Index

Performance Specifications for the SJ23 to SJ34.

NOTE: For the purpose of satisfying the equations, the feet and inches are shown as decimal feet.  I realize it looks screwy but the math works easier.  I will complete the chart below as I acquire the raw data for each model.  If you have this data, please email the specifications to me.

DISPLACEMENT / LENGTH RATIO = disp/2240/(.01*lwl³) (dimensionless, if you ignore the constant "2240" that converts displacement from pounds to long tons, low is good).  ".01" is another constant that scales the result.  Probably the most used and best understood evaluation factor.  Low numbers (resulting from light weight and long waterlines) are associated with high performance.  Cruising designs begin around 200 and can go up to the high 300's.  Many racing designs are below 100.  The general trend for new designs is towards lower ratios and high performance.  The trade off is more violent motion in storms, which requires constant attention to steering and sail trim, resulting in crew fatigue. 

SAIL AREA / DISPLACEMENT RATIO = sail area/(disp/64)^.666 (dimensionless, high is good).  "64" converts displacement to cubic feet.  This is basically a ratio of power to weight, calculated using a 100% jib.  Most monohull designs range between 16 to 18.  Racers can be much higher, motor sailors lower.  The ratio is independent of boat length (see "chart" page). 

VELOCITY RATIO = 1.88*LWL^1/2*sail area^1/3/disp^1/4/ hull speed.  (dimensionless, high is good).  The numerator of the equation calculates potential maximum speed, using an empirical relationship.  Boats with a generous sail plan and light displacement will have a velocity ratio greater than 1.  Under powered or extra heavy boats will be less than 1. 

BALLAST / DISPLACEMENT RATIO = ball/disp (dimensionless, should be 0.25 to 0.5).  One indicator of stability, but the center of gravity, center of buoyancy VS heel angle, and total weight is needed for a complete picture.  Values range from a low of .25 to a maximum of .5.  Another way to estimate stability is to divide the boat's roll period (seconds) by the beam (meters).  Values less then 1 are "stiff".  Values greater than 1.5 are considered "tender". 

LOA / BEAM RATIO = LOA/beam (dimensionless, 3-4 are "fine" hulls).  This ratio measures the fineness of the hull.  Fine hulls, 3.0 - 4.0 and higher, are long and slender which promotes easy motion, high speed (low drag), and good balance when heeled.  Newer designs favour wider hulls which have larger interior volume, sail flatter, and have high down wind speed potential.  One note of caution when making comparisons, longer boats tend to be finer then short ones.  This effect is plotted on the "chart" page. 

CAPSIZE RISK = beam/(disp/.9*64)^1/3 (dimensionless, <2 is good).  An empirical factor derived by the USYRU after an analysis of the 1979 Fastnet Race.  The study was funded by the Society of Navel Architects and Marine Engineers.  They concluded those boats with values greater than 2 should not compete in ocean races.  Values less than 2 are "good".  The formula penalizes boats with a large beam for their high inverted stability, and light weight boats because of their violent response to large waves, which are both very important during violent storms.  It does not calculate static stability.  Some modern coastal cruisers and many racing designs have problems meeting this criteria.  An interesting note, the study concluded that static stability was relatively unimportant in predicting dynamic capsize.  Beam and weight were much more important factors.  Wide boats give waves a longer lever arm to initiate roll and light weight boats require less energy to roll over. 

COMFORT FACTOR = disp/(.65*(.7*LWL+.3*LOA)*beam^1.33) (dimensions of "length" to the 2/3 power, 20=RACER, 60=CRUISER).  An empirical term developed by yacht designer Ted Brewer.  Large numbers indicate a smoother, more comfortable motion in a sea way.  The equation favours heavy boats with some overhang and a narrow beam.  These are all factors that slow the boat's response in violent waves.  This design philosophy is contrary to many modern "racer / cruisers", but it is based on a great deal of real blue water data, not just what looks good in a boat show.  A value of 30 - 40 would be an average cruiser.  Racing designs can be less than 20, and a full keel, Colin Archer design, could be as high as 60. 

PHRF RATINGS - 234 on Lake Lanier, Ga; 240 in Ontario; 243 on Lake Norman & Wabamun Lake; 246 on Chesapeake Bay.

