Speedmeters!!

Discussion in 'All Things Boats & Boating' started by vasher, Nov 22, 2011.

  1. vasher
    Joined: Aug 2011
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    vasher New Member

    Folks having seen a lot of speedometers that use GPS to measure the speed I was think of getting one. I experienced the gps in my previous app like flytomap it worked flawlessly on boat! As the GPS can only measure speed over ground (SOG) how does that effect its usefulness? Anyone using only a GPS for speed indication? What about EP calculation? Comments
     
    Last edited: Nov 22, 2011
  2. michael pierzga
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    michael pierzga Senior Member

    Gps is OK...not effective at slow speed and naturally only SOG COG ..... also its damping factor is less than perfect for a helmsman.

    Niether SOG COG makes any sense unless you know course and speed thru the water.

    People rely on GPS only because its cheap and easy. Speed log and compass are expensive pieces of gear that require a navigator to calibrate and keep calibrated.

    If you are just a weekend sailor, go GPS only then simply be aware of its limitations.
     
  3. Submarine Tom

    Submarine Tom Previous Member

    I agree Michael.

    Vasher, don't become complacent and reliant on your GPS because if it ever fails, you're screwed. It's a slippery slope and an incredible easy one to get sucked in to. I've seen it happen with catastrophic results. By all means use it but remember your eyes and a chart are your primary nav tools and you may need to stay familiar with the process.

    -Tom
     
  4. IMP-ish
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    IMP-ish powerboater

  5. rwatson
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    rwatson Senior Member

    Why is it non-effective at slow speeds ? Walkers and Hikers use it - and it works well at all sailing speeds. With way points, its fantastic at calculating your ETA.

    GPS is not just 'OK' - its mandatory on all boats because
    "Speed log and compass are expensive pieces of gear that require a navigator to calibrate and keep calibrated. "
    They are also potentially way less accurate.

    "your eyes and a chart are your primary nav tools"

    yeah right - If you can see despite fog, rain or being too far offshore, and if you cant, your chart is useless, unless you have been doing 'dead reckoning' every 15-30 minutes.
    One rain squall at the wrong time without a manual chart update, and you have to reverse course in case the island/rock/tanker you were about to pass might jump out to bite you.

    Name 1 commercial boat that sails out of sight of land without 1 or 4 GPS ?

    Being dismissive of one of the worlds number one technical assets, that drives 90% of all commercial vessels, and 100% of all naval craft is just crazy.
     
  6. Submarine Tom

    Submarine Tom Previous Member

    Mr. Watson you have much to learn.

    -Tom
     
  7. mike165
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    mike165 New Member

  8. whitepointer23

    whitepointer23 Previous Member

    well said, i haven't used my paper charts since i have had gps. i still have a compass and charts on board, just don't use them. i would much rather know the sog than speed through water. over 10 yrs now using gps on trips up to 3000 km and it has never let me down once.
     
  9. Submarine Tom

    Submarine Tom Previous Member

    I do believe my point has been completely missed here.

    What you are doing though, is confirming your complacency with electronic nav aids.

    I never said there was anything wrong with them. I did say that the slippery slope of dependance on them is a dangerous one for when you loose your electronics.

    I love the group think. Carry on.

    -Tom
     
  10. rwatson
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    rwatson Senior Member

    I'm sorry if my reply came across a bit terse here Tom - but I don't think its a matter of complacency, more an appreciation of the superiority of the GPS over the old manual methods. Making fatuous comments like "you have a lot to learn" without actually commenting on my points is not very helpful.

    This is the statement that irked me. It is just no longer true for anyone except people who want to practice the art of navigation by purely 'manual' methods. The postal service doesn't even give priority for items marked "Urgent - Navigation Aids" for the postal chart updates if you happen to subscribe.

    Perhaps, but it was strongly implied, and I think gave an inaccurate bias to the reader.

    Just to clarify my opinion on this - the main point of manual navigation is that you either do it constantly and continually, or you may as well not do it at all.

    On the commercial vessels that use the manual technique, you have to do a sighting every 20 minutes around inshore waters. The reason is, you have to know where you are in order to travel for the next twenty minutes.

    I have been out in a small boat in perfectly clear conditions close to shore, perfect visibility, and bam - sea fog comes rolling in. In a manual situation - if I hadn't been taking sightings regularly, I wouldn't know if I was in a position to safely drop anchor (water depth, shipping lanes, tidal effects). I would be in no position to navigate by compass either, as I would not know my exact position on the chart to start from.

    so ....
    what do you do ? If you have clear visibility, and if you have some landmarks, you have half a chance to start navigating by dead reckoning. (which if you don't know how to, as you say - you could be in trouble ). Most of the time, in clear visibility, the average sailor wont have any trouble getting to port safely, given the wide use of navigation markers etc around frequently used ports.

