Tidal Calculations - Secondary Ports.
HTML-код
- Опубликовано: 17 июн 2020
- Rarely do we sail only between Standard Ports so an understanding of Secondary Ports is essential.
Our 45 minute online training session aims to give you an Introduction or Revision to the following session content:
Almanac entries for Standard Ports & Secondary Ports
What secondary port data we find in the almanac
How to interpret the secondary port data
Calculating the HW and LW times and heights using secondary port data
Excellent, concise summary thank you. Decades since I last did this so the triangles are a welcome new technique.
Glad it was helpful!
These videos are brilliant!!
Thank you that was an excellent presentation of secondary port calculations
Excellent and clear explanation. Thank You.
Fantastic Presentation. You made it very understandable.. Thank You
Thanks for your very clear presentation on a potentially confusing topic . It is the way that you set out your working with clear labels that prevents serious miscalculation . I am sitting the Cruising Skipper instructor course in Sydney Australia . I will use your methodology with students if the topic comes up although in Australia the topic and method is a little simpler. This has been a big help for me because I have trouble with scales and interpolation as well as when to apply different time zones. I think this is a very confusing topic if you dont follow a precise method.
A superb tutorial - thank you.
You're very welcome!
Very good instructions
That was well explained, thanks!
Glad you enjoyed it!
To avoid any confusion the ports / times / locations use in this video are taken from the RYA Training Almanac and do not reference any real world locations.
Great Vid! My question is why did you use the LW at 9:47 instead at 22:22 to calculate the range in your DST example? Can I chose any LW-level which is close the HW? My second question is since in the question stem is has been asked after LW so why do you use HW?
Very well presented and thorough. Do you mention the rule of twelfths at all, even as a sense check for students, where the tides fit well with that method? Thanks
Phillip yes rule of twelfths is usually covered during our basic tidal height sessions rather than here. This session is really to introduce and demystify secondary ports. Thanks for watching.
@@CompassSeaSchool Do you have a link to video that covers rule of twelfths, or the name of the video? Thank-you ahead of time!
Many thanks, I had an example where the standard port low water was lower than the secondary port mlws.......does this mean the difference is outside the range and if the difference is 0.2 it cannot be less?
Andre - the secondary port entires are for the Mean ranges it is always possible that the actual HW/LW can be higher or lower than the figures in the secondary port grids. In that case you can extend the triangles to accommodate the extra calculations. Hope that helps - Thanks Kath
Thanks for the accurate explanation. Could you al me to understand at the minute 20 of the tutorial, concern the mean spring and neep curves, how can I know if is spring or neep in this case?
Hi Stefano, you take the range for the day from the Almanac (HW - LW) and compare to the box on the tidal curve to see if it springs or neaps.
If I may ask, why at the 22:17 minute mark, the tidal range is calculated from deducting 1.0 and not 0.8 from 3.5? I would have thought 0.8 would be more appropriate because the range window in question is where 1900BST would fall within. Am I missing something? Appreciate your clarification. Thank you.
Hi Joseph. Yes technically you can use 0.8 - but that calculation is simply to figure out if it is springs it neaps and either number will give you the same result. Hope that helps.
@@CompassSeaSchool Thank you.
where is seasonal correction here in the calculation please?
Hi - many thanks for your presentation - much appreciated but still rather confused. In particular in your height calculations - first you are comparing HW springs with LW Neaps & HW Neaps with LW Springs? Do you not compare like with like? And second why is the first triangle created with a right angle for HW and not for LW? thanks again
David - sorry if you are confused. I am not sure what elements you are referring to for us comparing HW Sp and LW neaps I am afraid. Do you mean where we compare MHWS and MHWN? Is so that is the extent of the difference for the HW calculation, we then compare MLWN and MLWS for the LW calculation. The triangle is calculated on HW as we are using this calculation to correct a standard tidal curve for a secondary port and most tidal curves operate from HW. Hope that helps. If you are still struggling then perhaps a paid 1-2-1 session would assist?
Clear as mud. Two confusing to work out, then I was no good at maths at school
What if the high tide of May 3rd in your last example was at 0900. How would you create the HW Time Calcs sketch in that case?
Laura thanks for the question. If your HW @ Port Fraser sat at 0900UT then you would create the triangle using the data in the Sec Ports table with the timeline at the bottom going from 0600 to 1200 and the minutes on the top going from -0024 to -0048. Make sure that you allocate the correct minutes to the correct ends of the timeline. Once drawn you can use the same method to find the difference for 0900.
@@CompassSeaSchool I am so grateful for your response, and the whole video! It is so clear, and methodical, and love that at the end you show how you can estimate also!