On this page I will try to
compare some different boats. (2000)
And the polar curve of the Pogo is on the bottom. You look at sail area, displacement and so on, but how to compare yachts with different lengths ?

You have to make the numbers dimension less, sounds difficult but there are only a few formulas to be dealt with. I will follow the System International.

I will compare the Coco, Pogo, the Dyflex (93) and the Mills mini. For a more overall view the Geodis (Finot), the J 24 (Johnston) and a Whitbread 30, Simon Rogers designed are added.

Picture

The formulas used are;
Length ((m)/ Displacement (m3) = Lwl / ( Displacement ^1/3)Displacement in Ton. Sail Area (m2) / Displacement (m3) =100 % main + fore triangle (jib) / (displacement ^ 2/3)
Ballast Ratio= weight ballast / weight total (weight total = displacement x 1.024 (density sea water ))

These numbers do not tell everything and are not totally realistic, i.e. take the displacement; is it empty weight, half loaded or fully loaded displacement.In my humble opinion the Mini's are the most seaworthy dinghies there are, and the most dinghie like yachts.

In general men can say; that an increase in SA/D and a decrease in L/D results to a higher performance. But men must be aware that a Open 6m50 is sailed single-handed and that sail changes must be kept to a minimum and that course stability is a must, so that sleeping under spinnaker is possible.To sail with minimum resistance the Beam at Waterline (BWL) must be small and flat to surf well. With the now standard beamy hull and a small depth of the hull it looks like a skimming dish.

Still there is enough for the designers to play with. Shall the underwater shape be made for planing (Finot and Mills) or more shaped (radius) for waves. And what about the entrance at the bow and how it flows over in the rear ? etc.etc.etc.

Another aspect is the influence of water ballast;

In the table right you can see the difference when thePicture water ballast is added.I included the Whitbread 60 (oops, Volvo 60) design to compare with.You can see the decrease in Sail area Displacement and Length Displacement.
This gives the boats there ability to carry huge roached sails, over canvased in lighter weather when stability is less important.

Performance:

Minis are know to have sailed into the 20 knots, even 15 knots average for longer times and a daily run of 269 miles as the official record.They are designed for surfing, lightweight is an important factor.Every boat that sails will meet a resistance.When the boat speed induced wave averages the length of the waterline the resistance becomes larger. When the boat is able to overcome this resistance then planing starts. At more boat speed the resistance decreases as the hull is lifted out of the water.

It is continues planing with high speeds.To design a boat that can sail close hauled and has a good planing character is a difficult one. Modern boats has a flat bottom at the stern, a U shaped underwater profile at the bow (to carry a spinnaker) and the depth of the hull is shallow.

Polar curve of the Pogo;

polar diagramThis is a plot of the speed of the Pogo and three speeds of a Finot proto Mini. The speed of the Pogo is real measured with Gps and wind speedmeter. The Finot measurement was done on a prediction program (VPP).The speed difference is not big, could be the VPP used or the fact that the Pogo is a good designed, modern production boat.
Black lines are the speed of the Pogo, with mainsail and jib, and with spinnaker.In twelve knots of wind. True boatspeed.The red dots are speeds of a Finot design, made with a VPP.

The Pogo;

At 12 knots of wind it is capable of 7.5 knots. Not bad at all. Even close hauled the speed maintains a good 5.5 knot. Notice the gap of performance in running in front of the wind, to luff 30 degrees your speed increases more then a knot. Making your way to downwind target approx 6.3 knots instead of 5.95. So in this weather to stay gybing from 150 starboard to portside could pay of.
Under Main and Genoa the speed close hauled is greater then dead running.I really like the Pogo for his weight, speed and appearance.

On the site of Finot there are more results of the VPP, I only used the 12 knots wind so it could be plotted in this polar.