The "Sib-Lim" Challenge

  • 17 Apr 2015 23:31
    Reply # 3306397 on 3144241

    To lift even a half-tonne keel needs a serious amount of horsepower to be applied by the crew, and this is not to be the kind of boat in which motorised hydraulics are to be employed. "Less is more", remember. That's why I've stuck to unballasted boards, with a fairly neutral buoyancy when immersed. They are fairly easy to operate, which is going to be important. 

    so yes, lateral resistance can be obtained with lifting boards; even better, positive lift is obtained from cambered bilgeboards; but when it comes to safety in big seas, a different question, there isn't a substitute for getting the ballast low. How low? Well, that's on a sliding scale, taking into consideration the use that the boat is to be put to. Annie is going to sail around Hauraki Gulf and Northland. Though it can get windy, the seas are generally not huge, having the whole of North Island as a breakwater to the west, and smaller islands to the east. So while I would be content to see Annie fit a very shallow keel (more of a slab of metal, really) to keep the draught down close to 2ft, if anyone wanted to go offshore in my version of Sib-Lim, I'd want them to fit some deadwood between the hull and the same slab of metal, to increase the draught.

    Having got my tall narrow sail working on Tystie, and having found that it is much better to sheet the sail to the arch over the cockpit, rather than at the transom (no sheets sweeping over the cockpit, for instance), I'd rather like to see this sail, scaled down, on Sib-Lim. It could be sheeted to a small arch over the companionway, with the advantage that hauling on the sheets can be done vertically - a big advantage for a skipper with a limited amount of horsepower and avoirdupois.

     

    Last modified: 17 Apr 2015 23:43 | Anonymous member
  • 17 Apr 2015 02:37
    Reply # 3304549 on 3144241

    Regarding the Fairey Atlanta. I sailed alongside a number of them and almost bought one when I lived in the UK as a young man. Yes they are interesting boats and would answer many of Annie's requirements for a boat. 

    When sailing to New Zealand from the United States in 1999 there was a boat sailing in the same group that I got to know quite well. She was a Breton 33, while larger than Annie requires it had a number of interesting design elements.  Draft with all appendages up was just a little over the two feet Annie specifies. She had twin bilge keels, twin rudders and a ballasted drop keel (half a ton with hydraulic lift) that increased her draft to six feet. She sailed well and the owner was half way through his second circumnavigation on the boat. He usually sailed the boat with the drop keel up and rarely felt that he needed the added performance that it gave. She would dry out level and the bottom could be scraped without having to haul out. When coming into a new anchorage she often sailed right through the fleet and anchored between them and the shore. At Palmerston Atoll he actually entered the lagoon and anchored close in to the home island and the western reef. He was the only cruising boat of the thirty or so there that was capable of doing this.

       I have not looked for the design on the internet but it should be there somewhere.

  • 17 Apr 2015 01:33
    Reply # 3304518 on 3144241
    Well, Arne, you can see now why I need someone to design a boat for me! For some reason, I had completely forgotten that the Atalanta's plates were ballasted - I thought that it was largely internal.  I have to say that it seems rather a shame to put an inboard diesel engine in such a boat, but I can imagine you'd have fun and games hand starting an outboard on the stern.  Thanks for finding the drawings, Arne.  I Googled the design some time ago but didn't get your results. 

    David (another one!) - what a lucky man you are to have owned one of these vessels, although I have to admit that your description of sailing at 30 degrees heel, has somewhat moderated my enthusiasm for the design.  I have a friend who is (very slowly) rebuilding an Atalanta here in NZ.  She apparently sailed from England, which I can readily believe.  I keep telling him what a splendid candidate she is for junk rig.  He's a professional boatbuilder, so quite capable of making any necessary mods: of course, a split junk rig might solve that problem.  

    My Sib-Lim, if she ever gets built, may not be as spectacular a sailor, but (and I know this is completely the wrong attitude), she is designed first and foremost my home, and that is more important to me than performance.  As long as she gave me fun and satisfaction when I did go out sailing, I would be more than happy with her.

