Sails on Wyliecat 30's in 2010 SHTP and PacCup

[jfoster]

I was musing about the successes of the only Wyliecat 30's in each of this year's SHTP and PacCup. This morning I ran across a posting on the Nonsuch user group list by "Jon Fitch" <jfitch@FLASH.NET> Jon has a rather rare Nonsuch model of a cat rigged ketch, something like the Wyliecat 65 in concept. http://yachtanomaly.blogspot.com/201...edit-just.html

If you think his thoughts about sail performance are "Anomalous" check out the picture on his blog of

The transom of Anomaly opens to the dinghy garage, and the dinghy rolls out and is launched from the door.

For me, all this explains a lot. Any thoughts about this his explanation of sail performance or his dinghy garage?

John Foster
Nonsuch 22 Blueberry sail #48

What the cat main has in common with a genoa is sheeting angle. A genoa is generally sheeted to the rail, or somewhere around 12-15 degrees to the boat centerline - the same as a Nonsuch main. The mainsail on a sloop operates in the downwash of the genoa and must be trimmed closer as a result. In the upwind condition it is really the trailing edge of a single airfoil with a slot, the genoa acts as the leading edge. Slotted airfoils generate greater lift than unslotted ones, at the expense of greater drag.

While much is made of the disturbance of the mast on the mainsail, it may have less effect than most assume. Several wind tunnel tests on the subject by Marchaj and people of that ilk show significant reductions in maximum lift - but these tests are typically done with very large mast sections, from 7% to 15% of sail chord. On a cat boat the sail chord is typically quite large, and so on a Nonsuch 30 the mast diameter is less than 4% of the sail chord. This is not aerodynamically insignificant, but (extrapolating trends in the test results) probably results in less than a 5% reduction in maximum lift in ordinary conditions (very light wind has a unique set of problems). On the other hand a sloop suffers great loss of efficiency at any wind angle greater than a close reach as demonstrated both in the wind tunnel and practically on the water. The 5% loss of lift on the cat is easily made up by a 5% increase in sail plan, the loss in efficiency off the wind by the sloop is unrecoverable without a large inventory of special sails and the crew to handle them. That seems a poor compromise. A sloop is really only a good rig upwind in underpowered conditions. An unstayed cat rig has consistent efficiency over a wide range of angles since its aerodynamics do not change from close hauled to a broad reach, nor does the trim required (to the wind). Over the same range of angles a sloop goes through three dramatically different phases: from a slotted airfoil, to an inefficient biplane, to a stalled biplane. These are the reasons why in development classes which are free to choose their rig (such as A and C class catamarans) sloops became uncompetitive nearly half a century ago compared to the cat rigs that replaced them.

A boom or wishbone serve the same purpose: to locate a point in space to which the clew is tensioned. The results on a perfectly trimmed sail ought to be identical though the means of achieving it differ. The wishbone offers semi-automatic balance between outhaul and downhaul forces, at the expense of the inability to adjust the ratio (and therefore sail twist); the boom offers more adjustability at the expense of more controls and attention required. Recent sail building techniques and materials have simplified this: the very stiff full battens and string construction of Anomaly's mainsail eliminate the need for routine adjustment of the outhaul, and it is in fact fixed and not routinely adjusted. This leaves only the sheet and vang, vs. the sheet and choker on the wishbone. I think 'Anomaly' is a better boat with the boom vs. a wishbone - but I am not absolutely sure of it. Each has its merits and demerits, and is therefore a compromise.

Jon Fitch
'Anomaly'
Currently lying Port de Quebec

[BobJ]

"On the other hand a sloop suffers great loss of efficiency at any wind angle greater than a close reach as demonstrated both in the wind tunnel and practically on the water."

"...the loss in efficiency off the wind by the sloop is unrecoverable without a large inventory of special sails and the crew to handle them. That seems a poor compromise. A sloop is really only a good rig upwind in underpowered conditions."

I dunno about all that - I'd be curious to know what data he has to back up his opinions. Moreover, I like my "large inventory of special sails" which allow me to tailor my sailplan to the point of sail and wind speed.

That said, it's a smart-looking boat -dinghy garage and all.

[jfoster]

Originally Posted by BobJ

"SNIP I like my "large inventory of special sails" which allow me to tailor my sailplan to the point of sail and wind speed. SNIP.

The sailing techniques of single sailed racing boats with unstayed masts has really evolved. For example,read the article about John Bertrand coming back to Laser sailing in http://www.sailingworld.com/experts/the-master-returns

What downwind techniques is this new generation using?
The current vang and outhaul systems really open up a different technique, a lot of different styles. We used to set the vang, and that was it. That led to one style of sailing downwind. But now, on any particular run, you can have any one of maybe four or five different styles of sailing. You can sail by the lee, and the transition between what they call “regular flow” and sailing by the lee is now really critical

As a personal example, I had Ryan Nelson, a guy fighting his way up the Laser sailing ladder near the top, driving my Nonsuch 22 Blueberry in a OYC beer can race a month or so ago. His sail trim and tactical skills were so far ahead of my own usual performance that my usual nemesis accosted me, with a huge grin, in the Oakland Yacht Club after the race about having a rock star aboard.

Not sure if I can master sailing Blueberry by the lee downwind, but I sure am going to try and move my sailing skills, somewhat, into the 21st century like those guys coming up.

Oh yeah, one more thing, the last time I was on an aircraft with wires on the wings was in 1938 when one of my mom's boyfriends took us up for a spin.

Things change. Try to cope (grin).

John