Technical query

Originally posted by Barty the coefficient for lift ahould be assumed relatively constant

Actually no. The coefficient of lift is proportional to the angle of attack (roughly speaking and up to to the point where seperation begins). See, for example http://www.allstar.fiu.edu/aero/lift_drag.htm

So one reason to move back in the boat is to increase the angle of attack, and hence Cl and hence lift. Unfortunately this also increases drag.

 

Originally posted by Barty   Its just maths for the masses

Unfortunately it is also wrong. Not "detail" wrong, or "second order effect" wrong but fundamentally wrong.

Calm down Children.

Look Barty, you must be aware that over simplistic sums create immense confusion. And that is an over simplistic formula - as you know in practice surface area is not a constant as it decreses as the boat lifts, and coeffient of lift varies hugely, probably close order of magnitude, on trim, on each wave, and probably nine dozen other factors. Then you also have aerodynamic lift from the rig (doesn't lift the bow, does lift the boat) aerodynamic lift perhaps even from the hull surface etc etc etc.

So what you have given is a formula that is technically correct and is relatively straightforward to understand, but practically useless and doesn't represent what really goes on. In the real world this stuff is very complex.

Agreed JimC but from an understanding point of view you have to start somewhere.  Sailing is a complex sport to understand and to succeed in knowledge transfer, you have to start somewhere.  From a coaching point of view, its all about building up the jigsaw piece by piece without getting to 'complex' at the start.  As a qualified naval architect, I am lucky to have been taught about the complexities of this subject over a number of years.  The majority of dinghy sailors haven't had this luxury and hence it is better to introduce a starting block from which to build on.

As for the rant, it just annoys me when someone just says 'your wrong at all levels' with no justification.

My posting on this subject is at an end, thank you and goodnight