J120 front copy

J/120 ORR - IRC Links & Specifications


With some of the new IRC type form boats that are now coming out, it is our recommendation it would be better to just buy a J/122 than rather to modify a J/120. Even though a J/122 is given time under IRC, a J/120 is at least 33 seconds per mile slower than a J/122 because it does not fit the IRC definition of a good typeform. However if the owner is determined to modify a J/120 to compete, another owner has modified their boat to race IRC. Here is a link to their web page:

http://www.avra.us/Boat.html

Here is a comparison for PHRF and ORR ratings

http://www.phrfne.org/page/handicapping/asdg

If the J/120 owner would like to get a fair rating in ORR here are some links below:

http://offshore.ussailing.org/ORR.htm

http://offshoreracingrule.org

IRC - US Web Site 

http://www.us-irc.org

ROYAL OCEAN RACING CLUB Rating Office in United Kingdom

http://www.rorcrating.com/

J/120 Preparation for Weighing for IRC (word document)

How to get rated

http://www.us-irc.org/howtogetrated.htm

Comparison Chart for Different Boats Worldwide (unofficial)  

http://www.navwiz.com

J/120 IRC US IRC numbers as of June 6, 2005 

J120_IRC_list.xls

Comparison Chart for Different Boats in US (unofficial)  

http://www.ussailing.org/offshore/irc/WEB%20IRC_TTCs.xls

PHRF New England IRC to PHRF Comparison (unofficial)  

http://www.phrfne.org/page/823

IRC Time-Difference Table - Used to  generate a time-difference and elapsed times table between you and your competition in IRC (Created by L. Kahl, Interactive Creations)

http://www.us-irc.org/irc-timetable.cfm

Understanding IRC Handicap Differences

ARE WE WINNING?

Simplistically, each 0.001 of rating difference between two boats represents a corrected time difference of approximately 3.6 seconds per hour. This will however only be absolutely correct for boats rating very close to 1.000. So how can you be certain whether you are beating your rivals on the race course?

Starting with boat A rating 1.010 and boat B rating 0.995, if Boat A sails for one hour, her corrected time will be 1.010 hours which is 1:00:36 (1 hour 0 minutes 36 seconds). Boat B will beat Boat A if her corrected time is less than that. To find out what this means in terms of time, we want to find Boat B�s maximum elapsed time. To do this divide Boat A�s corrected time by Boat B�s rating - 1:0:36 / 0.995 = 1:00:54. In other words Boat B can sail for up to an extra 54 seconds before her corrected time is more than boat A's. An easier way of doing the same thing is to divide the rating of boat A by the rating of boat B � ie 1.010/0.995 = 1.015 and 1.015 hours is 1:00:54. 

Notably, boats A and B have a rating difference of 0.015, thus confirming (54/15 = 3.6) the 3.6 seconds per 0.001 noted above. But if the boats are faster or slower, while the maths remains the same, the answer starts to vary from 3.6. If boat C rates 1.110 and boat D rates 1.095 (the same rating difference of 0.015 as A and B) the time difference for an hour�s racing is 1.110/1.095 = 1.0137 which is 1:00:49 � equivalent to 3.27 seconds for each 0.001.

Similarly, boat E rates 0.910 and boat F rates 0.895 (again 0.015 less). The time difference for an hour�s racing by Boat E is 0.910/0.895 = 1.0168 which is 1:01:00 � equivalent to 4.0 seconds for each 0.001.

For a given fleet of boats, this can then be dealt with by creating a table of time allowances for the fleet

Time Differences in seconds for various race durations
1 hr 2 hr 10 min 20 min 30 min
222 443 37 74 111
154 308 26 51 77
119 238 20 40 59
51 103 9 17 26
42 83 7 14 21
35 71 6 12 18
0 0 0 0 0
0 0 0 0 0
-42 -83 -7 -14 -21
-42 -83 -7 -14 -21
-51 -103 -9 -17 -26
-58 -116 -10 -19 -29
-93 -186 -16 -31 -47

The table above is the ideal way to deal with this. For occasions when you do not have this for whatever reason, another simple way of dealing with it is to divide 3.6 by your TCC. eg, 3.6/1.100 = 3.3 seconds or 3.6/0.900 = 4.0 seconds. The answer in each case will then be closer to the correct time allowance per 0.001 rating difference between your boat and a reasonably closely rated competitor. The answer will still be approximate, but rather better than just using 3.6!

Authored by Mike Urwin