CLT houseboat

Discussion in 'Boat Design' started by Eelco, Apr 11, 2020.

  1. Dejay
    Joined: Mar 2018
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    Dejay Senior Newbie

    Ok I'll give it a shot although I don't have any experience. I think this is an interesting process that has potential.

    From what I understand your barge design needs some kind of rounded surface to transition from flat bottom to bow. Aerodynamics are a multiplier to your already heavy tonnage so it really pays to make some accommodation of how you going to push through the water. So you'd want some type of planking type construction method for the bow at least.

    Having looked at some videos, the process and machinery looks really impressive! They use polyurethane glue. I wonder if they could make a batch with a bit more glue than needed to ensure higher level of encapsulation. Maybe they could even add a layer of fiberglass before the press cycle to create a waterproof finished surface with barrier coat.

    Is the price of 500€/t for CLT realistic? It's largely automated but not fully. The machines build for this represent a massive investment and probably have high running costs and maintenance. Prices you mentioned might be promotional, for a large project with much larger volume, using cheap lumber of from a timber "glut". You'll also want wood better suited for boat applications like larch (I think).

    It also makes me curious why plywood (marine or not) is so comparatively expensive compared to CLT. Plywood has been produced using industrial processes for decades so it should be cheaper. But the cheapest I've found is about 4000€ / ton of outdoor grade (non marine) plywood.

    Also why do you need 20cm thick walls? Is that an evidence driven decision? Is still seems like a lot of overkill to me, but maybe over-engineering is a valid approach. But something like 6-8cm but with better wood seems more practical.

    Why do you need interlocking joints? Panels would be joined using fiberglass and epoxy. Epoxy glued joints are stronger than wood. And I think you need your fiberglass to be the tensile strength bearing material so it won't rip. Interlocking joints might add nothing but headache. But I'm not a composite engineer so I'm just speculating.

    How are you going to get your high quality CLT panels (max 2.5m x 13.5m?) shipped to a low cost country and then your ginormous barge shipped back?

    What about cost of labor and overhead? You seem to be jumping from 50k in raw material costs for CLT alone to 100k with "a little bit of labour plus alu, glass, XPS". You'd roughly need 20 large 13.5m x 2.5m pre-manufactured panels to build a 25m x 5m two story boat. That are nice big parts and it's probably less work than building it out of plywood and stringers, but you still need to fiberglass and fair and barrier coat and paint it. Although laminating them before assembly with a floor sander and large tools might make this much easier.

    I mean you're saving a lot of work because you can disregard many structural consideration and work needed for plywood (at the cost of weight). But you still have the exact same problem of having to encapsulate the wood in fiberglass by hand which is where the work is.

    You'll also need to avoid getting either ripped off or falling prey to an inexperienced builder making a costly mess of things. My guess is that no qualified builder, low cost country or not, is going to jump at the chance to build a boat using unproven new technique for cheap.

    What is interesting is that looking at the processes I can imagine you could adapt the process to build curved panels that fit together for chine hulls. Hulls that could be quite sleek, efficient and lightweight like cold molding but automated. Basically a large press that can contort itself to produce developable CLT parts that are already laminated with fiberglass and can just be fitted and glued together. Imagine a boatyard that can mostly automate the production of 80' multihulls that are relatively lightweight and using rather cheap raw materials.
    Last edited: Apr 20, 2020
  2. Eelco
    Joined: Apr 2020
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    Location: Amsterdam

    Eelco Junior Member

    Well if I can move this thing at 8 knots im pretty happy, and under 5 knots hull shape does not matter much anyway. Id like to analyse this in more detail, but my feeling is a polygonal hull would suffice.

    Well that depends on the way you want to think about moisture. Ideally you keep it out altogether. But if you have a tiny bit seeping in, you could argue for making the wood as impenetrable as possible, and keep the rot localized; or the direction I have been leaning in; keep it porous that tiny drips wont suffice to get the wood properly wet over a significant area.

