SJR H28

  • 21 Jun 2018 01:27
    Reply # 6328118 on 6316327
    Deleted user

    How did you find the upwind performance on Fantail? I ask mainly because I live at Herald Island, which is even further up the Auckland harbour than most people have to travel. Especially with the prevailing easterlies it can be a menace even with a bermudan rig. 

    I notice that SibLim has a more regular HM style sail. Was that a design consideration or personal preference?

  • 20 Jun 2018 22:46
    Reply # 6327588 on 6316327

    I got around the problem of the mast landing in the middle of my pillows by raking the mast forward 6 degrees.  The only drawback of that was when going up the mast, one tended to swing around the front of it.  But going up the mast is not my favourite occupation a the best of times.  If you look in my profile, you will see several photos of 'Fantail', the Raven 26 I'm talking about.

  • 20 Jun 2018 19:42
    Reply # 6326570 on 6316327
    Deleted user

    Thank you David. This weekend I am sawing the forward cabin, but next weekend I would love to come for a sail!

  • 20 Jun 2018 10:33
    Reply # 6324574 on 6316327

    Hard work trying to work out what type of rig is suitable and where to put it. I am going through the same process with the new boat I have just started building.

    But I think at this stage it would be beneficial for you to come and have a look at a working junk rig, and talk through the practicalities of the different rig types, a good and bad points of each type. So, as already discussed and when you get some time available you are very welcome to come out on 'Footprints' and I can share some of my experience with you. As well as what type of junk rig, and where to place the rig, there are other issues such as mast material, batten material, and sources of these in NZ.

    For sure you will find a solution for your H28. My own feeling knowing a bit about the H28 yachts is that the generic fan shape sail might be a good option, and has proven so successful on the Raven 26 'Fantail'. Or possibly the shape developed by Arne. These sails are quite simple to achieve, and would probably suit the performance characteristics of the H28. The aero-junk may provide improved windward performance but will be more complex to build, and will require a taller mast. Also an option is the hinged batten sail type currently used by David Tyler on 'Weaverbird'.

    Lot's of good ideas to play with on these miserable winter evenings!


    Last modified: 20 Jun 2018 10:34 | Anonymous member
  • 20 Jun 2018 09:12
    Reply # 6324506 on 6316327
    Deleted user

    Oh dear, my pictures are squashed...

  • 20 Jun 2018 09:09
    Reply # 6324505 on 6316327
    Deleted user

    I have spent the last few nights drawing up some really simple sail plans for an aerojunk rig.


    The problem I am having is that no matter how I adjust the aerojunk’s dimensions and balance. the mast position moves around right in the space where I cannot have it. That is, it is right in the space where I need to put my bed.


    In the pictures below this is the area designated by the arrows. The mast must be outside the arrowed area.


    Even a moderate aspect HM rig slaps the mast square in the ‘zone’.


    I was sad until I had an idea. The working sail area CA of the H28 seems to be stopping me putting the new mast in a decent place, but the H28 can be rigged with a 135% genoa. I drew and calculated the CA of the new genoa and moved the total CE back by the difference. Putting the Aerojunk with its CA in this new position allows the mast to be fitted just outside the no go zone.


    My inexperience means that I cannot tell whether this is a clever idea or a stupid idea.


  • 19 Jun 2018 00:46
    Reply # 6319902 on 6316327
    Deleted user

    You guys are great, thank you!


    I will make some accurate sail plans this evening and post pictures.


  • 18 Jun 2018 23:50
    Reply # 6319809 on 6316327
    Anonymous member (Administrator)

    Actually there is no such thing as “centre of effort” or “centre of lateral resistance”. Both are theoretical points which, in the real world, move about as sail shape and hydrodynamic conditions change.

    If you have a reasonably accurate drawing of your hull profile and sail plan, you can find the position of two points, which are: the geometric centres of area of the sail plan and of the underwater profile. (Including or not including the rudder??) They are not centres of effort and lateral resistance – if they were, you would simply balance them. They are merely a guide which can be used together with past experience, and knowledge of the type of hull and the type of rig. With a boat like the H28 whose characteristics are well known – if you are designing a rig of a well known type – then someone with experience could fairly confidently use these guides and tell you where the mast should go.  Even matters such as the amount of camber in the sail can be taken into account. 

    If you were pioneering on your own and had no other option, working through the Hasler-McLeod PJR book is what you would have to do, and it is a good exercise anyway. In that case I would certainly also study Arne’s guide to junk rig design, which is on this website.

    However my suggestion is, after that, narrow your sail preference down to a couple of planforms and then consult with people who have experience, preferably designed or specialised in each of those planforms. I have suggested at least two different types, because eventually it will lead to the decision of where the mast will go – and that might or might not be the deciding factor for you, you might need a choice. There are well-known experts on this forum (and I think they really are experts) who have been very generous in the past in giving this advice.

    I am not one of these people, but I can see where you are at. Unfortunately there don’t seem to have been any other H28 conversions in NZ, for you to copy. (I am sure there will be in the future as there are plenty of these H28s around now, of an age begging for conversion.) So you are pioneering to some extent, but not by much as there is plenty known about this hull type. I would study the on-line forum discussions which preceded the final choice of rig for the already-mentioned Francis H.

