A 7 metre variant of SibLim

  • 16 Dec 2018 13:34
    Reply # 6961700 on 6010674

    Arne,

    I'm using Freeship rather than Delftship, but that doesn't matter, both will give answers on stability.

    The answer to the question on the stability of both Annie's Siblim, and this 7m Siblim variant, is that both have good initial stability, because of the chine just above the waterline; they should both have good form stiffness under sail in light to moderate conditions. But ultimate stiffness is entirely in the hands of the builder/owner, and how much draught is decided upon. Put the ballast lower, in the form of a deeper fin keel, and you could get more ultimate stability for offshore sailing, obviously. Decide to go for minimum draught, for trailer-sailing, or frequent gunkholing, or drying out at the top of the creek, and you'll get less ultimate stability, again obviously. Decisions, decisions... but decisions that have to be made by the builder/owner, not by me.

    Don't forget, Arne, that both these boats were planned for specific owners with specific requirements. Annie: being a comfortable home for the next twenty years rates as high as, or higher than good sailing performance. Gary: sailing along the NSW coast and into the many shallow inlets there, and trailing down to Tasmania, put different constraints on the design. If someone were to approach me for a variant that was specifically for Norwegian fjord sailing, undoubtedly it wouldn't be the same thing at all, though it might superficially look the same.

    Last modified: 16 Dec 2018 13:54 | Anonymous member
  • 16 Dec 2018 10:32
    Reply # 6961617 on 6010674
    Anonymous member (Administrator)

    Scaling a boat design down.

    I know, in these days of CAD, it is very tempting to scale any design up or down from the original. It can be done with just a few clicks and keystrokes. However, with boats, one has to do this with care.
    The problem with linear scaling a boat is that the righting moment varies with the 4
    th power of the length while the healing moment from the rig only varies with the 3rd power (..sorry, don't know the English  mathematical term for this…)

    If a 7.9m boat is crimped in all direction to 7.0 m, the righting moment will drop to only 61% of the original,

    David, how do you compensate for this, or do you reckon the original SibLim to have such ample stability that the 7m version will be all right, just like that? Or can the DeltShip program calculate stability?

    In the sixties and seventies, a whole range of the Swedish Maxi-boats was developed. None of them was just a crimped or expanded version of a former design. The Maxi 68 (6.8m long) came after the Maxi 77, and it was proportionally beamier than the 77, probably to both preserve space and stability.

    Arne


    Last modified: 16 Dec 2018 10:34 | Anonymous member (Administrator)
  • 15 Dec 2018 13:56
    Reply # 6960833 on 6010674

    The second layer of the bottom and bow transom glued and clamped in place.

    Yesterday, I went into town and brought back some 21 x 9mm PSE fir for the chine logs. At full size, that would be 89 x 38mm, which is generous, but not too far OTT.
  • 14 Dec 2018 08:17
    Reply # 6959460 on 6010674

    Now hang on a minute, Annie, you've entirely misunderstood what's going on here.

    In fact, Gary and I went through the same process as I went through with you: I asked him for a design brief and his input on the methods and processes that he wanted to use and was familiar with. And then we worked up the design together, with me submitting drawings and Gary coming back with what he liked and what he didn't, and making an initial model using his local CNC firm so that we jointly understood how we could meet the design brief.

    Which was for a shoal draught bilgeboarder, junk rigged, of a certain size, to be built in a certain way, because Gary likes doing things that way and wanted to take on this project.

    And such a boat is not available on the market, either used or as a kit, or as a design for amateur build. As you yourself found.

    Yes, if anyone just wants a boat, and any boat will do, I would strongly advise them to go to the current buyer's market and find something that's near enough. But if anyone wants *this* boat, and no other will do, then here it is. It may suit others, and they're welcome to build it, if that's the case. Those whom it doesn't suit will need to look elsewhere.

    Let's go back to the early stages of your project. I distinctly said to you that I was going to provide the bare bones of the concept of the accommodation, expecting you to flesh it out and lay things out to suit you, and build to a standard and aesthetic that satisfied you. When we built the model together, we stopped at the stage where we had established that there was a blank canvas onto which you could create whatever it was was that you wanted to create, once you'd worked out what that was. Knowing that I couldn't possibly design an interior that would satisfy you because at that stage I couldn't possibly have read that in my crystal ball, seeing as how it's all developing organically as you've gone along. You haven't got the spatial awareness that develops in someone who has worked in a design field, so you couldn't possibly have done it in any other way than working it out as you went along. And so, it's turning out very well, and it's going to be the beautiful home for the next decades that you need it to be - but it couldn't possibly be anything other than an entirely idiosyncratic expression of your needs. Yes, you started out with a low level of woodworking skill, and now you have a much higher level of woodworking skill - that's the case with many people who fit out a  bare hull. It doesn't alter the fact that fitting out a bare hull takes an inordinate amount of time, whatever the level of skill - I know, I've done it. Just to take the example of Tystie, which is freshest in my mind, six weeks from first cutting wood to bare hull, with main bulkheads in, turned over - and then over a year to fit out and complete the boat. And that was mostly a professional build.

