Sep 18, 2013

Cirrus R F18 -> TNZAC72: Trickle UP

Beyond all the other key parameters in the AC72, (Foils & Wings...) I always look hulls in more detail, as I've been drawing hundreds of cads since 2005 when I draw my first lines while at the office that ended being the F18 that launched the class here in Arg.
The F18 is still and will be floating mode for years to come so hull design is still king (I proved you that in the AC72 too, with TNZ 40knots pitch & tack handling) . When NZ AC72 was first launched I noticed an extreme rocker line resembling the also radical bottom of the Cirrus R. First glance at "Trickle Up" here.

I made some skecthes to compare finally their bottom lines, with an scaled down TNZ AC72 and without much surprise their rockers matched almost to the mm. This is just a sign of the good work done by Manu Boulogne while going for those features. The Cirrus as mentioned on Monday is one of the new performers in the F18. The Cirrus though has a flatter cross section.

While doing the F18OP I wondered how this extreme concave/negative sections fore & aft would affect their floating performance upwind, doing the CFD tests I started with a standard progressive rocker, to have a proven base (Infusion/C2). After the tests Ronan Currid recommended to apply a negative section aft (Present in the Wildcat, Cirrus R, Phantom and others) to reduce wake. For the fore concave modification I wanted to see how TNZ performed upwind,  and it is clear these features didn´t hold back NZ in any away beyond their lift power provided by the foils.

Check Cirrus R label for previous pics comparisons.
For TNZ the scaled version down gives you a too lower freeboard, so I assigned the typical modern F18 height, width I left it proportional to follow height and matched current F18 designs range too. No control point was modified in anyway from my last TNZ 22mts version.
Will post more next weeks.