Sail Battens

Discussion in 'Sailboats' started by BobBill, Feb 12, 2014.

  1. BobBill
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    BobBill Senior Member

    Just read an item that suggested that battens are not necessary...generally.

    I know about supporting the roach etc, but, for some sailing, particularly tacking outriggers and proas and some cats, are battens really needed?

    And, for that matter why a long leech roach?
     
  2. gggGuest
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    gggGuest ...

    All else being equal a triangle is about the least efficient shape you can have for a sail, and battens are about the easiest way to make a sail with two straight spars less triangular.

    A triangular sail can be good enough to use though, depending on requirements.

    From there on we run into about a zillion dogmatic assertions and circular arguments...
     
  3. Skyak
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    Skyak Senior Member

    Battens also greatly reduce the tension needed to produce a flat leach. Without a flat leach a sail drags terribly.
     
  4. BobBill
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    BobBill Senior Member

    I see, gentlemen, so a flat sail, is less efficient. What if it is bent from a yard?

    The reason I ask is that I was just about to order a sail for an outrigger I am crafting, and at near a 1k $scoots, I ran across that article and wondered if the "standard" for the sail was a mistake.

    Not much on the "Net" re the topic...and near every boat I have sailed has had battened sails (for good reason) but just covering my stern.

    Standard sail for this boat carries 3 battens with a recommended 13-inch luff round and a 18" max leech roach...

    The sail is a semi-crab-claw typical on Malibu Outriggers, which I am crafting using cast-off Hobie Cat hulls (long tale). See diagram...the last is the planned outcome.

    Frankly, if I could do without battens, I would give it a go, but seems the imprudent route.
     

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  5. bruceb
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    bruceb Senior Member

    Rig?

    If you have hobie hulls, (which ones?) a complete hobie rig just seems to make sense- why change a good thing? ;)
    "Crab claw" rigs can work fine, but seem to take a lot of experience to get the bendy mast /yard correct. Battens will be the least of your problems.
    IMO, any boat that gets up to planing type speeds works better with long and or full battens, and they can make most rigs easier to manage. On a small boat, you can get by with lighter and stretchier sails if the battens help keep the leach under control.
    B
     
  6. Petros
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    Petros Senior Member

    battens greatly improve the sail performance because it helps hold the sail in a more efficient shape.

    Lots of sails do not use them, but these are not the most efficient designs. Consider that the fastest sail boats of all types have more and larger battens, and virtually every record breaking sail has fully batten supported sails from leach to luff.

    If your intent is to just drift around on lakes and near shore, you will not need them. If you want to go as fast as possible with the available sail and wind conditions, than they are essential.
     
  7. BobBill
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    BobBill Senior Member

    Bruce, Thanks. I have port 19 and s'bd 16, they were cast offs...I was going for Tornado hulls in Texas donated by generous Marc Upchurch here and could not find trailer but oddly a gent closer said I could have the hulls if I took his trailer...a no-brainer for me. Still, those Tornado hulls would have been perfect for a much larger than current rig and I still droll over them.

    If you have sailed a Malibu Outrigger, you would understand that they are not difficult to sail (hoist and roll), but they are difficult to sail into a surf with a head or tail wind, being geared to reaches.

    Moreover, the secondary problem was landing in a heavy surf, for which they were designed in the 50s.

    I might add that the MO was the original beach cat and sailed no less than by Hobie Alter, from which he popped out the 14 and 16 asymmetrics...

    Nevertheless, I do not believe any Hobie-cat could sustain that kind of surf pounding that the overbuilt and heavy MO was designed for...but then, those days are long gone in Malibu and Oahu, aren't they?

    Right now, for me, it is the sail, a strong mast step and finishing the carbon yard that have me acquiring, scheduling and drawing specs comparable to the orig prints, but current.

    This boat should be 50 lbs lighter and have very low CG etc, while not as beamy for trailering and set-up.

    Just looking for some hints from our experience crew who have given me major help in past with my last glass restoration dinghy sailboat project-to far (and too cold) from good water to be cruising...for now.


