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Board » General Discussion » RRS rules about mark roundings

Posted by
Rod


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2010-06-24 22:30:48
2015-06-23 20:21:39 - RRS rules about mark roundings
28.2 A string representing a boat’s track from the time she begins to
approach the starting line from its pre-start side to start until she
finishes shall, when drawn taut,
(a) pass each mark on the required side and in the correct order,
(b) touch each rounding mark, and
(c) pass between the marks of a gate from the direction of the
previous mark.
She may correct any errors to comply with this rule, provided she has
not finished.

This was in response to a question that arose in the Practice Race at Kiele on 23 June 2014.
Do the SOL rules state it the same?

--- Last Edited by Rod at 2015-06-23 20:40:08 ---
If it breaks, it's not strong enough--if it doesn't, it's too heavy.
Posted by
kroppyer


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2010-02-05 15:25:55
2015-06-23 23:25:51 - Re: RRS rules about mark roundings
No.

One difference is that sol uses rhumb lines between marks. I'm sure that when drawing this imaginary string taut, it would follow a GC line, not a rhumb line. There might be more differences (I'm not sure because I find the RRS rule ambiguous).

In sol the course to be sailed in drawn on screen, order of roundings and direction of roundings is clear. While racing you can either round the next mark, or unround the previous, other marks are not in play.

Unrounding happens* when you cross the rounding line in the wrong direction and after crossing you've crossed the rounding line as many times in the correct direction as in the incorrect direction.

Rounding happens* when you cross the rounding line in the correct direction and before crossing you've crossed the rounding line as many times in the correct direction as in the incorrect direction.

Say we have marks A, B, C (in that order), then the rounding line of B is a line starting at B, moving away from A, B and C. Additionally, the rounding line lays on the bisector of angle ABC.

*) This is how I understand it should happen. I'm not entirely sure that this is the case when you sail multiple laps around the mark.

In any case, you should be able to round your next mark by sailing around it in the correct direction until it says "rounded", i.e. there's no "going in the wrong direction to unround". If you have trouble rounding the mark, it means you've already rounded in the wrong direction, all that's left is sailing around the mark in the correct direction.

----

Two more things:
- I don't like the RRS wording/theory.

- PRs are different.

--- Last Edited by kroppyer at 2015-06-23 23:34:20 ---
Posted by
Rod


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2010-06-24 22:30:48
2015-06-29 01:35:48 - Re: RRS rules about mark roundings
My interest stemmed from a consideration of the logic behind ANY mark rounding rule on the computer. If the SOL rule was to be applied to a spherical Earth, the projected 'rounding line' would circle the Earth and enter the mark from the rear, thus making the "miss, return and round correctly" of the RRS impossible. The field of action would have to be limited in total area to make it possible.
If the map used was to be a Mercator's projection, then no area limitation would be required.
In the case in point, if the turn mark had been just a small distance (3 pixels?) off shore, then the island could indeed have been rounded the "wrong" way,and all requirements for a successful rounding could have been met.
If it breaks, it's not strong enough--if it doesn't, it's too heavy.
Posted by
kroppyer


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2015-06-29 13:00:55 - Re: RRS rules about mark roundings
Rounding lines in SOL are loxodromic (straight on Mercator projection). This has previously resulted in some weird DTF numbers. It is indeed very hard to define rounding a mark on a sphere. Gates almost always work, so I'd say that rounding a mark is similar to sailing through a gate with the mark to be rounded on one side, and some point on the course boundary on the other.

If there is a mark 3px offshore from an island, and only the rounding direction of the mark is specified (nothing about the island), you could indeed round the mark correctly, while 1) not rounding the island or 2) rounding is opposite to the mark. Sol doesn't work with islands that way. If we want to have a course round an island, we place the mark on the island, forcing your to round the entire island.

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