Sail settings

I have a question that is relevant to all two sail boats but particularly noticeable on my canoe. Finding the sweet spot where the sum of the whole is greater than the sum of the parts. By this I mean that I can sail quite happily with both sails pulling well and going reasonably quickly but there is a sweet spot where at some point the two sails start working together and you get noticeably more power, especially in a canoe where such an easily driven hull gets an instant increase in speed.

 

So I keep playing around with sheet tension, sailing angles etc but don’t seem to be able to reliably find it.

 

How does everyone else go about finding it. What am I looking for…

 

Ian

Getting the slot right is a combination of many factors. The important ones as I recall are:

Jib luff tension (ensuring there is little or no sag).

Mast rake

Pre bend

Sheeting angle

Ultimately it is getting the correct sheeting angle for the mast rake to make the jib leech curve match the mainsail luff. Also the tension on the jib sheets is important. On a boat such as a canoe I dont imagine playing the jib is all that easy so it is getting the best average then playing the main (do correct me if I am wrong).

Basically calibrate everything that can be changed and note down all the settings that you can, over time you will build up a good understanding of what works and what doesn't and make finding the sweet spot less of a hit and miss affair. Some people even laminate the settings for every given wind strength and attach it to the boat.

It also helps to have sails that are cut to work together (ie dont mix and match unless you know the cuts are compatible).

I believe there are some sailmakers that float around here so they may chip in....

Paul

fundamentally only one way unless you have loads of experience - 2 boat tuning.  and then if you have loads of experience you can still only get close, and then you need to go 2 boat tuning.

so the answer is....  2 boat tuning.  this is another name for educated trial and error.  AC teams spend $$$$ doing this.

once you are tuned, practice.  then more practice.

With the canoe having a reasonably light and very efficient hull, dont try to create too much power.  It will be more about drag to power ratio rather than power to weight.  I'd opt for a flatter jib setup and really try to get a good tight leach on the main. 
I thought mark goodchild had joined wilsonian now?  surely he'd be able to give you a hand. 

Doug

A useful alteration is to fit leech tell tales to the jib.

According to North's and other studies on the web, the sweet spot for a fractional rig (i.e 99.9% of dinghies) is where the leeward flow of the jib combines or feeds the flow over the leeward side of the main and not so much how much it makes the main "sail in a header " by reducing the air-speed in the slot ( which is still an important function). When this combined flow is really smooth and working then the two sails give maximum power.

 

Thus a well positioned jib leech tell tale (and a window in the main if needed to see it), can mean you keep this key flow going and warns you when the slot needs to be opened, closed or when you should sail with more twist.

It's often hard to see your upper luff tell tales on the jib and while everything may look ok, and the main isn't backwinding, you are in fact detaching flow from the leeward edge at the feed/overlap area and hence sailing below optimum.

I'm having a sod learning this on the snipe which has an unusually high boom, so the very top of the jib is vital and I have no window on what's happening there!

 

Edited by damp_freddie