Top batten and twist

[Quoddy]

I assume “top batten parallel to the boom” means that when you sight from the aft end of the boom to the top of the mast the leech tip of the top batten should fall on that line for your basic twist setting.
Well, no amount of sheeting in can bring the top batten into alignment. Why? The particulars are this: Hunter factory sail with about 50 to 100 hrs on it, raised with vang loose, mainsheet loose, outhaul tensioned, a few horizontal wrinkles in the luff, no vertical wrinkles, no topping lift, boom kicker instead, leech line left slack as I was instructed that it was only used to stop flutter. There must be a simple answer but I haven‘t figured it out yet. Any suggestions?

 

[tsmwebb]

I assume “top batten parallel to the boom” means that when you sight from the aft end of the boom to the top of the mast the leech tip of the top batten should fall on that line for your basic twist setting.
Well, no amount of sheeting in can bring the top batten into alignment. Why? ...

That's right. Hard to say why you can't get there. A photo might be nice. One possibility is that your leach is stretched out or weak and or your battens are too soft or too short. If you sight up the leach do you have a hard spot between the end of the boom and the top of the sail with the leach falling off after that? Here's an exaggerated sketch (it may look more "corrugated" than I've drawn it):

If so then you need the help of a sailmaker -- just ask for a leach job.

If you've got a reasonably smooth foil from mast to leach then the issue is likely a trim or setup problem...

--Tom.

 

[Don Guillette]

Quoddy: Lets start with a few basics. To elimate as much twist as you can you are striving for the top batten to be as close as possable to parallel to the boom. Unfortunately, you'll get close but you won't be able to close the top completely. Here's why. The sail maker built twist into the sail. The reason for that is because the wind blows much harder at the top of the mast than it does at the bottom. Wind blowing at deck level is slowed down by the surface of the water (friction). If twist was not built into the top of your sail you would not be able to control it.

There are 2 mainsail controls for twist. The primary control is the boom vang. The secondary control is the mainsheet. You will never get even close to eliminating twist by only using your mainsheet.

Also, when you start cranking on your mainsheet your not only effecting twist but your also adjusting the angle of attack and draft position so you have to be careful because the effect you think your going to get is going to be a bit different.

Here's the problem a lot of sailors run into. There are approximately 8 primary sail trim controls for the main and 6 for the jib. In order to be able to trim your main and jib a sailor has to understand which control for the main and jib control draft position, twist, draft depth and angle of attack. I'll bet 50% (actually I'm being generous with that percentage because it is higher) could not expalin which control do what. If you don't believe me ask your dock neighbors and sailing friends to define the controls for you. To make it easy, I include a free QUICK REFERENCE with each SAIL TRIM CHART.

 

[tsmwebb]

Generally the advise to start with the top batten parallel to the boom means that the batten will be in a parallel plane to the boom but offset from it. With most sails that means there will be significant twist in the sail when the top batten is parallel to the boom. In the following sketch your looking down on the mainsail. The short section is at the top batten and the long section is at the boom. Notice that there is a line parallel to the boom that passes through the top batten even though in this case the top section has almost 20 degrees of twist wrt the bottom section.


Getting the top batten parallel or even past parallel to the boom should be readily achievable upwind on most boats with decent sails using only the sheet and traveler. IME in many boats hard on the wind in moderate conditions the twist is controlled primarily with the sheet and the angle of attack is controlled with the traveler. Vang sheeting upwind is an advanced technique. When cracked off, the sheet controls the angle of attack and the vang is used for twist control. Leach telltails are wonderfully instructive when learning this subject.

--Tom.

 

[Don Guillette]

Regarding the traveler. This is to over simplify. Picture a screen door that has a pin in the outside corner that rides in a grove in the floor. When you open and close the screen door does the shape of the screen change? Of course it doesn't. Same with the mainsail when you move the traveler. The shape of the sail does not change. The traveler has no effect on twist. The angle of attack has no effect on twist.

