Robi,

After reading you initial post, I thought I had couple of pointers for you, but after reading all the posts, i'm sure your well equipped to test & experiment with your sail.

As a sailmaker, I would like to share some of my experiences with mainsail & leech pressure.

1. Leech pressure is something that most sailors & sail makers strive for & cant allways sem to get enough of.

2. Sail design, more importantly the balance of sail shaping & luff curve after broad seaming is very important to how much leech pressure ( or how the leech stands up) your sail will have & of the any possible "hooking of the leech"

One thing you could try is when you lay the boat on its side to measure all the prebend & spreader rake is too put the sail up (keep the boat on its side) and look at the sail with out the battens & check out how much the battens are actually reducing the sail's cut shape. For example if the top third of the sail looks very full with out the battens & then looks quite flat with the battens in, I would suggest the sail is cut too full for the mast & the battens have been stiffened up to give a reasonable shape - but the sacrifice is too much leech pressure you may not be able to get rid of, no matter how much downhaul you apply.

Worth looking at - up to you.

3. It is not uncommon for the top Tornado sailors to carry a few stiffer battens out onto the course incase the breeze freshens for the second race of two back to back races, enabling the crew to flatten the head of the sail if need be.

Agree with what marcus is saying above. I went off line to write this and it has turned out to be a very long post. This is how I do it and what people should consider IMO.

Here is my method for setting up a mast :

1, Spreader length. If you can change it, remember, longer spreaders increase the effects detailed below

2, Spreader Rake, the greater the rake, the less support the mast has laterally as any tension added to the wire(s) bends the mast forward (in the masts plane). Less rake provides more support and so less bend.

3, Spreader (diamond wire) Tension. This needs breaking into 2 parts

3.1 Well raked spreaders, the more diamond tension, the more (initial) forward bend induced by the diamond wires, you have a bent mast - Ergo flat sail (macro adjustment) you will not be able to add fullness without reducing tension in the diamonds, but this will allow the mast to bend more.

3.2 Flat (or nearly flat) spreaders, Again more tension induces more (initial) forward bend, but to a MUCH lesser degree. You also have a mast that will bend less as the diamonds provide more support for the mast (and the loads a sail will apply). Because there is little rake, you will (effectively) only be able to put a small amount of prebend into the mast before the loads on the wires and/or the spreaders cause a failure (I've stripped a bottle screw once).

So, in summary, 3.1 gives a bendy mast with slack(er) diamonds and a bent mast with tight diamonds. Depending on the bend characteristics of the actual mast section this may be what you want.

3.2 gives a stiffer mast that will bend less.

4, Downhaul, The control does 2 things

4.1 It stretches the sail cloth (to some extent) at the front of the sail and so moves the draft forward and opens the leach of the sail.
4.2 It also bends the mast which opens the leach more and slackens the rig tension as the hounds are (a very small amount) closer to the deck.


Consider this (I'd not suggest trying it). Make up a bit of wire (or old bolt rope) and attach your downhaul to it. You will be able to induce more bend into the bendy mast than the stiff one for the same tension on the downhaul, with the raked spreaders and diamond tension, the prebend "gives" you a little for free.

5, Now we need to consider the interaction between 2 different mast setups (bendy and not so bendy)

5.1. Bendy

The downhaul will be easier to pull down with prebend already induced into the mast by tight spreaders, thus (usually) tight spreaders on well raked spreaders in a big wind = a faster boat as it is more docile.

BUT, there is a corresponding loss of power when you need it in the lighter (marginal trap) winds as the mast is bending more and so loosing some power.

5.2. Stiff mast

The down haul will be harder to pull as there is less prebend in the mast, so for the same amount of mast bend, you need more downhaul tension

But, you get the power when you need it.

6, Mast shape

We all have elliptical masts, some are slimmer than others so we have a range of different fore-aft vs. Port-stbd bend characteristics.

Consider sailing up wind with a round mast Bend will be constant until you add the spreaders, then, what ever rotation setting you have, bend will be controlled by the spreader settings (and downhaul and mainsheet).

Consider a totally flat(fore-aft) mast (impossible I know). The fore aft bend (mast) will be small, lateral bend will be high. introduce the spreaders and these will only control bend between the top mounting(hounds) and the bottom mounting. The rotation setting will have a massive effect on mast bend. No rotation at all and no mast bend will be minimal, 90 deg rotation and lots of bend.

