This article is from the Boats FAQ, by John F. Hughes with numerous contributions by others.

[Contributed by Roy Smith]

PHRF (pronounced "perf") is Performance Handicap Racing Fleet. Unlike

other rating systems (IOR, IMS, etc), PHRF ratings are not assigned

based on some sort of measurement, but rather on past performance of

similar boats. If you are racing in a club race or a local weekday

evening or weekend series, where different kinds of boats race against

each other, the odds are that PHRF is the rating system you're

using. In PHRF, boats are assigned ratings in seconds per mile. Your

rating is the number of seconds per mile your boat is supposedly

slower than a theoretical boat which rates 0. Most boats you are

likely to sail on rate somewhere in the range of about 50 to 250. All

ratings are multiples of 3 seconds/mile (i.e. the next faster rating

than 171 is 168). I think this is done as a recognition that the

rating process just isn't accurate enough to justify rating boats to 1

second/mile resolution.

Typically, a certain type of boat is given a stock rating based on

past experience. Just to make it a bit more interesting, ratings vary

somewhat depending on location; each YRA (Yacht Racing Association)

can assign its own rating to a class of boat depending on their local

experiences and conditions. For example, Western Long Island Sound,

under the jurisdiction of YRA of LIS, is famous for light wind, which

tends to give an advantage to certain types of boats, and YRA of LIS

takes that into account when assigning ratings.

On top of your regional stock rating, there are a variety of standard

rating adjustments depending on how your boat is rigged. The standard

PHRF rules allow you to have a 153% genoa. You can carry a larger

sail, but take a rating penalty for it. Likewise, you can chose to not

carry that big a sail and get a rating advantage. Having a

non-standard keel, extra tall or short mast, a fixed prop (the stock

ratings assume a folding or feathering prop), extra long or short

spinnaker pole, etc, all result in rating changes. Some boats have

several stock ratings for different common variations. For example,

there are 4 configurations of J/29's; masthead or fractional rig and

inboard or outboard.

Once you've got your basic rating, adjusted for location and

customizations you may have done, you still have the option of

petitioning for a rating change based on whatever evidence you might

care to present to prove that your rating is too fast (or the other

guy's is too slow), an area that quickly gets into politics and boat

lawyers. There are two flavors of PHRF, Time-on-Distance (TOD) and

Time- on-Time (TOT). TOD is the more traditional and easier to

understand, so let's start there. In TOD, you get a handicap equal to

the length of the race course in nautical miles multiplied by your

rating in seconds/mile. Thus, for a 6 mile race, a boat that rates 120

would get a 720 second handicap, i.e. her corrected finish time would

be 720 seconds less than her actual time to complete the race. What

people tend to do is think not so much about the actual rating, but

rating differences, i.e. if you rate 120 and the other guy rates 111,

he owes you 9 seconds per mile, so for a 6 mile race, as long as he

finishes less than 54 seconds in front of you, you will correct over

him and win.

The other flavor of PHRF is Time-on-Time (TOT). In TOT, it's not the

length of the race course that matters, it's the amount of time the

race takes. To do TOT, first you have to convert your normal rating,

R, in seconds per mile to a factor, F. The formula to convert R to F

varies from place to place, but it's typically something like F = 600

/ (480 + R). Actually, it's really something like F = 600 / ((600 -

Rav) + R), where Rav is the average rating of all the boats in the

fleet. Locally, we use an Rav of 120 which gives the formula with the

480 in the denominator. For reasonable values of R, you get an F which

is a number close to 1. For example, a J/24 rating 171 has an F of

0.9217, while a Newport-41 rating 108 has an F of 1.020. To score the

race, you take each boat's finish time, subtract their start time

(giving their raw elapsed time) and multiply by their F, giving their

Corrected Elapsed Time (CET). The theory behind TOT is that in a slow

race (i.e. light wind), the boats tend to spread out but since the

amount of time each boat owes the others is fixed by the length of the

race course (in TOD), slow (i.e. light wind) races tend to favor the

faster boats.

On of the problems with TOT is that there is no universally accepted

formula for converting R to F. With the sort of formula used above,

you can argue about what should be used for Rav. What we do locally is

use one Rav for the entire fleet, which is 8 divisions with ratings

ranging from 36 to about 250 or so. Some people think we should

calculate an Rav for each division, for example. Some people think TOT

is a total crock and want to go back to TOD.

