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Seeking input on PHRF

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CIORC have largely working with PHRF lately, however they have had discussions about engaging with the multi fleets. YNZ will make an approach to the Multihull YC to see if someone would like to come

The posting above by GUEST is ISAF wording they are promoting it / pushing it [ READ THEIR WORDING ] and the USA have joined the revolution towards it. Quoting Europe is a no argument. The argument is

That's no excuse if their is a better and fairer system.   OC

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READ the programme ORC VPP System already in existence.




Velocity Prediction Program (VPP)






Velocity Prediction Program (VPP)




It is intention of any rating system to give a boat rating which depends on her characteristics in order to equalize her with other boats of different size and characteristics. Characteristics that are positive for boat speed, like length of the water line or sail area, and those that are negative, like beam, displacement and wetted surface, are the most common influences in any rating system. Establishing which of these characteristics influences boat speed is therefore the problem that has to be resolved. Thanks to the developments in modern science and technology, ORC gives the most accurate solution to this problem, and establishes important principles of boat measurement and calculation of corrected times


The only possible way to rate boat fairly is to tell how fast she can sail in certain wind conditions or to predict her speeds.

To do so, ORC has developed with continuous research and update an ORC Velocity Prediction Program (VPP) as mathematical model which calculates boat’s performance from the set of measurements and gives rating which is


then applied for race scoring. ORC VPP is calculating boat’s theoretical speeds for various conditions: wind strength of 6, 8, 10, 12, 14, 16 and 20 knots, direction of true wind from the close-hauled to 52, 60, 75, 90, 110, 120, 135, 150 and 180 degrees. VPP program creates a computer simulation of the boat’s performance based on scientific research of boat hulls in hydrodynamic basins, sails in aerodynamic tunnels and measurements taken on real boats as well as computer fluid dynamics (CFD) tools available nowadays.


The VPP has a two-part structure comprised of the solution algorithm and the boat model. The solution algorithm must find an equilibrium condition for each point of sailing where the driving force from the sails matches the hull and aerodynamic drag, and the heeling moment from the rig is matched by the righting moment from the hull. 



The VPP determines the steady state conditions by satisfying 2 equilibrium equations: Firstly the net force along the yacht’s track (its direction of motion) must be zero:

Driving Force – Drag = 0

Secondly the aerodynamic heeling moment produced by the mast & sails must be equal and opposite to the righting moment produced by the hull and crew.

Heeling Moment – Righting Moment = 0


The boat model may be thought of as a black box into which boat speed, heel angle, and the sail trim parameters, reef and flat are input. The output is simply four numbers:

  • the aerodynamic driving force,
  • the heeling moment from the above water part of the hull and rig,
  • the drag of the hull keel and rudder and,
  • the righting moment from the hull and crew.
The solution algorithm iterates to a solution by interrogating the boat model with each new guess of the input values until a set of conditions is found that produces a match of thrust and drag and heeling moment and righting moment.  The solution algorithm also seeks to find the highest speed on each point of sailing by adjusting the sail trim parameters for optimum performance.


Aerodynamic model is calculating forces for each type and combination of sails. It has aerodynamic co-efficient coming out from various test form wind tunnels which in combination with sail area and center of effort height can give the total driving force on sails. This force is then reduced for the drag of hull, mast and crew windage as well as rigging wire.

Hydrodynamic model is from hull lines and in water freeboards measurement calculating boat's resistance comprised of several elements:

  • Viscous drag due to the friction of the water flowing over the surface of the hull and appendages, and the propeller if one is fitted.
  • Residuary drag due to the creation of surface waves.
  • Heel drag due to the change in wetted surface and immersed hull shape as the yacht adopts an angle of heel.
  • Induced drag created when the hull keel and rudder produce side force
  • Raw drag due to the yachts motion in a seaway.
Hydrodynamic model use results of tank testing and computed fluid dynamics in constant research of these values comparing it with real boat performance. It was shown that latest changes in the residuary resistance made the ORC VPP the most accurate so far.


