[RichH]

OK maybe this is a simplistic question but:

Scenario :

Beat to windward in a Force 3-4, flatish water, standard production 21st century cruiser/racer fractionally rigged

Dilemma:

If you have a choice between an overlapping 120% genoa sheeted around the shroud or a smaller say 100% blade jib sheeted to barber haulers inside the shroud.

Lets assume the blade will get you close to the speed the polar diagram predicts. Will you get anything more from the 120% genoa ?

Which do you go for ?

On a frac rig, most probably the blade will result in a faster sail plan output .... and enhanced pointing ability.

Reason: a blade 'can' be sheated INSIDE of the shrouds and without fouling on the spreaders .... and can be more easily adjusted to the defining 'slot open' distance. In F3-4 that 'attack angle' (tack to clew) is probably going to be somewhere on that 10° line offset from the tack.

If the 120 fouls with the spreader .... "no soup for you !"

Of course, you yourself have to do 'trials' with reference to correct 'slot open distance' vs. VMG once you get close to your final decision. When youre in this final stage of optimization, forget any so-called backwinding to the main ... simply finalize your plan based on speedo output and VMG.

 

[RichH]

Its pretty clear that any race boats, not constrained by class or formula rules to a non-overlapping headsail, use the largest genoas permitted by the wind strength.

In a serious race fleet beating to a windward mark in under 18 MPH wind speed, it is unlikely to be a single boat not flying a 150%, other than those boats whose rating/formula/class choses to exclude more powerful headsails. Maybe the more tender boats actually will drop to a 130%...

Thats not the current trend in maxis and other top class boats, especially with frac. rigs with square top mains, etc. The 'trend' is definitely going towards blades instead of large LP overlappers on FRAC rigs.

With mast head boats the only way you can adequately use a large LP is to shorten up the spreader length and usually to keep it inside that 10° tack-clew line.

Many of the one design fleets and 'development classes' are doing the same ...

 

[RichH]

Simply look at JeffH's avatar ....

Youll notice immediately that the leech of the jib is (for the most part) operating in close proximity and 'just before' to the 'point of maximum draft' (POMB) in the main. What this positioning of jib's leech to POMB of the main is doing is yielding maximum 'bootstrapping' of two sails or which affects the best 'dumping velocity' from the jib to the main ... for maximum interaction flow between the two sails. Once the jib leech overlaps beyond or aft of the POMB of the main, aero-efficiency of the combo will start to rapidly decline .... although one can 'muscle' more speed (but not necessarily more 'lift' in direct proportion to the increase in SA) by increasing SA with a larger overlap.

I perceive this configuration is why the 'modern' frac rigs are generally carrying a lower LP jib and rarely a large LP jib ... for the combo of best boat speed AND pointing ability irrespective of 'sail area' considerations alone, ... also ignoring the geometry problems associated with sheeting angles on large headsails.

Whether this config. was determined aerodynamically or simply iterated by trial and error, it 'seems' to be in accordance with that which theoretically generates maximum aerodynamic conditions and output.

 

[RichH]

IMHO, self-tackers without a boom are pretty much useless, but I'm not expecting anyone to share my small thought on the matter.

Totally agree you. Without a (vanged) 'boom' or clubfoot there is no effective way to control 'twist' when the clew is outboard. This is usually always seen especially on cutter rigs with only staysl and reefed main flying ... without a means to prevent the clew from rising, the upper panels of the stay'sl will be unattached to airstream flow/stalling, the foot overtrimmed and only a small zone of the middle part of the sail 'actually' working ..... same thing with almost ANY jib when the clew is well outboard. Even with fore/aft fairlead, etc. adjustment, etc. to control clew height ... with a sans 'boom' arrangement the jib will 'naturally' become deeper drafted .... more powerful but 'slower' when the clew is well 'outboard'. FLAT is faster in most conditions (in relatively flat water, etc.)

In the olden days before the 'rules changes' ... a reaching strut or jockey pole was used to help control the 'clew rise'. The Hoyt Boom in this respect is perhaps the best way to do this ... but unfortunately is impossible to apply to an 'overlapping' jib/genoa.
;-)

 

[RichH]

ahhhhhh .... leech timing to perfection.

;-)