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Sail battens

Postby Geoff Martin on Sun Nov 21, 2004 10:00 pm

Has anybody experimented with battens.
Do they accept what the sail makers give them or are some using tapered battens.
I have found that the ones usually suppled have max draft at 50%
My thoughts are this should be about 40% and every attempt that I make to taper a batten to perfom this function,turns out to be a failure.
Geoff Martin
 

Postby fitzwarryne on Tue Nov 23, 2004 10:19 pm

The simple test is to trial sail with a whole line of tufts and see where the airflow breaks down, From this you can tune the batterns. Its critical to get the same wind flow in all areas of the sail, not just in the full battern area. Remove the experimental tufts before a race otherwise you never get your hrad out of the boat!

Monosail boats usually need their maximum camber further aft then those where the jib affects the upwind airflow. However, some underpowered classes such as the 420 try to get the maximum camber well aft so the sail has a very tight leach to give maximal power and not worry so much about drag.

Remember the flatter the entry for a given camber the more critical is perfect sail trim. The performance grove is much smaller so while better for an expert is too difficult for the average club sailer.

If you get poor performance with 40%, stick wirth the results and to hell with the theory!
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Batten Tension

Postby Greg on Sun Nov 13, 2011 4:51 pm

I understand that I am replying to is a pretty old post but it seemed relevant to my query.

I was hoping for some advice about what tension to set the battens. It seems to have a resonable effect on leach tension.

The advice in the post below about test tufts seems reasonable, however before I get around to that a "rule of thumb" would be useful.

Cheers

Greg
Tiwi 1317
Greg
 
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Sail batten pressure

Postby fitzwarryne on Mon Nov 14, 2011 1:49 pm

A initial approach is to place the battens in without tension, then datum mark. Apply maximum tension, and datum mark. Then apply pressure so you are mid way between the two extremes, this is your starting point for tuning.

If you are a perfectionist, use a small fishing spring weigh scale which will give you are precise tension for future reference I also use the scale for measuring the Euler crippling load which gives an indication of the bendiness of the batten. If you are unaware of the concept; the more pressure you use to bend the batten the more it bends until at a certain pressure it will continue bending with no more effort. A stiff batten will require more pressure to reach this crippling load. Note, it will depend on the length of the batten so each must be tested, the shorter it is the higher is the crippling load for the same batten thickness.

Again, the perfectionist will measure the ECL and point of maximum camber. With a full length batten on a single sail boat the target is 50%, but if you want to point in moderate breezes then 55% aft can work.

However be warned, fiddling with boats is my hobby which is occasionally interupted by actually sailing which I find is more energetic and wet.
fitzwarryne
 
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Battens

Postby fitzwarryne on Mon Nov 14, 2011 1:59 pm

Sorry I should have made one point clearer; there can be a difference between the % aft of the maximum draft of the batten and the sail. Change the bend shape of the batten to obtain the desired shape of the sail.
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Re: Batten Tension

Postby CDance on Mon Nov 14, 2011 10:50 pm

Hi Greg,

Your sailmaker will be a good guide on this topic as preference/construction may change form sailmaker to sailmaker. I can only really comment about the Irwin sail but I suspect it'll apply to all.

As a general rule of thumb:

Lower/Short Battens: Take them how they come. Tension make very little or no difference to sail shape. I don't even know what they look like - I've never even removed mine from the sail! The sailmaker usually sets the "tension" by how they construct the pocket/batten.

Top/Full Battens: Use a tight tension so the batten starts to just show a tendency to "pop" from side to side in the batten pocket. This helps stops the battens from accidentally inverting in light conditions and keeps the wrinkles away in higher winds. Always remember to release the tension at the end of the day when you roll up the sail.

We've done quite a bit of work with battens over the past 12 months. Irwin Sails has two main shapes, both with proven race records. Linsay Irwin usually speaks to the sailor and will advise on the best sail to suit your weight, ability, target conditions and mast bend. Most of the sail development done over the past year has been around making very minor changes to this existing designs to broden the sail's optimum working range. Battens were one area we've experimented with. The idea being that battens can induce different shapes in lower winds but as the wind increases it's influence lessens. (They are also cheaper to change than a sail recut and can be changed on the water for same day testing.) We've tried:

* Different stiffness and tensions
* Various degrees of taper
* Using multiple sets of battens and changing them up the wind range

The end result is we've gone full circle! The conclusion is the symmetric battens and consistent tensions are best through all wind ranges. Any gains from "experimenting" were minimal or detrimental (like taper battens). For stiffness my preference is a slightly more flexible batten than Linsay usually supplies and this is achieved by sanding off the ridge.

The only advantage found was all this playing was it gave us something to talk about over a beer in the bar. :-)

Cheers,

Chris
Espresso 1778
CDance
 
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Postby Greg on Wed Nov 16, 2011 2:59 pm

Thanks for the info. It is good to have a starting point.

Cheers

Greg
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