The Four Length Zone

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John Ball
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The Four Length Zone

Post by John Ball » Sat Jul 01, 2017 4:55 pm

Would RC sailing be better served by moving to a Three length zone? The RRS defines the zone as three boat lengths, and Appendix E modifies that to four lengths. I wrote to the IRSA Rules Committee several years ago, suggesting this change. The answer was that there is no discussion nor support for such a change. So my intent here is to generate some discussion and gauge support for such a change.

History. The RRS used to specify a two length zone, and RC sailing adopted a four length zone to allow for more reaction time. Subsequently the RRS changed the zone to three lengths, but Appendix E did not change.

Why would we want consider changing Appendix E to use the three length zone? I suggest several reasons.

1. Mark Room rights conferred by R 18 are based on accurately placing the boats positions when the first boat touches the zone. Many skippers have difficulty visualizing the four length zone. It is easy to visualize one length, a little harder to visualize two, harder again to visualize three and so on. The larger the zone, the harder it is to visualize its location. So a smaller zone would assist a more accurate visualization. The counter argument is that a four length zone provides more reaction time that a three length zone.

2. The World Sailing Case Book examples all relate to a three length zone. It is possible with the larger four length zone for issues to develop which may not happen in the smaller zone. If we drop the Appendix E change, and use the three length zone, then all relevant cases would apply.

3. The RRS 2017- 2020 version introduced a change to RRS 18.3 Tacking in the zone. Under the new version, a stbd tack boat has to be fetching the mark from outside the zone for R 18.3 to apply. If R 18.3 applies then the port tack boat that tacks inside the stbd tack boat does not receive Mark Room and may not force the stbd tack boat above close hauled.

However when both boats enter the zone on port and tack to stbd, then 18.3 does not apply and when they become overlapped, 18.2.a will apply. This gives Mark Room to the inside boat as soon as she passes head to wind (HTW) and the outside boat must give her that room. With Mark Room comes R21 Exoneration, so even if the inside boat tacks close to the outside boat, she is exonerated for breaking R 13 Tacking.

There is a major shift in rights between these two scenarios, and it is all based on when the outside boat achieved stbd tack relative to the location of the zone. I wrote about this change on my Rules discussion web site and here is the link
https://drive.google.com/file/d/0B-S2o ... sp=sharing

Here is an example. We have two boats sailing close hauled on port tack and approaching the stbd tack lay line for a mark to be rounded to port. Yellow is to windward and about two boat lengths below the port lay line. Green is about two boat lengths to leeward of Yellow and sufficiently clear ahead that she can tack to stbd and not break R 13 Tacking. Green tacks on the lay line. Yellow tacks inside Green. Green goes above HTW and there is contact. Yellow touches the mark, and there is contact between the boats.

If there were a three length zone, it would be easy to infer that Green entered the zone on stbd and R 18.3 would apply and Yellow would be at fault. However with a four length zone, it is very close as to where Green passed HTW and gained stbd tack – inside or outside the zone. Yet the outcome for this incident and the applicable rule (R 18.3 or 18.2.a) is dependent upon this factor.

Here are the two boats – the diagrams are identical, except that the zone is changed from three lengths to four. Remember that there are no circles on the water, and we have to estimate the location of the zone, possibly from a distance of 30 meters or more.

John
John Ball
IOM CAN 307 (V8)

John Ball
Posts: 145
Joined: Wed Dec 04, 2013 7:12 pm

Re: The Four Length Zone

Post by John Ball » Sat Jul 01, 2017 5:05 pm

I had a problem attaching the diagrams to the post directly.

Here are links to the diagrams

https://drive.google.com/file/d/0B-S2oC ... sp=sharing

https://drive.google.com/file/d/0B-S2oC ... sp=sharing

John
John Ball
IOM CAN 307 (V8)

John Ball
Posts: 145
Joined: Wed Dec 04, 2013 7:12 pm

Re: The Four Length Zone

Post by John Ball » Mon Jul 03, 2017 2:34 pm

Here are the diagrams now attached, thanks to the web master.

John
Attachments
Three length zone R 18.3 applies.jpg
Three length zone and R 18.3 applies.
Four Lenght Zone R 18.3 or R 18.2.a applies.jpg
Four length zone - either R 18.3 or 18.2.a applies
John Ball
IOM CAN 307 (V8)

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