New (cambered) sail for Footprints

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  • 08 Jan 2013 22:02
    Reply # 1174608 on 829776
    Deleted user
    Thanks for that, Robert. It's great to see enthusiasm for cambered panel sails growing again - see the January Boat of the Month feature for confirmation of that. I'm looking forward to finally working up Paradox's cambered schooner rig when summer returns... From the little sailing we did last season it was easy to see the power in the rig whatever point we were on. 
  • 08 Jan 2013 21:09
    Reply # 1174553 on 829776
    During the recent Bay of Islands junket I had the pleasure of a short sail on Footprints. To say that I was impressed is an understatement - I was totally amazed! The whole boat was alive with power on and off the wind. She handled and tacked effortlessly - a real delight. To use the words of Graham Cox I am now addicted to cambered sails. For Pacific Spray we will be sticking with flat sails which are very appropriate for the style of boat but in the future a whole new world has just opened up. Thank you David for the sail and well done on your efforts to get the boat performing so well. My next move is to try and get myself invited onto Fantail for a sail and learn from another camber guru. 
  • 26 Nov 2012 20:32
    Reply # 1146301 on 829776
    Just looked at your photos David and I have to say you have done a very tidy job of it.
  • 26 Nov 2012 06:31
    Reply # 1145849 on 829776
    Deleted user

    Some 9 months after first starting the build of the new sail for Footprints the sail project is now officially complete apart from the usual ongoing tweaking. There has been blood, sweat, and even a few tears of despair but happily the new sail is now working as I hoped it eventually would, and the performance of Footprints has been dramatically improved. The final clincher was the forward raking of the mast which has put the centre of effort of the sail where it should be.

    I have posted some photos of details of the sail in my profile photo albums for those who might be interested. While there are some ideas of my own, the new sail has had input from many members of the JRA and especially David Tyler who has been so happy to share his knowledge and experience.

    [Webmaster edit: Note for new members - to view a member's photo album, click on his/her name to the left of this post, click Photos in the profile, then select the album.]

    Last modified: 26 Nov 2012 19:32 | Deleted user
  • 05 May 2012 07:07
    Reply # 912323 on 829776
    Deleted user

    David Tyler is really the person to answer this question. The top battens are not actually that vertical but I think the theory is that even if the panels are fairly vertical the curvature in the panel provides the camber effect for the sail. The sleeved batten is a very good way to build a sail. It may be a little bit of extra work while making the sail but once the sleeve has been made it is a very quick operation to insert the yard and just put a simple lashing top and bottom. rather than a track of some sort to insert the sail along the yard or the more traditional lashings. And the sleeve, as with the batten packets and boom sleeve already have cushioning and rubbing patches built in. The sleeve around the yard would I imagine provide more aerodynamic efficiency.

    Now that I have had several more weeks of sailing with the new sail on Footprints I am enjoying the advantages of this new sail over the old, heavy,flat sail. Footprints is proving to be much more responsive and enjoyable to sail. Last week I replaced the rope batten parrels with webbing and there is now noticeably less friction when raising or lowering the sail. The next job is to replace the remaining timber battens with carbon tube battens made for Footprints by David Tyler so this will result in another decrease in weight for the sail package.

    This cambered panel sail is very sensitive to the adjustment of various control lines to get just the right amount of tension on the upper luff hauling parrel so as to get rid of the creasing in the top panels but not induce a reverse crease in the lower panels. The tilting the sail forward for down wind work alters everything but it is really a matter of learning what the settings are for various sailing conditions.

    So overall I am very pleased with the way the new sail is working out. 

  • 03 May 2012 13:34
    Reply # 910640 on 829776

    Dear David,

    much enjoyed the article on your / Footprints new sails.   Footprints looks superb in the photo.  The sleeved yard looks very efficient, and is almost half the luff, so should make a difference,  will be interesting to know if you find any effect.

    One query.  The top two battens are very steeply inclined,  therefore the wind must be blowing across the batten and the cut-in of the sail.  Do you think this is significant? 

    Mark

  • 14 Apr 2012 08:26
    Reply # 889456 on 829776

    Paul, you wrote –“But when it comes to aerodynamics I bow to your superior knowledge.”

    I wouldn’t if I were you. Remember that this is home spun aerodynamics, so it’s every man for himself.

    You also wrote – “Thinking being that the sail deforms around the mast but your leading edge remains relatively undisturbed.

