Difference between IRC and IMS

What exactly is the difference between IRC and IMS handicap systems?

Was viewing the Rolex Middle Sea Race results @ http://www.rolexmiddlesearace.com/results2004.html

with results under both IRC and IMS, and there is a big difference in the results.

 

IMS is a measurement rule. The boats are machine measured and the rating results from a VPP based on the measurement. It has been shown to be quite flawed. The VPP seems to favor horrible slab-sided, high freeboard, low stability boats. At the highest levels it has become as bad as the IOR was. It is pretty much dead. I doubt another IMS boat will ever be built.

IRC is a rule that grew out of the old UK CHS. It seems to favor boats of a medium displacement with simple rigs. It uses few measurements, sometimes owner-supplied, and somehow gives a rating from inside a room at the RORC (or the French equivalent). No one outside the room knows the rule, so it can't be "designed to". The dirty secret no one wants to talk about is the fact that there is supposedly some arbitrary "knob turning" in the room to make the rating come out "right".

That makes it similar to PHRF here in the US. Surprisingly, some people in the US think it should replace PHRF, and most of those who support it don't seem to know about the "knob turning" aspect.

In regard to IRC, you can have a local group give you an arbitrary rating, or you can pay someone in another country to give you a "measured arbitrary" (IRC) rating.

 

I don't love IMS, but here in europe (almost Italy, Spain, Germany and baltic area) IMs is still alive and kicking, very far from death. I think it will survive at least for another decade.

fair wind
Mistral

 

You're correct, there are areas that still use the IMS. Will anyone in those areas ever build another custom raceboat to the rule? Probably not.

We had the same thing happen while IOR was ending. Some small areas did continue to use it for a long time. They had stable fleets of older boats and didn't see a need to change. Here in Southern California we had a small, fairly competitive fleet near the end. Then one boat from the last design generation arrived, won nearly every race, and that finally killed off the fleet.

I think the Grand Prix IMS Spainish is about to be killed off. All the Royal and sponsored teams that have been building the boats for the past 5 years are going a different way. Sounds like TP52s will be replacing the 500 fleet next year. I'm not sure about the Italians or the Germans, but if this becomes the GP way in the Med they will be following soon.

It is a shame there is no worldwide rating rule. It might inject some more work for designers. It would also be more fun to see what design solutions would be done in a fleet of 25 custom or semi custom 30 footers designed to a rule, rather than seeing 25 J105s bludgeoning their way through the water.

 

IMS and TP 52

Dear guys,
I red with interest you discussion about IMS and his future in Europe.
Let me say that, at this moment, IMS is the only rating rule that seriously rate different boats in order to race together. Obvioulsy this rules is complex and full of formulae that designers can use to predict the handicap of the boat, in other terms the VPP of the IMS is open to designer that can buy it from ORC. With this software in his hands a designer could test a lot of configuration before to start a definitive design and so, boat that are designed without a dedicated IMS design process will results handicapped if compared to boat designed foer the rule using "rule's instruments".
The thing is that in the last 2 year IMS has seen a lot of new prototype with extreme geometrys such as the "Boxy section" hulls of the Botin & Carkeek style. This boats has dominated the last 2 year in IMS race, with a lot of "normal" boat owners that protest against this kind of focused boat.
For this reason, ORC, has introduced some interesting modification to the IMS 2005 rules, in order to reduce the gap between the normal boats and the IMS focused boats. So, as IMS technical commitee is made from very fine technicians and professional Naval Architects, I think that IMS will not die as for IOR, but thanks to the continuative update of the rule, the IMS will change in the future.
I've made some analisys at the end of 2004, and a part of this analisys was focused on test of an IMS 52' against a TP52', both under the IMS rule and under the pure performances point of view. My task was to understand if IMS produce slow boats for their size, and if a TP 52 will race in IMS corrected time caoul win the race in corrected time. Well, from my point of view, the aswer to this question are: 1) Yes, at 2004, the IMS rule produce slower boats for their size 2) Yes, a TP52 racing in corrected IMS time can win the race against a IMS pure boats. I have ran a number of boats preliminary designed by me and choose the best IMS and TP52 for the pourpose of my analisys.
I hope that with the new trend in IMS (see changes in 2005 at www.orc.org) and the arrival of TP52 in Europe, IMS boats will become more performing and safe.
Let's see what happen in the next year.
Ciao, Alessandro

 

Allesandro, why do you say "Let me say that, at this moment, IMS is the only rating rule that seriously rate different boats in order to race together."????