    A couple of points to consider: If you go for a so-called “conventional” planform you may have the luxury of fine-tuning after the rig is complete. This has been hinted at by David. It is possible to alter the mast rake, at least from vertical to anything up to 6 or 7 degrees forward. If you do a drawing you will find this shifts the centre of area of the sail considerably, so it would make sense to plan for a moderate forward rake, with a view to altering the rake fore or aft a little if necessary. The other luxury you will have, I believe, is the ability to sling the sail a little fore or aft in relation to the mast, in order to get the helm that you like.

    With split rigs (at least SJR and I presume aerojunk) you are pretty much restricted to a vertical mast, and no ability to alter the position of the sail on the mast. So if you get it wrong, you will have to alter the mast position – or alter the underwater hull profile (not impossible, by the way, commencing with the rudder, but that is not going to be necessary in your case.) Also, Arne has pointed out situations where, if all else fails, a small jigger sail can compensate for lee helm – but again, I do not imagine for one moment this will be necessary in your case. Don’t try to do it on your own, consult with someone who has experience with that rig and that type of hull and can confidently advise you. Put a proposed drawing up on the forum and invite comments.

    With some trepidation (because I don’t have any accurate drawings of hull profile or sail plan) I have opted for SJR – and the structural work I am doing, for the new mast position, is going to allow for a possible small shift in mast position if it proves to be necessary.

    I am keeping my fingers crossed, and here is the good news for SJR: based on a remark once made by Slieve (who pioneered this rig), it seems that with SJR a reasonably good rule of thumb is to simply make sure the centre of area of the proposed SJR sail is about in the same position as the original Bermudan sail plan centre of area. In that case, together with the slightly more forgiving full keel profile and your decent sized rudder, you should be OK and don’t need to be chasing your tail worrying about percentage lead etc. If you do that, (just use the existing position for centre of sail area), and do the drawings, as I have done, you will find that your mast will be forward of where it is now – but not as far forward as it would be with, say, one of Arne’s sail plans, together with Arne's advice as to where the centre of his sail area should be positioned on your hull. (I found that a very heavy forward rake of mast on a Arne rig will actually leave the two mast positions fairly close). Depending on your internal layout you will then be able to choose what suits you best. And from there on, you will be able to work on your drawings and discuss with people who have experience in designing your particular rig. (And in my opinion it is no big deal to shift a hatch if that is where the mast needs to go. Also with the fore-body of your H28 you will not have a problem getting "sufficient bury")

    First: go sailing on a proven successful junk, and have a good discussion with David Th.

    PS I forgot to add: when fitting your preferred junk rig into your existing accommodation, it may help to know that the mast does not necessarily have to be positioned on the centre line - for the little bit of difference it might make, that is little more than just a cultural preference (a point Annie has well made in the past). It is more important to have a convenient space below, especially up forward, and not unusual for junk masts to be offset a little. Another one of the advantages of a free-standing rig. Annie: that takes it up to 54?

    Last modified: 19 Jun 2018 04:56 | Anonymous member (Administrator)
  • 18 Jun 2018 20:51
    Reply # 6319399 on 6319214
    Daniel Powell Conti wrote:

    Okay thank you. 

    I was drawing up sail plans last night using the Aerojunk guide in the latest JRA magazine. My problem arose when I was attempting to understand lead. But wherever I looked I got conflicting information. Even the Aerojunk instructions (which say CE aft of CLR) seem to conflict with the instructions for a cambered rig (which say CE fore of CLR). At least that is my interpretation of their instructions.


    What I was trying to understand is, as my H28's lead seems to be around 11%, if I were to rig an Aerojunk, would the lead necessarily remain the same regardless of the sail aspect ratio?

    There will be more knowledgeable people than me with answers for this. My reading of the Aero-junk notes is that he is saying the CE should always be ahead of the CLR. With a low aspect sail you need more lead because there is a lot of sail low down and further aft trying to force the bow of the vessel up into the wind. With a high aspect rig there is less of this force. The New Zealand H28 has a fairly low aspect rig so that the lead is 11% would be about right, and that would probably work for a lower aspect junk sail. If you go for a higher aspect rig then you would probably need less lead. I imagine with the long keel and good amount of buoyancy forward the H28 might be a fairly forgiving hull for the fitting of a junk rig, but they do have comparatively small rudders especially in fore and aft measurement so if the center of effort of your rig is too far aft you might have steering difficulties. Unfortunately there is a certain amount of experimentation involved in fitting a junk rig, but at least with a more conventional junk sail we do have the ability to alter the position of the sail on the mast. 
  • 18 Jun 2018 19:40
    Reply # 6319214 on 6316327
    Deleted user

    Okay thank you. 

    I was drawing up sail plans last night using the Aerojunk guide in the latest JRA magazine. My problem arose when I was attempting to understand lead. But wherever I looked I got conflicting information. Even the Aerojunk instructions (which say CE aft of CLR) seem to conflict with the instructions for a cambered rig (which say CE fore of CLR). At least that is my interpretation of their instructions.


    What I was trying to understand is, as my H28's lead seems to be around 11%, if I were to rig an Aerojunk, would the lead necessarily remain the same regardless of the sail aspect ratio?

       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
                                                               - the Chinese Water Rat

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