On 22 Jan 2006, "Bob Crantz" wrote:

How does one calculate time differences per
mile using PHRF?

Even if not one design and if conducted under a PHRF rating system,
not all races are scored on a "per mile" basis. IOW, there can also
be time against time or other variations (including, too, by building
in the handicap "up front" by stipulating which boats will start at
which different pre-agreed times based on their ratings in light of
the length of the course, then just calculating who finishes in what
order whether or not for the purpose of the particular race also
calculating the differences in finishing times).

Other race sponsors might also adjust the competing boats' ratings
over time based on some pre-agreed standard depending who finishes
when in the last # number of races; etc., etc.

Is it some type of square or cubic law?

For a straightforward time/disance conducted race, all that most
commonly is needed is a simple arithmetic calculation -- i.e., just
multiplying the difference in seconds at the finish depending on the
particular boat's rating by the number of miles of the race.
F'r'instance:

If a C&C 99 has a PHRF of 99 [is racing against a B] 35s5
with a PHRF of 132, wouldn't the 35s5 then be almost
indistinguishable from an Express 30 with a PHRF of 139?

In/for this example for a time/distance race, the C&C "owes" the B 33
seconds/mile, "owes" the Express 40 seconds a mile, and the B "owes"
the Express 7 seconds/mile.

Over even a typical 'round-the-cans (i.e., comparatively short)
course, e.g., 5 to 8 miles, on a seconds-per-mile basis these are very
far from "indistinguishable" differences (even if all three different
competing boats were to finish within seconds of one another, as also
is not uncommon).

Bear also in mind that (although in this respect, too, often with
pre-agreed variations) most race participants and race committees will
have agreed in advance that the course for a particular race will be
selected at race time to try to accord more or less equal lengths to
an as near as practicable upwind, downwind, and broad reach leg (or
something close to that) and that these different points of sail can,
in turn, materially affect different boats' over-all performances
depending far more on skill of crew (if the rating assigned has been
well-calculated) than on a particular boat's inherent design.

Of course, (if there are such) generally prevailing weather and
related sailing conditions can (more or less) "favor" some boats as
against others and, if/where so, it is open to the participants and
race committees to address this factor.

E.g., it may be that in some particular location it is quite common
for wind often to diminish beginning early in the evening and yet for
races to be held at that time of day and, if so, this factor may favor
the lighter/faster boats especially over comparatively shorter courses
quite apart from the rating assigned itself (which is one reason why
in such areas there might be some agreed adjustment in the otherwise
assigned PHRF depending on historical performance of particular boats
and crews; or not, as the case may be).

Granted, it is fun to win and the "type-A" personality-pariticpants
might feel a "need" to win; but the basic idea is: have a good/fun
time while more less fairly testing one's skills - not necessarily
(let alone preferably) a, "Yuh gotta be a 'rocket scientist' (or cube
root calculator)!" kind of Thing.

Thanks!