Under IRC, you can win major titles (Fastnet, Spi Ouest, the major Australian races and regattas, national titles, Admiral's Cup, Sydney-Hobart) with boats as different as Sunstone (very heavy S&S 40 Finnisterre style from '65), the Farr 1104 (1975 one ton), Open 60s, new 98' canters, 66' canters, ex IOR half tonners, a 1909 Fife designed metre boat (or was it a Linear Rater????), a Swan 48, Swan 65 ketch, Farr 40, Mumm 30, First 40.7 and 44.7, etc.

At the moment there seems to be a bias to maxis, but it's hard to find a single type of boat that has not recorded a win in a national-level regatta under IRC.

Some US sailors think IRC survives only "because it hasn't been under pressure", but out here in Australia & New Zealand we've had about 6 60'+ footers rebuilt and 6 maxis and two 66/68 footers built for IRC in the last 4 years. Four new 90-98 foot boats in 2 years (Nicorette, Zana/Konica, Wild Thing/Skandia, Alfa Romeo/Shockwave) have put the rule under a lot of pressure, and it's given very close racing between canting and non-canting boats etc.

Under IMS, how often has a Open 60 style boat won? How often has an old IOR boat won? How often has a canter won? How often has a water-ballasted boat won? IMS has advantages, but surely you can't say it rates a wide style of boats fairly?

Paul, out here we've been using IRC for years; back since it was CHS. There actually seems to be little arbitrary value left in it, from my many discussions with designers and measurers and the RORC office while researching for articles.

It's not hard to see that you can assign an accurate figure for general hull drag/lift etc given the measurements you take (displ, beam, draft, construction, a rough idea of C of G, after overhang, age, and a general "type" classification). There isn't any real need to have much subjective input.

Yes, there is a mild subjective input into areas like the selection of inputs like interior, but their impact on overall rating is fairly small. I know of boats that I'm sure the RORC office didn't know, with unusual design styles, that ended up pretty much right on the money under IRC.

In contrast, the only formula (apart from other rating rules) I've known PHRF handicappers to use is the Schell regression formula, which is wildly innaccurate in many cases. So you can't use a simple Schell type rule to help you with PHRF ratings much AFAIK, and if you use simple assessment of the way the boats are sailed you end up totally subjective.

If you have a problem with your IRC, there are numbers you can look at. You can look at the Rig Factor and say "hey, why have you got me down as having an RF of 1.06 when I've got a single spreader alloy rig?".....not that you would have such a RF with such a rig. You can (as I have done) look at the Hull Factor and see it's 7.5, and then see that comparable boats (same age, designed to the same rule but heavier) have a HF of (say) 7.2, while the bigger version of your boat has an HF of 7.5...and a Farr 40 OD is mebbe 9.6 while a Farr IOR 40 is 8.6 or summat.

That provides many more checks and balances than the committee for subjective rules just saying "we reckon your boat rates 172", or "we reckon we'll put your liveaboard boat, cheapest and oldest in the fleet, in the class for new production boats where it has to sail close behind boats 10 years newer and 4' longer...." That bloody hurt!

 

Replace "IRC" with "PHRF" and here in North America the statement is equally true. Does that mean PHRF is fair then?

You have admitted that certain types will not win in a typical IRC W/L regatta. For example, I doubt you'll want to race something really fun like a TP52 in a top level IRC bouy regatta. To me that's not good. If you owned one of those types and IRC was the only game, how much fun would you have? How much fun will it be for local fleets when someone buys a known "Good IRC Rater" and brings it in to demolish the fleet. I've seen it in local IOR, MORC, and IMS fleets. Typeforming is a sad reality without knob turning.

I can pretty much guarantee my boat won't rate worth a tinker's damn under IRC, unless there's a lot of friendly knob turning. It doesn't rate well under PHRF either (nor would it under IMS, IOR, MORC), so I'm not commenting in self service.

But you don't know if there is other subjective knob turning, do you? I'm sure there are hints at denials, but has anyone in-the-know told you outright there is none?

When the rating office says they use a measurement formula to arrive at the rating then I would call it a measurement rule. In fact, CHS/IRC is still a handicapping system. I think even old Olin would agree with me there.

What? I doubt you'll find more than one or two wingnuts who might think regression is the way to assign a handicap, outside of Portsmouth afficianados. If your perception is that most PHRF ratings are arrived at this way you'll need to do some homework.

