A 7 metre variant of SibLim

  • 13 Dec 2018 08:29
    Reply # 6957862 on 6956315
    David wrote:

    I have joined plywood panels with scarf joints, and also two layers of double bias tape on the inside to take the place of a conventional butt block, (butt plate?), and butt blocks. In fitting the hull panels of my new catamaran I have been using butt plates which are notched and glued into the stringers and chine log prior to fitting the panels. It has been very quick and easy for my small 6 meter boat and this has been the way I have done all the topside panels, fitting one panel at a time. I am thinking though that for the bottom panels I will put the joins in a different location than in the top panels, and rather than using the plywood butt plates i will use two layers of wide double bias cloth on the inside, if I can get a clean even join in the ply panels as I install them, and I can hopefully leave the taping of the inside of the joints until I have turned the hulls upright.

    So in the case of the 7m SibLim, if I were building I would be happy to go with butt blocks, or fiberglass taped joins on the plywood panels. Making scarf joints in plywood does require care and a level of woodworking expertise, and unless they are done well I do not think they would be as strong as a joint using butt blocks. 

    Regarding the length of panels which can be successfully glued in one operation; I am finding that in our New Zealand summer temperatures, and using slow hardener, it is a bit of a challenge to get a 2.4 metre long panel glued up and fastened, and cleaned up before the glue starts going off. I am doing this single handed so with a second person mixing the glue while the first person was applying the glue, things might go a little better. But having said that I am building the catamaran in a site where it gets full sun, next time I will choose a location in the shade. It is not all bad though, with the glue curing so fast I can move onto the next process very quickly.

    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/

    David,
    Thanks for the link, I hadn't found that one. What I see is:
    • They build their internal structure on a permanent jig, which will give good accuracy but is not sensible for a one-off build.
    • I see some very large puzzle joints in the bulkheads.
    • The parts are laser cut, not with a rotating bit.
    • I see no sign of tabs and through slots, but some grooves to locate edges, and possibly some holes for dowels.
    • 20mm radius colloidal silica fillets to join everything on both sides.
    • Between three days and a week, depending on size, to fabricate a hull (!!!)
    • Then they lift the hull off the jig and support it on oil drums while all the fillets and biax taping are finished on the inside.
    • Thank goodness I don't need a massive galvanised frame to support the keel and shroud loadings.
    • They leave quite a gap between hull panels, fill it and then round it off and glass over with biax tape on the outside. When the hull is turned over, they finish the join with more filleting and biax tape.
    • Hull panels are scarphed, not puzzle jointed.
    • I think there's glass sheathing inside and out as standard, kevlar as an option outside.
    • Foam-cored GRP deck.
    I can see why your Eco 6 needs both chine logs and stringers, as the ply is thin. I don't think I need the stringer, which reduces the amount of gluing.

    I think there are two options for me: either framing on the bulkheads and a filleted and taped join between hull panels, with the whole panels added as one piece; or a chine log at the upper chine and fillet and tape at the lower chine, in which case butt-joined single sheets are feasible. I think I'm going to need the chine log, as there are some inaccessible areas where it's too difficult to fillet and tape inside. I think I need the topsides to be added as one piece, or I'd also need a sheer clamp, but possibly the edges of the bottom and topsides can be faired in line with the bulkheads and then individual sheets of the middle panels can be cut oversize at the upper and lower edges, butt joined and trimmed after gluing on to those bevelled edges.

    Anyway, I'll press on and add the bottom and bow transom, as there is no doubt what I've to do there. At full size, the bottom can be 12mm, butt joined at substantial floors just forward of stn 3 and just aft of stn 6. Then two layers of 6mm form the forefoot and bow transom (with possibly a third layer of 6mm overall, though I'm not sure that's necessary, as the deadwood and ballast will do a great deal to stiffen the bottom).



  • 13 Dec 2018 07:41
    Reply # 6957857 on 6955396
    Len wrote:

    I am also assuming that the hull is more than one sheet thick? As you have stated, the hull is one of the quicker parts to build and so using two layers rather than one thicker layer makes sense so long as the base layer is thick enough not to have flat spots in a curve. Thinner means lighter and easier to lift and place. The second layer would be cut when placing rather than CNC-cut.


    Len,

    most of the hull is 9mm, so that it is not really feasible in two thin layers unless there is a great deal of extra support inside to keep them fair, and hardly justified anyway. I plan to do the bottom and bow transom in two or three layers, as this is the backbone of the boat, in place o of the laminated keel in other designs.

