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Chart Depth Numbers...

haydenfox!#$haydenfox!#$ Posts: 2,406 Captain
Are the depths listed on Vavionics, NCEarth, Hot Spot charts, etc high tide, low tide or an average depth?

Replies

  • reelstupidreelstupid Posts: 48 Deckhand
    Are the depths listed on Vavionics, NCEarth, Hot Spot charts, etc high tide, low tide or an average depth?

    Its always checked at the average low tide. They want to give you the average lowest water depth so you know what you can run in safely
  • Capt M BrennanCapt M Brennan Posts: 488 Officer
    Chart depths are represented by the Mean Low Water (MLW)

    From NOAA, "The average of all the low water heights observed over the National Tidal Datum Epoch. For stations with shorter series, comparison of simultaneous observations with a control tide station is made in order to derive the equivalent datum of the National Tidal Datum Epoch."

    Which is pretty much Greek to me, I just know that chart depths are measured from Mean Low Water and bridge heights are measured from Mean High Water.
    Captain Mike Brennan
  • haydenfox!#$haydenfox!#$ Posts: 2,406 Captain
    Chart depths are represented by the Mean Low Water (MLW)

    From NOAA, "The average of all the low water heights observed over the National Tidal Datum Epoch. For stations with shorter series, comparison of simultaneous observations with a control tide station is made in order to derive the equivalent datum of the National Tidal Datum Epoch."

    Which is pretty much Greek to me, I just know that chart depths are measured from Mean Low Water and bridge heights are measured from Mean High Water.

    HAHA, I read that to when researching, it pretty mich lead me to ask here. About the bridges, is this diectly below or in the "vicinity?"
  • Capt M BrennanCapt M Brennan Posts: 488 Officer
    Generally speaking it's the lowest point on the bridge in the marked fairway that may obstruct traffic.

    The water can be lower than it shows on the chart due to conditions that may enhance a low tide, i.e. weather, unusual atmospheric conditions etc. etc., but remember, never rely on any one source of navigational information. Conditions visible to you on the water, at any given time, are probably not reflected or depicted accurately on any chart.
    Captain Mike Brennan
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