Does the safety contour change with tide?

[Canopus]

Couldn't find this in the Opencpn faq...

Question: I can see the safety contour on the display, and can change it by entering a new safety depth. But, what I don't know is whether the safety contour changes as the tide changes. Sorry if this has been asked before.

[HankOnthewater]

No, the contours do not change. The measurements are done at LAT lowest astronomical tide.
When in that erea, you need to know the state of the tide at that particular moment, plus if one is pedantic,
any adjustment up or down due to surge, wind and airpressure.
So if the chart shows a depth of 4 metres, and the tide is 1.5 mt, then you can expect a depth reading of 5.5 metres

[JPA Cate]

In HankOnTheWater's post above, you can count on at least 1.5 m higher, but it depends also on whether the weather conditions lead the water to pile up along the safety contour you've set or not.

For instance, a catamaran was washed ashore on the ocean side of Huahine, when he was following a close inshore contour line when the enhanced trades had been blowing for 3-4 days. A wave just lifted him up and set him down 50 ft. west, instantaneously. Very sad.

Ann

[Kettlewell]

By the way, it is almost never a good idea to use a safety contour so close to land that the tide might come into play. I would use a huge safety margin for that, except in really shallow areas like the Bahamas.

[CaptTom]

Originally Posted by HankOnthewater

...The measurements are done at LAT lowest astronomical tide...

Interesting. In the US, NOAA charts have always used MLLW (Mean Lower Low Water) as datum for depths. So there is even less water than charted during spring low tides. I recall leaving an anchorage once during a spring low and seeing two sailboats heeled over quite a bit at anchor. Apparently they didn't factor in the phase of the moon when picking a spot to drop the hook.

[P_Dub]

In the future with the new S100 vector charts, it will probably happen. But this may take some times.

[P_Dub]

In the future with the new S100 vector charts, it will probably happen. But this may take some times. Personally I don't agree with such modification, because there are too many fools who would mess with this and furthermore, it will have to be in limited zone in connection with the actual tide gauge recorded stations.

[sv_pelagia]

Doesn't Navionics app have this as a possible setting/option? (i.e., adjusting displayed depths according to some nearby tide station)



Not a good idea in my mind