Now if taking the brakes off by moving the rig forward a little has improved the performance, just think what might happen if you also pressed the accelerometer by adding some camber (drive) to the rig. Keep up the good work.

Cheers, Slieve.

Richard Brooksby wrote:

Do you think this gives another option for improving the Coromandel's balance: extending the skeg forward? It's an interesting thought. 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

I believe raking the mast is quite easy to achieve and will be trying it quite soon. I should be able to get 5°, which should bring the CoE forward by about 7m/2 × tan 5° ≅ 31cm.

As documented elsewhere 'Footprints' used to have very heavy weather helm, especially after the new camber panel sail was added. This has been largely cured by firstly raking the mast forward which removed probably a large part of the problem. I cannot remember the exact amount of rake but by moving the mast step back by 80mm the mast head moved forward by 500mm. Additionally when sailing off the wind the sail is allowed to move across the mast thus creating in effect a 'jib' portion of sail. By having long batten parrels I can move almost half the length of the boom across the mast. Moving the sail forward in this way can produce almost neutral helm when sailing off the wind.

Further improvements to steering were achieved with a new rudder several years ago. Key features of the new rudder are a doubling in balance area below the skeg, filling in the gap between the leading edge of the rudder and the skeg, and a proper foil shape to the rudder. The new rudder is actually smaller in area than the old rudder as 100mm was removed down the entire trailing edge of the rudder. 

 

Chris Gallienne wrote:

Yes, I realise it fixes a symptom: the need for a heavy hand on the tiller. But it hasn't fixed the problem - the rig is still out of balance and the rudder is still compensating for it to the same degree, and thereby causing extra drag.

The amount of weather helm is the same, you've just compensated for it more efficiently. 

The amount of drag caused by the rudder may or may not be significant - but sea water is 840 times more dense than air so 1 sq ft extra rudder dragged through the water may be equivalent to 850 sq ft of hull/superstructure dragged through the air.

Chris

Sorry Chris, a rudder is part of the lateral area. It does not matter whether that part moves or not. When I served my apprenticeship as a NA some Na's did not include the rudder in their calculations but I was taught otherwise and have always had good results.

Arne Kverneland wrote:

Michael,

that depends: If the boat makes some leeway when close-hauled, the skeg should also produce some side-forces and ease the load on the rudder. If the keel is efficient and produces its lift with little leeway, then the skeg should be of less help.

Anyway, an efficient rudder is needed to control the boat on a reach and run, and also in a seaway (with any rig). The increased skeg will increase course stability, but the rudder is still needed to compensate for asymmetric forces by the rig.

Arne

Arne

In light winds I can steer my Coromandel by sitting to lea or to windward hands off the tiller. As wind force increases so does helm, as the shape of the boat underwater changes with heel and this gives rise to weatherhelm. It seems to me that either moving the CE by moving the sail forward (shifting the mast) or moving the CLR aft ( a larger skeg or moving the rudder to the transom) will have the same effect. Boat heel is a thing which can only be stopped with a multihull!

Arne Kverneland wrote:

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

So, what do you think would be the effect (on rudder angle) of enlarging the skeg?