    500/m3, so about 1000/t, is a figure ive seen cited as an industry average in a few places. A family member of mine is building their own house out of CLT, which is where I got the idea. I dont know their volume, but I do know the cost of the CLT was well under 10% of their total budget; as trucked in from the other side of europe, and installed.

    I can get 2x4 lumber retail at my local hardware store, for 400e/m3, per single piece. Whatever they pay for it in bulk, is probably a lot lower than that. Softwoods are just crazy cheap I guess; the entirely supply chain is super automated, and the northern hemisphere isnt about to run out of pine forest yet.

    As for gluts; I think you could try a worse time than the next few year ahead of us, to find some contractors eager to keep their workers busy. Seem like a terrible time to buy in any place where value is strongly tied to location right now; but if there is anything that does not have a location-based value its a boat so I dont have to sweat that halving in value either.

    Yeah, in the wood world, anything that isnt plain-sawn-softwood, gets expensive very fast. Its really only softwoods that are available for harvest by the square kilometer. CLT has relatively little sawing/machining per unit volume as compared to plywood; and probably you have to be pickier which trees you can use for plywood too; if its bowed or cracked at all its a complete writeoff for ply.

    No, I have not optimised that at all. I think 10-15cm is pretty typical in house construction; and since a house is but a poorly constructed boat, I thought id go a little higher than that in m initial assumptions. But I havnt been able to identify a reason yet why id need that much thickness, no. You need some minimum thickness to provide bending stiffness to the panels though, especially since they are flat in all directions. The biggest flat span is the bottommost panel at roughly 3m wide; youd want that to shrug off any flexing from being 1 below the waves, at least. Havnt run the numbers, but going by gut feeling there id say 10 vs 20 cm would make a difference.

    Interlocking joints may be overkill; but are generally considered stronger in woodwork than just glue. Sure its not hard to find glues stronger than the wood, but thats not the whole story, when it comes to grain direction, and the entirety of the yield curve if you start getting serious about prying things apart. A glue line might just crack and be done for at a critical strain where a mechanical joint would still retain a lot of its strength.

    The way im looking at it right now, the wood would definitely be the load bearing part, not the glass. But you could go the other way; just use the CLT minimally only as is required for framing, and add as much glass as you normally would for a boat this size.

    Delivery is part of the service the manufacturer sells. Many manufacturers go up to 20m per panel. As for shipping back; not sure of the details but more epic naval voyages have been undertaken than from poland across the baltic sea to the netherlands.

    I am only eyeing about 2t of glass-composite in total, to be put onto the wood. About 1t per mm all over, and I think 3mm on the bottom and 1mm up top would suffice. Could be chopped strand applied with a chopper gun for all that it maters. Now I dont have a great mental model of what this will cost, but going by other figures of glass hull construction per ton, I think 100k is conservative. Doors/windows/general yard fees are probably more than the cost of the glass. But I could be wrong

    Yeah, true.

    If this wasnt a one-off, but you wanted to set up a production line to make a lot of these, that would indeed open a lot of possibilties I think. CLT can be pressed into quite curved panels I believe, but it requires custom tooling. If you are willing to invest in that, you could make some very sleek boats quite cheap and fast. That said sleek boats usually care about speed, and hence weight, and I am not sure this is a very competitive process in that respect.
  3. de Noor
    Joined: Jan 2021
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    Location: Norway

    de Noor New Member

    Hi Eelco!

