Alberg 30 Conversion Viability

  • 20 May 2020 06:13
    Reply # 8980919 on 8975930

    Don't mean to hijack from the Alberg 30 discussion, but since Slieve has drawn one of his split junk rigs onto a Contessa 26, that immediately gains my interest.

    What would the advantages of the split junk rig be for me on my Contessa over the classic Haslar McLeod rig I have now (see attached).  I'd be reluctant to give up the 25 foot of sail area, but does the extra performance to windward of the split junk offset that?  What about downwind?  Could even more sail area be added on the split junk Contessa drawn by Slieve?    

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    Last modified: 20 May 2020 06:18 | Anonymous member
  • 20 May 2020 00:21
    Reply # 8980532 on 8975930
    Anonymous member (Administrator)

    Ryan, apart from the mast's relationship to interior accommodation and deck structures, the other reason why it might be desirable in some cases to prefer the mast further aft is to do with distribution of weight. The rate and extent of pitching can be affected by a mast which is too heavy and too far forward on a boat without enough buoyancy in the forward sections to accommodate it. As Arne has pointed out, this should not be an issue in your boat. 

    I will chime in here on the question of balance. It has sometimes been a controversial subject but in my view it need not be.

    The balance referred to is aerodynamic balance, that is, the ratio of the area of that part of the sail ahead of the mast centreline, to the total area of the sail. In a split sail, the area calculation includes the area of the slot. A convenient estimate which is good enough in practice is to simply look at the ratio in which the mast divides one of the lower battens.

    There is a limit to the balance which can be given to a junk sail, and this limit depends on whether it is split or contiguous, and also on the shape (eg yard angle) of a contiguous sail. The significance of too much balance in the split rig is that the sail might not weather-cock or automatically depower when the sheets are released. In the contiguous rigs, I am told that the mast will interfere too much with the shape of the sail if the balance is too great, but if a better explanation is required it would be best if the designers of the various contemporary rigs were to each explain where the balance limits of their respective rigs lie, and why. Also, these matters have been discussed in other forum threads in the past.

    The split sails are invariably given the highest balance (indeed there would be little point in the split if the balance were very low.) A by-product of balance is that it determines where the mast needs to be placed. Split rigs such as SJR and the aerojunk rigs lead to the mast being placed further aft than the contiguous rigs, as you will have seen already from this discussion. Each of the rigs has its own set of advantages and disadvantages and each has its following.

    Sometimes a junk rig conversion leaves the owner with little choice about where the mast should be placed, because of internal accommodation arrangements or (less usually) concern about weight distribution. Arne has already explained that this latter concern should not be a problem in your case. More likely the things for you to consider will be internal accommodation arrangements and/or deck structures which may be inconvenient in relation to the new mast position. By reverse reasoning, if there are restrictions on where you can place the mast, then this business of balance could determine the type of rig you will choose.

    If you are free of any restrictions as to where the mast can go, then you can move on to the interesting question of which rig is “best” and this is where the various afficianados will disagree. For coastal cruising you can be assured that all the contemporary rigs are good, each in their own way. Fortunately for us, each of the people who have most been credited with the development of these cotemporary rigs has been extremely helpful in giving advice on their particular developments, so whichever rig you choose you will most likely be given the all help you will need – an enormous advantage of being a member of the Junk Rig Association.

    The implications of aerodynamic balance (the question which you have raised), is probably not of huge importance provided you are within the range of balance which suits the rig in question. A sail which is large (relative to the boat) and wide, will be mostly out to one side when running down wind. If the balance is low, then this “all out to one side” characteristic will be even greater. If the boat does not steer well, this could be a problem, though there are various remedies. Also more force will be needed on the sheet, to pull the sail in and out. So one might reason that a sail with high balance (like SJR) might be more suitable, or a sail which is tall and narrow. At the end of the day, however, these are not rules or imperatives, not necessarily a serious problem, and there are other considerations. Hull shape, rudder etc are far more important co-factors. The rig sometimes needs to suit the boat, but you have a hull which should answer very nicely to whatever rig you choose. I sailed recently on a Contessa 26 which has a hull, I would say, slightly finer than yours but very similar in many respects. (It was Pango. see front cover of recent JR magazine.) Quite similar to Arne’s Ingeborg. We carried a big, wide, heavily cambered, low aspect ratio sail with not a lot of balance – and yet  the boat handled beautifully on all points of sail. I do not think you should get too hung up on the handling characteristics of the various rigs, as your boat will handle beautifully anyway, as long as you follow sound advice relating to your rig of choice.

    My rig of choice for my little boat is the Amiina-style SJR (for none of the reasons discussed above), with the top panel unsplit, and I am very happy with it. It has a balance of 33% as it was designed to have, and it is not a race boat. That figure suits the split junk rig as a coastal cruising boat, as has been demonstrated so many times now that it can be regarded as beyond any need for further discussion. David, who has accumulated a wide and deep experience as an ocean mariner (and as a sail maker) has speculated that this figure might be a little on the high side for an ocean cruising boat, and the response to your invitation to David to explain why that might be so, will be of some interest to all of us. Pete Hill has extensively voyaged successfully with a split rig (aerojunk) which suggests that David is perhaps being a little conservative, but that is the result of his own hard-earned experience as a pioneer. For those of us who are less experienced and less fitted to be pioneers, David has quite properly pointed out that to date, no major ocean voyaging has been done with a SJR.

