A 5.7m variant of SibLim

  • 04 Jan 2019 10:01
    Reply # 6982952 on 6979892

    This info about 2M beam gets me to spill a fair amount of design thought stuff/info on the subject, which I hope makes sense to those who might make the required effort to even make an attempt at following.

    Sure, a boat somewhat like Trekka, but with a Junk rig, would or could be a fair design compromise. However, research and deliberation has led me to a possible alternative, that might just be an answer to space restrictions in the building space as well as draught issues on a craft that is too small to carry a dinghy.

    Let us say 5M LOA rather than 5.7, even if only for the reason that this would fit with the length specified for the SETKA Transat challenge, although it does work better for me as far as building space goes.

    Still, the build method that I propose, could stretch length up to 5.7, because it is envisaged as modular construction design, based around bulkheads that join the modules where the mast step and lifting keel case come together.Making 3 modules.

    The largest module stretches between transom and bulkhead immediately forward of the mast, and is made of 2halves.Protruding into this(completed and joined module) , is the keel case,  sloping at roughly 45deg aft, beneath the mast step.

    Splitting the case` in a vertical line/join, is the mating bulkhead of the forward module.This alignment carries the keel down and stern wards below, or forward and upwards, to open(the case) through the foredeck.

    The keel is comprised of 1/4" steel plate bent into an elliptical section over a roughly 2"dia round bar, with a teardrop shaped box at the bottom, that is filled with molten lead,also filling up to at least 1/2M of the elliptical section as well.There is additional steel fabrication and a composites extension that needs to be explained, but not now.

    Slotting through the ballast plate in the SibLim type keel, this lifting keel has a suitably hardwearing contact area (around it's lower aperture). So, in the case of collision or when sat upon when drying out.

    In the fully  dropped position, the draught is slightly under 1M, and when lifted, is only slightly over0.5M, so that beaching and drying out is a possibility.

    As I find, when drawing and scaling  the SibLim lines down to 2M beam and 5M LOA, there is an approx 200sq ft  area of sail ; if rigged with a 5 panel Chinese lug main and a  quadrilateral unbattoned foresail like I had on JungJung.

    Standing headroom is allowable under a pram hood, over a companionway near amidships, with the galley  forward of this, which is centrally obstructed of course by the mast, making the obstruction of the keel case, hardly a problem.

    My design uses a single hoisting rudder, with a skeg, and below the cockpit is a holding tank, which can be pumped out through the transom.Making an OB motor option, pretty much limited to a torqueedo leg fixed to a bracket at the bow.

    I have the scribbled diagrams of all this, which I am looking at as  I write, which might explain it all better (if they were redrawn tidily and processed for repro and posting).

    Last modified: 04 Jan 2019 21:12 | Anonymous member
  • 02 Jan 2019 18:14
    Reply # 6980110 on 6980046
    Anonymous wrote:
    Len wrote:... while I can imagine only two, I would prefer not to think in terms of one. For a single person things are not so bad for short trips with a few nights camping aboard. Also, that is the size of my current boat which is big enough to get our camping gear to an island... but not to camp in. Yes it is nice to be able to keep it in a garage.

    John Guzzwell sailed Trekka around the world, singlehanded, in this size of boat!
    I'm soft...
  • 02 Jan 2019 17:48
    Reply # 6980046 on 6980034
    Len wrote:... while I can imagine only two, I would prefer not to think in terms of one. For a single person things are not so bad for short trips with a few nights camping aboard. Also, that is the size of my current boat which is big enough to get our camping gear to an island... but not to camp in. Yes it is nice to be able to keep it in a garage.

    John Guzzwell sailed Trekka around the world, singlehanded, in this size of boat!
  • 02 Jan 2019 17:28
    Reply # 6980034 on 6979892

    5.7 x 2 M? sounds a lot like the Birdwatcher (or one of it's shorter variations)... if BW form and layout are not what is wanted, there are still some ideas that might still be useful (2 M is not very wide). offsetting the mast and board trunk for example. I guess the square section helps too. With a square section the aisle does not have to be centre.

    In any case a 2M wide boat will almost have to be built around accommodation. And accommodation will have to be compromised to fit the hull too. so not only square section but wide (square) ends like the Trilo boats might be in order too.

    In other words a totally different boat or greatly reduced accommodation.

    Note: I am blinded by my own must fit 4 people that matches my situation. while I can imagine only two, I would prefer not to think in terms of one. For a single person things are not so bad for short trips with a few nights camping aboard. Also, that is the size of my current boat which is big enough to get our camping gear to an island... but not to camp in. Yes it is nice to be able to keep it in a garage.

  • 02 Jan 2019 16:00
    Message # 6979892
    Jeremy wrote:
    David T wrote:
    Jeremy wrote:

    Seven metres length and 2.5M beam is more than my garage space will allow, but I have just heard that David has a 6M design as well ...

    Well, that might be overstating it a bit. In response to a query about a size to fit within a 20ft shipping container, I had a quick look to see that it was feasible. I think it is, with  sizes of 5.7m LOA, 2.2m beam, 2.2m maximum depth. But that's as far as I've taken it, and would need a serious declaration of intent to build, and then a design brief (as with Annie and Gary) to take it any further.
    Thanks for that David. Although max beam and height dimensions of 2m would be about all I could manage, because of the door aperture, and Maybe there are others with similar restrictions, so a micro SibLiM thread could possibly be a way to get around to putting out ideas on this.
    Without moving toward thread drift, it might cover that last suggestion by admitting that the complexity of two drop boards and rudders are design features of SiBlim that I am grappling with. So, losing the 0.5M beam at the same time as inserting a single case for a lifting ballast keel is what underscores/mitigates the loss of beam proposal.
    So, would it be feasible, at 2m beam? Yes, with increased draught. If some form stability is lost by decreasing the beam, more stability must be added by putting the ballast lower, if we're talking about a seagoing boat. I think we're talking about the dimensions of Trekka, for example: LOA 20ft 6in, beam 6ft 6in, draught 4ft 6in; though as Trekka had very slack bilges and little form stability, she needed that draught, but Siblim, with more form stability, doesn't. Maybe 0.9 - 1.0m draught would be plenty.

    Trekka's keel: "The keel was a 3/8" steel plate with two big iron castings bolted to the bottom. It was fastened to the hull in such a manner that by undoing a few short bolts it could easily be removed should I want to store the hull in a garage or similar building during the winter months".

    That would answer, for a boat that's to be passed through a 2m square doorway or to be shipped in a 20ft container.

    When I sailed around Iceland in 2004, I met up with David Thomas, the designer, who was there to meet a guy who had built one of his designs. It was an extremely low budget racer, of plywood with a square cross-section like Sumner, and the keel was similar to Trekka's, in that it mated with a low, narrow closed-top case in the boat, with just a bolt or two to hold it in, and rubber washers to waterproof the bolts. That boat was built for the round Iceland race, and went like a rocket.

    With the narrower beam, too much internal volume is eaten up by bilgeboard cases or a lifting keel trunk. I think it has to be a single fixed keel, as above, or twin fixed keels if shoal draught is a necessity.


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

                                                              Site contents © the Junk Rig Association and/or individual authors

Powered by Wild Apricot Membership Software