Second equilibrium to match is one between heeling moment and righting moment. Heeling moment is calculated from the aerodynamic heeling force and sail plan centre of effort height taking also in account hull windage, mast windage, rigging wire and crew windage heeling moment.


Righting moment as result of stability measurement is reduced for the stability loss due to forward speed and increased for effect of the shifting crew.VPP calculations take in account additional weight on board for the total crew and sails and equipment on board while racing.




So you will see that crew weight is important. If a crew member is 26 stone then that crew member is wider and the windage slowing the boat is taken in to consideration and a allowance is given. Image if a boat has  4 x 26 stone crew. They [ the boat ] should not be penalised because they are fat and want to participate with a healthy sport.


If a boat changes there rudder from the original design and a boat does not have a propeller or has a retractable propeller system then adjustments should be made and will be spotted by the inspection process also. Should competitors find a loop hole or cheat, or not advise alterations to their certificates, then they should and correctly be protested and I suggest they should have a system similar to the rugby league citing process and given a banning period, say min 60  days from all yacht racing.


2nd offence a 12 month banning period from all yacht racing.


Hope this helps BOOBOO.




Their also is various Speed Guide software available that's helps crew with sailing skills, and the boat owner. Use of the Speed Guides can help a team improve their performance on the water by giving target boat speeds to achieve for any wind strength and any wind angle and with any sail combination. The packages collates and displays in both tabular and graphical form the theoretically predicted boat speed, in knots. The data is given for a wide variety of true wind speeds (6, 8, 10, 12, 14, 16, & 20 knots) and true wind angles, including optimal upwind and downwind VMG angles. The data is also provided for a variety of sail combinations: jib, genoa, asymmetric spinnaker, symmetric spinnaker, and Code 0.


The designers can also give various data predictions for boats to aim for. Can't achieve them then, have discussions with sail makers and sail trimming experts.

Jeez Rehab... TMI!

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  • 2 weeks later...

COPY As per member posting at






"All handicaps have a cost every year just part of racing

But At least the IRC yachts are weighed , hull measurements taken and sail's measured and signed off

PHRF is just a guessing game to a point

think the problem with IRC in NZ is boat owners can't get thee head around it and we don't have the yachts going to Australia or other countries to race like the years gone by so there is no real need to get IRC measured"






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Hey rehab, what was the last race you were in? I just try my best, and I know if I've sailed well or not and accept the lottery as part of the game.



We know what weather we need to feature on PHRF so we plod on in hope that one day it may happen again, it has once so it'll happen again fingers crossed. It's just the way the game's played so like it or take up Jelly Wrestling.

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Yacht racing is an arms race. It always has been and it always will be. We all know that handicapping in yacht racing is in once sense a method to keep the peasants on the battle field… But, sometimes, some of the peasants get lucky, and when you do you feel pretty good about it.


I know this thread has been bashed 4 ways from the mast, but let’s look at it in the light of what the PHRF is, a PERFORMANCE based system which does take into account your race history and a little bit about your boat.


One of the reasons, maybe, just maybe, that people feel it is inherently unfair in some way, and something that might also be a reason why many people with race able boats don’t come out to play, is perhaps because the PHRF works better if you have a regular crew. But many boats here in NZ have a regular skipper and maybe 1 or 2 semi regular 2IC. A regular full crew? How many here can say they they’ve raced a whole season with solid regular crew – and if you have, were you sailing much better at the end of the season? Yes I'm sure a few or even a lot of you who post here can boast a regular crew. But we, the vociferous, are not really representative of many of the mum and dad sailors who might go racing.


The effect of a single crew change can be massive. We once needed a ring in. Some boyfriend of a friend or so stepped up to the plate and took over the fore deck, called the start perfectly, made a number of suggestions as we went round the track, and somehow we had a blinder, finishing just a few seconds off the gun. Was bloody embarrassing, because simply by having a single person who could sail better, we realised we were normally shlt.


Just thoughts thrown into the wind...

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