Battens tapered and CE

If I taper the battens it will come ahead moved also the centre of effort?

thanks

Tapering too far forward and it will move the draft forward.
Rick

....... and move also the CE forward ?
..... and it reduces the weather helm ?

Thanks

Not sure what boat you are doing this to. If a sloop, you do not want the draft forward where the jib overlaps.
With boat with semi wing masts (large major axis, low minor axis) the mast becomes part of the sail. So, you can move the draft forward enough so the overall draft is still in the low to mid 30% range.
On a fixed stick or roundish type mast like the Wave, you do not want to move the draft forward.
Rick

I have a 20 ft. cat with wingmast ....and with more weather helm;

The issue is if moving the draft forward then reduces also the weather helm for the fact that moves also the CE forward.

Excused my very bad English .....

can't you just reduce the mast rake?

The mast is already now perpendicular. I have tried in the forum but I have not found arguments that they put in relation the tapering of the battens with the position of the CE.

Check the rudders; can you move the tip of the blade forward; this might help.

The short answer is "yes" the CE will move forward, but by a shorter distance than that of the draft movement.

The difference is due to the jib, obviously, and due to more complex aerodynamic reasons that I will leave for someone more qualified to explain.

I would only move the draft to move the CE if the sail would also perform better after the change. Otherwise, just change the mast and/or rudder trim, as already suggested.

.

The draft now is at 40% and i not consider the wingmast ..... i think that if the draft move to 30% the sail perform better ..... or not ?

Tilting the rudder forward solves the problem and reduces the possibility of ventilation.
If the mast is vertical, I would tilt the rudder forward as much as possible and then rake the mast back until the rudder feels right.
A totally neutral helm is not ideal, so don't try to completely eliminate weather helm.

How new is your sail? An old baggy sail will give the same result.

The wingmast is part of the airofoil and must be considered. If it is a 10% wingmast, the airfoil draft is at 50% and moving it forward should be beneficial.

Still, it depends on other factors. Best thing to do is check the draft position of the regatta winners in your class.

A few relevant questions:
What boat is it?
Does the jib overlap?
Do you use a downhaul? Is it powerfull enough?
How old are your sails and of what sailcloth?
Are the battens not tappered at all or you just plan to increase the tapper?

Thanks Luiz, but i don't understand the rule for which if I move the rudder forward i reduces the weather helm. please explains me. The sail is not old but it could be cut badly

in short: no for both questions.
the centre of effort is nearly not affected by the position of the draft, but by the amount of draft. Tapering the battens will increase the draft and you get more weather helm.

Too much weather helm is in most cases a too full main and/or a too flat jib.

Cheers,

Klaus

the boat is a prototype to which it has been adapted a sail...probably F18, the jib don't overlap ( i have self tacking ), i use the downhaul that is 8:1, the battens are tapered at 40%.......

It does not look natural, but tilting the rudder forward may improve its balance, depending on how it is now. Check the drawings:




They are from this website, which is recommended reading.

instinctively I think tilting the rudder forward move the CLR forward and inreases the weather helm ..... and don't understand ......

Take a look at my last post now that I edited to add pictures and a link.

seems much easier to try to adjust the mast/rudders than to sand battens (you can't unsand)

Thanks Luiz

I have read the link indicated and i have understand that in order tu reduce the wearher helm and tiller tug i must accept that the rudders work with extra drag from turnig, and to achieve a straight course slows the boat.
I have understand that for the hobie the advantages to increase the mast rake are greater of the disadvantages to make to work badly the rudders.

This is not my case .... I want to reduce weather helm in order to make to work the rudders with the smallest drag.

if you have weather helm and you need to pull the tiller, you create lift - something you need to go upwind. If your boat is neutral, this lift comes from the daggerboards and it will produce drag as well.

Cheers,

Klaus

It really sounds like the sails dont fit the boat very well. Draft at 40% with a rotating mast dont have to be too bad, depending on the geometry. How full the sail is and what the profile looks like on the other hand makes a world of difference.

These sails that have been adapted to your boat.. Is the mainsail designed for the mast? If not, was the luff of the main re-cut to fit the mast? It just sounds like you have a mainsail that dont fit the rig or boat too well.

Any hope of pictures?

The sail is designed for the mast .....

Yikes!

Look at those wrinkles!

Any way to add more batten tension?

X2

Yes, wrinkles are monstrous ..... but this is an other problem for an other day ......

Do you have another picture where the mast is rotated properly?

The battens are not tied in as tight as they should be. The current setup will not help on your weather helm issue.


What cloth is the sail built from? Some sort of fiber reinforced mylar with taffeta?

How tight is the downhaul on in the picture? The wrinkles between battens should go away when you tighten them, but the large wrinkle from the downhaul and between batten #1 and #2 is a different matter. I just hope it disappears when you rotate the mast.


If you are going to do another pic sometimes, it would be helpful if you could lie down under the boom when shooting.

wouldn't tightening the battens create more draft?

