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My chartplotter has a feature that allows me to look up tide information and multiple locations. Is this information preprogrammed into the plotter or does it come programmed with the map chip? For the record, mine is a Garmin 182c with bluechart preprogrammed chip.
I'm thinking of updating my sonar to a different product that will likely use Navionics Gold chips for maps.
Where does the tide and lunar information come from?
It is programmed on the chip, at least that was my experience with my old 178C. Easy thing to confirm...power down unit, remove card, repower unit and try to look at tide tables.
It is more likely calculated on the fly based on a number of factors that are pre-programmed and then updated from time to time. They probably don't actually program all of the tide points for thousands of locations.
It is broadly an estimate. I've seen them be off by hours for a specific location, and storms can throw them off. But it's better than nothing, and probably a little more accurate than the paper charts with offsets for various shore points.
__________________
Terry Jason 35, Yanmar 370 hp, Lots of fun at a leisurely pace
Hardly! Tide tables are programmed into the chip for several dozen locations covered by that particular chip. I've cross-referenced several locations with different sourced tables and found 'em within minutes of each other. Tide tables aren't rocket science, and obviously daily accuracy can be influenced by storms or high winds.
They are in the chip, in my case Navionics Gold +. Just like marina information. Think about it, the plotter itself is designed to be used anywhere in the world.
Water level is the result of wind direction and duration more than where the moon and sun are, but those postions are something that a GPS can calculate from a given lat/long. The tide tables you see in calendars and magazines are calculated the same way, from a relatively complicated algorythm. Even the less expensive handheld GPSs have a list of sites and positions to calculate this, and will find the one closest to you if you want.
In order to display actual water levels, a Chart Plotter has to have some way of receiving the information live, such as from XM or Sirius Weather satellite transmissions. Some NOAA sites are incorporating wind and weather history data to provide predicted water levels on an experimental basis. This is something to look forward to having on future systems.
__________________ If it ain't broke, I haven't played with it.
If you don't think it's rocket science, then I defy you to predict what position the moon will be in on a specific date and time.
The math is actually very involved, but it doesn't require that you have every day plotted and cataloged on a chip.
If you want to prove it to yourself, look at the tide tables for June 2nd, 1991. They are there on your garmin. Now why would they include data for a day almost 20 years ago on a chip they just sold you?
Now shoot ahead 20 years. Any data there (I haven't looked, just curious)?
The reason is that they calculate the info for any specific day and location using algorithms that only depend on a small amount of data.
I'm not saying that I know this is what they do, just that it makes the most sense.
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Terry Jason 35, Yanmar 370 hp, Lots of fun at a leisurely pace
Some devices have them built-in (pre-programmed), some are based on a chart-chip. Depends on the manufacturer.
Keep in mind that tide and current data is only a prediction. A variety of factors can alter the actual time of a tide, and the height of the water. Most notably, storms and local winds.
For example, a strong wind out of the west at low tide will blow most of the water out of the cove where my boat is moored for an extra-low tide. Tide tables can't predict this.
__________________ __________________________ "Jennifer B."
2006 Sea Ray 270 Amberjack
Setauket, NY (Long Island)
As an experiment, look up tides with no chips in your GPS. I think this capability is so fundamental that its built into all marine GPSs and doesn't need a data cartridge.
__________________ If it ain't broke, I haven't played with it.
In addition to what has already been said,... the plotters do not have to store 1000's of tide stations data. They simply store the station name and location (lat/long), and it's tidal offset to it's main station.
Example, ALL Long Island and most NJ tide stations (100's of them), are all based on the Sandy Hook NJ main station. Fire Island Coast gaurd station is simply an offset to the Sandy hook station. If Sandy hook is High at 1:00pm, and FICG has a -30 mins offset, then FICG's tide is high at 12:30.
Someone please explain this to me? 
