Classic Rating Formula (CRF) "Rig Factor"

Discussion in 'Sailboats' started by griffinb, Jan 30, 2018.

?

Which rig seems best-rated in the CRF?

  1. Jib-Headed: Sloop = 1.00

    0 vote(s)
    0.0%
  2. Jib-Headed Yawl = 0.91

    1 vote(s)
    50.0%
  3. Jib-Headed Ketch = 0.90

    0 vote(s)
    0.0%
  4. Square-Head: Sloop = 1.20

    1 vote(s)
    50.0%
  5. Schooner: Staysail = 0.90

    0 vote(s)
    0.0%
  6. Schooner: Gaff Fore, Marconi Main = 0.80

    0 vote(s)
    0.0%
  7. Gaff Headed: Sloop = 0.92

    0 vote(s)
    0.0%
  8. Gaff Headed: Yawl = 0.83

    0 vote(s)
    0.0%
  9. Gaff Headed: Ketch = 0.82

    0 vote(s)
    0.0%
  10. Schooner: Gaff Fore, Gaff Main = 0.70

    0 vote(s)
    0.0%
  1. griffinb
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    griffinb Junior Member

    The Classic Rating Formula (CRF) applies a "Rig Factor" to calculate corrected time. So, higher number=higher corrected time=faster boat.

    Which rig type seems most under-rated? As in, if you were to try to beat the formula, which rig would you choose? And why (if we dare?)

    Assume 15 mph wind, 1-2 ft seas, and square racecourse (upwind, reach, downwind, reach)

    Apparently these are the only rig types allowed by the CRF.

    Reference:
    http://classicratingformula.com/wp-content/uploads/2017/04/CRF-MkII-Formula_170425.pdf
     
  2. PAR
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    PAR Yacht Designer/Builder

    A double reaching course, seems to favor the divided rigs and this would also suggest, you can take advantage of those at the lower end of the rate. This is because, you'd get your butt handed to you uphill, but may have a greater advantage down hill and on the reaches, plus the advantage of the time you'll get, from the "disadvantaged" rig choice. As to which, there can be discussion about the yawls, ketches and schooners, but if they're traditionally proportioned, it seems pretty obvious.
     
  3. griffinb
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    griffinb Junior Member

    This is the exact discussion I am hoping to start. Slower rigs are rated slower. The question is, which of them is undervalued, or "underrated" the most?

    If it were obvious to me, I wouldn't be asking! They all seem pretty fairly rated (handicapped).

    Maybe the gaff rigs? Because those ratings were developed for wooden spared classics to compete evenly? But with those upper gaffs made of carbon, they won't have nearly the weight high in he rig that the Rig Factor is expecting?
     
  4. griffinb
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    griffinb Junior Member

    I don't believe the rigs needs to be "traditionally proportioned", though I do know the formula was revised to reclassify mini-gaff rigs (very short gaff, to the point of looking like a square-topped main), due to W-37 Racehorse trying to beat the formula (which didn't even work, because the boat has always underperformed):
    upload_2018-1-31_17-38-32.png
     
  5. PAR
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    PAR Yacht Designer/Builder

    If traditional proportions are allowed a gaff yawl would seem to have an advantage, though it would need to be designed to take advantage of the rule (both hull and rig).
     
  6. griffinb
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    griffinb Junior Member

    Obviously lots of hull design parameters in the rule, but this thread is just about rig type.

    For some reason they have ketches rated slightly slower than yawls. Why did you pick yawl instead of ketch? Were you thinking minimum size main gaff, minimum size mizen mast, minimum size mizen gaff, and masthead jib, make the sailplan act as "sloop-like" as possible?
     
  7. philSweet
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    philSweet Senior Member

    No, it's not just about rig type. You can't do that. Optimal split rigged hulls always want a bit more LOA than sloops. This rule directly penalizes LOA in the L calculation. You have to look at the entire rule structure. The rule has components that drive the hull shape and proportion the hull to the sail area. Just guessing, but 15 knots is probably not the center of the design box these rules were formed around. It's on the breezier side of the middle. The L component is seriously penalized by the rule relative to sail area. This might not be too bad for boats with a 60' measured L that will sail at 75' L when stepping out at 10 knots in 15 knots breeze, but it is pretty tough on smaller boats. So you end up looking at hulls that beat the L rule first. Think long stern overhangs and very slack bilges and medium displacements probably above d/l 250. This gets a measured 35 lwl boat up to 45' when sailing in 15 knots of wind. And that ducktail is a fine place to put a minimal yawl. Especially if you can use the extra Spar Factor for wooden spars on split rigs (which seems to be very generous, even in heavy air). I suspect the draft penalties also favor split rigs very slightly in the smaller craft.

