This has been a slow progression over 20 months of trial and error. Constantly trying to find the one magic thing to make the boat faster and eaiser to handle.
What I was doing was changing too many things at once and never really understanding what to expect. I spoke to an experienced ex hobie tiger sailor and now Nacra guy and his comments where the most telling. He sets his boat up the same way no matter what. Rake & pre-bend, only varing the rotater and obiviously downhaul.
What I needed to do is understand what the sails are trying to do and how the centreboards and sails work together.
The Jib curves/deflects
the airflow and leebows the main, hence the lower section of the main has to be set to match this deflected airflow from jib. However the mainsail above the jib has the airflow hitting at the same entry angle as the jib (say 45 deg versus 30 deg). Therefore the main must be able to twist off to leeward to match this.
First, the most important thing is to set the mainsail to match the expected airflow.
The 4 main leech tell tales 'tell the tale' and the top one tells the most important tale, expecially in light to moderate air.
2nd in light air run the main loose
and keep the top from hooking. This may require some light downhaul to flatten the top a bit.
As the airflow increases the sail will naturally be forced to leeward, however if the main is pulled on hard without matching downhaul the top will be still hooked to windward - this results in an un-balanced sail plan and the boat will be overpowered, literally the breeze is pushing the top of the mainsail away from the centre line of the boat - and then you fly a hull.
Think about what the sails are physically doing - and then relate that to what you are experiencing on the water. The main twists the boat to windward as the action of the force created acts behind the centreboards. The boat rotates towards the breeze. The jib force is in front of the centreboards - hence it rotates the boat away from the breeze. These two need to be balanced.
Once the boat starts moving the lift created by the centreboards increases and the main can be pulled on harder. You can tell when its working as the rudders will tend to stall if there is too much main tension.
in strong breeze (above 15knts) - if in doubt pull on more downhaul and then more
. Match this with the main and jib, set up a jib cunningham you can control from the front beam and use it to flatten the luff of the jib, just like the main. (This is a nice to have - not essential as you can always send the crew to the front
, Pre-bend - set to recommended settings for crew weight.
, Rig tension - follow the recommended settings - once again think about the rig's purpose - in light air a tight rig will not allow the mast to rotate very well, so set the rig a little looser, as per Mitch Booths comments. As the Breeze increases you want the rig to be tigher so its not creating stress when you tack and gybe, otherwise the rig is crashing back and forth, things break. If is likely to be very strong then set the tension very tight, if you know for sure its going to be light all day and you cannot get to the beach to adjust the tension - set it light. Otherwise set it firm for medium conditions
, the rotater - I'll upload some images they tell the story. The top and bottom left are with over rotation
. The right top and bottom are with the rotater to the back cross beam
. Top set downhaul on hard, bottom downhaul lighter.
On the bottom right notice how the mainsail leech is "hooking" - it has more shape but in a strong breeze this would be an over-powered sail. The Top right is better - with more downhaul applied - but it still has more shape than the left side. Using these images you can see effect of the three controls, sheet tension, downhaul and rotater.
The sail shape on the left allows the top section to fall off to leeward (it "twists" the main - the result is a very fast sail - HOWEVER - you cannot start off with this shape - you need to get the boat moving and then starting trimming and downhauling.
I now use the settings noted above for all conditions and then vary the mast rake:
1. If its around 15 - 18 go to the 2nd from the bottom on the side, 2nd from top on front - rig is very tight
2. Over 18 top hole on front and bottom on sides
3. Very light 3rd from top and 4th up.
Image courtesy of joclo