Now how do you think the RORC single rating is going to work for boats that sail in San Diego versus San Francisco. In SD something like a Capri 25 will be faster than a J24 around the cans. In the big breeze and chop in Ess Eff the roles would undoubtedly be reversed. Ditto something like a Santa Cruz 27 vs J30. PHRF regions can work these things out. IRC does not, as far as I have heard.

So if your SC27 in 'Frisco owes time to the J30 who will work you b-for-b, and the clubs all use IRC, do you take up golf?

Let's see, when the smoke clears, how many boats in North America end up with ratings within a reasonable tolerance from their PHRF numbers. Let's run some results on the next few big regattas under US IRC and compare to what it would be under PHRF TOT scoring. I'll wager things won't be far off in medium breeze W/L racing.

In a similar vein, I've heard a lot of moaning about TOD vs TOT on the net over the past few years. I ran some bouy regatta results both ways using the US Sailing TOT formula and guess what? Generally Positions 1-5 stay the same, maybe 6 and 7 flop, then a long string of same same. Of course both results are based on the same base ratings. I believe there are inherent problems in that TOT formula, although I would still like to see it use more widely and massaged, but it seems TOD isn't as bad as most of the whiners say it is. I will guess that a change to IRC will prove the same true for PHRF.

Believe me, I have a dislike of the way PHRF works. But I sure don't believe much in "secret, we're smarter than everyone else" systems. I don't believe that a small number of dimensions can be put into a formula and have it spit out a "better" number than a true measurement rule. By the way,
if not for an open measurement formula, how would we have found results problems like the Victory-at-SORC debacle?

If you have ever looked at the way owners in the US fill out their PHRF certificate measurements you will laugh at the notion of having these people fill out anything, send it to a foreign land, and and have an accurate rating assigned based on that.

 

"For example, I doubt you'll want to race something really fun like a TP52 in a top level IRC bouy regatta."

Well, the top IRC boat at the Admiral's Cup was the 66' R/P canter Wild Oats. Top short-course boat was the Ker 55 Aera; she's not as big-rigged as the TP 52s, but she still beats all the Farr 52 ODs across the line and on time so she's not slow.

Out here, the dominant boat in the short courses of our biggest regatta (Hamilton Island) was the 98 foot canter Skandia Wild Thing, which is much faster and more radical than the TP52s.

What design is your boat?

"How much fun will it be for local fleets when someone buys a known "Good IRC Rater" and brings it in to demolish the fleet. I've seen it in local IOR, MORC, and IMS fleets. Typeforming is a sad reality without knob turning."

Look at the results of something like Cork Week and you'll see boats of the same "good IRC rater" design at the back of the pack, as well as the front. I've yet to see a boat that can just drop in and demolish the fleet.

"If your perception is that most PHRF ratings are arrived at this way you'll need to do some homework."

No, I know it's not the standard way to create PHRF ratings. I don't understand the remarks about Portsmouth, which doesn't use measured formulae.

Re use of Schell; from "Sail" magazine, an article by a Cheseapeake/KWRW head handicapper'

"Several PHRF fleets also use a formula-based equation as a starting point for their assigned time-on-distance numbers. There are several different formulas, but all that I have seen involve sail area, water line length and displacement as a minimum. A typical example is Terry Schell's regression formula:

610-8.36*(SA/disp^0.333)+0.000051*(SA^2)-55*(P/(J+E)-30.8*(LWL^0.5)-602*(Draft^2/SA)

As technical chair for PHRF of the Chesapeake, I "crunch" numbers every year to calculate imputed ratings for all boats racing in the local PHRF fleet for comparison and possible adjustment to the assigned rating. However, to try to eliminate data "flukes", the primary data input is from windward-leeward courses, and races where the wind was under 6 or over 20 are discarded."

To me, that sort of sounds like he's assessing how well people are sailing, to see whether their finishes match up with how they match the handicapper's ideas of where the boats should finish. I don't want someone assessing how well I sail by looking at me, I don't think it's that easy.

Re "I don't believe that a small number of dimensions can be put into a formula and have it spit out a "better" number than a true measurement rule."

The dimensions (as of 2001) include displacement, LOA, LWL, BMAX, draft, length and height of bow overhang (IIRC), stern overhang (length and height of overhang); P,I,E,Forestay Length, actual luff length (no default to forestay length as in IMS & IOR), LP, keel material and type, kite luffs; presence of chines and IOR bumps; interior; age and series date, mainsail girths, internal ballast, # of spreaders and rigging like jumpers and checks, as well as the subjective elements like Hull Type (ULDB, IOR, racer/cruiser, etc). While some of these are definitely loose terms, they do allow the rule to incorporate allowances for factors like the bumps on old IOR boats - something which IMS misses entirely - or the deck layouts of fast cruisers; something that IMS misses entirely.

