Two different concepts are presently being used:
- Measurement Systems i.e IOR and IMS. (mostly International use i.e. 1Ton, ¾Ton etc..)
- Performance Systems i.e. PHRF, ASPN, Portsmouth Numbers. (Regional and Club oriented)
NStYA is presently committed to the PHRF performance system.
Performance handicapping systems are based on the speed potential of a yacht, and the ratings have been derived from observations of previous race data. Base ratings, have been determined from past performance of a class or similar type yachts, and some simple measurements are taken to make adjustments, i.e. larger sails, propulsion and others...
Sail and Rig Measurements may be done by the owner, but for consistency NStYA prefers that an experienced local handicapper to be present both to measure and calculate the yacht rating.
Time Correction Method:
There are two methods which apply ratings to convert "elapsed time" to obtain "corrected time":
- "Time on Distance" usually Time Allowances (TA)in sec/mile.
- "Time on Time" using Time Correction Factors (TCF) in sec/hr.
PHRF is primarily a "Time on Distance" (TA) method, NStYA uses the Time Correction Factor (TCF) conversion to convert to "Time on Time". To calculate TCF:
TCF = 695 / (525 + PHRF Rating).
Then multiply each "elapsed time" in minutes by the TCF. The results are the "corrected elapsed time" in minutes.
Measurements and Adjustments:
PHRF requires 9 sail measurements and the Spinnaker Pole Length (SPL). Five on the mainsail, which must be removed to be accurately measured, and there are 2 each on the jib and spinnaker. These measurements are used to calculate the actual sail area of the yacht.
Rig measurements required are: I, H , and J. (H is only required if significantly different than I.).
These measurements are used to calculate the theoretical sail area of the yacht. In addition there are adjustments for propulsion types, rudder and other variables.
Calculations are then done to determine the sail area factor or SAF for each sail, this calculation is then applied to a SAF adjustment table to determine the amount of deviation from the standard index value of 1.0000.
PHRF uses adjustment increments of 3 sec/mile.
PHRF Base Ratings
Base ratings lists are available from various sources, most conform to the following "Standard Configuration"
1. Spinnaker pole length is equal to "J"
2. Spinnaker maximum width is 180% of "J"
3. Spinnaker maximum length is 95% of jib stay length.
4. Perpendicular from Clew to Luff of largest headsail is between 150% and 155% of "J"
5. Yacht is in racing condition.
6. Yacht has a folding or feathering propeller, a two blade fixed propeller in aperture, or a retractable outboard motor.
7. Hull and appendages are unmodified.
8. IOR batten length restrictions are followed, except in cases where the standard yacht has full length battens.
For further information contact your local club measurer or