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  #1  
Old 08-03-2017
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Steve Steve is offline
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Default PHRF sprit length

Help me out with a question.

As I understand it, the effective sprit length as measured from jib tack to end-of-sprit, should be SPL-J.

So in the case of a JC figure, does that change the effective sprit length.
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Old 08-04-2017
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Quote:
Originally Posted by Steve View Post
Help me out with a question.

As I understand it, the effective sprit length as measured from jib tack to end-of-sprit, should be SPL-J.

So in the case of a JC figure, does that change the effective sprit length.

No, not any more....

PHRF - BC rules http://www.bcsailing.bc.ca/pages/PHR...d%20170421.pdf

JC:As designed base of the spinnaker foretriangle. For boats designed with asymmetric
spinnakers JC is measured horizontally from the fore side of the mast to the point where the
tack of the spinnaker attaches to the deck or bowsprit. For boats designed with symmetric
spinnakers and conventional mast mounted spinnaker poles JC is measured from the fore
side of the mast to the extreme end of the spinnaker pole


SPL: Measured base of spinnaker foretriangle. For boats with asymmetric spinnakers SPL is
measured horizontally from fore side of the mast to the point where the tack of the spinnaker
attaches to the bowsprit or articulating pole in sailing position. For boats tacking an
asymmetric spinnaker to their bow stem fitting, anchor roller or pulpit SPL will be considered
equal to JC (SPL = JC). Extended anchor rollers will be considered bowsprits. For boats
with conventional mast mounted poles SPL is measured from the fore side of the mast to
the extreme end of the spinnaker pole. For boats racing with both symmetric and
asymmetric spinnakers SPL is measured for the largest spinnaker carried


The Measurement of Asym now takes in to account the G > JC x 1.8 just like a regular spinnaker calculation

SPINNAKER - A spinnaker has a mid girth equal to or greater than 75% of foot length.
SLU: Spinnaker Luff length measured from head to tack when stretched taut.*
SLE: Spinnaker Leach length measured from head to clew when stretched taut.*
SGM: Girth of spinnaker measured from the midpoint of the luff and leach with the spinnaker
stretched taut across the girth. Midgirth (SGM) will be at least 1.8*JC.
SGF: Foot length measured from tack to clew when stretched taut.
*For symmetric spinnakers SLU and SLE will be equal.


After a conversation with Snick the other night, It got me wondering if this rule now favors spinnaker's projected area over Sail area.
In that the on water results for the given rating would favor an under sized asym on a standard articulating pole on the mast. (Rather then a larger asym on sprit)

So much for keeping the boats with Asyms simple

Geeks check this out http://www.research.ed.ac.uk/portal/..._2009IJSCT.pdf

Last edited by Blackice; 08-04-2017 at 10:14 AM.
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Old 08-04-2017
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Disclaimer: as a long time crew member and not a boat owner, I've mostly ignored the rules of PHRF measurement and focused more on just sailing fast. So despite racing in PHRF for all these years, this is pretty much new to me.

So tell me if I'm missing something here:

Boat A is 40 feet, has a J of 15 feet, but has a one-design symmetrical pole length of 20 feet. This might be an extreme example, but I'm exaggerating for demonstration purposes. The one design boat has a rating based on the JC of 20', or 5' longer than J.

Boat B is the exact same boat, but ditches the symmetric spin and mounts a fixed sprit for an A-kite. Does boat B get a penalty, relative to Boat A's rating, for a sprit longer than J? Does that make sense when Boat A has a 20 foot pole?
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Old 08-08-2017
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Do not use logic when it comes to discussions about ratings

Ok, so not many production boats would have a spinnaker pole that is 5 feet over J, but sure what the hell...

If a production boat A comes with a regular spinnaker pole and boat B wants to convert to a bow pole and Asym, they would receive a 6 point credit for the change from articulating pole to non articulating bow pole.
(The powers at be decided that loss of an articulating pole would slow the boat down, equal to a 6 points.

The old PHRF BC rule had an additional penalty, in that you would get hit 3 secs for every foot of bow pole that you added to J plus 1 foot. (The first foot was free) So if you add a 3 foot bow pole you would take a 6 point hit. (Not sure how 3 foot of bow pole is as quick as a articulating pole down wind, but there you have it)

The New rules have switched to a JC x 1.8 rule, in which the bow pole can be as long as you like, but the calculation of sail area will take that pole length in to account. So if your JC is 15 feet, your asym would need to have a mid girth of 27 feet or greater. ( Any girth smaller than this would be the same rating hit, as the bow pole would hold that mid girth at JCX1.8, or in this case 27 feet.

Then it just comes down to sail area, efficiency of projected area, efficiency of the sectional shape of the sail and the boats weight. Asyms really only start working like a foil at angles smaller than 130* AWA, there is some stalled out angles that can work at higher wind speeds, but for argument sakes, 130* is about as low as an Aysm can sail before it gives up too much VS the same sail area in a sym spinnaker. (Assuming square courses) See attached polar chart.

So under current PHRF BC rules, the bow pole its self does not penalize you more than a Symmetrical sail of the same size, but due to the limits of the fix on center line bow pole the AWA limits of an Asym, will all really hurt heavier boats with Asymmetrical sails more. (limited boat speed potential - can not dig down wind to save distance sailed)
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