  • 12 Dec 2018 22:17
    Reply # 6957454 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/

    From that link, this is an interesting plywood join:


  • 12 Dec 2018 05:05
    Reply # 6956315 on 6955021
    David Tyler wrote:

    Options

    A And in the specific case of these after joins on the SibLim 7, puzzle joints and scarphs don't seem to offer any advantages, and, hidden as they are inside lockers, butt blocks would be the quicker and easier way to go with no disadvantages.

    Any comments?

    I have joined plywood panels with scarf joints, and also two layers of double bias tape on the inside to take the place of a conventional butt block, (butt plate?), and butt blocks. In fitting the hull panels of my new catamaran I have been using butt plates which are notched and glued into the stringers and chine log prior to fitting the panels. It has been very quick and easy for my small 6 meter boat and this has been the way I have done all the topside panels, fitting one panel at a time. I am thinking though that for the bottom panels I will put the joins in a different location than in the top panels, and rather than using the plywood butt plates i will use two layers of wide double bias cloth on the inside, if I can get a clean even join in the ply panels as I install them, and I can hopefully leave the taping of the inside of the joints until I have turned the hulls upright.

    So in the case of the 7m SibLim, if I were building I would be happy to go with butt blocks, or fiberglass taped joins on the plywood panels. Making scarf joints in plywood does require care and a level of woodworking expertise, and unless they are done well I do not think they would be as strong as a joint using butt blocks. 

    Regarding the length of panels which can be successfully glued in one operation; I am finding that in our New Zealand summer temperatures, and using slow hardener, it is a bit of a challenge to get a 2.4 metre long panel glued up and fastened, and cleaned up before the glue starts going off. I am doing this single handed so with a second person mixing the glue while the first person was applying the glue, things might go a little better. But having said that I am building the catamaran in a site where it gets full sun, next time I will choose a location in the shade. It is not all bad though, with the glue curing so fast I can move onto the next process very quickly.

    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/

    Last modified: 12 Dec 2018 19:24 | Anonymous member
  • 11 Dec 2018 16:33
    Reply # 6955396 on 6955021
    Anonymous wrote: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.
    Doing the interior first as you have done and also as in Tapatya's build to some extent (final bulkheads used instead of temporary frames) makes a lot of sense. Being able to put the interior together while both sides are reachable has to be easier. The downside is that the stability of the frame without the hull's support is less and unless one has a great sense of imagination, it is much easier to decide/design a space when one can look at it as it is than as even the best computer rendering. I think a full size mock up (no cutting needed) would be helpful at least for me.
    But it seems to me that there may be an intermediate option. The hull panels of the SibLim 7 are made from three pieces (four in the case of the bottom panel and bow transom). The forward join is in an area of the hull where there is conical twist as well as more curvature, whereas the after join is in an area where there is no twist and very little curvature. Whether they are made with a scarph, puzzle joint or butt block, it is difficult to make that forward join in situ, but much easier to make the after join in situ. So there is an argument for joining the forward and middle sections of the middle hull panels and topsides flat on the floor, assembling them onto the prebuilt interior, then adding the after sections in situ. And in the specific case of these after joins on the SibLim 7, puzzle joints and scarphs don't seem to offer any advantages, and, hidden as they are inside lockers, butt blocks would be the quicker and easier way to go with no disadvantages.

    Any comments?

    I like butt blocks. I have only built a 16ft boat and so the butt blocks were able to be in a flat spot. puzzle joints are new to me and yet it appears from past posts they are considered as strong as needed even though the glued area looks less than scarph or butt. Anyway, the one thing I would say about butt joints, is that they should be faired. A faired butt joint need not be hidden as the block is thin anyway. However the fairing also makes sure there is no nook for water to collect in and so even when hidden I would make sure it is faired.

    I am also assuming that the hull is more than one sheet thick? As you have stated, the hull is one of the quicker parts to build and so using two layers rather than one thicker layer makes sense so long as the base layer is thick enough not to have flat spots in a curve. Thinner means lighter and easier to lift and place. The second layer would be cut when placing rather than CNC-cut.

  • 11 Dec 2018 15:50
    Reply # 6955344 on 6010674

    Upper and lower shelves glued, wedged, cable tied and filleted in place.The longer upper shelf is at the upper edge of the topsides.

    Floors added at stn 3 and stn 4. This is where two pairs of keelbolts will be.

  • 11 Dec 2018 10:16
    Reply # 6955021 on 6010674

    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.

    But now I'm getting close to adding those hull panels, and it's worth reviewing how these might be put on.

