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      Abbreviated rules   07/28/2017

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hoppy

Mods and IRC impact

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I'm wondering what impact various modifications have had on a boats IRC rating?

I know that the IRC rating system is a "black box" so the only way to truely know is to either do the mods and get it re-rated or do a test rating. So obviously there is no book that can be quoted, just  personal experience from mods performed (or tested) or what you've read online. It does not matter what boat it was....  

 

Some of the updates I'm mostly curious about are:

  • reduction of foresail area by going to non-overlapping jibs
  • Adding a bowsprit that extends beyond the spinnaker pole
  • larger spinnakers or asymmetrics
  • Carbon mast
  • removing running backstays

rating changes from any other mods will be appreciated..

 

I found this comment in an old thread about the Sydney 38 from 2008 when they allowed bigger masthead spinnakers in the OD class.

Quote

Rating will generally go up .002 for each 10sqm of spin area. THIS IS NOT FIXED! It is just my assesment based on what I have been involved with.

 

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You have a pretty good list of things there - all are pretty well known to be treated favorably by IRC. I'd speak with an IRC specialist about sizing the bowsprit and how finesse your declarations of Asyms and Syms for the best rating.

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One thing I was wondering about recently - I came across the following statement on a sailmaker's website:-

The curved sides of a spinnaker make the computation of area a complicated process. It is therefore an almost universal practice in the sail-making industry to compute the area as if the sail were a rectangle. We follow that practice, and the area shown on a price list is the product of the luff length times the maximum width. The actual area will vary from about 70% to 85% of the rectangular area, depending on the type of spinnaker.

Given different spinnakers shapes there may be an advantage in measuring a specific type of spinnaker (eg S1, S2, S3, S4 etc) if the IRC formula is not that sophisticated???

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4 minutes ago, 42 South said:

One thing I was wondering about recently - I came across the following statement on a sailmaker's website:-

The curved sides of a spinnaker make the computation of area a complicated process. It is therefore an almost universal practice in the sail-making industry to compute the area as if the sail were a rectangle. We follow that practice, and the area shown on a price list is the product of the luff length times the maximum width. The actual area will vary from about 70% to 85% of the rectangular area, depending on the type of spinnaker.

Given different spinnakers shapes there may be an advantage in measuring a specific type of spinnaker (eg S1, S2, S3, S4 etc) if the IRC formula is not that sophisticated???

I found this

https://www.ircrating.org/images/stories/pdf/measurement/spinnakers_faq_171122.pdf

Quote

21.6.2 Spinnaker area (SPA) shall be calculated from: SPA = ((SLU + SLE)/2) * ((SFL + (4 * SHW))/5) * 0.83 SLU, SLE, SFL and SHW of the largest area spinnaker on board shall be declared. The calculated area of this spinnaker will be shown on a boat’s certificate as the maximum permitted SPA.

 

 

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1 hour ago, hoppy said:

Yes I was already aware of this, but it is still only a general measurement. To accurately measure a sail with a curved luff and a balloon shape you would need to take many (say every 100mm) width measurements all along the luff - this is the method that sail design software would probably use. It's just pointing out that some spinnaker sail shapes may actually be more or less actual area than the IRC/AMS/Orci formulas allow.

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24 minutes ago, 42 South said:

Yes I was already aware of this, but it is still only a general measurement. To accurately measure a sail with a curved luff and a balloon shape you would need to take many (say every 100mm) width measurements all along the luff - this is the method that sail design software would probably use. It's just pointing out that some spinnaker sail shapes may actually be more or less actual area than the IRC/AMS/Orci formulas allow.

I realise that and it makes sense that the sailmakers look for the extra area in this formula and make sure they don't make a sail that has less area than the rating calculates.

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Just remember that 'slow it down' is not always the answer. Some times ya just godda go harder...

Check out the sprit on this IRC optimised Mumm/Farr 30: https://www.facebook.com/pegasusdekmarx/

To close out the mid range hole where they couldn't be competitive against the 40ers they race against then basically figured even faster was the answer.

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Regarding your comments:

  • reduction of foresail area by going to non-overlapping jibs
    • this typically is worth doing, unless your boat is very heavy and needs the 150% genoa
  • Adding a bowsprit that extends beyond the spinnaker pole
    • if the bowsprit is just as long as the spi pole, there will be no rating effect.
    • if longer, your rating might suffer; theoretically it will, but it might not. Some years ago I did order test certificates and there was no effect of a longer pole with the same spi area.
  • larger spinnakers or asymmetrics
    • larger spinnakers are worth the change, given that you race windward-leeward. The speed advantage is usually better than what you pay in rating
    • whether A or S depends on the kind of boat. We sail with S2, A3 and S4; tried an A1.5 but does not appear to work on the boat.
  • Carbon mast
    • this is expensive and might not be worth it.
  • removing running backstays
    • again this depends on your mast. I have seen a Mumm36 which removed them, but mounted a carbon mast instead.

