thanks for all the feedback,

unfortunately we drift slightly away from the main question.

actually i did not so much wanted to discuss how usefull is spreader rake (i let Greg Godall talk for me:
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Spreader rake

Spreader rake is the method of tuning the fore aft stiffness of the mast below the hounds. The ideal amount of spreader rake is dependent on the fore-aft stiffness of the mast and to a lesser extent, the amount of luff curve cut into the sail. Stiff masts require more rake to make the mast bend sufficiently, soft masts require less rake.

Crew weight effects the required amount of spreader rake as it has a significant effect on the amount power developed by the rig.

The spreader rake is measured by placing a straight edge or string-line between the diamond wires at the spreaders and measure the distance to the back of the mast. We are currently using 40 - 65mm of spreader rake.

To answer how much is sufficient rake can only be determined by sailing the boat and knowing what to look for.

If you have excellent height, but lack boat speed up wind and the boat does not want to accelerate in the wind gusts, then you need more rake. This helps the mast bend fore and aft which allows the sail to flatten and the leech to open in the wind gusts. ( See also notes on diamond tension.)

If you are lacking height and "grunt" in light to medium weather, then you have too much spreader rake.

Diamond Tension

This primarily controls the side bends of your mast. Loose diamonds allow the middle of the mast to bend to leeward and the top of the mast to hook to windward. If the diamonds are too loose the mast will bow into the jib slot in the wind gusts. When beating this makes the boat feel bound up and it does not want to accelerate in the wind gusts,. This also tends to cause the boat to heel very easily in wind gusts. Very tight diamonds do the opposite.

Downwind, tight diamonds keep the mast bent reducing camber and power. On our boats the diamond tension is set at 42 on the Loose gauge. )[/color]

but what I asked for if someone knows (or knows someone) who achieved more than 25mm spreader rake with the old glassfibre spreaders?

recutting the sails is not an option! furthermore I strongly believe in much spreader rake and to adjust diamond tension regarding wind conditions.

I think the most all aspects describing article for the relation of spreader rake, diamond tension and mast rotation angle comes from Andrew Landenberger:

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Landenberger One Design


Tuning Tips - Mast setup


Over the past few seasons it has become quite clear that many people who have been experiencing speed or

power problems have had little basic knowledge of what they can do with the mast settings. It is clear what do

with the cunningham, simply pull on it to get the pressure out of the sail as you need, but often the mast is left

unattended to, as a last priority. In fact it is one of the most important speed controls on the boat. It is important

to understand how to use it, and what you want to have in the sail shape for different conditions. It is not so easy

to just come up with numbers and angles that will suit every mast and sail so I will try to make some key points

to help understand this correctly.



1.The more pre bend set in the mast the more effect mast rotation has on the sail shape.



2.The effect of the spreaders means that the more the mast is rotated backwards, the more the lower mast

section can bend forward (in the direction of the boat) and the stiffer the top section becomes. Leaving the

cunningham tension out of the discussion at the moment, the result would be that the sail becomes flatter in the

bottom and fuller in the top.



3.Rotating the mast more forward allows the spreader to start to work and the lower

mast section becomes stiffer

in the forward direction and the top becomes softer backwards. The result is the sail will become deeper in the

bottom and flatter in the top.



4.Cunningham pressure flattens the sail and will tend to flatten the top more than the bottom since the top of the

mast is unsupported and more free to bend.


Understanding the sail shape that works best in the differing conditions is then very important. For example in

Flat water you would like to have a very even profile through the sail from top to bottom with good power in the

top and the possibility to pull the mainsheet quite hard without stalling the back of the sail. On flat water you can

sheet hard and point higher. By wave conditions you would want good power down low in the sail and have the

top more open and twisted. This gives you power and the twisted top allows the boat to accelerate easily letting

you steer around more and power the boat through the waves easier. Generally you can’t point as high as the

boat on flat water but because of the waves you can achieve a much better VMG (velocity made good).


The typical example is that with increasing wind the sailor will pull the Cunningham hard but not adjust the mast

rotation to go with it. The effect of the Cunningham is flattening the sail, but more in the top. This allows the leech

to open. The boat may feel ok but often the leech is to open and you can’t point high enough. This setup can be

good in big waves but on flat water the sailor would like to have the leech standing much straighter so they

should rotate the mast further back. If you go back to our original points you can see that the mast becomes

stiffer in the top and can bend more in the bottom. This is therefore powering up the top and flattening the

bottom of the sail. With the Cunningham pressure you can sheet on hard and point high with good speed.


The other typical mistake which occurs, is that the sailor by strong wind, simply pulls the mast back in line with

the boom and pulls full Cunningham pressure. Because the mast rotation is too far back the sail becomes

too full in the top and too open in the bottom. The sail will have a lot of twist which some sailors think is good for

strong wind, but because of the top of the mast reaching its maximum stiffness in the aft direction of the boat the

sail will remain too full in the top. The end result is a sail which is twisted to far and with too much profile for the

strong wind. The twist causes you to loose pointing ability and the depth is causing excessive drag, just slowing

you down. You are in effect going slower and lower than the correctly trimmed boats.


Spreader rake is also another significant factor in setting up you rig. It also plays a part in how much the rotation

angle affects the depth of the sail. That can be a whole subject of its own, so for now I make just a few

comments. Try to think of pre-bend as controlling the position the mast takes its bend. The more pre-bend you

make in the mast the lower the mast likes to bend. The lower the mast tries to bend the straighter the top

section becomes. The flatter the pre-bend the more the top section tries to bend. The normal reaction of sailors

is to increase the pre-bend for strong wind to flatten the sail and reduce it in light wind to increase power.

Principally that is correct, but it must be incorporated with the rotation to get the right balance in the sail. Like

most things, too much or too little can be harmful. It is a great failure made by many sailors to flatten the

spreader angle to far reducing the pre-bend in the mast to almost straight. For light wind this is doing more

harm than good. The heavier sailors also often request more luff curve because they are looking for power.

With more luff curve and flatter spreaders light wind speed can quickly come to an end. The sail will become

very full down low with a deep entry angle from the mast and a very closed leech section. When you get the first

wind in the sail you may get a feeling of power, but you may also experience the boat just wanting to fly a hull

but not wanting to go easily forward. The boat will not point and will not accelerate.


In many cases it is actually better to go the other way. By very light wind you can increase the pre-bend to open

the lower part of the sail and reduce the entry angle of the sail behind the mast. With the rotation angle set

correctly to get the head standing up just the right amount you can be very fast. Just remember flat is fast and

deep is slow. It has a lot more to do with entry and exit angles of the sail to achieve height and power.


Amongst sail makers there are many different ideas, and history has proven that there are many ways to build

fast sails. The most important thing is that the sailor can understand how the sail should work and manage it

well. Also restrictions on materials and designs in the boats themselves change the way the sail has to work to

achieve the best results. We design our A class sails to allow the mast to be rotated well back. The reason

being, that the mast itself creates a lot of profile over the rig and therefore it is very important to be able to

reduce the wind age over the mast by rotating back as the wind increases. At the same time the sail must

flatten rather than get fuller. That is the secret to success.




Good sailing.


Landy