SeaTalks about Coastal Navigation

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Posted 2016, Nov 09 12:36
I am confused on the tidal curve example (the first animated one)... it asks the range of time during the day when depth of water will be above 2m. However it uses the same High low tide slope for after the high tide at 8:52 (7:52) as well as before it. However the low tide before 8:52 which is actually at 2:52 (or 1:52 I can't remember since the sea talks page doesn't allow me to keep the module open at the same time) is 1.6m instead of the 1.0 m after the 8:52 (7:52) high tide. This would seem significant and indiate you'd need to do a different line. Furthermore it would also appear that the curve would not accommodate the prior low tide (it's out of the time range of the curve which only has a 5 hour range to either side whereas the low tide is more than 6 hours from the high tide. How does one adjust for these issues or am I overthinking this?
Posted 2016, Nov 10 03:45
"To get the height differences you should also interpolate for high tide between 0.2 meters (Spring) and -0.2 meters (Neap) for the high tide and since we are closer to Neap intuition would say about -0.1 meters. And for low tide between 0.2 (Spring) and 0.5 (Neap) - intuition = about 0.4 because we are closer to Neap. Thus on your tide curve the low tide number would be Frazer minus 0.1 meters and for high tide Frazer plus 0.4 meters." This reasoning is puzzling: For the interpolation which low tides at the Port are being used: 1.6 or 1.0; and similarly 3.3 or 3.6 for the high tides. The problem is, you can't use interpolation for the 1.6 or the 3.3 because they are outside of the ranges specified for the secondary station (for low: 0.4 to 1.1; for high tides 3.3-3.6). Which tides of the fictitious port are being used? Or are we deriving the height based on if the time is in the middle between the neap and spring high tides then it should directly in the middle of the neap and spring high tide heights?
Posted 2016, Nov 11 14:07
In the examples I think it would be useful to remind the reader... which side of the COG that you draw the arc for the 1 hr course - (the side you expect the current to be coming from ) and that you connect the head of the current vector to the COG and the tail to the arc. .... or if you begin with the current vector first you have the tail at the origin and.
Posted 2016, Nov 20 13:59
I am a bit confused as to how to label the ship's compass bearing and a handheld compass bearing in the TVMDC algorithm.
Posted 2016, Dec 10 17:59
Curious to know if anyone has any opinion on how many lines of position generally suffice for a reasonable fix? I suppose technically two is sufficient assuming perfect accuracy but lets say you had 4 as opposed to 3.. would it help that much?
Posted 2016, Dec 24 17:21
In the quick questions part of the module Q3... to solve this you said that May 7 was approximately midway between a Neap and a Spring. That makes sense. However in the Sample problem at the end of the module you compared the tidal range. If you did the same for the May 7 problem (and then compared it against the tidal curve tide range data) you would have actually found the range to be rather close to a neap and not mid-range. How do you reconcile the two techniques. If you have tidal range data should you use that rather than date between neap and spring?
Posted 2016, Dec 28 03:31
Is there standard notation for your planned route, (for example your waypoints) so they don't get confused with your Estimated Positions, Dead reckonings and fixes?
Posted 2017, Jan 07 22:04
NOAA only shows two charts but none with the suffix of TR. We find #12354JM and 12354GM. Any suggestions?
Posted 2017, Jan 10 13:19
How does / can the bow & beam, double angle technique work with leeway or current? I'm thinking it may need some modification since the boat's heading / course to steer might not match up with the course over ground.
Posted 2017, Apr 04 12:55
I found this chart online (NOAA Chart 12354) & have down loaded the PDF File. I brought it to the local Print shop as stated, but they are unable to print as we don't know the correct size to print the chart. There is a scale on the PDF that states it must be 6" long to be the correct scale, but it would be "trial & error" & possibly a few prints at my cost to ensure the correct scale. I did a bit of research online & it states that most charts are either 36" or 42", but this don't help much, which do I need. NOTE: I am in Canada & there is no NOAA "Print on Demand" service available locally.
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