My suggestion to anyone interested is the next time your out sailing is to test adjusting twist in your main. First try it with the mainsheet. Ease it in and out and watch the top of your sail. See what happens.

Next crank on the boom vang and then ease it off, all the time watching the top of your sail. See if the top opens and closes. Now you have the info you need to know which sail trim controls works the best.

After that move the traveler back and forth watching the top of the mainsail and see whether the top of the mainsail opens and closes.

You could get the top batten of the mainsail parallel to the center of the boat by moving the traveler car past the center line but your accomplishing nothing.

 

[RichH]

Quoddy-

Are you 'raising' the sail sufficiently???????
"Most" sailors, even those with very long term top class sailing/racing experience, simply dont know how to correctly "raise" a mainsail so that the 'raised' shape is somewhat like what the sailmaker designed !!!!! When designing a sail a sailmaker 'expects' that a precise amount of halyard tension be applied; and, if this precise halyard tension is ignored .... you can wind-up with a very badly misshapen and poorly performing mainsail.

Mainsails with 'boltropes' - *how* to raise them.
What Im referring to is the additional 'stretch' that MUST be put into the luff (of a sail that has a 'boltrope' - typically a 3-strand dacron 'rope' that is inside a sleeve at the luff) AFTER 'raising' so that then the 'boltrope' is **additionally stretched-out** to the proper *designed* length. I dont have my sailmakers design database at hand for the exact specs. for a Hunter 260 luff dimensions; but, the 'typical' needed extra-stretch for 99% of bolt-roped mainsails is as follows: 1 inch boltrope *stretch* for every 11 ft. of luff length. Example: For a 26 ft. luff length - 26ft./11ft X 1 inch = 2.4" 'extra stretch' - a boltroped mainsail that has a 26ft. luff length - AFTER being RAISED, needs to be 'stretched' by an additional 2.4 inches by the halyard. When designing a sail with a boltrope the sailmaker will cut a small amount off the boltrope (called 'pre-load) so that in maximum designed wind-ranges the sail's luff doesnt become stretched beyond the design limits; the boltrope is shortened so that the full dimensions will be 'stretched-to' by the wind pressure when the sail is in typically 15-18kts. maximum.
So, next time sailing - 'raise' the mainsail, THEN apply *additional stress* to the halyard so that you get at least 1" of additional 'stretch' for each 11 feet of mainsail luff length. You can put a 'mark' on the halyard vs. a 'mark' on the mast .... and see if this (you calculate based on YOUR luff length) additional stretch of the the luff doesnt 'correct' the shape of that first upper batten for you when you finally 'tension the mainsheet' (see ** below) when beating.
If you dont add this extra stretch, the sail will have too much draft, that draft will be too far aft, and the leech/battens will be slightly 'hooked up towards the windward side' --- slow boat, boat that heels aggressively, has WEATHER HELM.

Note **
BTW - the BEST for setting the 'exact' amount of halyard/boltrope tension is to go onto a hard beat with all tell-tales flying perfectly straight back (consult Don's Sail Trim Users Guide, etc.) .... and then *let go of the wheel* !!!! Then, if the boat's bow begins to head to windward, then INCREASE the tension in the mainsails halyard (boltrope/luff) until the boat goes STRAIGHT (NO weather helm and NO lee helm). After you by halyard tension find 'neutral helm', then 'ease off' the halyard tension by 1/2 to 1" ... and your boat will develop 'perfect helm' (very s-l-o-w-l-y turns to windward with very slight 'weather helm') and the boat will be automatically set for its **fastest possible speed with it best 'pointing angle'** for the conditions at that time. You should place a mark on the halyard and a mark on the mast directly in line with the halyard mark when you 'find' your desired 'helm pressure'. I use simple electrical tape - and this becomes your 'primary halyard tension mark' for basic halyard 'tension set-up'.

