Robi, here is how you measure these things. Spreader rake and prebend

By the way, Darryl refered to prebend as luff curve. Pretty much luff curve is used in relation to the round on the luff of the sail and prebend is the name used for a similar curve in the mast in its major plane.

Spreader rake is easy to measure. Just lay the boat over and hold a stiff tube or bar of wood to the spreader wires just above (or just below) the spreader arms. Now measure the distance between the back of the mast and the bar or tube. Together with the length of your spreaders (or overall between the wires) gives a good measure of the spreader rake you have on your boat.

Prebend. The best way to measure is it to used some 1 mm line (whipping twine) and have it tight between sailhook and boom fitting and fully tensioned. Make sure that the line touches the rear of the mast at the hook fitting and boom fitting. If a mast is set up with prebend that the line with move away from the mast with the maximum distance at the spreaders. Make sure that your mast is layed perfectly on it side as even a small amount of rotation will chance the prebend you measure due to the weight of the mast itself. Measure the distance between line and back of the mast at the spreaders. This is your prebend value.

Measure these for us some time and post the values on the forum so we can give better advice. Also note done you experiences with sailing the boat with the current settings. Things like; she is flighty or rather docile, she feels underpowered of overpowered, she points well or not in relation to other boats, She accellerated noticeably or not, In gust is accellerates rather then heels or pushing her bows down (or the reverse), She feels bound up, she has weatherhelm or leehelm when mainsheet is pulled and all other describtions of how she feels. These experiences together with your current settings will allow both you and others to hone in on the correct settings for your mast and sail combo.

As Mary says there in no single winning setting. In teh end all sails are a little bit difference from one another and especially sailor related style can be very different.

Example; I like the steer in the puffs rather than sheet. So I'm hunting for alot of automatics adjustment in my rig. Also I'm 85 kg's and between 150 kg and 160 kg with crew. So I'm looking for power as well, mostly to get my luff hull out of the water without making the boat flighty (heeling alot in gusts and not falling back in the water in the lulls)

Your situation may be totally the reverse.

But here is an example from my own situation.

Currently I'm running 50 mm spreader rake with 740 mm width between the wires. My prebend with these settings and my diamond wires tension (unknown) is 27 mm. I sailed singlehanded last night and my experiences with these settings are

-1- The boat feels flighty, putting on the downhaul makes her more docile but doesn't lead to much accelleration in the gust or higher speeds. Considering the wind strength and gusts I do expect both of these.

-2- When I totally release the downhaul my sail shows some medium sizes creases and shows the middle and part of the upper leach to pop up. When I apply only a little downhaul tension to get the creases out then the leech falls away already. I don't want this to happen, Don't need the leech to fall away in the middle part so easily.

-3- Pointing angle is acceptable but not particulary good. I feel there is more there.

-4- Helm is balanced, no problems there.

-5- Mast rotation was about 45 degrees.

-6- She feels underpowered for the conditions except for the gusts.

With these experiences I feel that despite the fact that I increased my spreader rake last weekend I also need to reduce my prebend by making my diamonds less tight. I'm hoping that the last will both make the top of my mast stand up and make the leach along the middle part stand up even when some downhaul is applied. This will allow my to apply some downhaul to get the creases out and shave the effects of the gusts off without losing pointing or depowering the middle of my sail to much.

I will first sail a few times with what I have right now to fully determine the effect of me increasing the spreader rake, but after that I will reduce prebend to 20 mm I think. Than of course sail several times with that and see how she handles different conditions like that. And so on till I find the right settings.

Best advice I can give you is to have a little booklet where you write down the settings used in each sail, the conditions and your experiences in sailing the boat. This really helps dialing in your rig and answer questions of others about how she handles. In found that memory is not dependable in these things.

Wouter