J/30 Class Association Forums J/30 Forum One Design Class Rules Class Rules & #1 Genoa Size Limits

Here is a question to promote class discussion on the size of the #1 jib. Class Rules section 5.12.5 covers the requirements for Genoa #1. Specifically 5.12.5.1 provides the allowable range for the LP based on a 163% sized sail - "The length of LP shall not exceed 5665 mm nor be less than 5250 mm".

Some have complained about the cost to have a 163% OD Genoa and a PHRF base 155% sail. Would it be worth while to consider expanding the range of allowable LP to a smaller dimension, thus allowing someone who sails with a 155% Genoa to be measured in as a legal #1? The net effect is that this would provide less sail area on the #1 for those who elect to go that route. It would still keep the 163% as the base OD sail.

It is not the intention that someone measures in both a 163 and 155 and select what sail to use based on the wind conditions. They have what they have based on para 6.2.4 (each class sail can be replaced a maximum once per calendar year).

If my math is right, I believe that the base LP for a right angle is 3299mm. This means that the current max and min dimension tolerances in para 5.12.5.1 equate to a sail size of 159.2% minimum to 171.7% maximum. Reducing the minimum dimension to 5150mm would provide an allowable size down to 153.1%, or minimum of 5000mm at 151.6% to allow for 155% sail shrinkage.

A potential change would rewrite the paragraph as follows:
5.12.5.1 The length of LP shall not exceed 5665 mm nor be less than 5000 mm

What do members of the class think about exploring this as a potential rules change?

I think LP% is LP/J, where J is 3505 mm (11'6"). That makes:
Max 5665/3505 = 162%
Min 5250/3505 = 150%.

Problem solved. It's a mystery why we call it a 163.

Bob,

I think the issue is the definition you use for LP%. There are different definitions, and you used a different one than I used. I used the ratio of LP on the sail being rated to a right triangle that is the LP of a 100% sail. You used the ratio of LP/J. Both seem to be accepted standards.

The definition I used is extracted from Wiki at this link: http://en.wikipedia.org/wiki/Genoa_Jib
Genoas are categorized by the percentage of overlap. This is calculated by looking at the distance along a perpendicular line from the luff of the genoa to the clew, called the LP (for "luff perpendicular"). A 150% genoa would have an LP 50% larger than the foretriangle length.

Below are the definitions with J/30 parameters in parenthesis, followed by the calculations I used:

I= Height of foretriangle. Measured from deck sheer line abeam the mast to the point of masthead/forestay intersection. (34 Ft = 10363mm)

J= Distance from foreside of mast to the point of intersection of the forestay with the deck. (11.5 Ft = 3505mm)

LP= Shortest distance between the clew and the luff of the genoa. (distance of line perpendicular from luff to clew).

A 100% LP sail is a right triangle that fills the area defined by I and J resulting in the base LP as follows (using math for right triangles)
LP(base) = I*J/Sqrt(I^2 + J^2) = 3320.2mm

Thus using values from class rules for max and min:
LP% max = 5665 / 3320.2 = 158.1%
LP% min = 5250 / 3320.2 = 170.2%

The new lower value would be:
LP% min = 5000 / 3320.2 = 150.6% (I had a typo above and said 151.6%)

I believe the class rules infer this definition because 163% is in the mid range of the specified parameters.

[This message has been edited by Rhapsody #348 (edited 10-21-2008).]

Well, I claim no particular expertise in the vagaries of PHRF, but a quick Google shows LP% as LP/J in: http://www.ussailing.org/phrf/fleetstart.asp http://www.ukhalsey.com/LearningCenter/encyclopedia/encyclopedia4b.asp

ISF's Equipment Rules of Sailing only define Luff Perpendicular. The referenced wiki uses the term 'foretriangle length' without definition. I understand your math, but what makes you think it's that complicated?

I'm an engineer. You'll need to check that question with my wife. I complicate everything :-)

In any case - whatever is decided, we probably ought to fix the LP% so they agree with the calculation used. LP/J is much easier to use!

I've added a spreadsheet with sail size calculations for other engineers to peruse

[This message has been edited by Rhapsody #348 (edited 10-22-2008).]

At the risk of broadening this topic just a bit ... the 163% probably is more detrimental to PHRF racing. that simple kick up over the 155% moves the trimmers job from OK physical shape to demanding physical shape. try to get fast and strong out of the typical crew pool featuring out-of-shape 9 to 5ers.

And consider how effective trying to detune the main with an oversize jenny compares with a nicely trimmed 155%/main and the crew limit on the rail. detuning main only works when all the other boats have to detune to the same extent. Which is a great way to justify an OD configuration from 1977. The OD configuration is overpowered ... and therefore only works well when every other boat racing is overpowered as well?

Also we "HAVE" to have a 163% to race OD which puts another handicap when the wind starts to hit say 15? My choice would be to get competitive Phrf wise and use that configuration for the NA. obivously not this year, but say two-three years from now.

given a choice the young kids want a Melges 24, or a J80 kind of boat. Lets reposition the OD to main stream instead of Odd ball.

Class rules state for the #1 genoa state:

5.12.5.1 The length of LP shall not exceed 5665 mm nor be less than 5250 mm.

The max is a 163% LP - minimum is closer to 155% (roughly, I didn't do the math). The 415mm range allowed within the rules is not insignificant.

So, if you want a smaller sail, it's allowable within the rules -though you would have to stick with the sail you start with throughout a regatta.

Interesting. the difference in Phrf is 3 between a 163 and ~155; But IS an OPTIONAL OD CHOICE at the OD Level? about a 2% difference? 3/138

At 10 kts the 163 is optimum and would be difficult for a skipper to want to handicap himself.

but what other elective options give us a 2% difference?
kevlar vs dacron Genny? ditto Main? ditto burnished bottom?
ditto oversized pole? ditto having an 18 lb stove allowance?

perhaps we should just extend the list of 2% performance options to mainsail fabric and let it sort itself out?

If we are looking at sail cost ... the fact that the class went to tech gennies was perhaps a more costly maintenance move than it would be to move to tech mains.

155 would last longer - the extra area on the 163 gets the crap beat out of it going around the shrouds and mast during tacks.

These boats are power hungry-those of us who race in light air most of the time would hate to lose the 163, I suspect.