Contributed by Stephen Bailey (sb)]

Sailboats racing under a "handicap system" have a function applied to

their elapsed time, producing a "corrected time," and the boats place

in corrected time order. This function, which differs among systems,

attempts to fairly represent speed differences among boats.

There are two major handicapping philosophies: "measurement" rules

which handicap based upon measurements, and "rating" rules which

handicap based upon observed performance.

The International Offshore Rule (IOR) is a measurement rule for racing

boats. The IOR evolved from the Cruising Club of America (CCA) rule

for racer/cruisers.

The IOR concentrates on hull shape with length, beam, free board and

girth measurements, foretriangle, mast and boom measurements, and

stability with an inclination test.

The IOR also identifies features which are dangerous or it can't fairly

rate, and penalizes or prohibits them.

The measurements and penalties are used to compute the handicap

number which is an "IOR length" in feet. A typical IOR 40 footer (a "one

tonner") has rating of 30.55 feet.

In a handicapped race, the IOR length is used to compute a "time

allowance," in seconds per nautical mile (s/M) which is multiplied by

the distance of the race, and subtracted from the boat's actual time,

to compute the boat's corrected time. Longer IOR length gives a

smaller time allowance.

The IOR is also used to define "level classes," where no time correction is

used. Every boat in a class has an IOR number less than some number.

The Ton Classes, (Mini Ton, 1/4 Ton, 1/2 Ton, 3/4 Ton, 1 Ton, and Two

Ton), as well as 50-footer, ULDB 70 and Maxi classes are examples.

To account for improvements in design and materials, boats are given an

"old age allowance" which decreases their IOR length as time passes. In

spite of the old age allowance, about 3/4 s/M/year on 40 footer, boats

over several years old are usually not competitive, which is why IOR

handicap racing is dead.

Peculiarities of IOR designs result from features which increase actual

performance more than they increase IOR length, or other odd rules; IOR

hulls bulge at girth measurement points; a reverse transom moves a girth

measurement point to a thicker part of the hull; waterline length is

measured while floating upright, so large overhangs are used to increase

waterline sailing at speed; the stability factor ignores crew, so IOR

designers assume lots of live ballast; after the 1979 Fastnet race excessive

tenderness was penalized; full length battens were prohibited to prevent

main sail roach area, but short battens became strong enough that the

IOR had to start measuring and penalizing extra main sail girth; main

sail area adds less IOR length than jib area, so new IOR boats are

fractionally rigged; The IOR encourages high free board, and high booms

and prohibits keels wider at the bottom than at the top (bulbs).

The Midget Offshore Racing Club Rule (MORC) is a measurement rule

for racing boats no longer than 30 feet. The MORC rule is similar to the

IOR. It computes a handicap length from various measurements, which is

used to define level classes and derive time allowances.

MORC seems to work better than IOR because the range of boats it

attempts to handicap is not as large, and it is more quickly modified when

problems arise. For example, the MORC recently adjusted their old age

allowance to permit older boats to be competitive.

The International Measurement System (IMS) is a measurement system

intended for racer/cruisers. The IOR was not fair to racer/cruisers, so the

Measurement Handicap System (MHS) was invented, in 1981, and

accepted internationally, as the IMS in 1985.

With a diverse collection of boats, relative performance varies not just

with design, but also with race conditions. A 33 footer can beat a 40

footer upwind in moderate wind, but the 40 footer will probably come out

ahead in heavier winds, or on a reach.

The IMS uses a Velocity Prediction Program (VPP) to predict speed on

different points of sail in different wind strengths. From the predictions,

and the distance, course type and wind strength of a race, a time

allowance is computed for each boat and subtracted from the boat's

elapsed time to give corrected time.

IMS rule designers believe the key to fairly handicapping diverse hull

shapes is measuring a large number of points all over the hull and

appendages, measuring sail area accurately, and using an inclination test

(which is the same as the IOR). The VPP uses these measurements to

account for heeling, crew on the rail, the immersed shape, and other

factors.

The IMS VPP doesn't yet account for dynamic drag of a boat pitching in

waves, nor for appendage shapes which result in reduced drag. Some

parameters are based upon incomplete experimental evidence. For

example, the VPP predicts a greater benefit from full battens than is

realized in practice.

IMS defines a "General Purpose Rating," which is a predicted time per

mile around a particular course, in 10 knots of wind. A typical IMS 40

footer has a GPR around 595 s/M.

