Chris, there are at least two schools of thought here:

One says that one should keep the boat so well balanced that the rudder is not needed to keep a straight course.

The other is the Chinese way of thinking which I share (and is used more and more in the West as well). Here the side forces are shared between the keel(s) and the rudder(s). To me the rudder is just another wing in the water, like fixed keels, centreboards and leeboards.

Any aerofoil or hydrofoil is held back by three types of drag; skin friction, form drag and induced drag, also called drag due to lift. As the need for lift at a certain speed increases, the foil will have to be set with a higher and higher angle of attack, AOA. That means increased leeway if the keel is struggling, or increased rudder angle in case of weather or lee helm. With increased AOA, the induced drag rises faster than the lift. If leeway or weather helm is a serious problem, then the permanent solution is to increase the size (better, draught) of the keel or rudder. As a result, they will produce the needed lift at a lower AOA, which means that the lift to drag ratio has been increased. The added skin friction due to the increased area is nothing compared to the reduced induced drag.

Paul’s bold modification has improved the rudder in three ways:

·         By moving the rudder further aft, its turning leverage has  been increased, so the actual load (lift) on it has been reduced.

·         The rudder blade has been made as a modern hydrofoil with high resistance to stalling and with end plates to cut wingtip loss.

·         By moving the rudder away from the hull, my hunch is that at least some of it will work in faster-moving water (as freestanding spade rudders do).

It is easy to be confused by ‘weather helm’. It may describe rudder angle or it may describe tiller forces. If Paul had just cured the high tiller forces by giving the rudder 20% balance, not much would have been won: If he were still sailing with 20° rudder angle, but with fingertip-light tiller, nothing would have been improved with respect to drag. However, I bet Paul can verify that the rudder angle has also been much reduced compared to on his original rudder. That is how he has cut the drag.

Arne

Arne Kverneland wrote:

Chris Gallienne wrote:

Arne Kverneland wrote:However, there is one more option: Build a much bigger rudder and fit it onto the transom....

PS: I hope you are not dragging the outboard engine in the water when sailing.

Arne

It seems to me that compensating for a badly balanced rig by increasing the size of the rudder is a poor solution. The rudder is effectively a brake, and increasing its resistance to the turning moment of the sail is also increasing its drag - probably to a larger degree than that of a typical outboard.

Chris

So why did the Chinese use the method on all their boats? As far as I know, that was how Paul cured the weather helm on his La Chica, as well
Arne

Yes, that is how I fixed La Chica's weather helm issues and took the opportunity to make it a correctly shaped airfoil section (NACA0015) at the same time. Both naval architects Angelo Lavranos and Robert Perry (both good friends) endorsed what I did. The change has been like day and night and La Chica has about as close as you can come to finger tip control for a heavy displacement double ender.

By the way, I'm planning to do some experiments this weekend by jury rigging my existing sail further forward and seeing what happens to the boat balance.  Slieve McGalliard suggested lashing down my yard by one panel to encourage the sail forward.  I can also shift my yard attachment; it's been a Dyneema lashing since my yard bail broke somewhere in the North Sea. The main problem will be the batten parrels, because the battens are hidden inside pockets for most of their lengths and I don't have a lot to tie them to. Anyway, I'll report back.

Arne Kverneland wrote:However, there is one more option: Build a much bigger rudder and fit it onto the transom....

PS: I hope you are not dragging the outboard engine in the water when sailing.

Arne

It seems to me that compensating for a badly balanced rig by increasing the size of the rudder is a poor solution. The rudder is effectively a brake, and increasing its resistance to the turning moment of the sail is also increasing its drag - probably to a larger degree than that of a typical outboard.

Chris

Richard Brooksby wrote:... So far I have collected these:

1. Extend the rig forward (e.g. Emmeléne's split rig)
2. Rake the mast forward (by moving the foot back)
3. Move the mast (usually into the front window)
   
4. Extend the rudder (as done on Ekaterini)
5. Extend the skeg forward

About the rudder: Chris Boxer mentioned to me that the rudder tangs on Corribees are a known weakness, as mentioned on the Unified Corribee site. He advised me to check my rudder for wobble. This means there may be a good reason to rebuild a Coromandel's rudder anyway.