OMR Review Committee Report – August 2011
Response to submissions (Final - 23/08/2011)
The committee has considered the diverse range of submissions and comments relating to the proposed changes to the OMR and extends its thanks to all who have taken the time to respond to the OMR Review Report 2011. While it is not possible to respond individually to every submission in detail, the committee hopes that the following modification to the initial proposal, together with the elaboration of the reasons underlying the more contentious changes, will go a long way towards their acceptance.
The general philosophy behind the OMR resides in the fact that it is a development rule in two senses.
· In the first instance, it is about providing an environment where new ideas in multihull sailing and design can be developed and tried without them being nipped in the bud by excessively restrictive rules and penalties.
· The second sense in which the OMR is a development rule is that it responds in a measured way to innovation where it can be quantified as a performance enhancing factor in multihull racing. Potential changes are evaluated within the principal three part paradigm of the OMR, comprising Rated Length (speed potential), Rated Sail Area (power factors) and Weight (inertia and drag factors). In this second sense, the OMR is also ‘reactive’ to change. It is prepared to give innovation time to prove itself on the race course before an appropriate compensating factor may be added to the rating.
While calls are regularly made to include subsidiary factors such as waterline beam to length ratios, overall beam, righting moment, and float buoyancy to name a few, these are considered as secondary factors that should be left open for the optimisation of designs within the ambit of the principle parameters.
Nico Boon, in originally setting up the Texel Rule, has strongly advocated the KISS principle in evaluating any change to the main parameters. There are secondary effects of increasing the complexity of the rule. As an obvious example, an increase in float buoyancy will only be effective above a certain wind strength, otherwise the likely added weight of the larger float and supporting structures and possibly increased wetted surface area, may lead to lower performance in light air requiring the overall sail area to be increased to maintain or add to the speed potential, adding more weight etc. As is apparent, this will have a complex effect on the rating, as well as requiring significant additional measurements.
Rated Length
While the existing measurement of Rated length has been adequate for rating multihulls in the past, the increasing trend of modern lightweight racing designs to float on short static waterlines while sailing to full hull length immersed waterlines has resulted in the decision to adopt a clear and simple rule for the future rating of waterline length under the OMR. It is noted that a high proportion of OMR listed boats have near plumb stems, reflecting a trend to maximise sailing waterline that has been in place for some years.
Forward Measurement Point:
The most forward projection of the stem or lower projections from the stem.
This does not include anchor fittings or bowsprit housings forward of the stem line at deck level. FOC will be discontinued for all vessels except for the exemption noted below.
Aft Measurement Point:
The furthest point of the hull proper or transom aft, excluding the rudder hardware
AOC as a measurement will be discontinued for all vessels.
In the interests of certainty for future designs and clarity of measurement for existing designs, this ‘Box’ rule approach will be adopted, where Length Over All of the longest hull will constitute the Rated Length.
In the case of trimarans, should the LOA of an ama be longer than LOA of the main hull, then the LOA of the ama will constitute the Rated Length
The committee recognizes that in the transition to this rule, some older designs with more pronounced raked stems will be relatively disadvantaged. A limited ‘Grandfather’ exemption clause may be claimed by boats designed and first launched prior to 1st Jan 1985. For these boats, FOC as currently measured, may be deducted from LOA until 1st Jan 2015 when the RL = LOA Box Rule will be fully implemented.
Any apparent discrepancies on the new OMR spreadsheet with reference to Rated Length should be notified to the OMR Data Officer or Chief OMR Measurer.
Rated Sail Area and associated Factors
Screecher
The revised rating of ‘Rated Screecher only’ and ‘Rated Screecher in conjunction with a Rated Spinnaker’ has generally been received without comment, other than to note the mathematical typo that appeared in the Review Report on P 8. The committee apologises for this oversight. Under Item 4 dealing with the latter combination above, the simplified calculation, i.e. the screecher rating component when carried with a spinnaker, will be taken as 0.0468* MAScr (simplified to 0.05*MAScr for the spreadsheet)
Boats without either a Spinnaker or Screecher
As alluded to in the initial 2011 OMR Report, vessels carrying no rated downwind sails (essentially in ‘cruise’ mode), will attract a default downwind sail rating, albeit a conservative one. The few affected vessels may elect to sail to this rating, or optimize their vessel to its rating by adding a conservatively sized spinnaker or screecher for this purpose.
A vessel carrying no downwind sails will attract a downwind premium on its rated sail area in the RSA algorithm equal to 75% of the rated working sail area. This is roughly equivalent to carrying a small cruising spinnaker or a smaller heavy weather spinnaker. This is a relatively small penalty which adds the equivalent of 22.5% of the rated area of the main, as a de facto spinnaker, to correct mathematical anomalies in calculating the rating of boats at the lower extreme of sail area relative to their size.
This is intended as an incentive for all vessels with working sail only and who wish to compete in an OMR division, to carry a small conservative spinnaker at least, to optimize their rating.
