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    Re: US. Navy fix accuracy and Interval.
    From: Jeremy C
    Date: 2013 Mar 27, 06:35 -0700

    Cables are a very common unit actually. Typically used up to 1 nm.

    On US ships the rate of turnover is "when it breaks," so many years. I don't see L2 receivers to be commonplace on US ships for a long time. It is sad since we are taught that single system dependence on position is a bad thing. The bean counters think that since we have several GPS's we are all good.

    I either have the wrong phone or the wrong app. I have a Titan II phone and a GPS locator program. I pulled it out mid-ocean this last trip and was told that position information was not available.

    I now have 2 portable backups. One is a pure GPS that interfaces with my ham radio. The second is my aforementioned L2. It's a Garmin Glo which is about the size of 2 matchboxes ($100 on Amazon). It also has bluetooth interface so I can put it in the window and set up my laptop somewhere else. It locks a position in within a minute, which is much faster than the GPS unit's I've used. Since I still have to use paper charts, I can easily use either of these receivers as a backup to the ship's 4 GPS units (assuming that the system as a whole is actually working). If the sat systems aren't working, I still have that sextant for deep sea, and a bearing circle and radar for piloting.

    I wouldn't say "Navigation is a solved problem." Look at the USS GUARDIAN. That was definitely a navigational failure. I think that, when the technology is working, finding position is a solved problem; certainly within the required accuracy of any vessel. However, until we get better charts and know what is underneath us, nautical navigation (the process of getting from Point A to Point B safely) still needs development.

    In the case of small boats, much depends on the density. If it is that packed, you have to go by the law of gross tonnage, and I just blow the danger signal as necessary since I can't leave the channel. So if the little boats don't get out of the way, there will be trouble. Unfortunately there is no way to really maneuver the ships to avoid one small boat without running into the danger of having to turn and run over another small boat. My advise to small boaters: give ships a wide berth because we can't stop and we can't really turn.

    The new standard for electronic navigational charts (ENC's) hopes to deal with the poor hydrographic data. There is actually a layer in the ENC that you can turn on and off that gives the level of verification/confidence for the bottom data. It goes from "U" to 6-stars. You would be really amazed at how much of it is "U", even close to the coast, and how very little of it is 6-star rated.

    By the way, ENCs of the US coast are available for free from the NOAA website. These are the best (and only official) electronic charts available for US waters. Most of the rest of the world is covered by the Admiralty and it costs some money to access them.

    You are right, even the ENC's aren't necessarily new data. They are just digitized versions of the paper chart. Many of those surveys were done in the 30's and 40s and so the accuracy is questionable, even if you don't factor in the change in the bottom over the interim.

    While I am usually quite confident of my position, I mostly worry about the chart I am using and if there aren't hidden dangers or incorrectly marked and/or positioned dangers I don't know about. I give them all as wide a berth as practical.

    Jeremy


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