Tricks and Tweaks - Part 2 - The Devil in the Detail
Establishing the fundamental balance of power between the rig and the under water section and foils has occupied several thousand man-hours of research time by America’s Cup designers, but at this stage the technical development is only part way through. Creating a balanced boat is one thing, refining every detail quite another. With so much more knowledge and data now available to smaller teams, gaining an advantage can often rely on getting the detail right.
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Here, during the build up to the 32nd America's Cup there has been a great deal of work and a wide variety of ideas.
Bat-wings
While inflatable battens go a long way to supporting the huge overlapping genoa leeches, the upper spreaders and their 'bat-wings' or 'flippers' as they are commonly known also help to support the leech of the sail when sailing upwind. When the boat is sailing downwind the bat wings flip up to prevent their ends bursting through the mainsail once it is fully eased.
But more recent bat wing systems have become even more complex. Several teams have developed systems that force the leeward bat wing profile outboard in order to open up the slot between the head of the genoa and the luff of the mainsail on its leeward side, in order to improve the air flow through this gap.
The system works by having a bat wing profile that sits around the outside of the top spreader. A block and tackle system led down to the deck can then be used to move the batwing outboard.
Jumpers…
Two kinds of jumpers
Further up the mast jumper struts and their stays are popular areas for development. The primary role of the jumper struts and its stays is to support the top mast, both laterally and in the fore and aft directions. Changing the fore and aft angle that the jumpers are set at alters the amount of bend in the top mast which in turn changes the leech profile of the mainsail.
Clearly the ability to be able to swing jumper struts fore and aft is important, but the new style overlapping headsails have made this requirement even more crucial.
In order to sheet the headsail fully home, the leeward jumper strut needs to be cranked aft to move the leeward jumper stay aft and keep it from fouling the genoa leech.
And no jumpers at all…
All of which adds to the workload of the crew through a tack where the bat wings and jumper struts now need to be trimmed every time the boat's bow goes through the wind. This in turn has led some to experiment with what appears to be an even more radical approach. No jumpers at all.
A boat without jumpers - BMW ORACLE Racing (USA 87) - Valencia Louis Vuitton Act 11
Eliminating the jumper struts and stays not only reduces the complexity of the rig, but reduces weight and windage at the top of the mast. Given that the class rules state a minimum weight and centre of gravity position that few have difficulty in achieving on masts fitted with jumpers, the main advantages would appear to be in reducing the windage and complexity. Yet the flip side is that the mast design and build, especially that of the top mast, has to be precise in order to support the mainsail leech correctly. Too little stiffness and the mainsail will de-power too early, too much and the sail could create excess drag.
Reducing the complexity, weight and windage in the rig has meant dispensing with topmast backstays for some teams. Among those to go topless last season were BMW Oracle, Emirates Team New Zealand and Luna Rossa, each of whom raced regularly with just running backstays and checkstays. Again, keeping control of the topmast through careful spar design is the key to making this configuration work.
These are the main changes up on the rig, but lower down, there are plenty of refinements and experiments taking place as well, from lattice booms to mast rake adjustments. But that’s another story…
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