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#121
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Heavy Air
Well, DUH!
"The_navigator©" wrote ... Hmmm. That's a worry. Might mean you'll need tide tables to decide if you can pass an overhead... |
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#122
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Heavy Air
Are you the same age as all your charts?
Scotty "The_navigator©" wrote in message ... But you're not that old are ya? Cheers MC Scott Vernon wrote: What, Charlie Brown? Did I not state it was my ''old'' chart? Scotty "The_navigator©" wrote in message ... 1927 datum? Good grief. Cheers MC Scott Vernon wrote: Well, right under the sea serpent and above the mermaid it says '' 1927 DATUM , Soundings in Feet at MLW'' Low Low Water Low Tide????? SV "Jeff Morris" jeffmo@NoSpam-sv-lokiDOTcom wrote in message ... How old is that chart? All of my US charts from the recent past use MLLW as the datum for soundings. I even checked in my Chesapeake ChartKit to see if they were different. OK - Here's a quiz: What's the meaning of LLWLT? BTW, I thought of commenting on the "8 feet above MLW" also - around here we have 10 foot tides and flooding is measured above MHW "Scott Vernon" wrote in message ... Found the 'old' chart. It reads '' controlling depths in feet at Mean Low Water (MLW)''. AND; depths reffered to soundings (MLW)''. Scotty "Scott Vernon" wrote in message ... Are you sure? Don't keep charts at the house, thus the ''I believe'' . SV "The_navigator©" wrote in message ... No they are not. Read the chart legend Cheers MC Scott Vernon wrote: I believe that charted depths are given at MLW and it's up to the sailor to know the tide table and apply it. |
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#123
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Heavy Air
Yup, here on the Bay, a strong South wind combined with high tide can make
for higher than MHHW. SV "Jeff Morris" jeffmo@NoSpam-sv-lokiDOTcom wrote in message ... Yes - In case anyone is following this, let me explain: Here in the States we use Mean High Water (MHW) as the datum for bridge clearances. This means that, on average, half the tides will be higher than MHW, so the bridge will be lower than expected. To make matters worse, with the common semi-diurnal tide, one tide (the "higher high") will often be significantly higher than the other, so the discrepancy can be large. From chart 13270 of Boston harbor there is a table: Height referred to datum of soundings (MLLW) Mean Higher High Water 9.7 feet Mean High Water 9.3 feet Mean Low Water 0.3 feet Extreme Low Water -3.0 feet Thus, the average "higher high" is 0.4 feet above the datum used for bridge clearance. However, today the Higher High is at 10.22 feet. almost a foot higher than the datum. Anyone thinking they have a foot of clearance could be in for a nasty surprise! I should add that a strong onshore breeze can often add an extra foot to the predicted tides. -jeff "The_navigator©" wrote in message ... Hmmm. That's a worry. Might mean you'll need tide tables to decide if you can pass an overhead... Cheers MC Jeff Morris wrote: We don't often use "spring tides" here in the States - people like RB would be saying they only sail in Summer. We just use MHW - that leads to excitement since the bridges will likely be lower than their reported clearances once a day! That reminds me - Happy Spring! "The_navigator©" wrote in message ... Heights on land and clearances are above MWHS -right? Cheers MC |
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#124
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Heavy Air
Well put, Scotty.
But MC does have a point - under the US system you have to check to see if the current tide is much higher than MHW; in other countries where the datum for bridge clearance is the Spring Tide level, or the Large Tides, its a bit easier. However the best thing to do is to read the gauge board on the bridge and ask the tender.Can "Scott Vernon" wrote in message ... Well, DUH! "The_navigator©" wrote ... Hmmm. That's a worry. Might mean you'll need tide tables to decide if you can pass an overhead... |
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#125
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Heavy Air
They are much younger than me!