Just glancing at the sail, it appears the draft at the top two battens are too far aft, 3 and 4 look pretty good, but should not be moved forward, Then the rest of the bottom of the sail has the draft way too far forward which will cause a backwinding by the jib (overlapped or self-tacking makes no difference -- the jib is still throwing air across the mainsail down there.)
Rick

Thanks to all .....
I don't have a pic with mast properly rotated, the sail is in dracon, the battens are soft and if tightening create more draft;
In this pic no downhaul and sheet.

that really doesn't look too bad. Iwouldn't try to move the draft any more forward....but even if you did try to fix it with battens, it wouldn't have too much effect. A sail with a bad draft position is just that...the battens won't change it an incredible amount..but again, that doesn't look too bad.

Jake is right IMO. Sail dosent look too bad I'm sure the winkle blow out especialy when you consider that it's Dacron. Battens simply hold the sail in shape it was designed.

Like the other guys said rake your rudders more under the boat. Think about it if you have a problem steering you should probably start with your rudders.

"Think about it if you have a problem steering you should probably start with your rudders."

Count me FIRMLY in the sails and mast trim first camp! Whenever I have a problem steering it is always because I have too much tension on the main sheet or too little jib tension, too late.. But I have to admit I'm no expert on cats yet having gained most of my experience on mono's. By all means, check your rudders for normal trim, but I wouldn't be taking a file to them unless it was a last resort. Raking forward does not improve anything IMHO. It just masks a trim problem by adding more force in the opposite direction (AKA drag). Its a bit like "shooting the messenger", if you ask me. Ie: The rudder tells you something is wrong so you take a sharp tool to it and "make him an offer he can't refuse"!
Rick and Marys book has some excellent explanations of the theory behind it all on page 72 and 73.
Dennis

I agree

I would agree with messing with rudders but since you used the word "prototype" I would ask if you have tried to sail the boat upwind without the rudders down? Is the front beam too far back on the hull? Does the main have too much roach? Are the boards in the right place? Good luck with your project!

Front beam and boards are in the right place, what do you mean for "too much roach" ?

Meaning the center of effort in the sail does not balance with the Center ofd lateral resistance on the boat and so you get weather or lee helm. More roach will give you more weather helm as more sail goes into the top aft portion of the sail. Pin head sails have little roach, the sail you show has a fair amount as it is a fairly "fat head" sail. Fat head sails have a LOT of roach. By adding more roach, you move the COE back.

A boat will exhibit weather / lee helm whet the boat is not balanced with the sails.

As I am sure you are aware this is because the center of effort / blanace of the sails does not balance where the center of lateral resistance of the hull is acting.

This can be for a number of reasons

1, COE of sail in in front or behind CLR of hull or visa versa

How do we fix this?

1.1 Rake the mast fore or aft to move the COE of sail
1.2, Change the shape of the sail by changing the camber position and thus COE. You get this to happen by adding more downhaul, but the sail also flattens. YOu are sailing with enough downhaul to remove most creases in the sail?????
1.3, Changing the shape of the sail by adding or removing cloth to move the COE
1.4, Moving the mast forward or backward on the platform (move beam(s))
1.5, Moving the position of the dagger/centerboards or skegs
1.6, changing the length of the hulls
1.7, Moving the position of the rudders further aft by adding gantrys (it's difficult to move them forward without removing hull!!)

2, Rudders are not correctly trimmed, with the tip in the incorrect fore/aft position

2.1 Adjust them via designed adjustments within the rudder system or get the files / wet and dry out or make the rudders bigger.

I would suggest that if your mast is vertical and you still have issues with weather helm you have the following possible problems

a, Dagger boards are in the wrong place - you state this is not the case
b, Mast (so front beam) is in the wrong place - you state this is not the case
c, Hulls are the wrong length
d, Sail is the wrong shape, too much roach maybe? (as stated above), too full too far back.

e, all of the above!


If you were to sail in "normal trim" and let go of the tiller, how long does it take to go head to in say 10 kts of wind?

I think is the sail with wrong shape; the max draft is at 40% with 10% camber.
you have seen the pic?
you it seems too much roach?

"If you were to sail in normal trim and let go of the tiller, how long does it take to go head to in say 10 kts of wind?" 5/7 seconds.

Without seeing a full picture of the boat, with the mast rotated from full on side view, front and looking up the boom, it's impossible to shay what is wrong.

5 - 7 seconds is not THAT extream.

As I stated abouve. WH results from an unbalanced boat. Could you take a few pictures showing the WHOLE boat from one side with the sails up and mast rotated correctly; same from the front (again showing all the boat). Same from the back shwoing the whole boat, same from the back, but focusing on the sail (please sheet in to "normal" upwind tensions) and finally lying on the tramp, looking up the sail, ideally showing as much of the sail as possible.

ALL with mast rotated. and main sheeted in.

IF you have the time can you do all the above for the following settings

1, Light wind setting - Downhaul on just enough to take most horizontal creases out; mainsheet as you would have it for sailing up iwnd
2, Medium wind setting - Downhaul on "medium" and sail sheeted for upwind
3, Strong wind setting - Downhaul on MAX and sail sheeted for upwind

Remember to also change the outhaul to the proper setting for upwind in each one.

this will give a total of 15 pics

Side, front, bacl all boat, back just sail, lying on tramp looking up for Light, med and strong wind trim.

Cheers

Simon

5 to 7 seconds for the boat to round up in nice wind.. That is not bad, that sounds about perfect to me. Move the crew a bit forward and you will track straight.
A natural round up can be a safety feature if you fall off the boat.

Thanks to all
I will try to apply the councils and will make the photos as soon as possible.