    The only way you can isolate rig type the way you are asking to do is to specify the total rating you are aiming at. Or by showing us the hull you are putting it on, and providing all the other factors that contribute to the entire R6 rating. And optimizing for 15 knots is probably going to put you in a small corner of the design space. Some of these old boats were optimized for 3 to 5 knots of wind. The rule as it is written seems to favor these.

    Somehow, when I read those rules, I think of stuff like this - [​IMG]
     
  8. latestarter
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    latestarter Senior Member

    I suggest you read the home page of the Classic Racing Formula
    Classic Rating Formula CRFMkII http://classicratingformula.com/
    Part of which says:-
    "The original version of CRF was developed over a number of years thanks to the efforts of Chris Wick, Bill Doyle, Steve White, Maynard Bray and Joel White who, between them, shouldered the thankless task of maintaining and administering the rule for decades. Many years of competition and growth in classic yacht racing inevitably exposed shortcomings in the original form, however, and the development of CRF MkII in 2016 drew on a combination of the original formula, experience gained from other successful rating systems and on new access to sailing yacht performance data.

    The goal of CRF MkII is to provide an objective, accurate and transparent rating system. To that end, it is anticipated that adjustments to the formula to take into account new performance data may be made from year to year. The 2018 formula has been modified to reflect biases that were identified by an objective, in-depth analysis of 2017 race results. Specifically, yachts with relatively narrow beam and heavy displacement (e.g. Universal and International rule yachts) were observed to be advantaged, while yachts with unusually deep draft (via either fixed keel or centerboard) were observed to be disadvantaged. Therefore, the 2018 CRF MkII ratings for nearly all yachts will change relative to their 2017 ratings, but most only slightly. Those that see a significant change will find that other yachts of the same type will have changed by a similar amount, so the competitive balance within groups should be maintained."

    Basically you are trying to second guess a committee of experts working on up to date data.
     
  9. philSweet
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    philSweet Senior Member

    And the best way to do that is look at the biases build in to the fleet by type. It looks like the spar factor for split rigs is a bit high, perhaps reflecting more on that fleet than the physics of the situation. But I only just saw the other thread where you mention a length of 26 feet. What length is that? LWL, LOD, LOA, or rated length?
     
  10. philSweet
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    philSweet Senior Member

    Looking at the foretriangle area rating for LP% > 1, there seems to be an error in the formula. An LP of 1.01 with a J of 9 feet drops the rated area by 38% compared to a LP% of 1.00. This is in reference to the 4/25/17 formulas referenced above and on the website. These foretriangle formulas should blend smoothly.

    edit - I suspect the second open parentheses should fall after the 1, not before, thus guaranteeing a number bigger than 1.
     
  11. griffinb
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    griffinb Junior Member

    I've read their whole website.

    I agree that Classic Rating Formula (CRF) seems to have been created by some dedicated, smart people. And I understand that the formula continues to be updated in an effort to improve parity and discourage optimization.

    That's why beating the rule could be such a great challenge! (although if someone built a true rule-beater, they could change the formula after a year or two...)
     
  12. griffinb
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    griffinb Junior Member

    upload_2018-2-3_0-13-21.png

    I originally picked 26 feet because I think there are some other classic races with that limit. But let's keep it simple: 24' LoA.
     
  13. griffinb
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    griffinb Junior Member

    That boat certainly looks optimized for 3mph breeze.

    Optimizing for a very narrow band of conditions is one way to win. For example, if you plan for 30mph winds (probably the maximum wind before the race would be canceled), with a very small rig, and you're the only boat that isn't reefed, that would probably produce a win. But local weather conditions mean the race normally happens with wind between 5-15mph, so the small-rig boat wouldn't win very often...
     
  14. Bruce Woods
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    Bruce Woods Senior Member

    I suspect the rig correction factors have been arrived at through experience and time.

    At 0.91 its time to step a broom stick with a token 2 sq ft of rag on it down aft on your sloop and call it a yawl. What does the rule say about % division of SA?.

    Better still lash your broom stick to the pulpit and call it a schooner. :)

    Nah second thoughts that will probably determine your spinnaker size.
     

  15. gggGuest
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    gggGuest ...

    One thought is that you are clearly seeing the event as a competition between the designer and the rule writers. The event organisers may not see it like that. If they consider that the rule is simply there to attempt to provide as fair as possible racing between a fleet of disparate boats, then they may see a deliberate attempt to design to the rule as being against the intention of the event and against the interests of the vast majority of competitors. In which case they may simply decide that the best interests of the majority are served by refusing your entry.
     
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