The OMR is a developmental rule, and therefore periodic reviews are necessary to ensure that the ratings remain current and relevant, taking into account advances and innovations in multihull design and racing and the changing nature of the multihull racing fleets. This latest review follows other periodic reviews that have been undertaken since the inception of the rule, all of which are progressively working to keep the rule up to date and as fair as possible for all who utilise it.
The OMR is about providing the opportunity for serious and fair racing for a diverse fleet of multihulls in an environment where the progressive development of multihulls can still take place. The OMR is used extensively in Australia and internationally and has more active multihulls racing under it than any other multihull rating system worldwide.
The basic premise of the rule is that the optimisation of a vessel, its rig and crew to the rule, coupled with superior team work and sailing skills, should offer the greatest opportunity for success in OMR events. It follows that there will also be a group of vessels that are less optimised, either by virtue of older, less efficient design, inefficient rigs and sails, less effective crew work, or crew numbers or weights that may be incompatible with the size and efficient operation of the vessel to its rating, such that these vessels have a reduced opportunity to do well under OMR.
The latest review of the rating system has been undertaken using recent racing data as well as feedback from interested sailors to fine tune the underlying formulae and the factors that are form the basis of the rule. In particular regatta results such as Airlie Beach Race Week 2015, Hamilton Island Race Week 2015 and the Surf to City 2016 have been used to evaluate any modifications to the rule – these events on the whole represented multihull sailing where all boats were in the same division and hence sailed the same course in similar weather – this does not often occur and allowed an opportunity to benchmark all of the currently racing boats from the smaller trailerable boats through to the larger blue water boats. The approach used was to generate an elapsed time factor for each boat with respect to a reference boat in all of these events, then to plot this elapsed time factor over a large number of races and compare the profile with that of the OMR ratings. In this way a number of discrepancies could be observed with a grouping of boats in troughs indicating a lower OMR than their performance suggested and a grouping of boats in peaks indicating a higher OMR than their performance suggested. These groupings were then examined to see what similarities existed and what aspects of the rule may need to be changed to improve the fairness of the ratings.
A summary of the key changes that have been made to the OMR in the 2016 review are as follows:
The rule applies an overall drag and lift factor to the rating based on a number of variables, the main one of which is the propeller factor. Different factors are applied for fixed or folding/feathering props. Some good research has recently been undertaken by a number of organisations on the drag forces of fixed, folding and feathering propellers. This collective research has been used to re-evaluate the drag factors for the different kinds of propellers. The results are more in line with the experiences of skippers who have sailed with various types of propellers – the main change is to reduce the drag factor applied to feathering or folding propellers, hence boats with these will see a reduced reduction in their OMR.
General consensus is that the increase in OMR rating due to a rotating mast is too high, with several boats finding that the improved rating they achieve through fixing the mast more than offsets the loss in performance that they experience. This has the effect of slowing boats down just to improve their rating which is contrary to the objective of the OMR. A minor error in the formulae was discovered and this was corrected, in addition the magnitude of the correction that is made for rotating masts has been reduced. What this change means is that boats with rotating masts will not have their OMR increased by as much as was previously the case and hence will see a benefit.
Removing Sail Efficiencies
Efficiency factors for sails had been introduced in an earlier review of the OMR to fine tune the rating and to try to reduce the spread of yachts. However, with modern sail design and construction, even sail shapes that may have been deemed inefficient by the aspect ratio calculations still sail very effectively, not reflecting the large range of efficiencies that were previously calculated, ranging from 73% to 93%. Removal of these efficiency factors sees a much more natural alignment of boats theoretical performance with their actual performance. The impact of this change is that boats whose sails had been deemed more inefficient under the old rule will see their OMR increase relative to those who were previously deemed to have efficient sails.
Introduction of RL Factor
Analysis of various race fleets and results indicate that there is somewhat of a disconnect in the performance versus rating of smaller vessels compared to larger vessels. Model fitting of the length factor over many years of data indicates that smaller vessels should have a lower factor applied to RL than larger vessels. This effect has been taken into account in the new rule with a variable factor applied to RL based on the vessel length. For the smaller racing multihulls this factor is around 0.29 while for the larger multihulls the factor is around 0.3. This factor was previously 0.3 for all vessels. A smooth curve has been used to modify the factor to avoid any steps or disconnects, the impact of this change is that any vessels smaller than 10m rated length will see a decrease in their OMR, with the magnitude of the decrease increasing as the RL gets smaller. The rationale in support of this change is that smaller vessels have greater difficulty in achieving their speed potential consistently, especially in choppy water or offshore swells.
The impact of all of these changes on each vessel will be different, and each owner or skipper should familiarise themselves with their new rating and how it compares relative to the vessels that they sail with. In general, vessels that are impacted by several of these rules (i.e. larger vessels with feathering or folding propellers, vessels with non rotating masts and vessels with sails that were previously deemed inefficient) will see their rating rise in comparison to other vessels – with the corollary being that smaller vessels with no propellers in the water, rotating masts or sails that were deemed to be efficient previously will see their rating decrease relative to other vessels. The overall modifying factor that applies to the OMR has been reduced to bring the average of all OMR’s of active vessels back to what the average was under the previous iteration of the rule. Hence on the whole ratings will be of the same order of magnitude, with division thresholds etc. likely remaining similar.
In addition to the formula changes described above a number of administrative changes have been made to the OMR system. In summary these are:
- The spreadsheet layout has been revamped and modernised, hopefully becoming easier to read and understand. All formulae have been checked for each vessel and then protected to prevent inadvertent errors being introduced in the spreadsheet.
- The validity period for ratings has been reflected in colour coding in the spreadsheet. Vessels with measurements older then 4 years will see their rating date shaded yellow indicating an update is needed, vessels with measurements older than 6 years will be shaded red indicating that the rating is no longer valid. This aspect of the rule has always been in existence but has not been consistently enforced in the past – the intention is that this will be the case going forward.
- The preamble has been completely updated to reflect the changes described above.
Date of Change / More Information
The changes to the OMR will take effect as of the 1st of July 2016, any races or regattas after that date should utilise the new OMR rule and ratings. The new spreadsheet will be uploaded to the www.mycq.org.au website from this date, along with the new preamble. The old OMR ratings may be displayed on the website for a short period to assist people in the transition.
An OMR information night and discussion forum is planned by the MYCQ to assist in familiarising people with the basis and objective of the OMR system, with the details of changes and impacts of these changes from the latest review and to gain feedback for future reviews. This night is planned for Thursday 28th of July at the MYCQ clubhouse in Manly and all interested parties are invited to attend – separate details will be sent out once planning is complete, or please visit the MYCQ website at www.mycq.org.au for any information about the club, the OMR or the OMR information night.
Thank you and all the best in multihull sailing!