If a true measurement rule like IOR and IMS is so great, why do we get strange boats like the current B & C IMS racers? So having perhaps some subjective element (which seems to amount to no more than putting in "IOR racer" or similar terms, or not telling designers the difference between a bulb keel and a low C of G keel) is the best way of getting around the problem. The advantage over PHRF style ratings is that most of the inputs are there on the cert., and the subjective terms come out in the hull and rig numbers which are open to comparison and query.

I wonder how the number of measurements in IRC compares with the numbers in IOR, which relied heavily on the AGS, FDI, AOHCC, MDI and other measurements; there weren't too many of them off the top of my head. AOHCC and AGS are fairly similar to the IRC OH factor, I think. Displacement under IRC is MORE accurately measured when boats are weighed.

Re "Now how do you think the RORC single rating is going to work for boats that sail in San Diego versus San Francisco. In SD something like a Capri 25 will be faster than a J24 around the cans. In the big breeze and chop in Ess Eff the roles would undoubtedly be reversed. Ditto something like a Santa Cruz 27 vs J30. PHRF regions can work these things out. IRC does not, as far as I have heard."

So if your SC27 in 'Frisco owes time to the J30 who will work you b-for-b, and the clubs all use IRC, do you take up golf?"

Dunno. Maybe you get more single-conditions areas in the USA, but these are not great problems here or in the UK. I know there are some boats that have the same rating in widely-varying places; IIRC J/24s are the same in HI as LIS, as are Farr 727s - same length, but prefer very different conditions.

The main thing I wonder about is that once you have a small # of boats, then you start tweaking for different locales, your fleet becomes so small that comparison is extremely difficult. It's also arguable that anyone who buys the "wrong" boat is a turkey....if you chose a Mac 26X to race to Hawaii do you deserve a rating change just 'cause you'll sink??? OK, extreme example....I also realise that allowing people to race the boat of their choice is important. However, in the tight tide-constricted water of the Solent, a Swan 65 ketch kicks *** on breezy days. Out here, a 1909 Fife metre boat won the IRC nationals at Hamilton Island in 7-10 knots, flat water and tide. She then was in with a big chance of a win the next year, in 20 knots and big chop.

 

Here in France we practice IRC (ex CHS) since 1985, I could affirm you there is nothing
inside IRC. it is only based on 2 subjective Coefficients (Hull factor ang rig factor) a
large amount of Age alowance. And please stop to read Seahorse Mag to get info on handicap system it is not an objective way to lean about IRC or IMS !!!!!

A sorry I miss one factor for IRC ....politics.....

dont wast your time with IRC and Good luck......


Pierre

 

Rating rules

Dear CT249,
I want to say that here in my area IMS continue to be the only rating rule that define properly the performances of different boats.
I know that in your area IRC in the most used rating rule, and this is fine as in your area there are boats like Open 60, canter boats, eccc. Sometimes I dream to live in Australia, but reality is different!!!
I also understand that major title are raced under IRC rule, and I appreciate this.
The fact is that if I bring 2 different boat that race here in Italy, and compare their handicap both with IMS and with IRC, many times the rating difference with the IMS is more realistic that the rating difference with the IRC.
At present, Ims is the rating rule that take into consideration a wide number of hull, rig, interiors factor. This thing not occour under the IRC rule. No displacement measurement are done, and every owner must input the boat's displacement...the result can be the same of the Sydney to Hobart race, where there are important boats with a lot of disrepancies on their cert (http://www.sailinganarchy.com/index_page2.htm).
So, I'm not pushing the IMS rule (for me the important are the boats, not the rules) but I understand that from the technical point of view this rule is the one that TRY to set the proper handicap to wide range of boats. In the future, if it survive, IMS rule will better accept the cantig keel and water ballasted boat (but here there is not a lot boats like this) and give to this boat a better handicap than last years, and other thing like to try stop typeforming boats. Also Wing masts will be threated better.
Yes, with the current IMS rule not a wide range of boats are rated, but I also admit that rules that rate a wide range of boat (kanting keel, water ballast, open,cruiser, etc...) may have problem in give the proper rating to a vast range of boats like this. So, I think the problem is the same: if you want a rating rule that rate a vast range of boat, you have to accept discrepancies.
I see now that IRC in my area is becoming the natural choose for a lot of owner not satisfacted from IMS, this is fine and may be that this is a trend that will continue, but I also see thar ORC are working hard to let IMS change in the proper manner.
My dissertion about the TP52 against IMS 52 under IMS rule, want to focus the things about the fact that, if a boat like a TP52 (that is punished by IMS for a lot of factor like carbon hull, sail area, etc..) will be sailed properly, can win races in corrected ims time. I am wondering if the same thing will occour in IRC race....
Another thing here is that race of maxis are raced with ORC CLub certificates, that are not IRC, but simplified IMS certificates...