    It would be quite feasible to do as we did with Annie's SibLim, and notch the corners of the bulkheads, add chine logs, fair them in and then apply the hull panels one 8 x 4ft sheet of plywood at a time - not CNC cutting, but offering up the plywood sheet, drawing around the perimeter, cutting out, and making scarphs or butt joints in situ. This would be slower, but would save some CNC-cutting expense, and would avoid having to handle very long assembled hull panels.

    It's also quite feasible to make up the full length of the hull panels and add them - provided that there is enough manpower available to handle them and manage the gluing process. RM do it this way. The longitudinal joints are done by stitching, filleting and glass taping, but the joins to the bulkheads can be done either with filleting and taping or with traditional framing and gluing.

    But it seems to me that there may be an intermediate option. The hull panels of the SibLim 7 are made from three pieces (four in the case of the bottom panel and bow transom). The forward join is in an area of the hull where there is conical twist as well as more curvature, whereas the after join is in an area where there is no twist and very little curvature. Whether they are made with a scarph, puzzle joint or butt block, it is difficult to make that forward join in situ, but much easier to make the after join in situ. So there is an argument for joining the forward and middle sections of the middle hull panels and topsides flat on the floor, assembling them onto the prebuilt interior, then adding the after sections in situ. And in the specific case of these after joins on the SibLim 7, puzzle joints and scarphs don't seem to offer any advantages, and, hidden as they are inside lockers, butt blocks would be the quicker and easier way to go with no disadvantages.

    Any comments?

  • 11 Dec 2018 09:27
    Reply # 6954945 on 6010674

    Outer side of the bilgeboard case glued in, after resin coating all the interior faces.

    On reflection, it would have been better to make up the bilgeboard cases flat on a horizontal floor, after completely finishing the interior surfaces, so as to ensure that they are flat and untwisted.

    Adding more framing to support the bottom hull panel. This is three layers of 6mm, and the first layer needs plenty of support to keep the curvature fair. At the top of the photo is a more substantial floor which is where the aftermost keelbolt will be.

  • 11 Dec 2018 09:01
    Reply # 6954893 on 6953026
    Annie wrote: Well, I'm not sure how prudent I am - my form over the past couple of decades would appear to indicate the opposite if anything - but if the 7m variation can sail around the world, then taking my 8m to Fiji (as I have tentative plans to do) seems less than foolhardy.

    Hey, you might as well dream while you build.

    I wouldn't for a moment want to claim that the SibLim 7 can sail around the world. Only that it should be able to tackle the easier "milk run" trade wind passages across the Atlantic and South Pacific. Size does matter, bigger is better, more is more (BibMim), when the height of breaking waves is more than the beam of the boat is when knockdowns become more likely. As the GGR entrants are demonstrating, 32 - 36ft is a bit marginal for going nonstop south of the Great Capes. 40 - 50ft boats have a rather better track record, eg Hawk, sailed by Evans Starzinger and Beth Leonard, 47ft LOA.

    I would say: dream on, but happiness is adjusting your dreams to realities and practicalities. Yes, SibLim 8 can go to Fiji, as could SibLim 7, but I would hesitate to take either down to Stewart Island. Can SibLim 7 sail from Japan to NZ? According to World Cruising Routes, it could be somewhat of a windward slog to get out to Guam or the Marshall Islands, so the rig had better be pretty good, but then it should be easier on the SE trades past Vanuatu.

  • 10 Dec 2018 21:47
    Reply # 6954290 on 6953026
    Annie Hill wrote:
    David wrote:
    Well, I'm not sure how prudent I am - my form over the past couple of decades would appear to indicate the opposite if anything - but if the 7m variation can sail around the world, then taking my 8m to Fiji (as I have tentative plans to do) seems less than foolhardy.

    Actually, the more I work with this boat, the more confidence I have in her sturdiness and potential seaworthiness.  And I shall certainly have a strong and waterproof companionway/pram hood area.  I have a friend rebuilding a Trekka, who says he's planning to sail with me: it would be interesting to compare our experiences at the end of the passage.

    Hey, you might as well dream while you build.

    Having just re-read the book 'Swirly World Sails South' by Andrew Fagan I have been reminded of how even small yachts can complete a successful ocean crossing provided the vessel is of a seaworthy design and well handled. So when ocean crossing in small boats it is probably not so much a question of is the boat capable  but equally just what comfort level there will be, because the smaller the vessel the less comfort. I have no doubt though that Annie's new boat will be ocean capable, and I think that despite it's small size there will also be a very acceptable level of comfort.
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