The Performance Handicap Rating Factor (PHRF) is a subjective rating

rule. PHRF was developed to handicap monohulls that didn't fit under

the rubric of other handicap systems. It has since become the most

popular handicapping system in the US, being almost universally used in

club racing.

PHRF assigns a boat a rating, in s/M, which is multiplied by the length

of the course and subtracted from the boat's elapsed time to give

corrected time.

Ratings are assigned by a committee of the local racing authority,

formed from representatives of the member clubs. The initial rating

for a boat is based upon any information available, such as the boat's

rating in another area, ratings under other handicap systems,

information from the designer, ratings of similar boats, and a set of

standard adjustments to basic ratings (e.g. fixed prop, extra large

sails, etc.) All ratings are multiples of 3 s/M. For example, a J/24

rates around 171 s/M, and a J/35 around 69 s/M in many areas.

Since ratings are assigned and administrated locally, they may account for

local conditions. A good heavy air boat would rate faster in San Francisco

Bay, than in Long Island Sound.

A member may appeal a rating, presenting evidence, such as race results,

which supports the appeal. The local committee's decision may be

appealed to a committee of PHRF handicappers from all over the country.

Although PHRF is subjective, it still attempts to rate the boat, in racing

trim, with a perfect crew. Just because a boat never wins, or always wins

doesn't mean its rating should or shouldn't be adjusted.

Using this system, the slower the race, the smaller the percentage by

which a faster boat must beat a slower boat. To correct this, some PHRF

races are handicapped by multiplying a boat with rating R's elapsed time

by (C / ((C - Rav) + R)), where Rav is the fleet's average rating, and C

is a constant around 600-700, to compute corrected time. This system is

called "time on time", the previous, more common, system is "time on

distance."

The two systems only differ substantially when ratings span a large range

(> 30 s/M), or races are long (in time). It is not clear which system is

ultimately fairer.

The Portsmouth Yardstick (PY) is a statistically based rating rule. The

PY was developed by the Dixie Inland Yacht Racing Association to

handicap any boat, including multihulls, which are excluded from all the

previously described handicap systems, based on performance in races.

The PY begins with a boat which is well sailed, and ubiquitous, called the

"Primary Yardstick." This boat is assigned a Portsmouth Number (PN),

which is the time the boat takes to travel a fixed, but unspecified

distance. In the US, the Thistle the primary yardstick, and its PN is 83.

Elapsed times are collected for races. The fastest boat of each type in a

race is assumed to have sailed a perfect race. The ratios of the fastest

boat's time to the fastest yardstick boat's time, normalized by the

yardstick boat's PN are averaged over all races to compute that boat's

PN. Statistical techniques are used to discard outlying data points. A

class with a large quantity of data, and no recent change in PN may

become a "Secondary Yardstick," used in the same fashion as the Primary

Yardstick. The Laser and J/24 are examples of Secondary Yardsticks.

The usual way to handicap with Portsmouth numbers is to multiply

elapsed time by 100/(PN) to compute corrected time. This is a "time on

time" system (see PHRF).

In addition, PY has begun to compute numbers for different wind

strengths. The Primary Yardstick is defined to have the same number

for all wind strengths. Using these numbers, clubs can more fairly

handicap races in various wind strengths.

Since the PY data are not broken down by course type, it assumed that

boats racing under the PY are racing courses similar to an Olympic,

triangle or Gold Cup course.

Below are formulas for converting among different system's ratings.

Accuracy of these conversions may vary. (And indeed, the last one has

been called into question by one reader, so you should probably treat it as

suspect).

PN = PHRF/6 + 55 PHRF = GPR - 550 PHRF = 2160/sqrt(IOR) - 198

Since we know that the IMS GPR is the time taken to cover a mile (of a

particular course), in 10 knots of wind, we can estimate a boat's speed

over this course given its PHRF rating:

v = 3600 / (PHRF + 550)

So, a J/24's (171 s/M) speed is 4.99 knots, a J/35's (69 s/m) is 5.81

knots. The J/35 is 16% faster. Note that the standard PHRF increment

of 3 s/m represents around a 0.4% change in boat speed.

Using the IOR conversion, a one tonner might rate 72 s/M, whereas they

are actually much faster than that, rating around 54 s/M PHRF. This

illustrates the "advantage" designers can take of the IOR.

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