A 7 metre variant of SibLim

  • 03 Jan 2019 11:58
    Reply # 6981337 on 6010674

    Before I stow the part-built model away for the time being, here's what it looks like right way up:

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  • 02 Jan 2019 17:59
    Reply # 6980062 on 6978522
    Gary wrote:

    Now while I feel there is still some to learn about the final skinning of this vessel, it probably won't be learned other than at full scale. I am also mindful that David Tyler is a scarce resource (only one of him in the whole world apparently) and I would not want to think about him contemplating how many puzzle joints can dance on the head of a pin when he could be working on his new improved soft wingsail or answering the loads of other interesting queries that come his way.  

    I think I'm going to act on that, and lay the model aside pending further impetus to take it further. Building a hard chine plywood hull is not new technology, it's been done for years in many different ways which can be employed here, according to taste.
  • 02 Jan 2019 03:42
    Reply # 6979419 on 6010674

    Couple of things here - Without vast experience in plywood sheeting, the work done has gone Ok (working alone) by having a ledge to place/locate the sheet, then turn in one screw to fasten and prevent movement of that edge.Then the sheet is progressively bent over the frame/stringer structure, with more screws turned in to arrive at a fair panel.Slots and tabs with wedges would obviously aid the process

    As for preference of wood over alloy masts  -- when I was  not yet aware that an alloy of say 6061 with a T6 temper was up to the task , a grown spar was chosen and proved to have been a good choice, both in performance and price.

    Now I would probably buy the alloy tube and trust its integrity.

    Still, before forking out on such a thing, I would make a timber box section wooden mast with internal composites reinforcement (If I had the shop facilities to do so), or (if a tent was a make-do option) I would do epoxy infusion of long S glass inside  thin wall alloy tubes that have been TIG welded together, making up the required length.

    This way, the made-up composite wall (inside the alloy tube) can be made thicker near the partners, and can also have a taper where the wooden topmast piece is inserted.

    Last modified: 02 Jan 2019 04:01 | Anonymous member
  • 01 Jan 2019 06:44
    Reply # 6978522 on 6976845

    I did the rough fairing of the chine logs on Annie's Fánshì (as we must now learn to call her) using an electric plane. It took quite a while, and I made buckets and buckets of shavings. On the model, there's less physical work, but it's harder to work accurately. I'd like to get away from that, but retain the fairness of having solid timber there. So I went back to the Gougeon Bros and looked at their stringer-on-frame method. They put 1 1/2in x 3/4in stringers on edge, to get the maximum stiffness, and therefore fairness, using the least material. I think we can do that here:

    I have been thinking about this quite a bit. Chine logs are a bit of a pain to fair and poorly done can also lead to wobbly chines. I was thinking that something like the above only using ply, notched into the frame. Alternatively GB's stringer could also be readily notched to assist frame edge placement / stability. A stringer however is also stronger and easier than ply to get a fair result. And if its in the Gougeon brothers book its probably been tested a zillion times. Incidentally their book has been a free download for some time now:

    https://www.westsystem.com/the-gougeon-brothers-on-boat-construction/

    I agree with David on Topsides first, and I particularly liked his idea of "hangers" incorporated in the frames from which to hang them. that should ease their installation dramatically. Once hung they will sit patiently awaiting wire or cable ties or whatever. 

    I am curious about why Jeremy is happier with a timber mast than an alloy one. I _think_ I read recently that Michael Storer says the performance of a box section mast is better than a birdsmouth and lighter than alu. (hope I am not misquoting him). He does mostly do dinghies however. Then again C-Tech in In-Zud seem to be offering almost affordable rices for carbon: http://www.carbon-tube.com/index.php 

    Really don't know about butt joining the bottom a piece at a time. I would have thought that it would be easier to get a fair twist with a contiguous piece of ply, but if the butt joints landed on something substantial with a good deal of overlap its not going to be a big deal to do and the outside is glassed anyway so for sure there is more leeway. 

    On the topic of cleanup and clamping being required for puzzle and scarf joints then its hard to see it being terribly different amounts of work, and having just built all my kitchen worktops from 45mm wide hardboard planks I can attest to the prowess of the Makita BO6050J which will make cleaning up anything fairly trivial. So I am still inclined to use puzzle joints where applicable.

    Now while I feel there is still some to learn about the final skinning of this vessel, it probably won't be learned other than at full scale. I am also mindful that David Tyler is a scarce resource (only one of him in the whole world apparently) and I would not want to think about him contemplating how many puzzle joints can dance on the head of a pin when he could be working on his new improved soft wingsail or answering the loads of other interesting queries that come his way.  




  • 31 Dec 2018 20:21
    Reply # 6978217 on 6977744
    Anonymous 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 of2M would be about all I could manage, because of the door aperture, and Maybe there are others with similar restrictions, so a micro SIBLiiM 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.



  • 31 Dec 2018 13:35
    Reply # 6977744 on 6977460
    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.
  • 31 Dec 2018 04:21
    Reply # 6977460 on 6975958
    Anonymous wrote:

    All good points, Gary. High rotary moment of inertia is important, and that is a function of having a deep keel and high mast, which give good windward ability in good conditions - but then when the wind versus current chips are down, in a Strine southerly buster, or the Gulf Stream, or the Agulhas Current, or something more local like the Pentland Firth, Corryvreckan or Portland Bill on a bad day, then I'd rather be in a heavy shoal draught boat with a low, stout mast. Always compromises to be made, but I think we've got things about right for your usage.

    Currently, the draught is 0.58m at 2 tonnes displacement, with the 125mm deep steel plate ballast. I think I'd add another 0.1m for oceanic use, but not more, to avoid the "tripping up" scenario; and if it makes things more difficult for most of the cruising you want the boat to be able to do, trailing the boat to faraway places or poking into the upper reaches of eg Port Stephens or Port Hacking, then I'd stick with 0.58m. I think that's a wholesome compromise.