    The case is different for builders with a different set of skills and life experiences to draw upon. Different people want and need different things from their boats. But again, in the present case, I'm not dotting all the Is and crossing all the Ts. I'm leaving the galley detailing and the filling in of other areas to be worked out by the builder, and I'm saying nothing about the standard of finish and general aesthetic that is to be achieved. I'm dealing with the structural aspects only, and expecting - nay demanding - that a builder should take up the baton and run with it, making the project their own as you have done with yours.

    Size matters. In a boat of this size, 7m, there's very little scope for laying out the accommodation in a different way. Just make that small step up to the size of your boat, and more things become possible. So if I had a "client" wanting a CNC cut version of your boat, or larger, I'd go through the whole process again of establishing exactly what was wanted, and what constraints there would be.

    Just because you build quickly, from precut components, doesn't mean you're not getting a bespoke boat, just the way you'd dreamed it. You are.


    Last modified: 15 Dec 2018 10:11 | Anonymous member
  • 14 Dec 2018 06:22
    Reply # 6959380 on 6959023
    Annie wrote:

    To me, this 7 metre variant is very clever - a designer's dream.  But the builder is going to end up with the interior the designer has decided s/he wants.  In fact, there is absolutely no flexibility at all.  So why would you build it?  Why not go out and find an existing boat that is almost what you want and remodel it?  It would take little less time, be cheaper and, in the meantime, you could be sailing.

    And what is all this business about saving time?  You don't build a boat to save time, you build a boat because you want to and because the journey is a large part of the pleasure.  The concept is brilliant, no doubt about that, but it is a concept much more suited to a small factory producing several boats than one person building alone.

    Ya, that was my first thought, "how do I visualize the interior?" However, do please note that this can be done one off. That is, the cost of cutting is $x per minute no matter if it is one off or twenty. So it is still possible to customize the interior. The hull shape is pretty much set but the bulkhead position does not have to be every 100 cm (or whatever the designer specs). It is possible to shift a bulkhead for or aft by quite a bit to fit the interior rather than having to build the interior later around preset bulkheads. So rather than getting what the designer wants, you can actually get something closer to what you want with this method. Also a lot of the gluing can be done with more elbow space before the hull is formed.

    The problem I see is still having to decide before the first cut is made. I think maybe something in between where some of the major stuff can be prebuilt in. Then the interior can be finished after. I would give examples here but I don't have the experience of anything more than day and overnight where it is easy to make do. I am more interested in seeing the full size finished out and the time it takes.

    I think if I were to use this method of building I would have to set up some sheets of plywood and add chairs, benches, boxes and tables to help me figure out a layout before cutting. Because the cutting can be per sheet, it may be worth while to cut in smaller batches. Cut a few sheets of bulkheads that I know, set them up (right side up), put one over top if needed and try things out for space. Move things around. Even those bulkheads already cut could probably be moved a bit with minimum cutting or adding at that stage. Then the rest of the bulkheads and longitudinal bits could be cut and assembled... if you have space right side up (or maybe dry fit right way up) and the walk through continue and more interior things could be done at this stage.

    Perhaps the thing to do is start with a boat of similar size and "I want this size but set up this way". Really it just means knowing what _you_ want before you start building and I think that is the hard part.

    As for speed of build, building is fun, but being on the water is still what it is all about.

    Anyway, I am looking at a glass boat/hull for free (24 foot-ish by the picture) to change the rig on... so taking your advice ;)

  • 13 Dec 2018 22:35
    Reply # 6959023 on 6955021
    David Tyler wrote:

    Options

    Annie has been giving us an ongoing demonstration of just how long it takes to install the interior items into a hull - measure, make templates and patterns, cut, offer up, scribe, trim, add framing, resin coat and glue in. The method of building the interior first from CNC-cut interlocking pieces has to be much faster, and actually, building the hull is the quicker and easier part of building a boat, whether it's done before or after the interior, and whether it's being done by a first-time amateur or by a fully experienced professional. I'm now fully convinced that doing the hull skin afterwards is the quicker way to complete a plywood boat.


    Now hang on a minute: let's heave to and think about this.  I don't want to rain on anyone's parade but, quite honestly, you guys have just got so carried away with the cleverness of this way of assembling a boat that you have, literally, lost the plot.

    Yes, I am taking a long time to "install the interior items into a hull - measure, make templates and patterns, cut, offer up, scribe, trim, add framing, resin coat and glue in."  Even if, in fact, I make very few templates or patterns.  But ignoring for a while the fact that not only had I never built a boat before starting this project, I had hardly any woodworking experience or skills, may I remind you all of why I - and no doubt most people - would want to build my own boat in the first place.  To get what I want.  Not what someone else thinks I want, but what I actually want.

    Now, I've talked to heaps of people who have done extensive work on their boat, and what do you think the major modification they make is?  They alter the accommodation from what the designer decided they wanted to what suits them.  One of the reasons fitting out my version of SibLim has taken so long is because, in spite of long discussions with David around the subject, when I started fitting out the boat, I ended up ignoring a lot of what had been 'drawn' to substitute something that would suit me better, either because of aesthetics, being better at sea or being more comfortable in harbour.

