This article refers to the Survey Down Restriction Grade table. More information about this system can be found here.

RESTRICTION GRADES:
POTENTIAL REVISIONS

• by Rory O’Keefe, September 1, 2022

In developing the measurement-based restriction grading system I have considered a few additional features that I would like to describe here as potential future revisions.

Each publication of the measurement-based restriction table must display a version number. This is to allow future modification to the system if it is deemed necessary.



1. AN UNDERSCORE REPRESENTS A LONG RESTRICTION

The proposal is that a grade should be underscored when the restriction is sustained for approximately 3 m/10 ft or more. 

The rationale is that a longer-than-bodylength restriction is significantly more challenging than a short restriction. When there is open space on either side of a short restriction, divers can use this space to easily correct their positioning and assist their passage. If the restriction is more than a full body length, this advantage is lost. Therefore, the classification of an extended restriction should be reserved for areas that confine the entire body of a diver with no possibility of reaching out into an open space for assistance. 

Note that 3 m/10 ft is the standard increment on knotted exploration line, making this an easy distance to measure for the cartographer.

2. A “+” SYMBOL DESIGNATES A GRADE THAT IS CLOSE TO A HIGHER RATING

Most rock-climbing grades use of a + symbol to indicate that a climb is approaching the difficulty limit of its rating. With that said, climbing ratings are largely based on opinion, whereas the restriction grading system will be measurement-based, which theoretically makes the + symbol unnecessary.



However, cartographers are still presented with the challenge of measuring and grading unusually shaped restrictions. In these cases, the use of a + symbol may actually be of some use.

There are two possible ways that this + modifier can be used. It can be applied to individually to each of the width and height ratings, or applied to the overall grade. Examples of this would be as follows:

• D+3 = Width is close to an E, height is a confident 3.

• D3+ = Width is a confident D, height is close to a 4.

• D+3+ = Width is close to an E, height is close to a 4. 

• D3+ = The restriction is not easily measured and may be more challenging than indicated. 


As seen above, a simple + modifier can complicate the grading system, particularly if a cartographer develops a bad habit of overusing it.

I also want to emphasize that the measurement-based grading system was created to remove personal opinion from a restriction rating, and implementing a + modifier will insert an option for opinion into every grade. 

For this reason, the + modifier was not chosen to be part of the grading system at this time, but I do feel that it deserves consideration from the cave diving community.

3. EXPAND THE TABLE TO INCLUDE ALL PASSAGE SIZES

Expanding the grading system to include ratings for all passage sizes is feasible, however, in my trials this presented one major flaw: The restriction ratings became difficult to find. 

With that said, the restriction rating could be shown in a different color than the passage ratings, but this doesn’t change the fact that there would now be hundreds of passage ratings cluttering the map. 

Remember: A passage rating must be shown whenever the cave changes enough to be categorized under a new rating. This happens almost constantly. 

To reduce the number of passage ratings, the passage measurements could be recorded in larger increments of 3 m/10 ft, however, at that point they are no longer describing the passage dimensions to a useful degree.

One argument for including passage ratings would be for their usefulness on a stick map. Stick maps do not typically show any information about the passage dimensions, and so even heavily generalized ratings would provide useful information to a diver. However, a surveyor’s efforts would be better spent in estimating LRUD data that can be used to automatically compile a basic map.

I ultimately decided not to include passage ratings in this system as I found that they cluttered the map. However, the idea still holds merit in the case of stick maps and so it should be presented as a possible future implementation.

SUGGESTIONS?

We're open to ideas so please send your thoughts and/or suggestions to info@surveydown.com.