Ciao,
Alessandro

 

a great advantage, that will make IMS living in Italy for still a long time is that is both suited for pure fixed-keel racers and for cruiser/racers; there's not a plenty of pure racers here, so most of IMS fleet is made by cruiser/racer; 90% of sailboats that you can see in the italian marinas are fixed keel sloop, so the kind of boat for whom the IMS rule was chiseled!! of course if marinas were full of multihulls, canting keeler, mini 6,50 and so on, IMS would lie in his grave now. IMS will live as long as it will suits well the existing fleet, even if everybody knows and hates his limits and distortions.

Ciao
Mistral

 

From much reading and listening it seems to me that:-

IMS is thoroughly scientific VPP based, shouldn't be type forming but is, IRC is working from a measured formula leading to a empirically rather than scientifically based VPP, could be type forming but isn't.

IMS probably does a better job at handicapping between similar boats of the type it favours if you are happy with the complexities and that type of boat, IRC is less hassle and much better at handling a disparate population of boats, so you are more likely to be able to race a boat you like.

It would appear that the science isn't yet sufficiently advanced for IMS to work with a disparate population of boats- the alternative being that the administration is up the chute and I don't believe that.

 

I fearlessly predict another century of unsatisfactory rating systems and sailors whining about their ratings.

There is something wrong with the statement "My boat does not rate well under PHRF." As I see it, either your boat has the WRONG rating, or it's not well-suited to being a racing boat. You can blame the PHRF implementation, but not the PHRF concept for a unfair rating.

When I have scored fleets under boat TOD and TOT, I consistently found that the time spread is less under TOT. This intuitively suggests that it is better, though it does not prove it. Many sailors resist a system that complicates the calculation of who is ahead during a race. (I think they are mostly focusing on the wrong thing, but ...)

The only sane paths are to accept that race scoring is flawed, or race one-design.

 

You hit the nail square on the head there. Handicapping a sailboat race is always bogus. But it can still be fun to go racing...

 

The IRC has somehow decided that a 36 footer is the fastest boat in the UK, hasn't it? So as a boat's design approaches that extreme type it will obviously be going into the red, rating-wise.

I think the IRC obviously has their canter number wrong. Once they sort that ratings will change. Maybe they'll go too far like the old IOR did with centerboarders and the canters won't win.

Also, the old MORC timetables were skewed toward lower rating boats. Seems maybe IRC is currently skewed the other way. Time will tell.

I sail an 800 kg, 8.5m sportboat with an etchells rig and overlength boom, roach, pole, and near-masthead kites. I don't think IRC is geared for this, with or without my trapeze.

Seems to me that a couple of IRC specials came to the BBS and applied a hiding to the fleet. Maybe they were better sailed. Maybe they have a good advantage under the secret system.

One of those boats just followed on with the Hobart win. Trend?

I'll repeat. Results have many other reasons than the potential of the boat. Regression is silly. It is golf handicapping. That's also what Portsmouth does.

The numberson the IRC certificate provide nowhere near the information needed to determine the pace of a boat. IOR and IMS were not "so great", but at least you knew where you stood and why.

You better look closely at an old cert. Lots of measurements, trying todefine the shape. Not really successful due to bumping and localised distortions.

MORC was perhaps a better rule, and they weighed the boats as well.

The J24s do vary a bit,maybe from 168 to 174 or so. However, they are one of the boats that PHRF uses as base boats ot compare others to.

The 727 I sailed on in SoCal rated quite differently in PHRF than the ones sailing in breeze.


IRC may end up being the silver bullet. But worldwide there are probably 5 times as many boats sailing under PHRF type schemes. It seems to serve the club racer quite well. IRC was not intended to be a GP rule,although some seem to think that it is the successor to IOR and IMS.


The other thing I can't see IRC handling are one way wonders. A Cheetah 30 sportboat sails to nearly a 0 rating downwind, but closer to 90 or so upwind. Sausage course rating is 66 PHRF, Offwind rating is a gift at 36. Under IRC if it had any chance in bouy races it would dominate all offwind races. If it was rated well for offwind it would stay home for all bouy races, or show up and finish last.