7, Traveller, this controls the exhaust of the sail (and the angle of attack on a large scale), Mainsheet controls the leach tension and angle of attack. Mainsheet will also move the shape of the sail as mentioned in previous posts. Wouter has talked about hooked sails (too much mainsheet).

8, Battens also (as said by others) effect sail shape - I subscribe to the stiff top batten group for "Fat head" sails and soft top battens (reversed if windy) for "pin top sails"

9, Sail cut - you can have a sail cut to be very full, or flat.

so we have a collection of different options we can use to control our mainsail shape and the effect of each can be listed in an order of changeability for the conditions



Least (or most difficult to change) first

1, Mast shape - we don't want a low and high wind mast section do we - it would be a pain changing them for each days forecast - if our class rules allowed.
2, Mainsail, you can have a full or flat sail, but we don't want to have a light, medium and heavy wind mainsail do we ?
3, Spreader rake - we can change it off the water by slackening the diamond wires, but it is not a quick job.
4, Diamond tension - we can change this on the water, but it is not a "gust by gust" trim option, it is a set and leave for the race trim.
5, Mast rotation - we can change this whilst sailing, but generally it will be set for the current leg and only changed because of a large wind strength or direction change.
6, Traveller - we will change this at times on the leg, but will not be used as a constant trim adjustment.
7, Downhaul - we will trim this regularly, up to max or min amount, it will be "played" in gusts
8, Mainsheet - we will trim this constantly.

so to set your mast and boat up you need to consider many things !

Finally I set my spreaders flat (usually approx level with the bvack of the mast track) and my prebend so the sail falls down easily (around 20mm on ny I17). And then go sailing.........

Having either tight or slack diamond wires also affect bending off that the very top of the mast (above hounds) does.

Go to :

http://www.ahpc.com.au/wingmastrig.html

to see what I mean. Look at the 4th picture from the top (or bottom picture)

Say I can show that pic in this post of course, so I will :



Wouter

Hey robi, do you have that new (french) Sailing DVD ?

If so then there are a few excellent bits of video that show exactly what happens with your mainsail when you pull on the mainsheet or downhaul oir on both simultaniously.

This DVD is a real benefit for cat sailors. Even experienced ones.

Wouter

Great discussion everyone.
As was stated above, increasing DH moves the draft forward on cats with masts that aren't too stiff. So does anyone know why on windsurfing sails increasing DH moves the draft aft even though their masts are very bendy? I've always wondered why it's opposite. The only thing I can think of is that since there's no mainsheet to stand up the leech the "effective" sail becomes smaller, moving downwards (as the upper to mid leech twists off), and the draft at the lower 1/3 of the sail doesn't move forward like the mid to upper part so the net result is a "relative" draft movement aft. Anyone know for sure?
Jerry

Geez, this forum is THE best source of information (and another reason to consider an F16) - thanks!

By the way, is it so that failing to loosen cunningham prior to mainsheet reduces mainsail life drastically ?

PK

GOOD readings!

Hey Wouter, where can I get a hold of this video?

I got mine here:

http://www.multihulls-world.com/us/boutique.php?id_product=262

You won't be disappointed.

Shaping a mainsail , unless anyone reading these posts hasn't realised yet, is like skinning a cat - there are thousands of ways to skin a cat and it is not the way that it is skinned that is important but the best end result that counts - similarly there are thousands of combinations by the use of the various "controls" in shaping a main sail. The various methods that are used aren't as important, as the end result.

Glenn Ashby seems to think so :

http://www.taipan.asn.au/Tips%20and%20Tricks/Resident_expert.htm

he says :

"To make the sails last. it is ESSENTIAL that the cunningham be let of before big sheet is eased around the top mark for eg. Even in a big wind I always let of half the full amount to avoid over stretching of the luff as the mast straightens from being super bent fore aft. I thinks sails can last up to twice as long by doing this. If you dont ease it it is like pulling the cunningham another 2 or 3 numbers down."

You guys can all find more Taipan trim and tuning tips on the official Taipan website (part is written by Glenn himself) :

http://www.taipan.asn.au/

by clicking on tips 'n tricks

Wouter

Robi Posted:


Look no farther, It and over 4000 other items (most with same or next day shipping) are available Right here on Catsailor's www.onlinemarinestore.com

Here is the URL for the video:
http://store.catsailor.com/tek9.asp?pg=products&specific=jnjpmrfmi0

Just click on it and order.
Rick

Robi, I skimmed the posts and I didn't see this mentioned so I'll add it: Put some tell tales on the leach!! I know Wooter said tie 11/2 feet of ribon but that's way too much. Just get some of the 8" red or green ones available at any sailing store, with the white round sticky patches to hold them on. Put 3 on the leach, one up high, one low and one in the middle.

