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  1. #41
    Join Date
    Jan 2015
    Location
    Solent Area
    Posts
    413

    Default Re: Portsmouth Small Boat Channel

    They have removed 3 million cubic metres of crud to straighten and deepen the channel, they have not long since finished. As Giblets said in post #8 the survey ship HMS Gleanor was out surveying recently. What they have done will no doubt alter and settle in after some winter storms and strong spring tides, so I would expect the underwater profile to change with time and no doubt they will need further dredging works to maintain what was done.

    I personally do not not believe that a shallowing lump would have been left sticking out of the Hamilton Bank, the phrase asking for trouble springs to mind. You could of course go back to Navionics and ask just how new their depth data is......

  2. #42
    Join Date
    Dec 2008
    Posts
    1,164

    Default Re: Portsmouth Small Boat Channel

    The Navionics depth data appeared quite recently when I updated the chart on my iPad. It does not seem to appear on other platforms.

  3. #43
    Join Date
    Mar 2006
    Location
    Surrey
    Posts
    7,878

    Default Re: Portsmouth Small Boat Channel

    On my Navionics iPad app (updated) if the SonarChart option is turned off then the "lump" disappears. I believe the data used for the SonarChart feature is user generated so I would be inclined to take any info shown with a pinch of salt. Has anyone actually sailed a line from 4 Bar Buoy to BC Outer and confirmed the "lump" actually exists from soundings?

  4. #44
    Join Date
    Sep 2005
    Posts
    2,406

    Default Re: Portsmouth Small Boat Channel

    Quote Originally Posted by chrishscorp View Post
    I personally do not not believe that a shallowing lump would have been left sticking out of the Hamilton Bank, the phrase asking for trouble springs to mind. You could of course go back to Navionics and ask just how new their depth data is......
    Or just sail over it at anything but a very low water and find out the depth profile definitively.

  5. #45
    Join Date
    Dec 2008
    Posts
    1,164

    Default Re: Portsmouth Small Boat Channel

    Hi Giblets

    Thanks for the tip; I feel much happier now!

  6. #46
    Join Date
    Dec 2008
    Location
    Hertfordshire
    Posts
    3,035

    Default Re: Portsmouth Small Boat Channel

    Quote Originally Posted by richardbrennan View Post
    Hi Giblets

    Thanks for the tip; I feel much happier now!
    .... and as I pointed out back in #29.

    And DJE in #22 before me.

  7. #47
    Join Date
    Sep 2005
    Posts
    2,406

    Default Re: Portsmouth Small Boat Channel

    Quote Originally Posted by chrishscorp View Post
    They have removed 3 million cubic metres of crud to straighten and deepen the channel, they have not long since finished. As Giblets said in post #8 the survey ship HMS Gleanor was out surveying recently. What they have done will no doubt alter and settle in after some winter storms and strong spring tides, so I would expect the underwater profile to change with time and no doubt they will need further dredging works to maintain what was done.

    I personally do not not believe that a shallowing lump would have been left sticking out of the Hamilton Bank, the phrase asking for trouble springs to mind. You could of course go back to Navionics and ask just how new their depth data is......
    I sailed over with a friend this afternoon to find out. Well, we all need an excuse for a sail. You’re right Chris; there’s no shallowing lump there. The floor's flat. Widened compared with Navionics' regular (non-SonarChart) chart, and now pretty uniformly deep. The tide was about 1.5m above chart Datum when I was there, and that whole area, including the spit that shows on SonarCharts as shallow as 1.5m below CD, was 12-13m actual depth.

    Of course, that says us nothing about whether that spit used to be there whenever they last ran their algorithm on recent user measurements and published the result as the current SonarChart. After all, we know the area has been dredged lately, and we don’t know how recent Navionics' latest SonarChart data is. But certainly you can now sail up the small boat channel from south of no 4 Bar buoy, in deep water.
    Last edited by BelleSerene; 05-11-17 at 21:12.

  8. #48
    Join Date
    Jul 2010
    Location
    location location ...
    Posts
    862

    Default Re: Portsmouth Small Boat Channel

    Out of curiosity, I switched to the SonarCharts view on my Android tablet while negotiating some channels in an archipelago in Sweden. The results bore no resemblance at all to what my echosounder was saying.

  9. #49
    Join Date
    May 2013
    Posts
    104

    Default Re: Portsmouth Small Boat Channel

    Quote Originally Posted by BelleSerene View Post
    I sailed over with a friend this afternoon to find out. Well, we all need an excuse for a sail. You’re right Chris; there’s no shallowing lump there. The floor's flat. Widened compared with Navionics' regular (non-SonarChart) chart, and now pretty uniformly deep. The tide was about 1.5m above chart Datum when I was there, and that whole area, including the spit that shows on SonarCharts as shallow as 1.5m below CD, was 12-13m actual depth.

    Of course, that says us nothing about whether that spit used to be there whenever they last ran their algorithm on recent user measurements and published the result as the current SonarChart. After all, we know the area has been dredged lately, and we don’t know how recent Navionics' latest SonarChart data is. But certainly you can now sail up the small boat channel from south of no 4 Bar buoy, in deep water.
    good to know.

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