  • 16 Apr 2015 21:59
    Reply # 3304422 on 3144241

    re Atalanta Arne,

    I owned a 26ft Atalanta and single handed her regularly along the South Coast of England.  One sailed to Galapagos from UK.  Another previous owner was, if I recall, a sometime technical director for JRA. 

    They would sail very well in Force 7 to windward (for me a real safety feature) and I would usually outsail most modern cruisers (of even longer water length) in almost all conditions except a short chop, as the bow is quite blunt but therefore good in a big sea.  However they sailed in any wind above F4 leaning over at an angle of around 30 degrees as it was where the firm bilge which was almost a barge shape in the centre formed a good keel bottom with the two centre plates acting as balance. Downwind the flattish bottom gave a great surf ride and with the later changes to a deeper rudder (which mine had) some good safe fun sailing. 

    Mine still had the manual gear to lift up the plates - very efficient with a bit of work - and the Volvo MD1 (marine diesel 1) engine, as replacement for the original petrol ones that were fitted.

    it was an 'engineer's boat in that the hull was a very lightweight egg shape around a strong centre comprising of an angled bulkhead with the pivoting keels at the bottom end and the mast foot at the top.  The cooking and navigation space formed part of this at the still centre of the boat. The hulls, being hot-moulded ply are famous for being resistant to rot or other decay and there are stories of some being buried in mud and then simply washed clean.  The interior woodwork is not like that, so often needs more treatment.

    I would have kept her if I could have worked out how to put a junk rig on without redesigned the front end inside. So if you find one that needs some TLC and you can do some interior redesign, that would make a good project. 

    Being blurry-eyed at the happy memories!

    David





    Last modified: 16 Apr 2015 22:04 | Anonymous member
  • 16 Apr 2015 10:53
    Reply # 3303285 on 3144241
    Anonymous member (Administrator)

    Annie,

    I checked up Uffa Fox’s Fairey Atalanta 26.

    There are a couple of good reasons for their performance:

    ·         Long waterline and moderate beam and displacement makes for an easily driven hull, better than any of the Sib-Lim contenders (at the cost of live-aboard space). See here.

    ·         Flat bottom and all the ballast in the two very deep, retractable boards ensures both good working power to windward and sufficient ultimate stability. I understand the boards (each at 215kg) are now operated by (manual?) hydraulics.

    These two factors put the Atalanta in a different league than any of the Sib-Lims, but at the cost of complex construction  -  the Atalanta was produced by an aeroplane maker...

    Here is a list of data I found about it:

    Fully Equipped LOA 26ft (7.9m)
    LWL 25ft (7.6m)
    Beam 7ft 8in (2.34m)
    Draught:
    Boards raised 1ft 8in (0.5m)
    Boards lowered 5ft 9in (1.75m)
    Displacement 4000lb
    Ballast 950lb
    Sail area 270ft²
    Berths 5 (+2 cockpit berths)
    Engine 12hp Mitsubishi Vetus
    Designer Uffa Fox


    Arne

    Last modified: 16 Apr 2015 17:30 | Anonymous member (Administrator)
  • 16 Apr 2015 09:33
    Reply # 3303213 on 3302738
    Deleted user
    Annie Hill wrote:Lovely design, Chris.  The brown/orange sails are pretty nice, too.  A good second-best if I can't find purple ;-) Are you joining in the Challenge?

    Surely the bilge-boards provide the lateral resistance required?  And the beam of the hull keeps her on her feet?

    I'm still influenced in my thinking by the Atalanta, which apparently sailed perfectly well to windward and floated on a heavy due with the boards up.  An extra 8 inches of draught means that I am floating more like half the time than a third of the time.  Our tides are nothing like those in the UK, don't forget, David.

