Flapping mainsail on schooner rig

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  • 23 Dec 2014 00:59
    Reply # 3174653 on 3151671

    Many thanks for all the comments.  Very interesting that Samson's sails are fine, but Zebedee's and La Chica's flap. .I think the following were big factors in Zebedee.

    The sail's chord is 2 inches longer than the batten, so quite slack.

    The pocket stops 3 inches short of the luff, unlike the foresail where the pocket goes right to the luff

    The bolt rope is too tight causing slight puckering.

    In stronger winds the sail between the pocket and the luff seems to bag.

    I cut 2 inches off the luff and re stitched the bolt rope. The pocket now comes to the luff and the sail is reasonably taught (not very tight tho) along the batten. Last week I sailed against the wind in about 20-25 kts, 2 reefs in the main, none in the fore. (In lighter winds no reefs and no problems)

    Huge improvement in the stronger winds, less weather helm too. The luff still lifts very slightly, but the fore starts to lift just after, so it's as close to the wind as we can go.

    The fore sail still has the extra 2 inches of chord,but the pocket stops the bagging at the luff. 

    I think it's best to have the mainsail tight along the batten, just as described in Samson. It reduces the camber but maybe that's a good thing with the main.Having the pocket right up to the luff is also helpful.

  • 22 Dec 2014 10:10
    Reply # 3174176 on 3151671
    Anonymous member (Administrator)

    Hi Paul

    The new rudder for La Chica looks great. The introduction of balance area, alone makes it a good idea. I have struggled enough at the tiller of a 20ton Colin Archer, so know what I am talking about (.. I soon started to bring a 3-part handybilly to make steering easier...).

    A bit more about Samson’s mainsail, which works well close-hauled.
    I designed it with only 8% camber (in mind). The max camber point was drawn 40% aft of the luff (2,7m of a B=6.75m). Now, this sail was made by a sailmaker, so I don’t really know what he did, but the sail came out OK.

    I haven’t control-measured the actual camber of Samson’s sail, but experience from my own sails is that the camber designed with my “chain calculator” will only be right if one keeps the sail a bit slack along the battens. Photos of Samson indicate that the sails are well stretched along the battens, so the actual camber may have been limited to 7%. On the other hand, the sail is big and the cloth soft, so maybe it still reaches 8%.

    One thing, which has been discussed here and explained by Slieve, is the usefulness of some curve in the camber right at the luff. I must admit that my use of wooden spline for drawing the Round curve along the battens has not resulted in much curve close to the luff. This and the aft-set max camber point could be a reason why Samson’s mainsail points so well. I have also noted there is more bend in the curve of the actual camber at the luff than the one I make when cutting the Round of the barrel-shaped panels.

    I will therefore keep on my old practice with not torturing the spline that much when drawing the Round curve at the luff (sloop or foresails). On a mainsail, meant for a schooner, I would make very easy (almost straight) curves near the luff to avoid those lifting luffs of the mainsails, as seen on Zebedee and La Chica.



    Last modified: 22 Dec 2014 12:13 | Anonymous member (Administrator)
  • 22 Dec 2014 00:19
    Reply # 3174024 on 3156414
    Arne Kverneland wrote:


    in case the mainsail’s bagginess at the luff causes it to lift early, is the problem the same on both tacks? As can be seen on this photo of Samson, with the sail on the weather side of the mast, the bagginess is much restricted by the mast.

    How about the shape of the foresail’s camber near the leech? Is it nice and straight or is there some ‘hook’ in it? It is well known that blown out and baggy old staysails tend to make the mainsail lift early.

    I should like to hear Paul J T’s experience with the JR of his schooner-rigged La Chica on this matter.


    LC has similar problems to what Alan is reporting. The foresail (with 12% camber, max at 35%, entry angle 8%) sets perfectly and like Alan, I regard it as a real work horse. I do not think that it has to much camber.

    The main (with 10% camber, max at 35%, entry angle 8%) works just fine once the sheet is eased but when close-hauled and wind speed over F3-F4 I also experience the luff collapsing. For this sail the luff is 4 layers of mustang (starting at 200mm with last layer 50mm) Have to admit that I have not tried using a downhaul on the luff yet.

    I have considered flattening the sail but decided to wait until I've built my new ruder (that's done now, some photo's in my member album) as I did not want to change more than one major item at the time.

    I suspect that the foresail is interfering with the main. Sheeting the main harder may fix it but with the old rudder, that resulted in a great deal of weather helm. When I made the new rudder, which is also repositioned further aft and vertically so as to maximize efficiency and move the CLR as far aft as possible, things should be much improved.

    If that still does not get things right, I may have to flatten the main a bit but I'm reluctant to do that as LC is a heavy boat and needs all the power she can get. On the other hand... if the main is not able to work properly, then flattening it and being able to sheet it right in may be just what is needed.

  • 04 Dec 2014 03:18
    Reply # 3163764 on 3151671

    Hi Arne, I haven't actually measured the camber.  I'll give it a go soon. I didn't use a batten.  I used  frequent measurements from the straight edge and then drew a line joining them. It was very near curved so easy to cut.  It was a tight curve, no way a wooden batten could be flexed that much.  May be too much camber early on? I'm thinking of re-cutting the main. 

