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BOARD DATA

The camber/slopes steps for sailboards function like a step at fast planing speeds but are unlike any other step in both how they look and how they function as steps. This is because they have almost no wave or turbulence drag unlike other vented or un-vented sailboard steps.  They have the following demonstrated properties:
(see the following figs.).
 
1) A board with these camber/slopes plane at the same force as the same board without the camber/slope
(fig. 6 series 1 vs. 2)

2) At higher planing speeds the board has less drag, 15-30 %, and faster speed
(figs. 5-7 and sailing data).

3) Because of 1) these camber/slope steps can be placed further forward which allows the board to plane at a more optimum angle at higher speeds and results in 2).

4) The camber/slope steps are designed to prevent ventilation of the fin.

5) Sailboards can now be designed with a wider back yet at high speed will have a narrower back planing
surface.

Figures

Figure 5 shows drag data of a sailboard obtained with 170 pound person on a 76 cm wide board. The board with a 40 cm True Ames SB weed fin was being towed by a boat with the person adjusting his position to obtain the lowest drag for a given speed. However, the person did not move behind the sailing position for a sailboarder in the foot straps so as to simulate only the position for the center of gravity of a sailboard and sailboarder of 200 pounds total. The series 1 data is for a normal prior art ventilated step 35cm from the end of the board, an average of 9 cm wide and 2 cm deep on each side of the back part of the board. This data show that it
took 40.5 lbs of force and a speed of 10 mph to get the board to plane and 36 poundat a speed of 14-16 mph which was the minimum planing force for this series.

 fig5resized0002
(click to enlarge)
 
Series 2 was for camber/slope steps, again 35cm long, an average of 9 cm wide, depth of 0.3 cm 5 cm behind the step and depth of about 0.6-0.8 cm at the end of the board. For this camber/slope step, the board transitions to planing at 7.4 mph and only 29.7 pounds of force. Yet at the high speed planing of 14 to 22 mph the force was the same or possibly slightly less. These series 1 and 2 show that the camber/slope step has lift behind the camber/slope step to get the board to plane at both less drag force and lower board transition speed. Yet at higher speed it reduced the planing area behind the steps as effectively as the theoretical operation of a
normal step including a vertical surface.  Note that there was a 20 to 25% reduction in the drag force at transition speed even though the step area represents only about 10% of the board planing area. This could be due to the rocker in this board or the wave and turbulence drag behind the normal step with a vertical 2 cm depth.
 
Figure 6 shows drag data for no camber/slope step as shown in series 1 and a camber/slope step with a camber/ cup of about 2 mm shown in series 2. This drag data was obtained with 170 pound person on a 98 cm wide sailboard, which had two 39 cm True Ames shallow weed fins. Again the person adjusted the board angle by moving where a sailor would move while being pulled by a boat.
 
(click to enlarge)

One can see that this 98 cm sailboard loses its wave drag at 6.0 mph due to its winglets (see US 2003/0003825 A1) not discuss here. All data series show essentially the same drag, within experimental error, from 6-8 mph. Starting at about 9 mph of board speed, the series 2 & 3 data show less drag.  At 15 mph the series 2 drag is about 20% less than the series 1 data with no camber/slope step.
 
Series 3 is for the camber/slope step at 45 cm from the end of the board with a camber/cup depth of 6mm. These data show 30% less drag for board speeds of 12-19 mph from that of no camber/slope step and up to 20-25% less than series 2 data. This is because of the increased lift in front of the camber/slope step, due to the increased camber , allows the board to sail at a more optimum attack
angle, which has greater lift/drag. The increase in drag in the series 3 data from 10 to 19 mph is less than the increase of drag on the two fins between these speeds,
while above 19mph the major increase may be due to a decrease in attack angle o.  
 
Figure 7 shows drag data for the 66 cm wide sailboard with a 35 cm Select Eagle fin. Series 1 data is for this board with prior art vented steps similar to those on an “F2 Slalom” sailboard with an average distance from the back of the board of roughly 30 cm. Series 2 data is for an camber/slope step with a cup depth of 6 mm made from two layers is 3 mm Divinycell under the fiber glass skin, which were 45 cm from the end of the board. The series 2 data again show less drag at the transition speed even though the step is further form the end of the board. More important above 13 mph board speed, where the surface behind the step dewets, the drag is almost flat
to the top speed tested, of 28 mph. This is due to both the camber in front of the step and the step location, and is also due to a cusp extending from the end of the camber to the end of the board, which is to prevent the vortex flow, from the region near the fin, from wetting the area behind the camber/slope step at higher planing speed.  

(click to enlarge)


 



 
 
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