Aerodynamics 

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Our SmartRig is the best you can have on an ordinary sailboat. It is the most effective tool to utilize as the combination  wingmast – sail. ( The absolutely best is a solid wing but for practical reasons this is impossible to handle .) 

Since we first presented our rig we have been asked - many times - about the efficiency compared to an ordinary rig. Many people have declared that you sail better with two sails. They refer the so called slot effect , and the influence it makes to make the boat go faster – they suggest.

We are very puzzled by how unaware people are in this field. Some sailing enthusiasths still think that slot effect increases boat speed when in fact it decreases speed.

Let us start from the beginning. What is meant by the slot effect ?  The world is meant to say that an effect exists in the slot (space) between a foresail and a mainsail. When sailing into the wind. Someone has,  probably in the beginning of the 20^th century, come up with and got the message out that the air between the two sails should increase in speed  and by that give an effect to the mainsail which should increase the efficiency and make the boat sail faster. These statements, never proved, have after that lived on and are deeply rooted. To clarify what really happens let´s think logically and clear this up by using a few examples.

 At airports and on bridges we can see red and white cones showing the wind direction. Their shapes are tapered off and they are quite steady. Now, think of the misconception of the slot effect and let´s make a comparison. According to the statement the air inside these cones  should be compressed and increase in speed when passing through. Air should come out of aft end faster than the surrounding air. Of course  this is impossible  and can only be achieved if you place a fan in front of the opening . In the same way think of holding a funnel up against the wind. We have the same answer here – ther is no change in wind speed. Now, if we transfer this to sails we can simply state that the theory that the windspeed should accelerate between the sails is false - period.

 Let´s assume that the two sails are of equal size. If you use just the foresail the speed will of course be reduced, but the speed is comparatively rather good. On the other hand, if you sail with just the mainsail the speed will not be as good despite the same sailarea - why ? Well, back to logics again. The whole foresail is used properly but not the whole mainsail. In front of the mainsail we have the mast bringing bad air into the sail making this sail just partly acting properly.

Is there no advantage having two sails. Yes, there is a small advantage. When the wind is forced in between the narrowing space between the sails the excess air  has to go somewhere.

Some is forced in front of and around to the leeside. By that the foresail becomes more effective but – the total effect is very bad compared to our SmartRig.

If you sail with the two sails we know that we have to sheet in the mainsail in order to get rid of the bad air coming from the foresail. This also makes the mainsail less effective. We always aim to let the sails out as much as possible but here you have to do the opposite in order to create a perfect shape.

After having described the things which effect  an ordinary rig in a negative way let us know compare and look at the advantages of our rig.. Starting as above we begin with the first thing in contact with the wind – the mast (wingmast). It acts in the same way as the most effective sail on an ordinary rig – the foresail. Our mast has the best aerodynamically made shape there is.  It is on the leeside accompanied by a perfectly shaped sail helped by through battens in line with the leeside of the mast. On top of that the sail has a state of the art shape. By this we use the whole area – mast and sail as effectively as possible.  The mast is movable relative the tube inside the boom and forces this tube to move to the other side when tacking and by that you always have a perfectly shaped combination mast – sail.

As we are using the whole area to it´s full effect this means that we have a more effective area than that on an ordinary rig. When sailing into the wind we can also let our single sail out more than a mainsail of an ordinary rig and thereby increasing the efficiency even more. Everything is in our favour.

We have our prototype rig on an ordinary folkboat. The sailarea is 4 sq.m less than the ordinary and our mast has 3 sq.m “sailarea”. Despite this reduction we sail faster, especially when easing the sheet. We then have the same excellent sailshape as close hauled . An ordinary folkboat looses the good shape in the foresail when easing the sheets.

With our rig we have just one single sail. On a big boat this makes the sail quite large. To make it more handy we the suggest the big boat have two (or more) masts.  Of course this makes the boat slightly slower when close hauled but the boat will be easier to balance. When easing the sheets the two(or more) units will start working separately making the boat very speedy.

To be able to build a very high mast is one of the advantages. We have the very superior method of easy reefing (or actually adapting the size of the sail to the wind) by using the automatic “roller curtain”- method. Carbon fibre makes a light and strong mast and modern sails with through battens creates a big sail high up. May be we have to alter the size quite early – so what – it´s so easy. And the bare top still is an effective driving wing – no braking pole. As our help driving the boat in survival weather we use the bare mast. The folkboat has done close to four knots with the help of – the bare mast.   

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