    Petros, ggg and Skyak, thanks also. You have convinced me to go with the battens, but I had a vague hunch that the semi crab might permit a beneficial deviation as upwind the MO sail is not quite the best. Still, that means I need all the help I can muster, and I do plan to add a jib set out on a short carbon sprit to improve pointing...
     
  8. messabout
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    messabout Senior Member

    I reckon I can start an argument here.....I do so by saying that a jib does not neccessarily make the boat point higher. In some cases the jib might help the boat tack more smartly.
     
  9. Petros
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    Petros Senior Member

    In most boats I have seen with properly designed jibs, if you sail on the main alone you can not point as high than with the jib in place. The jib alters the flow over the main to allow for a higher angle of attach before the sail stalls, and increases the total sail area. Again, all of the fastest sailboats have a high aspect ratio sloop rig with a large jib.

    A poorly configured jib will harm its pointing ability of course.

    The design of the crab claw is very interesting, and I suspect simple to handle, but I do not think it is as efficient or versatile as a modern sloop rig.
     
  10. BobBill
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    BobBill Senior Member

    Messabout and Petros, thanks. No argument from me.

    I am surrently planning to use a Hobie 18 or FJ (used to recycle) jib and have no clue, really, what the end results will be; however, I suspect positive over no jib, even with the semi-crab claw mainsail, if that is what it is called.

    My concern is that the jib sail will be so far forward...relatively speaking.

    Candidly, the idea did not originate with me. It came from an original (wood) Malibu Outrigger sailor. He added a small jib and apparently found it to help point his boat higher on a beat, which, I must assume, made the big sail more efficient on that point of sail.

    Keeping in mind the rig is unstayed, my thinking is it cannot hurt on a reach, where the semi-claw and the boat excels. It will be the last item on the list for topside play...

    I have a tall/narrow second sail plan that is more conventional, but harder to stack, bend/strike. Of course, I will have to see how the first works first...

    Besides, all this play can get a bit spendy, these experiments.

    Here are two pix for comparison, sans jib sails. Both sails are comparable in mainsail area at about 175 sq ft but could be a bit smaller; jibs about 35. No stubby with the high aspect rig...one tall carbon stick, which is planned to be substantial to point where forestay touches...madness, I know, but how else does a dodger like me find out?
     

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  11. gggGuest
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    gggGuest ...

    I don't think there's any particular evidence, from the serious racing classes, that a properly designed sloop rig points higher than a una rig or vice versa. Some of the fastest boats of all - Moths and A Class Cats - have no jib.

    My personal impression is that a sloop rig with a non overlapping jib is rather easier to get "in the groove" going fast upwind.

    A jib is also rather handy if you are having a bad day tacking. The trick is probably to have a self tacking jib put with "backing lines" fitted so you can back the jib if you need to go hove to or just get out of irons.

    There's certainly evidence for the main/jib interaction being beneficial in a well designed installation. If I understand Bethwaite correctly the mainsail makes the bottom of the jib more efficient and the jib makes the top of the mainsail more efficient!
     
  12. BobBill
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    BobBill Senior Member

    Now that is interesting information. ( I am not knowledgeable in aero dynamics etc.

    I have a small cat called a Kite (it's like a simple Finn) and the highest I seem to get it to point is say 50/60 degrees...I thought if I put a sprit on it (I would not-just thinking) and a jib, it would move say 10 points closer to the wind on a beat? I am more or less thinking in terms of what I have read on this site and some others.

    I appreciate the Bethwaite reference re the relationship between the sails...much appreciated, was not aware of that per se. Everything helps.

    That said, I do know from practical experience that the boat (Malibu Outrigger) is a flyer on a reach and in light pressure (though this is lighter and plastic), and the original Malibu Outrigger more less "sucks" on a beat...

    The semi crab sail is more of a reacher by design (Seaman) to handle surf and launches (I think), so I more or less figured I might try to spiff this version up with a jib (that would work with either sail). But, like I said, that is to be later, like next year...
     
  13. gggGuest
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    gggGuest ...