To place this change in a wider context, of the OMR listed vessels carrying rated spinnakers, 97% (sample size of 136 most recently listed vessels) carry spinnakers of 110% of the measured working sail area as a minimum.
The relevant changes to the RSA formula are as follows:
Current RSA4 - If no valid screecher or valid spinnaker,
Then RSAM + RSAG
New RSA 6a - (RSAM + RSAG) + 0.75*(Rating of Working Sail Area
[= RSAM+RSAG] where RSAM +RSAG is rated as a defacto spinnaker)
This equals - (RSAM + RSAG) + 0.75*(0.3* (RSAM+RSAG-RSAG)
This simplifies to:
(RSAM + RSAG) + 0.225*RSAM
The committee will monitor the premium applied to vessels in ‘cruise’ mode without any rated downwind sails and reserves the right to increase this correction factor if deemed necessary.
Canting rigs
While canting rigs are starting to make an appearance on a small number of vessels, their full advantage is still to be evaluated in OMR events. On longer passage races, they may play a role. Their value in short ‘round the buoys’ races, or in light conditions is subject to question. The committee will continue to monitor their use.
Rotating masts
The increasing use of deep chord wing masts has raised questions about the suitability of the current basic mast rating factor in the OMR. As these masts have a significant interaction with the mainsail and have the potential to generate additional efficiencies, and hence power for the overall sail plan, the committee will put this question on notice for investigation for the next review.
While the committee does not expect the imminent appearance of full wing sails in our fleets, their potential rating also will be considered in this context.
Foils
While a provisional rating penalty has been allocated for ‘lifting’ foils, the committee notes that their use in local fleets is still limited and developmental. This provisional rating penalty will not at present be included in the calculation of the OMR formula. The relevant spreadsheet columns have been set up initially to gather data on the number and type of vessels with lifting foils, as well as for performance evaluation.
Vessels fitted with lifting foils are requested to notify the OMR Data Officer of the type of foils fitted for inclusion on the new spreadsheet. The committee reserves the right to activate a penalty on lifting foils at the end of the 2011 – 12 sailing season.
Racks
The question has been posed as to whether ‘Racks’ may be penalised under OMR. This question has been asked in previous years. The committee does not have a view on them for the purposes of an OMR rating. However, in so far as multihull events are staged under the auspices of Yachting Australia, owners are advised to consult Part 4, Para 49.1 of the RRS (Blue Book), to ensure that they comply.
Crew weight factor
The OMR Review committee received a considerable number of submissions, both for and against, and with various qualifications, concerning the implementation of a new crew weight policy in the rule.
The history of OMR and crew weight allocation has been a ‘can of worms’, since its inception when the OMR diverged from the parent Texel Rating, and has been subject to exploitation in each version. When the club recommended a formula based crew weight at the time of the 2008 OMR review, based on a return to the then Texel model, there was a ‘palace revolt at the boat ramp’ as crews perceived the formula as unfair, for the various reasons detailed in the current OMR report. The formula was a fairly arbitrary RL*40 – 70 and originally designed for lean ‘off the beach’ style cats and crews. This replaced the 100 kg per crew version of the original OMR, which was probably reasonable for big boat crews with gear going to Gladstone
Most of you will know the recent history of the “Declared Weight of Crew” (WCD) model in its couple of forms, also subject to excessive manipulation by some parties. Anecdotal evidence suggests that some boats carried crew numbers in excess of the crew normally required to sail the boat effectively, with the primary purpose in mind of lowering their rating. Although the practice is legal, and that it may be seen to be providing more opportunities for participation, the committee’s concern is that it is not in the best interests of sportsmanship and the generally accepted sporting goal where achieving the highest levels of performance from both vessel and crew is the desirable outcome.
Some respondents to the review have argued that it is important to take the full crew weight into account in the formula. However, it needs to be appreciated that the notion of ‘Rated weight’ is a mathematical construct for the purposes of the formula, with various assumptions attached. For example, food, fuel, water do not form part of the rated weight. The underlying assumption relies on the fact each vessel will be proportionally treated according to its size where the mandatory Sailing Instruction requirements on the minimum fuel and water etc. are concerned. There is plenty of room for optimization here.
In the same way, on the same basic assumption, it would be possible to simply not rate the weight of crew at all for an OMR rating of a vessel, and leave it to minimum crew limits that may or may not be specified in the Sailing Instructions, as well as the skipper’s decision on the number required sail his boat efficiently and safely. This hypothetical option was statistically tested for the 2008 OMR Review, and in an early series of races analyzed, showed no significant difference from the Texel crew formula above, that in turn was better than the original OMR 100 kg model. Subsequent testing of the ‘no crew’ model on further races however, had the Texel crew formula showing better results overall at the time of the last Review.
