Question by a newbi

[kkk]

I am currently designing a 4.9m racing catamaran. the cat has a tidy size main and a small jib. To find the center of effort I work out the area of the mainsail encluding the Large roach on the sail, then I devided the mainsail area by 2 and then simply found the centre of the mainsail by adding up the bottom section of the mainsail untill the area reached half of the mainsail area (including the roach) ----> is that correct? what do I do about the jib? - because sometimes the jib the jib won't be out when sailing. I understand that if you have a genao, you find the centre of the genao and then find the average distance between the center of the mainsail and the centre of the genao, then the final step would be to find the distance from the waterline to the center of the sails. but on my cat it has a very small jib and if you find the centre of the jib, the distance between the the center of the the jib to the center of the main sail is huge!
Can anyone out there give me some advice?

[Tim B]

See Lars Larsson and Rolf E Eliasson's book 'Principles of Yacht Design' you will find enlightenment therein

[Baycat]

My rough way would be as follows:- A very small jib (say 25% of main) will therefore only move your centre of effort forward by 25% of the distance between the centre of efforts of the two sails( from main towards jib).
Something to think about however is this small sail would make tacking a bit easier so perhaps you might consider using all the time.
Also consider what might be happening with your centre boards as these may need to have some ability to alter rake or area to maintain balance (you could alternatively look at changing rake of mast but that's another story!).
There might be something around on the "Mosquito" (Australian catamaran) - mark I & markII use same hull but change rigs from mainsail only to jib & main and are similiar size to yours ( but fairly old design now)
good luck