Revamping one designs: your experiance

How will the square top design to deliver the same performance as a standard?

Technical Response:

It can’t deliver the exact same performance in the same way - as having some span width at the head can change the downwash angle (depending on applied depth and twist). They can be made to perform in similar manner depending on set up. A narrow headed main sail will have little or no attached flow near the head (the span width is too narrow) so this part of the sail is nearly always "form drag" with little or no lift. I imagine the vortex rollup is at the head but can’t say for sure. I would estimate the roll up will only move down if the head produces up-wash (negative lift). A square top should be able to get a more efficient L/D ratio. As both sails area are similar and the luff length is the same the form drag on both will be the same (perhaps a little worse on the square head as the head sits in faster moving are stream compared to the bottom and form drag goes up with wind speed squared).

Simple Response:

All this tells us is what we already know - it’s likely the square top will be better in underpowered conditions and the narrow head in over powered conditions. But as the total sail area is the same and the span height is the same there should be little difference overall as we have witnessed to date.

How will we ensure that the current crew weight to performance ratio is maintained?

Sail area is the same - span height is the same - equates to same weight to sail performance.

Why do we not need a new rig for the RS200 such as lowers with the Square top configuration?

Sail area is the same. Span height is the same so the load on the mast will be the same. OK so the top 10% of the rig has a little more area and the mid span is a little narrower so we change the load distribution a little

We only need a new rig if the head won’t stand (top mast is too soft to take the load) but there is no evidence of this in testing. In fact the early iteration sails stand up too much (won’t washout) indicating either the sail is too full or the mast too stiff.

Isn't a square top just the current fashion accessory? Does it have longevity?

See question 1 - They are closer to producing an elliptical load distribution and constant downwash angle = most efficient L/D. (Although sails rarely operate with an elliptical span due to too much wash out (twist)). When over powered we are probably getting a small up-wash at the head so span load is defiantly not elliptical. A tip with little more than zero span width (girth) will never have attached flow. So narrow head sails like jibs and older design restricted sails carry the top part of the sail only to support what’s underneath. So if you can support what underneath without carrying the bit above you would have much improved L/D.

Is there likely to be more loading on the rig with a Square top?

We are confident that this will not be an issue - when it’s washed out completely little or no difference - when its carrying a full aero load yes but as the mid sail will be carrying a little less load so based on the span load distribution calculation we are within tolerance.

As a female helm will I not find it harder to play the main?

Technical Response:

Same area / same span length - the head of the sail is carrying more load; the middle less. However once we have zero AOA at the head the aero load drops away but form drag is higher — but you can argue the square top is closer zero L/D max more of the time …….

Simple Response:

Based on the testing conducted to date we have not encountered any increased loading with the square top from female helms.