• SOME HISTORY - Before 1976, cruising yachts on the Chesapeake Bay raced under various handicap measurement rules.  Each rule used a formula to predict the potential speed of the yacht compared with the speed of the others.  The calculated result was the yacht's rating in equivalent feet.  This was used to determine the time allowance handicap.  Most measurers charged fees, and the classes charged fees for running the rating calculations.  Some of the rules also required the yacht to be lifted out of the water and weighted.  This improved measurement accuracy but added to the cost.
  
  When yachts are similar in design, a simple rule with few measurements can be equitable.  As boats vary more widely in their design, a fair rule becomes more complex and difficult to develop, requiring more measurements and becoming more expensive for the owners.  Good yacht designers study measurement rules to find ways to design yachts that are fast but appear slow to the rules.  To correct the handicaps of such "rule-beaters" requires adjustment of the rule.  Most any adjustment affects not only the rule-beater, but all other yachts in the class as well, sometimes unfairly or contrary to the intent of the rule makers...
  
  What was needed was an inexpensive handicapping system that could correct the handicaps of individual rule-beaters without affecting other yachts in the class.  The boating industry expanded rapidly during the 70's.  Low maintenance fibreglass boats were built by the thousands, hundreds out of the same molds.  The number of new sailors racing increased just as rapidly.  Many of them came from one-design day sailor fleets.  They did not understand the measurement rules and they didn't want to spend a lot of money on ratings.  They simply wanted to get out on the water and race.  Many of the "old salts" as well were tired of the expense and complication of the measurement rules.
  
  In Southern California a group of yachtsmen developed a new approach to handicapping in the early 1970s, and organized the Pacific Handicap Racing Fleet.  The British were already using the Portsmouth Yardstick system of handicapping different classes of day sailors to facilitate their racing together.  Portsmouth numbers were assigned on the basis of observed performance.  Similarly, the Pacific Handicap Racing Fleet assigned handicaps to classes of cruising boats based on observations of actual performance, instead of operating on measurement or design information.  They made supplemental use of the same measurements when performance data was not available, but not in a rating formula.  The system was inexpensive, easy to administer, and produced ratings quickly.  The method of rating yachts became popular and spread to other parts of the country, where "Pacific" in Pacific Handicap Racing Fleet was changed to "Performance" to become Performance Handicap Racing Fleet, which we now know to be PHRF. 
  
  In 1975, a Chesapeake sailor, Auzzie Jackson, visited Southern California and became interested in this new and popular handicapping system after picking up a policy book and reading it.  He was so enthusiastic that he brought the system home to the Fishing Bay Yacht Club to be used in club racing.  The first Chesapeake PHRF system under the patronage of Auzzie and Fred Williams soon spread throughout the Southern Bay and to clubs in the Northern Bay as well.  Thereafter it became recognized by CBYRA for High Point competition.
  
  During the late 70's and early 80's the growth of PHRF of the Chesapeake was spectacular and its administration became a big problem.  The original file card system, suitable for the small fleet became inadequate as the class grew from 340 rated yachts in 1979 to 673 in 1980 to over 1,000 in 1981.  In 1981 the management of the class moved from Richmond to Baltimore and computer-based records were established.  By 1986, the number of rated yachts had climbed to more than 1,400, and the vast array of information was loaded onto an IBM DOS based PC system.  There were about 50 measurements and specifications for each yacht or a total of more than 70,000 pieces of information kept on file.  In 1994, PHRF of the Chesapeake moved to Easton, Maryland.  Over the next few years PHRF membership declined at about 100 members per year.  In 1997, PHRF of the Chesapeake moved to Prince Frederick, Maryland.  The DOS based data was converted to a MS Access 97 (tm) data base on a Pentium (tm) processor driven PC system.  The data base presently holds records on approximately 2000 boats totaling over 100,000 pieces of data..
  
  The PHRF Executive Secretary, appointed by the President of the association, maintains the PHRF database and performs administrative and clerical tasks necessary for the day to day operation of the association.  The Executive Secretary also provides annual renewal forms to members, application forms for prospective members, produces Valid Certificates, and maintains a complete mailing list.  PHRF administration has truly taken on the proportions of a business and is treated as such.
  
  What began as the Pacific Handicap Racing Fleet in Southern California has become a nation-wide handicapping system, following the overall guidance of the US PHRF committee, under US Sailing.  Members of PHRF of the Chesapeake have taken turns serving on the US PHRF committee, providing a continuous presence there for many years.  The PHRF handicapping racing fleet, administrated by PHRF of the Chesapeake, continues today as the largest handicap racing fleet on the Chesapeake Bay.     Reference http://www.phrfchesbay.com/ 
   

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