Generic "Fantail" sail planform drawing

  • 13 Jul 2014 19:13
    Reply # 3044523 on 1060993

    It will be a few more months before I'm reunited with my boat, but I can at least do some planning. I took Davids generic fantail plan and made a model of it in Rhinoceros, and tried scaling it to my planned 3 masted rig. It sure looks pretty, compared with the parallel batten plan I had before.

    Several questions come to mind: is there any reason this planform would not work out on a multimasted rig? Also, my foremast will be canted forward about 15 degrees - would it still work with that much angle? Lastly, if I were to change the aspect ratio by scaling it a bit on the horizontal axis would that be a bad idea?

    Having never sailed a junk rig before I expect a rather steep learning curve when I first set sail. I'm thinking I could make my mainsail out of the real stuff, that's the most straightforward. Perhaps I should make my foresail/mizzen out of cheap polytarp, just to be sure the sailplan works before making permanent ones?

  • 06 Jan 2014 22:31
    Reply # 1469009 on 1060993
    Thanks Paul, I appreciate that wringing loads could be severe if the drift is too small, I just wasn't sure if 900mm was insufficient having seen the rather tight halyard arrangements on some JR boats where the maximum sail area has been squeezed into a limited LAP.  Johanna and Peregrine come to mind.

    And thanks Oscar, your JR calculator is a wonderful resource, especially for a blundering non-mathmatician like me. I can now play around with all the variables and come up with reliable data instead of my usual vague guesswork.

    Last modified: 06 Jan 2014 22:36 | Anonymous member
  • 06 Jan 2014 21:34
    Reply # 1468959 on 1060993
    As a result of briefly discussing the mast LAP of a Fantail rig with David I came to the conclusion that you should be able to safely use 1.497 instead of 1.562, which would give a 9 m LAP for a 36 sqm sail (check out my JR calc for quick calculations). However there are certain advantages to using a longer mast as it allows you make adjustment to sail height, plus you can add more sail area next time you sew sails if you deem it necessary. Added to that the issue Paul mentions about the load between halyard blocks and masthead.
  • 06 Jan 2014 18:48
    Reply # 1468775 on 1468719
    Jerry Stebbing wrote:Is it acceptable to reduce the recommended 1.562 LAP a tad to allow the use of a somewhat shorter mast?
    The thing that you need to bear in mind is the drift between the masthead halyard block and the one on the yard. The less drift there is, the greater the wringing load on the mast/masthead. This load is significant because a large moment is involved (the distance between the masthead and the partners. Think how a screw driver multiplies force to enable you to drive a screw in). So it depends on how robust your mast is, since you are thinking of a steel mast, you can likely get away with it but do be aware of the issue.
  • 06 Jan 2014 17:17
    Reply # 1468719 on 1060993
    Is it acceptable to reduce the recommended 1.562 LAP a tad to allow the use of a somewhat shorter mast?

    The dimensions I calculated for my proposed 36sq metre sail using the generic 'Fantail' sailplan seem to suggest I could get away with an LAP of 8 metres (allowing me to use a relatively low cost standard 10 metre steel conical tube from Fabrikat) and still have 900mm drift between masthead and yard sling point, and 750mm clearance between partners and boom. Using the 1.562 factor however suggests an LAP of 9.3 metres requiring a considerably longer mast with its greater windage, weight and cost.

    I could go with David's suggestion of drawing a bigger sail and then dispensing with the bottom panel to make an even lower aspect ratio planform. This would reduce the required mast height but I'd much prefer to have a simply rigged sail like Annie's that doesn't need shifting fore and aft to balance, and that places limits on how low the A/R can go.

    Are there disadvantages in reducing the LAP I haven't foreseen or does it just mean having to accept the yard being a bit closer to the masthead and a smaller gap between coachroof and boom?

    Also when calculating my sail's dimensions I noticed the 0.0013 offset shown at the top of the luff didn't look right. Using 0.013 gave a better result so I guess an extra zero might have crept in by accident.


  • 25 Nov 2013 19:51
    Reply # 1446019 on 1060993
    Deleted user

    Thanks David, very helpful


  • 25 Nov 2013 01:07
    Reply # 1445300 on 1060993
    The primary reason for the luff round on the Fantail sail is so that even though the battens are fanned, they can still be of the same length with a more-or-less straight leech, which is much to be desired for ease of sheeting. A secondary benefit is that a luff hauling parrel is further away from the mast and thus more effective (in fact, looking from the cockpit, it appears that the luff hauling parrel is actually pulling the luff into a straight line). The round cannot be straightened out with luff tension, Ash, even if I were to try to do so, which I don't. I don't use batten downhauls, or even a fixed tack downhaul, since I move the sail across the mast for downwind sailing. 
  • 24 Nov 2013 23:26
    Reply # 1445255 on 1060993
    Deleted user

    I have recently made 0.5m2 models of the Fantail rig and also of Arne's rig in order to see batten stagger and other considerations at 'work'.

    I understand that the rounded luff on the Fantail planform  as designed  by David is in order to stabilise the sail horizontally, and oppose sheeting loads etc, but whilst I can see that 'round' being pushed aft by luff tension on a full sail assisted by a  tackline - but what will be the effect once reefed, will it need downhauls at each reefed panel?  With a slack luff tension would diagonal creases be caused by that round in the luff? David can you explain its function please?

    Both models look very business-like, and when laid over each other only differ in a slight dimensions and batten angles - to me they are so similar, I'm surprised how different they seem when apart.

    I have almost read my new copy of PJR so will soon be able to ask really 'intelligent' questions ... "all the gear - no idea!"



  • 30 Dec 2012 21:43
    Reply # 1168988 on 1168971
    Paul Thompson wrote:
    Gary Pick wrote:Could someone explain the the significance of David's factor of 1.562 please?
    My sail is about 30.32 sq metres and if I use that factor I get a LAP of 8.6 which means my mast is nearly a metre short!
    My sail is the same design as Arne's.
    Gary, it's just a factor used to calculate the LAP length for a "Fantail" type sail of certain proportions. You do not need to be concerned, it has no bearing on your sail. The fact that you have a shorter mast, just means that should you ever want to put a "Fantail" type sail on your boat, it would have to be a lower aspect ratio sail than the one under discussion.

    Paul you must have got in just before I deleted the post. I realised I was doing a mild panic. Thanks for the reply anyway.:)
  • 30 Dec 2012 21:21
    Reply # 1168980 on 1168901
    Robert Prince wrote:I have Gary's sailplan which is 32.5 sqm, good looking sail. I have checked the diagonals as per PJR and it will reef and furl perfectly. The problem is that the distances between battens on the leach are all different and will give rise to sheeting issues. Given my experience with Pacific Spray in this regard I want the sheeting to work out from day one. 

    Well by the time you are ready to commit to a sail, all issues should have been worked out with the "Fantail" type sail (it's not quite there yet). For now, an "HM" type sail made using the info that Arne has so freely made available is the one that would "just work". As for Gary's sail, I have not seen it but your concerns are valid.
       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
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