There is no magic I know of. Wish I did ...

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For a 36 footer a carbon mast will cost you around 0.004 also if your bowsprit is longer than the pole then that's the measurement they take for your rating calculation

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Here are some things I went through with Misty Mountain after we bought her. 

Put water bladders in to replace tanks taken out. Installed three burner stove with oven to replace the one taken out. Replaced stored powered backstay system with manual pump system. Replaced the two blade folding prop with a Gorilla three blade folder. These items equated to a .006 reduction in the rating. Recently I put the cushions back on and that got me another .001.

the mainsail that came with her was one of those short E types. And jibs were short on the luff. So I ran two separate Trial Cert to see the affect of each sail.  By maxing out the P and E, the trial main would increase my rating by .013.  And by maxing out the LL and LP of the Jib, my Trial increase would be .013.  IRC harshly treat the Jib vs the Main.  So I went the mainsail increase and kept the jibs as is. 

Now I am looking at going with a longer bowsprit setup from a short sprit with pole setup.  So I purchased the IRC Cert. of our sistership and using their data, I ran a Trial Cert.  With a one meter increase in the sprit and with the increase in Spinnaker sail area, our trial rating only went up .001.  So we are going to go with the new setup and see how things go?!

 

i hope that what I have gone through will be of help. 

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7 hours ago, JL92S said:

For a 36 footer a carbon mast will cost you around 0.004 also if your bowsprit is longer than the pole then that's the measurement they take for your rating calculation

That does not soundI have no idea how much a CF mast will cost, but I think that it would be the killer...

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18 hours ago, George Hackett said:

Here are some things I went through with Misty Mountain after we bought her. 

Put water bladders in to replace tanks taken out. Installed three burner stove with oven to replace the one taken out. Replaced stored powered backstay system with manual pump system. Replaced the two blade folding prop with a Gorilla three blade folder. These items equated to a .006 reduction in the rating. Recently I put the cushions back on and that got me another .001.

the mainsail that came with her was one of those short E types. And jibs were short on the luff. So I ran two separate Trial Cert to see the affect of each sail.  By maxing out the P and E, the trial main would increase my rating by .013.  And by maxing out the LL and LP of the Jib, my Trial increase would be .013.  IRC harshly treat the Jib vs the Main.  So I went the mainsail increase and kept the jibs as is. 

Now I am looking at going with a longer bowsprit setup from a short sprit with pole setup.  So I purchased the IRC Cert. of our sistership and using their data, I ran a Trial Cert.  With a one meter increase in the sprit and with the increase in Spinnaker sail area, our trial rating only went up .001.  So we are going to go with the new setup and see how things go?!

 

i hope that what I have gone through will be of help. 

With the pole change are you still rating for a moveable pole with s the and a sails or just the spirit and a sails? 

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23 hours ago, JL92S said:

For a 36 footer a carbon mast will cost you around 0.004 also if your bowsprit is longer than the pole then that's the measurement they take for your rating calculation

 

15 hours ago, hoppy said:

That does not soundI have no idea how much a CF mast will cost, but I think that it would be the killer...

Don't know what happened to this post. It should have read 

That does not sound so expensive. I have no idea how much a CF mast will cost, but I think that it would be the killer...

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11 hours ago, Cats Rule said:

With the pole change are you still rating for a moveable pole with s the and a sails or just the spirit and a sails? 

This will be a straight Bow Sprit setup, no Pole.

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1 hour ago, George Hackett said:

This will be a straight Bow Sprit setup, no Pole.

There are a reasonable amount of boats racing offshore in the uk running A sails only offshore and then switching back to s sails for solent racing. As you point out you can have a bigger kite and spirit for little or no increase. 

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I think that the general wisdom is that a carbon mast will benefit you more than the penalty on the TCC. At least this is what some of the top IRC boats in Brittany seem to think as aluminium masts get swapped for CF ones.

Bizarrely contrary to what cats rule has witnessed in the UK, people here tend to use symmetric sails inshore and asymmetric offshore.

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10 hours ago, Panoramix said:

I think that the general wisdom is that a carbon mast will benefit you more than the penalty on the TCC. At least this is what some of the top IRC boats in Brittany seem to think as aluminium masts get swapped for CF ones.

Bizarrely contrary to what cats rule has witnessed in the UK, people here tend to use symmetric sails inshore and asymmetric offshore.

Reread what he wrote. 

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On 20/01/2018 at 2:10 AM, George Hackett said:

By maxing out the P and E, the trial main would increase my rating by .013.  And by maxing out the LL and LP of the Jib, my Trial increase would be .013.  IRC harshly treat the Jib vs the Main.  So I went the mainsail increase and kept the jibs as is. 

Question is which change would enable you out sail the 0.013? My bet would of been on maxing the jib luff length.

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21 hours ago, rgeek said:

Question is which change would enable you out sail the 0.013? My bet would of been on maxing the jib luff length.

Can you explain why?

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