    I've been thinking about the outboard, Arne.  There is no weight difference between the Nissan 6hp and the Nissan 10hp.  Another argument in favour of the larger engine.  And I don't see that it would use a lot more fuel.  In theory, I don't like the idea of relying on my motor, but in practice I would use it if necessary.  Feeling sick with worry that something would go wrong! 

    It is true that more beam on the waterline in combination with properly shaped sections will increase initial stability while ultimate stability will be better if you have a narrower and deeper hull. Tink of a plank that you put in the water. It will be very stable floating with it's flat side down. Now try to turn it 90 degrees and make it balance. Impossibe, right? Now you put a weight on it and it will easily ballance standing up. Turn it upside down and it will right itself. Put it flat side down again and put the same weight under it and it will be slightly more  stable. Turn it upside down so that the weight is on top and it will stay that way quite happily. My point? While a broad shallow hull can be quite stable initially due to it's shape ultimate stability will be poor, but what's worse is that when turned upside down it will be quite stable that way too. A rule of thumb is to keep draft 50% of beam or 1/7 of the waterline length whichever is greatest if you plan on undertaking some serious offshore trips. As far as I understand you don't plan on doing anything like that? 


  • 16 Apr 2015 02:01
    Reply # 3302738 on 3144241
    Lovely design, Chris.  The brown/orange sails are pretty nice, too.  A good second-best if I can't find purple ;-) Are you joining in the Challenge?

    Surely the bilge-boards provide the lateral resistance required?  And the beam of the hull keeps her on her feet?

    I'm still influenced in my thinking by the Atalanta, which apparently sailed perfectly well to windward and floated on a heavy due with the boards up.  An extra 8 inches of draught means that I am floating more like half the time than a third of the time.  Our tides are nothing like those in the UK, don't forget, David.

    I've been thinking about the outboard, Arne.  There is no weight difference between the Nissan 6hp and the Nissan 10hp.  Another argument in favour of the larger engine.  And I don't see that it would use a lot more fuel.  In theory, I don't like the idea of relying on my motor, but in practice I would use it if necessary.  Feeling sick with worry that something would go wrong! 

  • 15 Apr 2015 20:39
    Reply # 3302441 on 3144241

    Arne,

    I'm right with you on this. I'm hoping to persuade Annie to increase the draught to 2ft 8in, for all the reasons that you give, and because there may be other builders for whom ability to survive a knockdown is important. I think Sib-Lim will sail at 2ft draught, but clearly, she would sail a whole lot better with greater draught. There's no need to go to 1m draught, though - my Sadler 25 was stiff and weatherly with, as far as I remember, a little less than this. And I could creep into all the gunkholes I needed to.

    Last modified: 15 Apr 2015 20:49 | Anonymous member
  • 15 Apr 2015 13:57
    Reply # 3299663 on 3144241
    Anonymous member (Administrator)

    Yes, Chris,

    I anyway expected that the shoal draught boats would have adequate "wings" in the water. My concern is rather how to produce enough righting moment to provide the required sailing power to windward, against strong winds and heavy seas.

    Your shown design looks interesting and Chinese, but how powerful would such a boat be to windward? Remember, most offshore junks were a lot bigger than this and big is beautiful when it comes to upwind performance.

    This has been well demonstrated my country: The Colin Archer sailing rescue boats (around 47’, 30tons) were legendary, and if you see them sailing on Youtube (search for RS14, Stavanger), you will see that they sail really well. However, being so popular, many made downscaled copies at around 30’ and even down to 25’, and these are no good at all, being way too tender.

    Therefore, small boats needs comparatively more ballast and bigger keels to work to windward. Annie’s Fantail is great in this respect, and so is my new  26’ IF (disp 2150kg, ballast 1250kg).

    Arne

    Last modified: 15 Apr 2015 14:17 | Anonymous member (Administrator)
  • 15 Apr 2015 11:17
    Reply # 3299403 on 3144241
    Deleted user

    Or take the Chinese approach and have lifting rudder and plate. I've even put in your favourite livery :)

    Last modified: 15 Apr 2015 11:18 | Deleted user
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