    Going back a few years when I had about 20 sheets of 9mm plywood and a 6x3m garage building space limit, the plan to build a small junk rigged boat took hold. So this 7M design is interesting and  characteristics along with dimensions mentioned above are relevant to design ideas still bouncing around in my head.

    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, so a few thoughts  related to the above quote might not go amiss.

    Having a short 'stout' mast is good for surviving a rolling (IMO) if shrouds are included, along with stepping firmly between key and partners. But then w/ward performance and handling ease is compromised. So a  very strong mast (especially in the lower half) is the suggested option.

    Usually(in this day and age) a carbon composite item is touted as the answer, but a hybrid is  most likely the more affordable option.

    Swapping an alloy flagpole for a grown spar is something I do not regret having done, which was a move that included shrouds set up lightly (rather than hard and taught).Since that time(opting for a grown spar), my composites experience has been considerably augmented, so a taller mast having a variably thick wall reinforcement strikes me as the way to go.


    Last modified: 31 Dec 2018 04:40 | Anonymous member
  • 30 Dec 2018 22:33
    Reply # 6977201 on 6976845
    David wrote:
    Len wrote: As an exercise in thought, I would be inclined to assemble the hull panels ahead of time and apply in one piece as giving the fairest curves unless I was doing two layers in which case the second layer could act as a butt block and I would install piece at a time.

    Fair curves are still possible with the panels added in pieces. But thin plywood doesn't lay in a fair curve over frames alone. There's nothing that identifies an amateur-built boat more than wobbly chines, and although it's easy enough to adjust them in a dinghy before filleting, it's harder in this size of boat.



    I'm sorry, I have been reading BBBB too much :) I think G Buelhler would probably not go less than 1/2inch for a dingy and a 7 metre boat he would use over 25mm (over an inch) thickness. So I was thinking two layers of 9 to 11 mm ply. I agree 9mm is about as thin as one can get and get fair curves. For this kind of build avoiding double layering is the right way to go. (and considering the abuse our almost 20year old hull with 9mm unsupported ply has gone through 9mm is probably fine)
  • 30 Dec 2018 20:21
    Reply # 6977088 on 6010674

    Another way to do the chines is to put a light stringer on edge about 50mm either side of the actual chine position. After the ply panels either side of the chine have been fitted, the chine edge is rounded over and several layers of fiberglass tape are applied along the exterior length of the chine.  After the hull is turned upright the valley between the two chine stringers receives a heavy layup of fiberglass. Thus the actual chine corner itself is mostly fiberglass. This is a way to create a chine without needing to use a heavy timber chine stringer. The frames or bulkheads need to be no more than about a meter apart in order to maintain a fair curve for the chine.

  • 30 Dec 2018 15:07
    Reply # 6976845 on 6976596
    Len wrote: As an exercise in thought, I would be inclined to assemble the hull panels ahead of time and apply in one piece as giving the fairest curves unless I was doing two layers in which case the second layer could act as a butt block and I would install piece at a time.

    Fair curves are still possible with the panels added in pieces. But thin plywood doesn't lay in a fair curve over frames alone. There's nothing that identifies an amateur-built boat more than wobbly chines, and although it's easy enough to adjust them in a dinghy before filleting, it's harder in this size of boat.

    Having read the G bros. epoxy guide, I might be inclined to use puzzle joints (also looking at the RM Yachts build) because they should be quicker and I suspect no weaker than scarphs. 

    Using them in practice might indicate to you that though they are quicker than scarphs because you don't have to cut them, you lose that in extra cleaning up time. Both scarphs and puzzle joints need great care to clamp them flat with a stiff strongback. I would use butt joints for adding the hull panels one sheet at a time.

    I feel that chine logs and sheer clamps should be thickened epoxy with tape covering both sides.  Anything else would go anti-purpose to the method of build followed so far as hand shaping would become needed. I think the chine joint should have the plywood panels leave a gap between each other of 6mm or so (I was about to say 1/4 inch :) ).

    I did the rough fairing of the chine logs on Annie's Fánshì (as we must now learn to call her) using an electric plane. It took quite a while, and I made buckets and buckets of shavings. On the model, there's less physical work, but it's harder to work accurately. I'd like to get away from that, but retain the fairness of having solid timber there. So I went back to the Gougeon Bros and looked at their stringer-on-frame method. They put 1 1/2in x 3/4in stringers on edge, to get the maximum stiffness, and therefore fairness, using the least material. I think we can do that here:


    putting fillets on either side to make up for the loss of the bonding area of a conventional chine log. There is only minimal checking for fairness to do, not major fairing in.

    This way the hull panels should just get their shape from the bulkheads and turn out fair without having to fit the edges.

    Not the case. See above.

    I would start with the bottom as you have done, but I am not sure if putting the sheer on next or the bilge would be better.

    It has to be topsides first, bilges second. I strongly suspect that the bilge panels are going to be difficult to do in one piece, because small inaccuracies in the setup are going to be magnified in the bow area due to the twist. Also, I have to work around the bilge board cases. I may end up getting more plywood and fairing the bottom and topsides flush with the bulkheads, so that the bilge panel sheets can be put on one sheet at a time, cut roughly, a little oversize, glued on and then trimmed. I think this would be safer. Butt joints would be easiest and also fairest.

    In either case the last one would have to be filleted from inside... perhaps if the bulkheads had tabs that fit through the panels so wedges could hold them on that would help. My other thought is that if the sheer panels are added first, it may be possible to do the turn over before adding the bilge panels. I am probably over thinking all this.

    I think you are. Conjecture only takes you so far, getting hands-on takes you further - that's why I'm making this model.


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