How PHRF Ratings are Made

A basic explanation...

How PHRF Base Ratings are Made

There are over 40 PHRF regions in the United States.  US Sailing, as the Governing body has no established system to create a Base Rating.  There must be a standard condition for the boat to be configured so that when it is compared to another there is a common foundation.  In most regions it is established that:

·         Headsails:

boats with headsails shall be measured by an LP measurement as a percentage of the J

o   Overlapping Headsail Boats shall be 155% LP as a Base

o   Non-Overlapping Headsail Boats shall be ~100% LP as a Base

·         Spinnakers:

SPL is based on J for Symmetrical Spinnakers to establish maximum girth (SMG)

JC or TPS is for Asymmetrical Spinnakers to establish maximum girth (AMG)

·         Main Sails:

Main Sail size or girths are based off the E and P dimensions

These are some of the options available to PHRF Committees to establish Base PHRF ratings:

·         Schell Regression Analysis Formula

·         Results Analysis

·         Observed Performance

·         Measurement Rule Conversion

·         Excel/Database Tools

Schell Regression Analysis Formula:

This was developed by PHRF NORCAL and it reads

R' = 610-8.36*(SA/Disp^.333)+0.0000511*(SA^2)-55*(P/(J+E)) -30.8*(LWL^.5)-602*(DR^2/SA)

where SA= .5*(I*J)+.5*(P*E)

This formula is very dependent on Draft, Draft can cause significant changes in the results.  For the most, part this formula works well for standard displacement boats.

Results Analysis:

PHRF-LO (Lake Ontario) uses this process to fine tune their ratings season to season over a 5-year span.  PHRF-LO does not go into too much detail as to how they use this data or if it is normalized for course/weather or boat configuration.

Observed Performance:

This is typically achieved from either firsthand report from Committee Members or from trusted racers.  This method is usually used to fine tune initial ratings or as confirmation of the initial rating.

Measurement Rule Conversion:

PHRF NE (New England) has a page of conversions.  These allow the PHRF Committee to see how the Measurement Rules (ORC, ORR, IRC, etc.) compared to a PHRF rating.  Care must be taken to ensure that the boat configuration matches so that the comparisons are equal.  Measurement rules do have bias, and some do type form so the result of the conversion should be used as a guide and not a direct conversion.  Of note, ORC no longer uses GPH on their certificates.  The conversion that works for APH is

PHRF = APH – 469

Excel Tools:

Excel represents a powerful way to analyze large or complex sets of data.  PHRF NB (Narraganset Bay) uses several worksheets for Base Ratings and also for Adjustment determination. 

Three tools that see the greatest use are:

US Sailing Critical Dimension Database:

            New boats are entered, and a query is run to compare boat dimensions and ratios which have the closest matches

VPP Compare:

            This Excel sheet utilizes the VPP table from an ORC certificate.  It compares two boats’  VPP across all wind ranges and simulates a Windward / Leeward course.  The results of the race will generate a rating for the boat being compared.  This sheet works best for boats of similar performance (within 10-12 sec/mi)

ORC APH/GPH Compare:

              This Excel Sheet uses the ORC Single Number W/L and AP ratings compared to the PHRF rating.  The table of compared boats is then plotted on to a Scatter Plot with a trend line.  The Trend line is then used to gauge how far off the PHRF rating is to the trend.