  • 25 Nov 2014 07:26
    Reply # 3157607 on 3151671
    Anonymous member (Administrator)

    another two questions:

    • Have you actually measured the camber with the sail flying, like this (remember to subtract the batten thickness)? 
    • When you lofted the batten panels and created the Round (barrel shape) along the battens, did you use a wooden spline to create that curve?

    I ask the last question because that is how I do it. This use of that wooden spline results in a fairly straight curve of the Round at the luff. Still, it appears that there is more curve in the finished sail. In other words, I see little reason for torturing the spline  into a sharper curve at the luff to get the sail camber right.

  • 25 Nov 2014 03:31
    Reply # 3157532 on 3151671

    Zebedee sails better on the port tack, with the sail pressed against the mast. The fluttering is less apparent. I'm just doing a little maintenance on a mooring, but I should do a sail in a couple of weeks time. I'll look very carefully at the leach of the fore sail. I think it's OK, but to be fair, I hadn't thought of that, so I didn't look carefully. Using the Arne method means it's quite easy to reduce the camber, or reduce the curvature near the luff, while keeping the max camber at the 35% point. The other thing I have is pieces of wool pushed through the sail at the aft third point. These show the wind is flowing fine at this point, even when the sail is fluttering.  Unfortunately the camber means I can't see the lea side piece of wool.

  • 23 Nov 2014 09:17
    Reply # 3156414 on 3151671
    Anonymous member (Administrator)


    in case the mainsail’s bagginess at the luff causes it to lift early, is the problem the same on both tacks? As can be seen on this photo of Samson, with the sail on the weather side of the mast, the bagginess is much restricted by the mast.

    How about the shape of the foresail’s camber near the leech? Is it nice and straight or is there some ‘hook’ in it? It is well known that blown out and baggy old staysails tend to make the mainsail lift early.

    I should like to hear Paul J T’s experience with the JR of his schooner-rigged La Chica on this matter.



  • 23 Nov 2014 00:22
    Reply # 3156291 on 3151671

    Many thanks for all your comments. the 500 NM was from Norfolk Island to New Zealand. I'll look very carefully at the leach of the foresail as well as the main bolt rope. I have tell tales on the sails and they fly while the main is lifting.. I feel that the airflow at the luff is wrong at the higher windspeeds,.  Interesting that the Bermudan also allow a small amount of lift. On Zebedee as the wind increases the flapping is far more than acceptable. A mini batten would be interesting. The fore sail  is cut the same as the main and sets perfectly,Could the main need a different cut? I have alot of camber right by the luff. Maybe this is good for the fore, but the main needs a more gradual increase of camber?

  • 16 Nov 2014 03:48
    Reply # 3152127 on 3151811
    Deleted user
    Alan B Martienssen wrote:

    Hi Arne,many thanks for the your reply. The problem has always been there. The main is now 6% camber. I have fitted a downhaul and it did help a little. But as the wind increases, the flapping becomes worse, extending including the forward third of the sail. I seem to sail faster and closer without the mainsail!

    Gday Alan

    Can't say I've seen the same phenomenon on our Badger. We've just completed 400Nm of wind on the nose, tacking back and forth for 2 weeks, but only F2 to F3, we managed around 30 Nm/day made good, which I thought was quite acceptable. (Boats going the other direction, downwind, were with sails furled and motoring! They probably subscribe to the rule; under 3 kts switch on the power..)  I find using the main is quicker to windward than without, in lighter winds anyway, better balance helps pointing closer to the wind too. Also I found with schooners, the main is supposed to be sheeted in closer than the foresail (an argument for less camber in the main too), but some slight flapping only occurs when luffing. We use a Raymarine Tiller Pilot now, which does a sterling job of holding the course with weather helm.

    Our foresail has 7.5% camber, the main 6%. Maybe the foresail would be better off with 10% but that would mean more distortion with the lazy jacks digging into it, so I wonder if it really would help much.

    On the final day into here, Gove NT, we had a dream run, hard on the wind, 4.5 to 5.2 knots most the way. Only spoilt by some big bermudan who raced past us as if we were standing still. A 45 footer, holding at least 6.5 knots on the same 45˚ off apparent wind. Amazing what an extra 12' of WL and one less mast gets you..

    Last modified: 16 Nov 2014 03:49 | Deleted user
  • 15 Nov 2014 22:45
    Reply # 3152048 on 3151671
    Anonymous member (Administrator)

    Ok, Alan,
    if I get it right, the area just aft of the luff of your mainsail is just distorted by the airflow. As long as the cloth there is not repeatedly flogging back and forth, that will at least not wear out the sail. I have crewed a lot in Bermuda-rigged sloops (as late as yesterday, actually), and it is quite usual to sail with some distortion in the mainsail close to the luff, when close-hauled. I am no expert on sail trimming, but I read somewhere that this distortion is not so detrimental; it was more important to watch the leech telltales to avoid oversheeting and stalling the sail.

    Could it be that the foresail has a bit hooked leech in its camber? Hooked leech on jibs is reckoned to be no good and encourages the slot airflow to blow into the mainsail.


    PS: BTW, where did those last 500NM sailing take place?

    PPS, A sudden afterthought: Could it be an idea to test-fit a short (20-40cm) Bermuda style batten at the luff of one or two batten panels, midway between the JR battens? Maybe they could tame the luff.


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