The number is a function of the weight of the first 10 (I think) yards of
the fly line.

Therefore it's simply how much weight you need to put the optimal tension in
the rod to achieve maximum casting distance. If you don't (or can't)
aerialise the appropriate length of line you won't load the rod adequately
and won't maximise the cast.

This means two things. Firstly if, for instance, you fish small streams with
a short line you probably need to fish a heavier line than the rod is rated
for and secondly if you overload a rod with too heavy a line it could well
break. With an unmarked rod it's going to be trial and error, but bear in
mind how you are going to use the rod in practical situations as well as
simply heading for your local park with a selection of lines.

Mark

"W. D. Grey" wrote in message
...
In article , Ian D
writes
On Thu, 7 Apr 2005 06:38:29 +0100, "simon"
wrote:

How does one find / calculate the AFTMA number on a trout rod that is
notmarked with one?


Only practical way is to try a number of lines and find out which
weight suits both the rod, your own casting style and the intended
use.
AFTMA ratings for rods are purely arbitrary anyway, and are based on
the judgement of whoever tests out the prototype, so doing the above
could often be a good move even when you 'think' you know the AFTMA
rating.
I've often used rods where I've had to use lines up to +/- 2 AFTMA
sizes from that specified, to suit the occasion.

Cheers
Ian D

Good advice Ian, but I'd offer a word of caution to anyone having to
follow it. A line which is one or two # over that for which the line was
designed will usually fly out of the rings. I have had a rod break when
using a line only one # higher than the rod design. Rods will usually take
1 # more than the rated #. but enthusiastic casting could prove disastrous
:-).
--
Bill Grey
http://www.billboy.co.uk