Re: [Sailcut-users] Help on saildesign / drifter for 18ft cruiser

[Robert L. <rob...@sa...>]

On Sunday 06 April 2008 14:57, Florent Renaudin wrote:
> Dear all,
>
> I've got a french Beneteau First 18, a small 18 feet day cruiser; very good
> boat, except for very light airs (as it is a little bit heavy-800kg)
>
> So, I plan to make a very big nylon headsail to play with winds strictly <4
> kn, like a big drifter or code 0 sails.
> * For the sail dimensions (luff, foot & leech), I took almost the maximum
> values minus 200-300 millimetters
> * For the rounds :
> -1% luff
> -1% leech
> + 5% feet
> Is this first step correct ? I'd rather take a lower leech ?
>
> I have measured the expected sheeting angle on my boat (around 9°) and I
> modified the twist angle to 8° to "better keep the wind", as I plan to use
> the sail only in light winds (Sailcut is initialized with an angle of 18°
> for headsails). But I'm really not sure about my correction ! For the same
> reasons, I have also modified the bottom profile with a higher deepth (2%
> changed to 5%). So now, the mold is top to bottom : 6%,8%,5%
>
> Do you think I am the right way ?
> Any comments are welcome, as I was unable to find reliable(or not)
> informations on existing litterature about this kind of sails !
>
> Best Regards,
> Florent
> http://first18.over-blog.fr/

Florent,
Thank you for the feedback that printing work on your Vista+brother printer.
It helps to know that it works also for others.

Apart for the luff length which has to take into account the length of the 
shackle at both end, for foot and leech there is no need to remove 200mm for 
the maximum, it loose area.

The twist angle of 8 degree will be very small for light wind and as you will 
ease the sheet the top may fall over to leeward.
Increasing the foot depth is OK BUT having only 8% in the middle and 6% at the 
top is very flat! A good rule of thumb for light conditions is to put more at 
the top than in the middle and more in the middle than at the foot. Reason is 
that when light, there is much more wind up than down on deck and you need to 
go for power more than fine pointing. It is also the reason for keeping a 
high twist. 
With nylon sailcloth, do not forget to increase the leech factor of the upper 
and middle mould profiles to stabilise the leech. 

-- 
   Regards / Amitiés
     Robert Lainé
http://www.sailcut.com   Free CAD for sails and hull
http://sailcut.sourceforge.net  GPL source code
----