    But if the electronics fail out at sea, or if you get poor visibility in a coastal situation - what do you do ? Your manual systems are a really poor fallback. At least our 'chronometers' ( the digital watch) are a darn sight better than Captain Cook had, but in poor visibility ( say overcast conditions which can last for days) taking a 'sight' isn't an option. In fact, you are just as 'stuffed' as if you didn't know how to navigate manually. You can guess your way around the chart on your table, but really, you had best stand out to sea from any hazards (if you can) , until the visibility gets better, or you can follow someone in with a working gps.

    Just take a look at the wreck list up the west or east coat of australia in the years when there was no gps, under the command of experts in manual navigation.

    In summary - manual navigation is a possible fallback, (so yes, you better know how to do it for the 5% chance of having to rely on it), but as for being your "Primary navigation method" - it better not be, as it is a really fraught option.


    Absolutely - and many thanks for the opportunity to discuss things nautical
     
  11. CatBuilder

    CatBuilder Previous Member

    This is a good thread. Both "sides" have valid points, but I have to go with Rwatson here.

    While I do carry the paper charts, they seem to just grow mold and grow more yellow each year. I use a computer for chart plotting which overlays my GPS position (and SOG, Heading, Bearing, course with waypoints, weather and brand new, freshly updated charts) all in one window.

    That is my primary navigation system. Like the space shuttle's computer systems, I have no less then a pair of independent backup GPS units, making 3 total. The third backup unit operates on batteries, so it is independent of the boat's electrical system.

    Seems to me, if a triply redundant set of computers is good enough for the Space Shuttle, it's good enough for my boat.

    All that, plus paper charts and skills in dead reckoning, sighting, set and drift, etc.. etc...

    To the OP's question, I think SOG is the only thing that you really need to know and I'm a guy that grew up sailing on a navigable river with the 2nd strongest current in the USA. It doesn't matter what the current is doing if you have a good nav system set up. You automatically adjust your boat's heading to keep the course correct. It's easy to do after a couple of hours getting used to it.

    SOG is pretty much the only speed that matters because the distance between your waypoints, the distance from port to port, any distance on a chart is always measured over the ground. The current has no effect except to boost you or slow you, since you will automatically account for any side currents by turning the boat's angle of attack to keep the little "boat icon" on the screen on the course line.

    The only time I can really see GPS based chart plotters being useless is if there were a war or severe solar disturbance.

    That's why I keep my paper charts and skills handy... just in case.
     
  12. rwatson
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    rwatson Senior Member

    Succinctly put !

    Can you imagine the drop in water traffic if the GPS was turned off or the satellites were burned out by solar flares or North Korea ?

    I would estimate that over 80% of commercial traffic wouldn't be able to operate.

    Would that destroy civilization- or what ?
     
  13. michael pierzga
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    michael pierzga Senior Member

    You better by a good chart plotter if you expect to sail without charts. The plotters based on Navioncs charts are just junk....riddled with errors.

    A defect of all chart plotters is the lack of cartography on the chart. No longer can you identify geographic features inland. Most modern chart plotter sailors dont even know were they are..only lat long and a little boat on the screen.

    Also be aware that when navigating in mountanoius regions from you may go for long periods without a fix.
     
  14. whitepointer23

    whitepointer23 Previous Member

    i do see your point tom, i do have compass and charts for back up. just haven't needed them yet.
     

  15. CatBuilder

    CatBuilder Previous Member

    That's a good point about mountainous regions, fjords, etc. I use what all large ships in the states use. I use NOAA ENC charts, which are instantly updated with new wrecks and way more current than even buying the newest paper chart out. If I want to see land based features, they are right on the electronic chart. If I'm feeling like looking at the srandard paper chart format, I just hit a button and the normal paper chart comes up instead of the ENC. That's called a raster chart. It's just the paper chart format overlay right on the screen.

    There is no navigational difference between using paper and an electronic raster chart. They are the same chart. Have a look.

    http://www.gpsnavx.com/index.php?page=Screenshots

    They didn't have a direct link to the screenshots for the ENC program, but if you go to macenc.com, then click "screenshots" at the top, you'll see the ENC display type added to the screen shots in the link above.

    Look at all the information at your finger tips. Far more safe than just a paper chart.

    However, a prudent navigator will never rely on one source of position data. The eyes and ears, magnetic compass, etc, should all agree with the electronic charts. Nothing worse than those people who pilot a boat face-down in the electronics!
     
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