Then, get out and practice. You want them all to fly straight back, most of the time. Then you can experiment with the down haul, traveler, sheet tension, etc. all day long and you will see the results immediately. When the leach tell tales are not visible, it's becuause they are being blown to the back side of the sail, because the air is not flowing cleanly off the leach, the leach is stalled, and that's slow. Keep them flying most of the time.

There will be times when you have to choose between the tell tales on the front, back and leach of the sail, you won't be able to get them all flowing all the time. In that instance, you always want the ones on the back of the main flowing, always! Next priority is the leach, then the inside near the mast is least priority.

If you constantly try to keep the inside ones, near the mast flying, you will often be oversheeting and stalling the leach, and maybe even the backside of the main, which is REALLY slow.

Also, as the wind builds, DO NOT PINCH!! The more it blows, the more you want to foot off to keep it moving through the chop, and don't worry about the inside forward tell tales too much. You will have to ease the traveler and mainsheet in the gusts, the forward inside tell tales will stall a little, especially if you have the mast rotated, but keep the leach and backside tell tales flying.

But more than anything (messing with prebend, battens, etc...), you must get out and practice so you can see what works and what doesn't. So, get well soon and get out there!!

If you want to drive up to Sebring (two hours?), we can get together on my lake and I'll show you what I'm talking about. Make sure you pick a windy day, maybe we can get Matt and some of the Snakes out too...

Good advice Timbo. Telltales really are the ONLY way of being able to actually see how well (or badly) your sail is working. I have put 4 leech telltales on my main - I have 1 in the lower third, 1 halfway up and two near the top of the main about 2ft apart. (It's surprising, but sometimes one will fly cleanly while the upper one will twist all over (tip vortex?)) When the top two are flying clean the boat just FEELS fast.

I have 6 other tell tales around the sail and as Timbo says, you can't get them all flying, but even when they aren't they're still giving you information about the flow over your sail and that means you can make INFORMED adjustments.

While I'm still learning this new boat I'll use the telltales a lot. Eventually (as with previous boats) I'll know the boat/sail well enough to only refer to them to briefly check settings and be able to concentrate on speed and tactics.

In other words they are a tool to get a job done. Don't become obsessed with them or you won't be sailing efficiently.

This sounds like a fun plan. I wonder if Matt McDonald would be up for it. Let me see what I can do after my recovery. I am always up for sailing somewhere diferent. Quick question what lake are you talking about sailing in? NOT lake placid right?

I will get a hold of a few more tell tales and attach them to the leach. That sounds like a great idea.

As far as trimming goes, I really need to get out more often and sail more, get used to it all. I just wanted to know the theory behind it all.

No, not in that alligator infested, weed choked, infamous bass fishing Lake Istapoga of the Lake Placid area...I'm 15 miles north, on the beautiful, clear, Lake Jackson, in Sebring. Do a Yahoo map search for Sebring, it's the big lake in the middle of town, I'm at 2127 NE Lakeview drive, right on the north shore.

Wait for a good windy day. There's a seafood restaraunt on the south side and a Mexican restaraunt on the west side, with sand beaches, we can pull up and eat/drink when we get tired. Or drink on my beach...before we sail, or both!

When you guys are talking about leech tell tales, do you mean so the ribbon is fluttering off the sail completely or just in from the leech?

Off the sail completely?

We're referring to telltales (telltails?) attached to the leech of the sail that fly in the breeze behind the leech (the trailing edge) of the mainsail. Mine are made of ripstop ribbons but I find that when wet they stick VERY well to the Mylar sail. Although they do tend to dry very quickly. I don't know whether anyone can suggest a better material for them? (I've tried wool but find the same problem).

One of the guys at the club suggested cassette or video tape.

Instead of using Yahoo, try maps.google.com (No www.)
Type in "Sebring, FL"
When the map comes up click on "Satellite" in the upper right
Zoom in and you might be able to see your house on the Satellite photo of the area.
Way Cool

I kinda assumed you would all have a forest of telltails on your sails - I do.

And cassette tape works well, but does stick. It's also cheap, I have about 20 C90's the the garage, I am sure it will last me mutiple lifetimes

I was talking about the one that are off the leech, not right behind it.

And I was only talking about the one at the very top and yes it has to be a long one.

I wasn't commenting on a stalled main. I was commenting on a hooking squaretop with a draggy tip vortex which is something completely different

Wouter