    David has also hinted at some inherent weakness in the SJR though none has been reported so far by anyone who has actually owned one. The jibs do not have any particular tendency to “flutter or flog” (mine don’t anyway). They don’t need battens and I would not put battens on mine. There is, however, no arguing with David’s insistence that a sail for ocean cruising should be stoutly and soundly built to withstand heavy-duty and continuous use.

    In my humble opinion you are in the fortunate position of having a boat which will respond well to whatever rig you place in it, and you can simply follow your heart, and be concerned mainly with what changes you are willing to make to your internal accommodation and deck structures. You mentioned sail area, and if that is desirable for you, then the Johanna style seems to give significantly greater sail area for a given  length of mast, than the other contemporary rigs. Good luck. Lovely boat.

    Edit: Slieve's post popped up while this was being written. Slieve, great to see you back in the forum and keeping a watchful eye. (And to see that lovely avatar - the Poppy sail being the most beautiful of all the junk sail forms, to my eye.) Yes, in that rough diagram I made the sail areas perhaps too small - and also placed the rigs a bit too low, not enough deck clearance. Sorry about that. It was just a quick stab to see roughly where the mast placements would be.

    PS If we are lucky we might soon see some details of a boat in Whangarei which has recently been fitted with a SJR with a balance of 30 percent (or less?). I believe interior accommodation was a factor in the choice. Word of mouth reports so far are favourable. This will add more to the body of practical experience which has been documented so far.

    Last modified: 20 May 2020 08:38 | Anonymous member (Administrator)
  • 19 May 2020 23:42
    Reply # 8980476 on 8975930

    Hi Guys, Yes I am about and Yes, this is an interesting thread.

    The Alberg would appear to be a typical design from the '60s heavily based on the iconic Folkboat. In those days of pencil drawings and slide rule calculations many designers simply took the basic FB and added their personal attachments, and normally above the water line. The successful Contessa 26 was a FB with a couple of extra planks raising the sheerline and improving the accommodation. Jeremy Rogers then made it a Contessa 32 by adding a beautiful transom behind the rudder stock, and adventurously cutting away part of the keel to make the fin and skeg, and producing the 'yardstick' boat for seaworthiness. The Halberg Rassy 29 lines diagram is virtually identical to the Contessa 32, but simply shortened at the back end. The Alberg 30 appears to be in the same vane as Arne pointed out and should be an excellent boat to convert to JR.

    Now the reason I've mentioned all this is to compare it with the Contessa 26 simply because in the last few days I have just cut and pasted (with scissors and sellotape) an Amiina rig onto a Contessa 26 drawing with an area of 305 sq.ft. The drawings by Graeme are interesting but as he says, the areas are only guesstimates and I feel that by being small give a distorted view.

    In the attached you will see that the rig and mast is about the same height as the Bermudan original, probably because the original has a big overlap with the masthead No.1 Genoa, and the lower rig that was used on many FD copied designs.If you scale the drawing and superimpose it on the Alberg you should find great similarity.

    Needless to say, I think a SJR would be fine, and as Arne mentioned could easily be reinforced for the type of sailing intended. I would stick to the 33% balance as the biggest balance produces the lowest stresses on the rig, and even for the area required I would lean towards the 5 panel Amiina set up with no split in the top panel. Having experimented with short jib battens, I wouldn't bother with the extra complication as every reinforcement often just moves the stresses to another point. Kiss.

    On Poppy I nearly always dropped 2 panels for the first reef and the rig seemed to be very tolerant to sail area, and for stooging about would use only 3, so am convinced that the 5 panel rig would be fine. It makes for a simpler rig to build and maintain.

    Enough from me as it's bed time.

    Cheers, Slieve.

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    Last modified: 19 May 2020 23:55 | Anonymous member
  • 19 May 2020 21:48
    Reply # 8980238 on 8975930
    Anonymous member (Administrator)

    Ryan

    It would not surprise me at all if you when closehauled perform evenly with an original Alberg, and when reaching and running you will be a good deal faster.  However, it depends: As you know, a good crew (with new sails) are much faster to windward than a cruising crew, so you may be overtaken to windward by the best ones. You also have to make the sail with camber in it; I would say 8%. A flat sail will just disappoint you.

    If you can make a mast which is not heavier than 3% of the vessel (122kg), or better 2.5% (102kg), the mast will not add any problems in a seaway. In addition to that weight comes the yard and battens, but these will be gradually lowered as you reef.
    On this page there is a good deal info on how to actually make the sail.
    Finally, here is a little report from a short race between a Nordic Folkboat and my IF with a JR.

    Cheers,
    Arne


    Last modified: 19 May 2020 21:50 | Anonymous member (Administrator)
  • 19 May 2020 21:15
    Reply # 8980154 on 8975930

    Thank you everyone for the invaluable support and ideas.

