IRC optimisation, an interview with Mark Mills

Mark Mills - Mills Design - IRC

Interview Mark Mills on IRC Optimisation

Unveiling the secrets of IRC


A common conception about IRC is that it is not transparent. I disagree with that, the IRC is a simple system with a very limited number of measurements. With ORC the rule provides and requires so much information, it becomes more difficult to compare different boats.


Optimisation, where do I start?

 Start with the question:


Where are we compared to the good performers in our class?”


For a small amount, you can buy the IRC certificates of the good performers. With these certificates you can compare those performers to your own ship. A useful way to do this is to put all the information in a spreadsheet. The visible differences can shed a light on where their performance-gain could be found. You can use these insights as a starting point for your optimisation.



A single number-rating system like IRC means that your rating will represent an average performance of your boat in all circumstances. For example: It could be based on 50% upwind, 30% downwind and 20% reaching. How much this is true for you is depending on the courses that you sail.

Your boat can have a performance bias to its rating, for example: a Fast 40+ class or TP52 will probably be a lot faster then the rating predicts when going downwind in big breeze. So if you live in areas were there is generally a lot of breeze like San Francisco or Cape Town, a boat like that could be a good choice.

To make an older boat competitive, it often pays to use that bias. You will pay a penalty if the conditions are not favourable for you, but your chances of winning will increase when you do get the right conditions.


"There are several general observations in IRC. Overlapping jibs get penalised quite heavy. Whereas draft is an easy way to gain a lot of performance"



The emphasis on rating or performance changes with the size of the boat. The break-even point for this lies somewhere around 45 ft. For boats that are longer the emphasis is more en more on performance. The smaller the boats get, the more important the rating is.



The number of boats sailing under IRC and/or ORC are difficult to compare. ORC counts all certificates that they issued, including the trial ones that boats use for their optimisation, which IRC does not do.

IRC managed to open up the sail areas more than ORC. The general trend is that IRC is more performance-oriented then ORC. Which in the future might develop as a problem for IRC, since there are more cruiser-racers then thoroughbred race-boats.


Offshore worlds

Cool to have the championships together. It will be quite interesting to see how the different rating-systems are integrated. Based on earlier comparison, the 2 systems do not produce radically different results.

Looking at the future, I think it is highly unlikely that we end up with one rating system, instead of the 2 that are primarily being used now.


> Discover how annalisa can help to optimise your performance.

Mark Mills

Mark Mills is founder and head of the Mills Design Ltd. They are one of the leading design offices when it comes to IRC, designing Maxi72 World Champion Alegre 3 and multiple IRC Championship winners Mariners Cove and Tiamat to name a few. Mark is also a member of the RORC technical committee and advisor of US and Irish IRC owner groups.

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