The point of this laboured explanation is that the notion of crew weight as part of Rated Weight is essentially a mathematical construct. Variations in absolute weight between vessels are accounted for by the ‘Power of Weight’ in the final component of the OMR algorithm. (Obviously, changes in the value of final ‘Powers’ have been tested when other hypothetical internal changes to formula components are subject to evaluation.)
While using a ‘fixed weight’ crew allocation may appear to be a radical new approach for the OMR, it should be noted that both the OMR parent rule, the Texel, and its close French counterpart, the Multicoques 2000 Rule, have had fixed crew weight formula allocations since their inception. In the latter, crew weight is not even mentioned separately, but is built in to the Rated Weight component of the formula.
The philosophy of both of these rating rules resides in the fact that it is solely the “boat” that is being rated. Crew weight is viewed as ‘moveable ballast’, in part being used to balance the boat, and as such, should not be fully rated as ‘dead’ weight on the vessel. How the vessel may be crewed is left to the skipper, and takes account of his ultimate safety obligation, his decision on the number of crew required to efficiently sail the boat in the race conditions, and any prescriptions of the Sailing Instructions.
The Texel Rule Committee has kept abreast of changes in the OMR. They have recently reviewed their own approach to rating crew weight and have introduced a new formula based on Rated Length alone that correlates reasonably closely to the proposed OMR formula. The new formula does provide for a higher crew weight allowance than the previous Texel formula. As the Texel Rating lists multiple ratings based on sail area however, they preferred not to include sail area as a modifying component in their formula for allocated crew weight.
The intention of the discussion above has been to set the proposed change to rating crew weight in its wider context and to allay the fears of some that this is a radical or untested approach. Many of the responses acknowledged that the OMR formula delivers amazingly close results for a mixed fleet of multihulls. This does not happen by accident and is the result of ongoing statistical research of current racing over an extended period of time, as detailed more fully in the OMR Review Report. To reiterate, initial back testing of the formula over a number of multihull regattas, showed that the new formula for deriving crew weight provided significantly closer race results, (i.e. lower coefficients of variation than either the current WCD system, or if using the Texel default formula alone when examining the same vessels in the same events.)
It should be appreciated however, that although a rating formula may provide for close corrected times for the majority of the fleet, there will always be boats that are outliers on either end of the normal distribution curve with extremes of either weight, including crew weight, or sail area or both, relative to their length. Any formula may not always cater for those on the extremes as effectively as they would like.
When some of the responses to the Review Report are prefaced by the assertion that “changes are being made for no real reason”, then such respondents have failed to grasp the significance of the fact that the change, based on statistical research over a number of recent events, has a higher probability of delivering closer corrected times across the fleet on average, than is likely to be achieved when compared with retaining the current WCD model. Put in a different way, some skippers are essentially asserting, “I would prefer to nominate my own crew’s weight, and have my competitors do the same, knowing that in doing so, my own chances of winning, as well as those of the rest of the fleet, are diminished”.
For the future development of multihull racing under the rule, the committee considers that the new fixed crew weight factor is in the best long term interests of skippers, designers and sail makers seeking to prepare new vessels under the rule.
A number of responses to the review were concerned with safety issues in the proposed new crew weight model. The OMR is about rating boats and does not make direct pronouncements on safety, other than to remind skippers of their ultimate safety obligation to their crew in deciding how their vessel will be sailed. Safety is the province of the Sailing Instructions and ancillary documents governing yacht racing. The crew number nominated for each vessel by the crew weight formula is merely intended as a guide, for the basis of the rating, to the number of crew likely to be needed to sail the vessel efficiently (Default Crew Rating).
Unlike the OMR’s counterpart European Rating Rules that have no conditions placed on allocated crew weight, the revised OMR, will apply a penalty of 80kg that will be deducted from the rated weight of the vessel for each crew member fewer than the designated default. This is intended as a disincentive to, although not a prohibition of, short handed sailing.
The Review committee further recognizes the special case for extra crew and personal gear that may be required for offshore races that are rated at Cat 3, Cat 2 or higher. For events of this category only, an additional 15% of the formula allocated crew weight will be added for these particular events.
It is intended that for these events only, a separate OMR spreadsheet will be set up for entrants in Cat 3 & Cat 2 or higher events. The optional WE column (additional claimed weight for life rafts etc.) will be retained for this spreadsheet and removed from the principal OMR listing.
Summary
In summary, 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. Within this context, 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. 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 committee is very conscious that the rule cannot be “all things to all people”, in the sense that it can provide a highly competitive rule for dedicated racers and at the same time cater for those sailing in a less optimised mode with older designs, sails, extra crew etc. Certainly they can go out and sail their best in an OMR fleet or sub division, but the expectation of doing exceptionally well in the fleet may be diminished. For this latter group, performing well under PHRF may provide an alternative and more realistic sailing goal.
Committee: Mike Hodges, Bob Forster, Garry Scott, Rob Sherwood
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