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#1 Polaris

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Posted 21 September 2008 - 10:57 PM

I am trying to do some comparisons for each system for different boats. Does anybody know the equation to convert Americap/ORR number to a phrf equivalent?

Thanks.

#2 NACAnutz

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Posted 21 September 2008 - 11:49 PM

42

#3 walterbshaffer

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Posted 22 September 2008 - 12:43 AM

Primarily, the answer is found here:

http://209.85.173.10...l...us&ie=UTF-8

There are a number of other handicapping systems that can be useful information when looking at empirical handicaps. Although none of these can be expected to be identical to PHRF, they are useful for determining if you are in the "ballpark". Here are several conversions for going from one handicapping system to another.

IRC: The RORC web site recommends a conversion factor to Time on Distance of 600/IRC. However, the following formula seems to give better results:

PHRF = (650/IRC) - 555

IMS: The IMS General Purpose (GPH) number can be useful. You have to keep in mind that IMS does not do a great job of handicapping boats that are not designed to the latest version of the rule. The most common conversion is:

PHRF = IMS GPH - 550

The 550 factor should perhaps be decreased a little if the boat is an older one and increased a little if the boat is a state of the art racing machine. Another conversion, determined by Nils Nordenstrom of Norway is:

PHRF = - 480 + 0.9 * IMS GPH

The accuracy of these can vary from year to year as the IMS rule changes. For boats not designed to the rule this can give answers that 10 to 10 Seconds per Mile, and more, in error. The error is usually to over estimate the speed. Some sprit boats are prime examples of this error. Ligh displacement boats also tend to be severly handicapped by IMS.

Dixie Portsmouth: The PHRF conversion from the Dixie Portsmouth system used in the United States is:

PHRF = 6 * DPN - 330

ASPN: The Atlantic Speed Potential Number is a Time on Time factor used by the Nova Scotia PHRF. The following is the relationship to PHRF Time on Distance:

PHRF = (63000/ASPN) - 400

Argentine PHRF: The Argentine PHRF handicap is given in feet, as the IOR was. Converting to PHRF Time on Distance is similar to converting from the IOR itself. The conversion into a Time Correction Factor is:

TCF = (2.6 * R)/10

LYS: The LYS system is a Time on Time system used in the Nordic countries. The conversion to PHRF is:

PHRF = - 480 + 720/LYS

The LYS handicap itself can be related to the IMS by:

LYS = 800/IMS GPH

The LYS handicap can be related to the ORC TCF by:

LYS = 600/ORC TCF

ECHO: This is the "personal" handicapping system used in Ireland. Basically they start out with an empirically derived base number. Then a crew factor is applied. This system also has a "Jockey Factor". For instance, if you import a ringer for a regatta, your handicap will be adjusted accordingly.

The time correction factor can be reasonably converted using the standard formula.

PHRF = (600/ECHO) - 500

IOR: The International Offshore Rule presents a difficult conversion problem. Being a very type forming rule, conversion is very sensitive to when the boat was designed. For boats not designed to any version of the rule, all bets are off. The formulae shown here attempt to represent the extremes, early and late, of IOR designs.

Early IOR Conversion: PHRF = - 9.7 * R + 384.9

Late IOR Conversion: PHRF = - 10.8 * R + 379.8

The actual PHRF handicap "should" be somewhere between the two numbers generated above.

Time-on-Time: Time-on-Time scoring can help, over Time-on-Distance scoring if there are unusual race conditions.

#4 Polaris

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Posted 22 September 2008 - 01:05 AM

Awesome.

I am going to print this one.

#5 hard aground

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Posted 22 September 2008 - 01:29 AM

I'm waiting for the Portsmouth Yardstick conversion.

#6 walterbshaffer

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Posted 22 September 2008 - 02:57 PM

For some reason the full conversion table of time allowances does not appear under the link I posted above, but the link at the top of that HTML page does contain the full table of conversion factors.

What boat are we talking about here, P?

#7 Bump-n-Grind

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Posted 22 September 2008 - 03:46 PM

E= MC2

#8 SemiSalt

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Posted 22 September 2008 - 09:08 PM

I'm waiting for the Portsmouth Yardstick conversion.


D-PN = PHRF / 6 + 55
PHRF = D-PN 55 x 6

Portsmouth and PHRF don't agree very well, however. Keep in mind that they were developed for very different sorts of boats.

#9 SemiSalt

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Posted 22 September 2008 - 09:12 PM

Given that any PHRF-style 1 number system is going to be pretty limited, the Americap idea did make me wonder how much better a 2 number system would be. It seems a obvious idea to use the PHRF as the main corrector and use a small TOT adjustment. Has anyone ever seen a system like that?

Probably not.

#10 hawaiiseadog

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Posted 27 September 2008 - 01:23 AM

I saw the above calculations a long time ago but with a 530 instead of a 550 (for the IMS conversion). Any comments??

Also any comments on using your ORR certificate to justify a PHRF#? It seems reasonable to me that if you have gone to all the effort and costs to get an ORR certificate, you should be able to derive a phrf# from your certificate (thus avoiding the "politics" of the comittee)....

can of worms...... now open!!! :unsure:

#11 Polaris

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Posted 27 September 2008 - 01:33 AM

I was using the conversion to phrf as a base to compare the different systems for a boat that we were buying. I know that you can't compare apples to oranges. An idea is all I was looking for. In our case, the boat is a surfer and does better under ORR.