    This is a question I have been pondering for many years. I agree that turbulent flow may re-attach after skipping over the mast on the leeward side of the ‘foil, but there is also the windward side to consider. Here the bulky mast would be sticking out and slowing and disturbing the airflow a lot, and possibly acting like the lower half of a glider scissors type airbrake. If that is the case then, rather than improve the circular flow and hence the lift, it may simply increase the drag like a split flap set further forward than the usual position. I believe this is a case of ‘suck it and see’, and so far I have always found better ways to crack this particular Hazel nut. Having got a low stress rig with better performance that most and possibly any other junk rig I’ve sailed on I am reluctant to experiment with this idea, though I would love someone else to have a go. There could be some very interesting results.

    Cheers,  Slieve.

    Last modified: 14 Apr 2012 08:27 | Anonymous member
  • 14 Apr 2012 03:29
    Reply # 889400 on 889305
    Slieve McGalliard wrote: 

    Paul, I understand that camber forward makes a sail less critical to heading and easier to find the ‘grove’.


    Slieve, yes I understood that but I also understood that if you go too far forward the groove becomes vague and harder to find and stay in. But when it comes to aerodynamics I bow to your superior knowledge.
  • 14 Apr 2012 03:22
    Reply # 889398 on 829776
    Something that struck me while working on LC today. The mast is always in the way of getting the desired camber on one tack. Mostly everyone has tried to get it into the foremost part of the sail because of the bubble that develops on the leading edge and to do that we have kept the balance to minimum (mostly).

    But what if one were to put the point of maximum camber at or close to the position of the mast (the mast would then of cause be a lot further back than it is on most rigs)? Thinking being that the sail deforms around the mast but your leading edge remains relatively undisturbed. We know that the airflow will ignore sudden indentations and small irregularities so the flow could possibly just flow quite smoothly over the mast and not even really see it.

    The mast probably would not even  have to be at max camber, just far enough aft of the leading edge to get buried in the sail without totally destroying the leading edge shape.

    Sounds like heresy but am I on to something? What am I not seeing?
  • 13 Apr 2012 23:27
    Reply # 889305 on 829776

    I’m sure everyone knows by now that I believe 100% that the camber over the first third of the sail is critical, and that the run aft should be flat. With this conviction it should be obvious that whenever I look at a rig I look for camber forward and flat aft as a method assessing how well a rig will perform. If trying to draw a single cambered panel I would plan the maximum camber point to be around 35% and no further back that 37% chord.

     

    In sailing, as with life, it’s not what you put in; it’s what you get out. No matter where you plan your maximum camber position to be, you have to assess what you end up with under sailing conditions. By the time the parrels have pulled it this way, the halyard that way, gravity the other way and then the wind blows, what do you end up with? Looking at the various photos of Poppy I know I have not got what I wanted in the first place, and thought I had sewn into the sail.

     

    The problem with looking at photos is that they are just a snap-shot in time, and do not necessarily show the average situation, but sometimes they are all you have to go on. The boat of the month photo of Footprints is a case in point. Look at that snap-shot in time, and take a horizontal line about one third to one half way up the sail where the airflow should be somewhere around horizontal. Then try to draw the shape that the airflow will experience as it passes along the sail from luff to leech. As there seems to be is a crease running from the top of the luff of each panel to about 50% chord at the moment the photo was taken, then it would appear that this crease has removed the extra material over this most important (in my eyes) area of the sail and flattened the camber, pushing the maximum camber point further aft than planned. As Arne has pointed out this increases weather helm, and reduces the sailing performance.

     

    It could be that by swinging the rig forward to the more balanced position used for off wind sailing helps reduce these creases and returns the camber to the planned shape and improves the performance by reducing the weather helm. Please remember that these comments are really a stab in the dark, based on one photo. I think it is an attractive rig and am disappointed to hear that it is not giving the planned performance, yet. It is interesting and useful to see how things are working out with Footprints.

     

    It is easier for me drawing split rigs as I feel it is appropriate to put the centre of area of the sail in the same position used by the Bermudan rigs. I have no problem with masts distorting the forward part of the rig, and the higher balance rig does not try to distort the camber shape. To those who haven’t tried it, designing a rig always seems to produce a few problems that you haven’t planned for. For example at the moment I am trying to define the practical range of the ratio of panel height to panel length for a well cambered sail. PJR gives answers for flatish sails, which is no real help. There is still so much to learn.

     

    Paul, I understand that camber forward makes a sail less critical to heading and easier to find the ‘grove’.

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