Thanks! That makes life easy :cool2:!
Is 9'8" per section (to allow for stretch when wet) a standard for all lines?
No, different types and thickness lines will have different stretching characteristics, but as someone posted if you want better accuracy use a surveyor's tape. Fofo and I often use the reel line for our quick and dirty surveys, but use a tape (normally run along a taut line) for higher precision mapping. BTW, IIRR this book:
Basic underwater cave surveying (Open Library)
describes two different methods of tying knots every 10 feet. Fofo's got a copy, and will probably be willing to loan it if asked nicely
If you want to avoid tying knots, it's also possible to use an indelible ink pen. I marked my reel line by wrapping the end around a nail on a fence, then stretched it horizontally over another nail ten feet down the fence using the weight of the reel. After I made each mark I'd move it to the first nail, then hang the next length over the second (letting out line from the reel as necessary).
The advantage of using an indelible ink marker instead of tying knots is that it takes up far less line and/or you can get more line on the reel, and you can mark the line for distance so that you don't have to count knots. The disadvantage is that this only works when you can see the line to read the marks, so isn't adequate in siltouts, but works fine in Monterey (I've used it in vis as low as 1').
I mark mine as follows:
A narrow (ca. 1/10th inch) ring every 1" for the first foot; a narrow ring every 1' from 1' to 5'; a narrow ring every odd five feet (i.e. 5, 15, 25, 35' etc.; one to four narrow rings every even multiple of ten feet -- one at 10 feet, two at 20 feet, three at 30 feet, and four at forty feet; Every ten feet from 50 to 90 feet, precede the narrow ring(s) with a medium ring, either 1/4", 1/2" or 1" wide as you prefer. So, at 50' there's one medium wide ring, at 60' one medium ring and one narrow ring, at 70' one medium ring and two narrow, etc. At 100' use a wide, 1" or 2" ring, and then combinations of narrow and medium rings as appropriate. This method will allow you to run your line without having to count knots, and you will always be within 5' of a distinctive distance marking.
HTH,
Guy