#12 walterbshaffer

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Posted 27 September 2008 - 03:34 AM

I saw the above calculations a long time ago but with a 530 instead of a 550 (for the IMS conversion). Any comments??

Also any comments on using your ORR certificate to justify a PHRF#? It seems reasonable to me that if you have gone to all the effort and costs to get an ORR certificate, you should be able to derive a phrf# from your certificate (thus avoiding the "politics" of the comittee)....

can of worms...... now open!!! :unsure:


HSD: The 530 number that you see in Hawaii is probably a reflection of the local fleet: the 550 number discussed was pulled form a discussion of the fleet in a major sailing center (Newport RI) and was only intended to reflect the reality of the greater prevalence of higher performance boats in that area. As such it would be equally acceptable in Annapolis, Chicago, Los Angeles or other areas with faster boatsc but not in Hawaii, Alaska or St. Loius. This is not a reflection on the conditions or skill of the sailors but simply upon the relative prevalence of very fast boats.

As for phrf vs ORR, ORR (like IRC) is a rating based upon a measurement system and phrf is a rating based upon observed performance, so no, I don't think your local phrf committee would be impressed. That would be like the owner of one observedly slower phrf boat asking IRC for a rating that reflects more closely a slower boat regardless of the measurement: the J120 vs. the J122 comes to mind in this regard. If IRC were to ever "open that can of worms" it would essentially become another observed performance rating system.

For a pretty good analysis of ORR (Americap II in some qrtrs) there was an article by Tim Kernan on SA (SA...what a great resource. Thanks Scot!) which you can view here:

http://www.sailingan.....1 12-5-05.htm

Polaris, you're not going to fake anybody out with the Synergy!

#13 BalticBandit

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Posted 27 September 2008 - 03:54 AM

D-PN = PHRF / 6 + 55
PHRF = D-PN 55 x 6

Portsmouth and PHRF don't agree very well, however. Keep in mind that they were developed for very different sorts of boats.

I prefer to instead interpolate. IE if I have a boat with a Portsmouth rating but no PHRF, I go look up 2 boats near in PM rating, and interpolate between them proportionally in PHRF. And vice versa. I use the US Sailing Portsmouth ratings.

#14 Polaris

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Posted 27 September 2008 - 05:10 PM

HSD: The 530 number that you see in Hawaii is probably a reflection of the local fleet: the 550 number discussed was pulled form a discussion of the fleet in a major sailing center (Newport RI) and was only intended to reflect the reality of the greater prevalence of higher performance boats in that area. As such it would be equally acceptable in Annapolis, Chicago, Los Angeles or other areas with faster boatsc but not in Hawaii, Alaska or St. Loius. This is not a reflection on the conditions or skill of the sailors but simply upon the relative prevalence of very fast boats.

As for phrf vs ORR, ORR (like IRC) is a rating based upon a measurement system and phrf is a rating based upon observed performance, so no, I don't think your local phrf committee would be impressed. That would be like the owner of one observedly slower phrf boat asking IRC for a rating that reflects more closely a slower boat regardless of the measurement: the J120 vs. the J122 comes to mind in this regard. If IRC were to ever "open that can of worms" it would essentially become another observed performance rating system.

For a pretty good analysis of ORR (Americap II in some qrtrs) there was an article by Tim Kernan on SA (SA...what a great resource. Thanks Scot!) which you can view here:

http://www.sailingan.....1 12-5-05.htm

Polaris, you're not going to fake anybody out with the Synergy!


That was not our intent. We just wanted an idea of how it would rate since the boat has never raced in IRC or ORR and PHRF was the only conversion that we have. I know that a surfer usually does better under ORR than IRC. In PHRF it does excellent. We have won enough, and nobody cares who wins a race other than the guy that won, we just want an exhilarating ride and we didn't buy the boat to play the rating game. If that was the case, we would have kept our Tripp 40 that won big races under every rating system. No games here!

#15 SemiSalt

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Posted 27 September 2008 - 06:20 PM

I prefer to instead interpolate. IE if I have a boat with a Portsmouth rating but no PHRF, I go look up 2 boats near in PM rating, and interpolate between them proportionally in PHRF. And vice versa. I use the US Sailing Portsmouth ratings.


That's a good idea.

It's also true that boats of similar form designed and built around the same time for the same purpose usually sail about the same. So for PHRF, if you find the boats closest in loa, sa, and disp, you will have a pretty good idea of what the rating should be.

#16 walterbshaffer

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Posted 27 September 2008 - 06:52 PM

That was not our intent. We just wanted an idea of how it would rate since the boat has never raced in IRC or ORR and PHRF was the only conversion that we have. I know that a surfer usually does better under ORR than IRC. In PHRF it does excellent. We have won enough, and nobody cares who wins a race other than the guy that won, we just want an exhilarating ride and we didn't buy the boat to play the rating game. If that was the case, we would have kept our Tripp 40 that won big races under every rating system. No games here!

I was only kidding.

Maybe.

(IIRC phrf is 54?)




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