    David, when you suggest conservatism on balance which balance are you talking about exactly and what are the implications of too much.

    How significant is the benefit of having the weight of the mast more aft in the case of the SJR?


    Arne, I love your plans especially the higher AR one. That would bring my sail area up by 12%. I wonder if it would outperform the stock rig on all points.


    My plan before I started looking into the JR was to add a code zero sail on a short sprit pole to improve light air performance. I hope to at least meet this level of light air performance on average. Here is a clip of such a configuration https://m.youtube.com/watch?v=zXdS0ufiu1I&feature=youtu.be&t=39m10s 


  • 19 May 2020 11:35
    Reply # 8978871 on 8975930
    Anonymous member (Administrator)

    A Johanna-style sail

    Now I had a go to see if a Johanna-style sail could be fitted. With the mast at the aft end of the fore-deck (for easy installation), it seems that a batten length of 5.20m is best. The sail can of course be made taller or shorter than the shown one.

    Arne

    Edit:
    On the version below, I have shortened the battens and increased the AR. This gives a nice long leading edge for upwind work, and a slim sail for easy steering downwind. The drawback is that the mast will collide slightly with the end of the trunk cabin, so some glassing will be needed at the partners. At least the hatch is not destroyed, so I think it makes sense.



    Last modified: 19 May 2020 14:23 | Anonymous member (Administrator)
  • 19 May 2020 09:22
    Reply # 8978725 on 8978709
    Anonymous wrote:


    ... By rough measurement on the computer screen, the one on the left (the "Poppy") shape, has a aerodynamic balance of about 29% and the mast seems to go through about the front of the hatch....
    the middle one (the "Amiina" shape has a balance of about 33%.

    Yes, that looks practical and seamanlike to me. Poppy being only a little larger than the Alberg 30, the planform, number of battens, etc, are in the right ballpark.
  • 19 May 2020 09:16
    Reply # 8978724 on 8975930
    Anonymous member (Administrator)

    Mast position

    The choice of JR version depends quite much on where the mast is to sit. The mast position is often dictated by deck layout and interior. A forward set mast will lead to sails with less balance and longer chord to achieve the right position of the CE. Moving the mast further aft will favour a sail with more balance in it and/or a sail with a shorter chord. A SJR is fine in that respect. A sail of about 45sqm (487sq ft) should do well.

    Nowadays, after I have learned to make masts weighing no more than 2.5 – 3% of the boat, I am less afraid of moving the mast forward, and this has resulted in making sails with low balance (12-17%), which lets me have a 70° yard to maximise the luff length.

    If a SJR is chosen, I would take a closer look at Poppy’s original 7-panel rig. This has two un-split top panels, which are as strong as any for heavy weather. I think this version suits better for offshore cruising than the 5-panel version meant for racing in Edward Hooper’s  Amiina. I would not worry too much about the jiblets. They can be beefed up with tablings at the leech, and anyway, the integrity of the whole rig does not depend on the jiblets: They can all be blown to shreds, and the rig will still be operational. Better with broken jiblets than broken battens .

    I hope Slieve will join in here and explain the details about the SJR.

    Conclusion. Find a place for the mast first and then make a sail, which suits that mast position.

    Arne


    Last modified: 01 Feb 2021 23:38 | Anonymous member (Administrator)
  • 19 May 2020 08:56
    Reply # 8978715 on 8978709
    Graeme wrote:.... and a Weaverbird wingsail rig as referred to by David ...

    No, I wasn't proposing a wing sail, just the planform of the first JR sail that I made, either with hinged battens or with cambered panels, or preferably a little of both.
  • 19 May 2020 08:45
    Reply # 8978709 on 8975930
    Anonymous member (Administrator)

    Just for comparison of mast positions, here are a couple of approximate "fits" for SJR rigs. They are approximate only and sail area was just a guess. They will, however, give you a good rough idea of where the mast would probably go with SJR.

    I took a vertical line through the geometric centre of the lower sail panels, and fitted it over the "Centre of Effort" which is shown in the bermudan sail plan. This has been shown in the past to give a satisfactory result for SJR.


    From this you can say with reasonable confidence that a normal SJR rig will put your mast just a little forward of the original mast position, somewhere within the area of the forward hatch.

    (You can click on the image for an enlargement. By rough measurement on the computer screen, the one on the left (the "Poppy") shape, has a aerodynamic balance of about 29% and the mast seems to go through about the front of the hatch.The middle one (the "Amiina" shape has a balance of about 33% and the mast seems to go through about the middle of the hatch. If you were to follow David's advice and opt for 25% balance, your mast will probably come through the front edge of the hatch or the front of the cabin top or thereabouts.)

    As you can probably guess, a Johanna-style rig as referred to by Arne, and a Weaverbird wingsail rig as referred to by David, with their lower balance, would be expected to put mast position forward of the cabin trunk and into the fore deck.

    A lovely classic hull shape, if I may say so.

    the middle one (the "Amiina" shape has a balance of about 33%.
    Last modified: 19 May 2020 09:03 | Anonymous member (Administrator)
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