Cheers MC Scott Vernon wrote: Are you the same age as all your charts? Scotty "The_navigator©" wrote in message ... But you're not that old are ya? Cheers MC Scott Vernon wrote: What, Charlie Brown? Did I not state it was my ''old'' chart? Scotty "The_navigator©" wrote in message ... 1927 datum? Good grief. Cheers MC Scott Vernon wrote: Well, right under the sea serpent and above the mermaid it says '' 1927 DATUM , Soundings in Feet at MLW'' Low Low Water Low Tide????? SV "Jeff Morris" jeffmo@NoSpam-sv-lokiDOTcom wrote in message ... How old is that chart? All of my US charts from the recent past use MLLW as the datum for soundings. I even checked in my Chesapeake ChartKit to see if they were different. OK - Here's a quiz: What's the meaning of LLWLT? BTW, I thought of commenting on the "8 feet above MLW" also - around here we have 10 foot tides and flooding is measured above MHW "Scott Vernon" wrote in message ... Found the 'old' chart. It reads '' controlling depths in feet at Mean Low Water (MLW)''. AND; depths reffered to soundings (MLW)''. Scotty "Scott Vernon" wrote in message ... Are you sure? Don't keep charts at the house, thus the ''I believe'' . SV "The_navigator©" wrote in message ... No they are not. Read the chart legend Cheers MC Scott Vernon wrote: I believe that charted depths are given at MLW and it's up to the sailor to know the tide table and apply it. |
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#126
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Heavy Air
Are you saying the American charts use a stupid system for indicating
clearance? Cheers MC Scott Vernon wrote: Well, DUH! "The_navigator©" wrote ... Hmmm. That's a worry. Might mean you'll need tide tables to decide if you can pass an overhead... |
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#127
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Heavy Air
How do you have a tide guage on an overhead wire?
Cheers MC Jeff Morris wrote: Well put, Scotty. But MC does have a point - under the US system you have to check to see if the current tide is much higher than MHW; in other countries where the datum for bridge clearance is the Spring Tide level, or the Large Tides, its a bit easier. However the best thing to do is to read the gauge board on the bridge and ask the tender.Can "Scott Vernon" wrote in message ... Well, DUH! "The_navigator©" wrote ... Hmmm. That's a worry. Might mean you'll need tide tables to decide if you can pass an overhead... |
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#128
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Heavy Air
Well, this can be a problem. However, I've traveled the entire East Coast of the US and I
only remember one overhead that made me nervous - in Pine Island Sound, FL going to Sanibel. Its listed as 80 feet, but sure looked like it was sagging a bit! However, the differences between MHW and highest astronomical tide are maybe 3 or 4 feet in a worst case. I've gone under bridges with 3 or 4 feet of clearance - a few times only a few inches - but I wouldn't go under a powerline with that little clearance! "The_navigator©" wrote in message ... How do you have a tide guage on an overhead wire? Cheers MC Jeff Morris wrote: Well put, Scotty. But MC does have a point - under the US system you have to check to see if the current tide is much higher than MHW; in other countries where the datum for bridge clearance is the Spring Tide level, or the Large Tides, its a bit easier. However the best thing to do is to read the gauge board on the bridge and ask the tender.Can "Scott Vernon" wrote in message ... Well, DUH! "The_navigator©" wrote ... Hmmm. That's a worry. Might mean you'll need tide tables to decide if you can pass an overhead... |
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#129
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Heavy Air
"Jeff Morris" jeffmo@NoSpam-sv-lokiDOTcom wrote in message ... Well put, Scotty. But MC does have a point - under the US system you have to check to see if the current tide is much higher than MHW; in other countries where the datum for bridge clearance is the Spring Tide level, or the Large Tides, its a bit easier. However the best thing to do is to read the gauge board on the bridge and ask the tender.Can Hmmmm.... You assume that every overhead obstruction has a guage! I suspect that "busier" waterways have guages, but most of the rivers that I have gone up, have not had such useful aids to navigation. I need to read the charts! Regards Donal -- |
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#130
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Heavy Air
Subject: Heavy Air
From: =?ISO-8859-1?Q?The=5Fnavigator=A9?= Date: 09/23/2003 14:58 Pacific Standard Time Message-id: Are you saying the American charts use a stupid system for indicating clearance? Cheers MC Scott Vernon wrote: Well, DUH! "The_navigator©" wrote ... Hmmm. That's a worry. Might mean you'll need tide tables to decide if you can pass an overhead... I think he's saying that US charts require the operator of the vessel to pay attention to his/her surroundings, know how to read the charts, know how to make use of the information provided, and know how to apply that information to other variables which may make the "datum" inaccurate, for a given moment .... now that I think about it, so do B.A. charts. No chart/system, is perfect. You need to know which system you are using and what it's plusses and drawbacks are. Shen |
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