rig is off of the water (and pray that some thunderboat hotdog doesn't roll a wake your way the one time that you are testing your measurement accuracy to the limit).
You shouldn't have to ride or sweep as long as you know how high the top of your rig is off of the water (and pray that some thunderboat hotdog doesn't roll a wake your way the one time that you are testing your measurement accuracy to the limit).
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Tim
Check Your Charts
This discussion got me curious because I was pretty sure that the answer was to be found on your NOAA (or whatever they're called now) navigation charts. Two examples from my neck of the woods - as shown on the charts: Agate Pass Bridge FIXED BRIDGE VERT CL 75 FT FOR MIDDLE 300 FT OVHD PWR CAB AUTH CL 96 FT LaConner Bridge FIXED BRIDGE VERT CL 45 FT (75 FT FOR CENTRAL 310 FT) In each case, it not only give you the vertical clearance, but also tells you how wide that clearance exists for - and relative to what. In the case of the LaConner Bridge, it's 45 ft for most of the bridge, except the central 310 feet where it is 75 ft. Check your charts! Tim Brogan April IV C350 #68 Seattle
This discussion got me curious because I was pretty sure that the answer was to be found on your NOAA (or whatever they're called now) navigation charts. Two examples from my neck of the woods - as shown on the charts: Agate Pass Bridge FIXED BRIDGE VERT CL 75 FT FOR MIDDLE 300 FT OVHD PWR CAB AUTH CL 96 FT LaConner Bridge FIXED BRIDGE VERT CL 45 FT (75 FT FOR CENTRAL 310 FT) In each case, it not only give you the vertical clearance, but also tells you how wide that clearance exists for - and relative to what. In the case of the LaConner Bridge, it's 45 ft for most of the bridge, except the central 310 feet where it is 75 ft. Check your charts! Tim Brogan April IV C350 #68 Seattle
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Paul Akers
Measuring Your Mast Clearance
You may know what your mast clearance is based upon the spec of your boat. That's a fair assumption to make. But I have heard where boat owners have not accounted for added appendages such as lightning rods, antennaes, LORAN antennaes, VHF antennaes, etc. and have ripped them off on the bridge.
You may know what your mast clearance is based upon the spec of your boat. That's a fair assumption to make. But I have heard where boat owners have not accounted for added appendages such as lightning rods, antennaes, LORAN antennaes, VHF antennaes, etc. and have ripped them off on the bridge.
Keel Mod is another factor
I have the original manual on this boat which has all of the critical dimensions of the stock boat...however, it may ride a slightly lower now given the keel modification the PO had done. Mars Metals of Ontario engineered a shortening of draft from around 6'5" to approx. 5' by dropping 18" and 1100# off and adding back a bulb of 1300#. I will be dropping a 100' tape from the top tonight in order to determine what it really is. When this boat came across the scales it weighed 12,300# or so, (empty & dry), when the book had it at around 11,000#...so I am a little sceptical of the spec book accuracy anyway. My chart has the Shands Bridge at: FIXED BRIDGE HOR. CL 91 FT. VERT. CL 45 FT. Chart note: 'Soundings in feet at mean lower low water' (...unlikely that I'll see the upper St. Johns on this boat.)
I have the original manual on this boat which has all of the critical dimensions of the stock boat...however, it may ride a slightly lower now given the keel modification the PO had done. Mars Metals of Ontario engineered a shortening of draft from around 6'5" to approx. 5' by dropping 18" and 1100# off and adding back a bulb of 1300#. I will be dropping a 100' tape from the top tonight in order to determine what it really is. When this boat came across the scales it weighed 12,300# or so, (empty & dry), when the book had it at around 11,000#...so I am a little sceptical of the spec book accuracy anyway. My chart has the Shands Bridge at: FIXED BRIDGE HOR. CL 91 FT. VERT. CL 45 FT. Chart note: 'Soundings in feet at mean lower low water' (...unlikely that I'll see the upper St. Johns on this boat.)
charts are not always
correct. around here on the ICW all the fixed bridges are suppose to be 50ft min. the Destin or East Pass Bridge shown on the charts to be 50ft is actually 48ft on a low tide. my mast ht is 48, no go in the East Pass. the Navarre and Brooks bridges are touch and go. I always ride the low tide and make sure there are no other boats in sight before making my pass under, even if this means doing a couple of circles on approach is make sure the coast is clear! charts are great reference but, there is no substitute for local knowledge.
correct. around here on the ICW all the fixed bridges are suppose to be 50ft min. the Destin or East Pass Bridge shown on the charts to be 50ft is actually 48ft on a low tide. my mast ht is 48, no go in the East Pass. the Navarre and Brooks bridges are touch and go. I always ride the low tide and make sure there are no other boats in sight before making my pass under, even if this means doing a couple of circles on approach is make sure the coast is clear! charts are great reference but, there is no substitute for local knowledge.
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Tim
Soundings vs. Heights
Dale commented below: "Chart note: Soundings in feet at Mean lower low water" Soundings typically refer to depth of the water rather than height of various features (bridges, towers, hilsides). There should also be a notation on the chart (assuming we are talking about NOAA nautical charts) that says something like: HEIGHTS HEIGHTS IN FEET ABOVE MEAN HIGH WATER There is a cool diagram on page 2 of this page - from NOAA Chart #1 http://pollux.nss.nima.mil/NAV_PUBS/Chart1/Sec_H.pdf The diagram shows a bunch of the common measurements and shows where they are typically calculated from. Two things become particularly important: 1) the unit of measure (Fathoms, Feet, Meters) and 2) the point of reference (MLLW, MHW, etc.) The diagram does a good job of pointing out that your "observed depth" will be different than any of those reference points. Tim Brogan April IV C350 #68 Seattle
Dale commented below: "Chart note: Soundings in feet at Mean lower low water" Soundings typically refer to depth of the water rather than height of various features (bridges, towers, hilsides). There should also be a notation on the chart (assuming we are talking about NOAA nautical charts) that says something like: HEIGHTS HEIGHTS IN FEET ABOVE MEAN HIGH WATER There is a cool diagram on page 2 of this page - from NOAA Chart #1 http://pollux.nss.nima.mil/NAV_PUBS/Chart1/Sec_H.pdf The diagram shows a bunch of the common measurements and shows where they are typically calculated from. Two things become particularly important: 1) the unit of measure (Fathoms, Feet, Meters) and 2) the point of reference (MLLW, MHW, etc.) The diagram does a good job of pointing out that your "observed depth" will be different than any of those reference points. Tim Brogan April IV C350 #68 Seattle
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