Testing a new sail yesterday and making adjustments to the sail tuning has reminded me that when you change something you need to change everything else to get the balance right (although to be scientific it is best to change just one thing at a time to see what effect that change makes).

What is the best order to change things to optimise your gear?
ie
downhaul
outhaul
mast track position
boom height

Comments welcome

IMHO, Mast track position is dictated mostly by the sail type/size and downhaul setting, so start with the first two and adjust the second two to suit.

ideal mast track position is where the sail can sit just off the deck when fully powered on a reach/broad reach without it dragging in the water. If it drags, set further back. If too high off deck, set further forward.

You need to have a reference point to start from. I wrote this a few years ago and Erik added to it for his site, good starting points: www.speedsurfingblog.com/2010/01/how-to-do-basic-tuning.html

Downhaul will move the center of effort in your sail, more moves it forward so you will need to move the mastfoot position back to stay balanced. So always consider them working together. Boom height will allow you to control the sail better, moving it lower as the wind increases lets you get your weight further out and down lower to counteract the increased pull from the sail.

Roo

Thanks Roo.
It is a long time since I read that and I had forgotten about it.

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Roo said..
You need to have a reference point to start from. I wrote this a few years ago and Erik added to it for his site, good starting points: www.speedsurfingblog.com/2010/01/how-to-do-basic-tuning.html

Downhaul will move the center of effort in your sail, more moves it forward so you will need to move the mastfoot position back to stay balanced. So always consider them working together. Boom height will allow you to control the sail better, moving it lower as the wind increases lets you get your weight further out and down lower to counteract the increased pull from the sail.

Roo

Roo, I was reading this the other day and checking a couple of items.

3. Make sure the rear foot strap is mounted with the rear screw in line with the leading edge of the fin.

Is this correct as my boards are nowhere near like that.

It's a starting point to get everything balanced, not a definitive ruling! Some of the all out slalom boards have the straps mounted further back which is fine once your comfortable sailing with them there. Wave boards tend to have the straps more forward for better maneuverability. The trick is to get everything balanced then start experimenting to see what works for you.

Roo

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Roo said..
Downhaul will move the center of effort in your sail, more moves it forward so you will need to move the mastfoot position back to stay balanced.

Interesting reading. I'm a bit confused though. Above you say more dh moves the draft forward, but your article says you use less dh which moves the draft forward.

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Roo said..
8. Most sails have their max draft around 33% so this is a good balance point for most sails. Downhaul, battens and outhaul influence the max draft, I often used less downhaul to move max draft forward.)

Am I misunderstanding?

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N1GEL said...

Roo said..
Downhaul will move the center of effort in your sail, more moves it forward so you will need to move the mastfoot position back to stay balanced.

Interesting reading. I'm a bit confused though. Above you say more dh moves the draft forward, but your article says you use less dh which moves the draft forward.

Roo said..
8. Most sails have their max draft around 33% so this is a good balance point for most sails. Downhaul, battens and outhaul influence the max draft, I often used less downhaul to move max draft forward.)

Am I misunderstanding?

Select to expand quote

N1GEL said..

Roo said..
Downhaul will move the center of effort in your sail, more moves it forward so you will need to move the mastfoot position back to stay balanced.

Interesting reading. I'm a bit confused though. Above you say more dh moves the draft forward, but your article says you use less dh which moves the draft forward.

Roo said..
8. Most sails have their max draft around 33% so this is a good balance point for most sails. Downhaul, battens and outhaul influence the max draft, I often used less downhaul to move max draft forward.)

Am I misunderstanding?

8. Most sails have their max draft around 33% so this is a good balance point for most sails. Downhaul, battens and outhaul influence the max draft, I often used less downhaul to move max draft forward.


Nigel I'm not sure why Erik added that, it was his comments in italic he added to my original tips. Less downhaul will definitely not move the draft forward but less outhaul will.

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Roo said..

N1GEL said..

Roo said..
Downhaul will move the center of effort in your sail, more moves it forward so you will need to move the mastfoot position back to stay balanced.

Interesting reading. I'm a bit confused though. Above you say more dh moves the draft forward, but your article says you use less dh which moves the draft forward.

Roo said..
8. Most sails have their max draft around 33% so this is a good balance point for most sails. Downhaul, battens and outhaul influence the max draft, I often used less downhaul to move max draft forward.)

Am I misunderstanding?

8. Most sails have their max draft around 33% so this is a good balance point for most sails. Downhaul, battens and outhaul influence the max draft, I often used less downhaul to move max draft forward.


Nigel I'm not sure why Erik added that, it was his comments in italic he added to my original tips. Less downhaul will definitely not move the draft forward but less outhaul will.

I agree with Erik. From my experience with modern Freerace and Race type sails, adding downhaul past a certain point with bend the mast more, flatten the entry shape and move the draft further back. But it will also move the centre of effort down and slightly forward in the sail, depending on the shaping of the sail and luff curve and this is what I think many feel as added stability and control. The outhaul has an influence on draft and stability too, as he states, but in sails with a lot of seam shaping, changing the batten curve often does little to change the powered shape of the sail which is dominated by the seam shape.

But Roo's statement will certainly apply to some types of sails.

When tuning a sail, can you tell how draft forward it is when it is at rest ? Or can you only tell when sailing and under load ?

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Haggar said..
When tuning a sail, can you tell how draft forward it is when it is at rest ? Or can you only tell when sailing and under load ?

In my experience, you can often see the difference when tuning, but it is often quite evident when sailing under load.

There's always the old trick of getting someone to stand on the mast foot, while you apply pressure to the tip. Not quite the same as wind pressure bending the mast, but it can give you an idea of what happens to the draft under load.