also BTW - 'most' mainsails are shaped/cut so that when beating and the traveller is on the centerline, ..... the SECOND from the top batten will be more or less parallel to the boats centerline - for maximum speed (in 'flat' water). In contrast, and perhaps erringly so, blindly setting the topmost batten to parallel the boom and without regard of how the topmost telltales are flying (should be flying straight back) may NOT be the correct 'twist' setting ... generally the faster the boat is going - the less amount of 'twist'; the slower the speed - the higher amount of twist; .... iceboats and very fast planing hulls need almost NO twist; but as always, the tell-tales will show how much or how little twist you 'actually' do need.
If you dont have a full set of tell tales ... then you'll never know good OR bad set/shape.

 

[tsmwebb]

....The angle of attack has no effect on twist. ...

If you choose to set your twist using your main sheet then you will also be changing the angle of attack at which point it is common to use the traveler to maintain the correct angle of attack. That is what I meant when I suggest you would use the main and the traveler. To be sure this is a little more complex than using the vang to adjust the twist. But, there can be advantages:

1) with end boom sheeting the main sheet is far more powerful than a typical vang. If you have a 4:1 end boom main sheet and an 8:1 vang set at 45 degrees about a quarter of the way down the boom the same pull on the main sheet will produce close to twice the moment around the gooseneck as the vang.

2) placing high loads on the leach (like those required for beating) with the vang makes large demands on the stiffness and strength of the boom. At 45 degrees about 70% of the force you put on the vang will be compression against the mast and goosneck. Also your boom becomes a cantilever and is likely to bend in the puffs allowing twist and your boom may buckle.

3) If you put on a lot of vang and backstay and then release the backstay before you release the vang you can destroy a sail.

While vang sheeting upwind is used, particularly in small boats when overpowered, it is more common to use the sheet and traveler as the primary mainsail controls for twist and angle of attack on all points of sail where the boom is over the traveler. Indeed, many multihulls and and even some very wide monohulls dispense with the vang entirely because they can install travelers that allow them to use just the sheet and traveler all points of sail. But, of course, people should experiment to see what works best for them. I suggest keeping #2 above in mind especially to weather in a breeze and, of course, telltails to help visualize the flow.

--Tom.

 

[Quoddy]

Solution?

Thanks for the suggestions and diagrams.

I think there might be something basic here right from the start. My top batten is full length and it curves in an almost equal radius curve from the luff to the leach. There is no straight part towards the leech and that's why I thought “parallel to the boom” meant the tip should be along the boom-mast sight line.

I looked at a picture I took and it appears that the draft is about 50% back at the top batten. This may account for the even radius curve of the top batten.

I assume the solution is to increase halyard tension substantially to move the draft forward? This would allow the aft portion of the batten to straighten as it should giving me a proper indicator of basic twist.

I have not focused on the second batten but I will note its position in my attempt to optimize performance.

 

[RichH]

The greater the halyard/luff tension the more you 'open' the leech (leech moves slightly to leeward) ... and that will characteristically reshape a full batten to become more nearly straight/flat near the leech; the exact same thing will happen if you radically bow the mast forward (if you have that ability)/ Beware of any leech shape (parallel to the 'horizon') that is 'rounded' or causing draft increase in the aft/leech sections of a sail ... that section should be relatively 'flat'.
OTOH - applying hard mainsheet tension a few boatlengths before you tack will allow the boat to 'power-pinch' up to windward by causing the aft end of all the battens and leech to 'hook up to windward' - a very good 'racing trim' tactic. Hooking up the leech to windward is the equivalent of an airplane 'putting down the flaps' - power shape for slower airstream speeds - the boat will slow down a bit but will be able to point like a banshee.

Batten shape - Try differing batten end compression on the top batten .... if you have that ability - usually a velcro 'tab' thats 'pushed in' to the batten end, etc. The more the compression, the more a 'tapered' batten will change shape - for 'powering-up' a sail; flat or less shaped battens for 'speed sailing' and sailing in extremely 'light' winds.