14 technology - part 2

Today we look at the latest in foil developments

To read part one of this article - click here

Foils

At present no one seems to have taken the development of daggerboard foils further, but current thinking suggests that you are nowhere unless your 14ft beast has some form of T-foil arrangement on the rudder.

Following on from Bieker's experiments at past World Championships, there was some home-grown development mostly using the skegs from windsurfers. Today, as with hull development, foil technology mostly falls into the Beiker or Morrison (more accurately Richard Woof) camps.



T-foils - Variations on a theme...

The Morrison arrangement last year had the T-foil at the bottom of the rudder, the theory being that this provided an endplate effect for the rudder. However on this year's incarnation it has moved half way up the rudder like the Beiker arrangement.

"We’ve stopped using them at the bottom because the boat is narrow and you do sail it at angle of heel occasionally. With the foils at the bottom they tend to capsize the boat. They are just further down and have a bigger lever arm to work on," explains Richard Woof.

The standard foil shapes are slightly different. The latest Morrison ones have a bigger span and narrower cord, while the Biekers tend to have a slightly greater cord and come in symmetrical sections or a smart looking asymmetric type, vaguely ressembling the shape of a whale tail.



Above: Chris Turner's Bieker T-foil

Most significant of the differences between the two types is the mechanism used to alter the pitch of the T-foil. On the Bieker the T-foil moves relative to the rudder thanks to two long rods that run down the inside of the rudder. One is spring loaded and attached to a lever at the top of the rudder. The spring mechanism keeps the foil in the neutral or negative position while cranking down on the lever applies positive pitch to the foil. A downhaul is attached to the end of the lever and this runs forward up the boat to a double ended purchase and from there out to the racks where the helm can trim the foil.
The rods running down through the rudder have a thread and so can be wound in or out to fine tune the degree by which the foil operates.



The latest Morrison/Woof system has a T-foil rigidly bonded to the rudder. The pitch of the T-foil is altered by pivoting the entire rudder blade relative to the boat using a type of slack gudgeon and pintle system. The advantage of this system says Richard Woof is that the foil is fixed to the rudder and no internal mechanism is required, hence foils with a thinner cord and therefore lower drag can be used. The rudder is kept in its default position by bungy running forward along the bottom of the cockpit.

"The stock is rocked by the interference of a metal plunger in a socket on to the rudder axis which pushes it aft in a slot," explains Woof of the detail of the inclining mechanism. "That’s operated by a small cascade in the floor of the boat through a flip-flop block. It is very simple and easy to graduate."

The latest Morrison foil is 1.1m wide, narrow and very thin. "There are practical limitations," says Woof of the size of the foil. "The boat is quite narrow and there are certain points of sail where it is impossible to sail the boat flat. And at that angle of heel, the T-foil breaks surface. We’ve seen it looking back at us!



T-foil arrangement on Andy Partington's Morrison 11

"We’ve tried some innovations this year with an upside down Y foil. It was fantastically efficient but as soon you put any angle of heel on the boat it felt that there was somebody on the leeward rack trying to pull us in." However he adds that the 11 is just an interim step and there is more development in the pipeline...

Another variable is how much pitch can be applied to the foils. The amount required obviously depends upon the area of the foil and the larger area of the Morrison foils suggests they need less pitch. Richard Woof says their foils can be varied by around 5 degrees - 1.5-2 degrees of negative (ie pushing the stern down) and 3-3.5 of positive (ie providing lift).

The Bieker foils can have as much as 10 degrees of pitch applied to them. Again the foils can be set to either lift or sink the stern, biased towards the former.


How the foils are used

Asking those sailing the 14s how they use their T-foils the answers vary greatly, although this is also due to the variation in the set-ups from boat to boat.

In theory there is a maximum amount of lift you are ever likely to need. "You don’t increasingly want more of it," confirms Richard Woof. "It is only 14ft long and you need to maintain a certain amount of equilibrium in the boat!"

Considering that the lift generated by the foil increases as the boat goes faster then less foil should be needed in windier conditions. Equally somewhere at the bottom end of the wind range there should come a point when the foil will be creating more drag than lift and should be neutralised.

In our brief poll of 14 sailors there seemed to be a small degree of "new toy - will use". So the slab-handed are tending to wang it on most of the time, conditions be damned.

Conversely "as it gets windier we use less of it," says Zeb Elliott of his Bieker 4 foil. "In light winds we use it pretty much all the way round the track. When it's full foam up we tend to ease it back. It's really upwind that makes the difference."

"4 degrees - just to stop the pitching," says POW winner Rob Greenhalgh of how he uses it on his Morrison. "We normally have it off downwind to stop us going down the mine!" Woof counters this saying that downwind in light conditions it is appropriate to use a small amount of T-foil lift to reduce the wetted surface area of the boat.

Even if there are variations on how the T-foils are used, what is certain is that they have a definite effect and have improved performance. They dampen the boat's pitching. This stabilises the air flow over the rig, increasing the efficiency of the sailplan. Adding stability also makes it easier for the helm to trapeze in awkward conditions and as mentioned yesterday they have made the narrower more slab-sided Biekers easier to sail.

Most profound is how T-foils have dramatically altered the way 14s are sailed upwind. With the T-foil developing lift the crew now can trapeze from the back footstraps while sailing upwind with the boat sailing almost on its T-foil alone (see the photo at the bottom of this page).



It moves! (If it doesn't move - click to refresh) This is a variation on the Morrison theme

For all their bonuses a side-effect of the foils is what happens to them when the boat heels. Generally heeling the boat causes the T-foil to increase the amount of helm. While this could be seen as a downside, Dave Spragg says that this accentuation of the helm gives the boat much more feel and makes it more obvious when you are not sailing it right. It is also felt that this feature has made it easier to get the boats to turn corners. Being relatively weight-less 14s are similar to catamarans in stopping dead during tacks.

In our poll we didn't speak to anyone who has applied negative lift to their foils, although all the foil arrangement seem set up to offer this. The only occasion it is felt you would want to sink the stern would be to help keep the bow out of the water blast reaching in big conditions.

Aside from the bit in the water, future developments are in hand to improve the controlling mechanism for the T-foil. One neat development is the prospect of being able to control T-foil pitch using a motorcycle-style twist grip fitted to each tiller.

Tomorrow we look at the latest developments above the deck and what lies in store for the International 14 class