    I think your project is exciting! You have many good arguments but encounter a lot of good and bad skepticism. The bad criticism is that you have to stick to the tradition. There are so many new materials and methods that they are not absorbed by the industry yet.
    I'm planning a clt houseboat myself.
    I live in Norway towards skagerakk sea.
    After hearing a radio program entitled "ice, the perfect foundation" I stopped thinking about a hull and the plans took shape. The floor is the hull bottom, 140mm thick.
    I plan a boat width of 4.2 - 5 meters and a hull length of 12 meters. In addition, there is a platform at the front and rear.
    The size is based on locks and that it should be possible to build alone. I'm thinking of building the hull upside down with reinforcements to lift it around. The superstructure is then sealed before winter.
    I have the resources to do this indoors with a lot of technical equipment. But as the plans have evolved, I want to keep the project as simple as possible but with a professional approach.
    I want to build with pine 19 x 100 mm. four layers. A transverse layer at the bottom then two 30 degree diagonal layers and finally a longitudinal one. Norwegian advice for technical wood has recommended me to use RPF glue instead of PU or MUF glue. I'm still unsure of the type of glue in terms of diffusion. On the outside, I will lay a non-woven fabric saturated with polyurethane that is self-sealing around threads. I will then screw on xps 50mm 300 kN / m2. On top of this I am laying a new membrane against water intrusion. Against wear from ice in winter, the bow and sides will be covered with a hard material. Not yet decided. All interior surfaces covered will have diffusion-open materials. Indoor climate will be automated. Walls above 1,2meters wil be light weight materials. Center of ravity will consist of heavy equippment and a 2000kg combined swing keel and anchor.
    The exciting thing about CLT in a boat hull is price, time, formability and strength. Even double-curved surfaces are easy to make.
    I have spent a few years collecting information, among other things. at the Ligma Hannover fair. There is a lot of automation, technology and special products. After a long time, I have come to the conclusion that the most important tools are nail gun, saw and a good glue. Then this goes radically timber by timber.
    An important part of the construction is joints in corners and edges as well as against other components. In the spring of 2021, I will make a small part of the boat for destructive testing. I hope this will provide experience before construction.
    When it comes to the architecture behind the boat, I have tried to balance between tradition and function. The goal is safety but also the least possible friction in relation to other people where the boat will be. It is intended as a permanent home.

    Jeg er glad jeg fant denne tråden og vil sette pris på tilbakemeldinger på mine planer samt tips om andre som har prøvet dette. Takk:)

    If interested, I can upload a temporary sketch.
  4. Eelco
    Joined: Apr 2020
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    Location: Amsterdam

    Eelco Junior Member

    Hi; sounds like a cool project. As I understand you correctly, you intend to perform the lamination work yourself? Thats more physical labor than I can imagine myself getting up to, but sure sounds like a cool project. Indeed I think there are more complex and labor intensive ways to build a boat, for sure. It might be hard to get the same bond strength as a factory pressed panel, but strength isnt really limiting anyway, and indeed in doing it this way it should give you a lot of design freedom in terms of curvature that I wont get from any factory pressed panels.

    Ive been actively thinking about this again in recent weeks as my financial situation has improved to the point I might actually get started on such an experimental project without a mortgage. And indeed my thinking has not really shifted since earlier this year. Put together a CLT frame, put on a puncture resistant vapor barrier, then glue on XPS blocks that id probably cnc-wire-cut to match an elegant outside shape as defined in CAD, and then put glass fiber on top of that using standard boat building techniques; although a relatively light coat since the CLT is the primary structural element.

    I had not really considered the effect of ice yet. Not as much of an issue down here but something to consider nonetheless. Beefing up the glass at the waterline and keel hopefully will suffice.

    Rather than dealing with the complexity of integrating a heat pump loop in the bottom of the hull, and the construction complexity and repair problems that would create, ive warmed up to the idea of simply throwing out a loop of tubing overboard on the bottom of whereever you are, and disconnecting and reeling that back in when moving around. Again this boat would be stationary almost always, so its probably the simpler option.

    Did you mean 'screw on xps' literally? Would you not be puncturing your inner lining, and creating cold bridges? Also the foam wouldnt like the stress concentrations of screwing and would readily start cracking there. Some kind of adhesive seems much more suitable to me.
  5. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    You are reinventing the wheel. As I have mentioned in the past, a square wheel is novel, but hardly better than the traditional round ones.
  6. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Not really. The argument is that some methods work and something different is not better simply because of being different. You seem to think that "sticking to tradition" is the only reason to find fault in a bad design.

  7. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Are you saying that all the studies on hydrodynamics and naval architecture are wrong? That is a pretty big claim. Maybe you should take your arrogance down a notch and listen to good advice.
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