    How high a boat will point is a combination of a whole host of factors, not the least of which is the sheeting setup.
    If we exclude designs in which the sheeting position is fixed, and the actual amount you can pull the sails in is limited, then for almost every boat its possible, by really sheeting sails in close to the centreline, to sail closer to the wind than the actual optimum angle, but the closer you go then the slower you go and your actual progress to windward is less than if you are pointing a little lower.
    The optimum angle is controlled by all sorts of aerodynamic and hydrodynamic factors, but the guts of it is that slow but very efficient low drag craft point very high to best advantage, and faster and less efficient craft point lower.
    So if your cat won't point very high then maybe she's not very efficient aero and/or hydrodynamically - or else your sheeting/sail setting needs sorting out. Best option sis a good boat setter up going for a ride. Photos from directly behind when on a beat might help diagnose if there are any rig issues. Underwater, well if the hulls are reasonably well finished, the boards a nice aero shape and properly aligned then those are the main things. Well set up catamarans go upwind like crazy so the potential ought to be there.
     
  14. BobBill
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    BobBill Senior Member

    I certainly agree, but are not cat-boats limited (sorry, using "cat" above might have been ambiguous term, I meant cat-boat and like new and new sail) simply cannot point up as a sloop might...

    And at best, the Malibu Outrigger is similar to a cat-boat but with a semi-crab claw rig and not so good on a beat.

    With the Kite dinghy (think simple Finn, I will put up pic from other machine later) with the original sail, I might get to 70 degrees, as the sail is old and blown...but, when I sit a new sail on her, she points much higher, which I understand, but not as high as a sloop rig I daresay. No slot etc?

    If I understand, you are suggesting I not worry about pointing etc and do the sail(s) as I am inclined, while paying closer attention to leads (barber haulers) and sail shapes, etc, as well as not condemning my plan because it involves the semi-crab.

    On that note, the comparison between the tall standard rig and the claw will be interesting indeed, I get that far.

    Your wisdom already has me downsizing the main from 200 square feet to 150-175, sans jib - 35 sf. (Traveler, as it is, is end-boom and line is limited to practical length from a 13 or 14 inch beam of the hull.)

    No vang (being a semi-crab claw)

    This is very enlightening and I appreciate the input and heads-ups. Just wish it was not so cold and messy...hot to get back to the project.
     

  15. Petros
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    Petros Senior Member

    the action of the jib is to alter the flow, and pressure distribution on the main. there is unfortunately much wrong information about the so-called "slot" effect in sailing circles, aerodynamics is not always intuitive so improper conceptual ideas take hold. the Jib operates in the up-wash field of the main, and the main operates in the down-wash field of the jib.

    The main effect is when at high angles of attack with a single foil element (such as a main sail alone), the pressure gradient right behind the leading edge is very sharp and will result in flow separation (known as a stall). this reduces the amount of "bending" or accelerating the air on the low pressure side at the leading edge, and also affects the flow over the rest of the low pressure surface (the lee side). the more air you accelerate the more lift (or thrust in a sail) is generated. the effect of the jib is it reduces this harsh pressure gradient on the lee side of the leading edge, allowing a higher angle of attack with the apparent wind before the stall occurs, allow it to point higher.

    It actually does not make it more efficient, it increases the drag and the flow disturbance (turbulence) over the surface as compared to having no jib. But it does allow the flow to stay attached at higher angles, therefore providing more thrust (or lift) at higher angles of attack, allowing you to point higher and still make headway. The two surfaces overall accelerates more air without having the sharp pressure gradient at the leading edge of the main sail.

    This is also why the shape, position, size and curvature (controlled by the lead location and tension) is so important for both the jib and main, to optimize the flow conditions over both surfaces.

    For a home made configuration it is enough to know this and to built-in enough adjustments to allow you to trim both the main and jib shape and location relative to each other. It will take a considerable amount of trial and error to optimize all of the adjustments, so do not permanently place any of the leads or travelers until you have it all dialed in. Of course if optimum performance is not a high priority, than convenience might be more important than the last 1/4 knot of speed.
     
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