    To me, this 7 metre variant is very clever - a designer's dream.  But the builder is going to end up with the interior the designer has decided s/he wants.  In fact, there is absolutely no flexibility at all.  So why would you build it?  Why not go out and find an existing boat that is almost what you want and remodel it?  It would take little less time, be cheaper and, in the meantime, you could be sailing.

    And what is all this business about saving time?  You don't build a boat to save time, you build a boat because you want to and because the journey is a large part of the pleasure.  The concept is brilliant, no doubt about that, but it is a concept much more suited to a small factory producing several boats than one person building alone.

    I couldn't conceive of handling the panels and gluing them on my own and, believe me, from harsh experience trying to get people to mix epoxy as it should be mixed is an uphill struggle.  I shouldn't want a couple of casual mates doing such an important job for a few beers and a barbie.

    I'm not knocking your conception, David, not for a microsecond, but I do think you and all your enthusiastic supporters have got distracted from one of the main reasons why you would build a boat in the first place, when second-hand ones that are almost good enough are being almost given away.

  • 13 Dec 2018 17:25
    Reply # 6958465 on 6010674

    Dry trial fit of the topsides.

    Starboard quarter, with a gap (though the port quarter is OK) - topsides could be a bit longer.

    Both topsides could be longer - a trimming allowance could be added, also a tab extending forwards with a hole for a spanish windlass to haul the two sides together.

  • 13 Dec 2018 15:36
    Reply # 6958255 on 6010674

    First layer of bottom hull panel and bow transom glued, wedged, cable tied, filleted and weighted in place.

    The aperture for the outboard motor.

    Bow transom filleted in place. The foredeck is not as wide as it should be - an error to be corrected on the drawing.

    Puzzle joint glued in situ. A lot of pressure and stiff strongbacks are needed.

    The tab and wedge in the centre of the bottom panel helps with initial positioning.

  • 13 Dec 2018 14:59
    Reply # 6958137 on 6957940
    Gary wrote:

    To me the idea of a CNC kit of parts is a somewhat different experience - one tries to get the CNC to do as much as possible in order to rule out misalignment or idiot mistakes. Any tabs dowels or whatever that speeds this process are fair game to me.

    Although I've managed to design out most of the chances of misalignment, there's still one: the bulkheads at stn 1 and stn 3 and the transom need to be truly aligned with no twist around the longitudinal axis, so centrelines should be marked and checked as being truly vertical and parallel with each other. The main chance of error is when making the join between deck stringers and berth fronts; it will help to wedge the transom in place dry, and check for verticality when gluing this join. A little bit of twist will make it a lot more difficult to fit the hull panels in one piece, and is an argument for fitting them in two or three pieces. I think I may have a little bit of twist, which has affected the fit of the topsides.

    Personally I would still be looking to assemble the bottom panels as single pieces I do not see a 7 metre strip of 9mm ply being too much of a physical problem to get roughly in situ, but juggling it into precisely the correct location could easily consume inordinate amounts of time.

    I've done a trial assembly of the topsides, and the tabs at the sheerline are working well to support the weight and induce curvature. I'm altering the tab and slot in the middle of the panel so that it acts as a hook to hang the panel on, but allows a little bit of rotation in case of errors in the setup.

    I do think David's upside down and inside out technique is a novel approach, one that I believe speeds things up.

    It certainly does.

    I do fancy taping inside things with gravity assist however so I think turning the hull before internal taping would be my preference if physically possible.

    Absolutely. Only sufficient initial filleting to keep the hull in shape without damage during turnover, while the hull is upside down, then completion of filleting and taping after turnover. If there are chine logs, the hull will have a lot more strength during that manoeuvre.


  • 13 Dec 2018 11:34
    Reply # 6957940 on 6956315

    BTW for more info about how Rm yachts put their plywood boats together this link is worth following.

    http://no-frills-sailing.com/at-rm-yachts-of-la-rochelle/

    Yes thanks for that - I have always been a big fan of Marc Lombard and RM whose smallest boats I have come across in some improbably remote parts.

    RM have developed their techniques over quite a long time but they are constructed using some slick tooling using skilled shipwrights. 

    To me the idea of a CNC kit of parts is a somewhat different experience - one tries to get the CNC to do as much as possible in order to rule out misalignment or idiot mistakes. Any tabs dowels or whatever that speeds this process are fair game to me.

    Personally I would still be looking to assemble the bottom panels as single pieces I do not see a 7 metre strip of 9mm ply being too much of a physical problem to get roughly in situ, but juggling it into precisely the correct location could easily consume inordinate amounts of time.

    Two things stick out though - I dont fancy sitting on a milk crate inside an upturned hull taping seams, and kevlar is amazing in tension but poor in compression. Ideally it should therefore be on the inside skin rather than outside. Obviously the construction method RM adopt does not allow for this.

    I do think David's upside down and inside out technique is a novel approach, one the I believe speeds things up. I do fancy taping inside things with gravity assist however so I think turning the hull before internal taping would be my preference if physically possible.


    Cheers

     


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