CLT houseboat

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

  1. bajansailor
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    bajansailor Marine Surveyor

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  2. Rumars
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    Rumars Senior Member

    There is no real need to reinvent the wheel. Most floating homes are buildt either on a barge or pontoons as a platform. The "basement" takes the ballast and tanks and the "house" is above deck. House and hull materials are usually different with steel, concrete and aluminium beeing the most used for hulls. Making a timber hull is of course possible. A sheet material like CLT would need a chined design. CLT doesn't bend so you need a design that accounts for that (a box with one sloped end like a landing boat). You also probably need real wood chines inside, I doubt stich and glue will work (maybe with dovetailing the panels at the chine). Also some transverse framing (bulkheads or frames) will be needed. Abrasion resistance and waterproofing is easy, just put on enough fiberglass and kevlar in epoxy and also coat the inside with epoxy. Of course this defeats the purpose of using CLT, you could just as well build the hull from monolithic glass and kevlar with poly or vinylester. Or if you put steel plates over it just put the money for the CLT in more steel and welding and painting.
    The house part above deck you can do however you like, preferably something lightweight, CLT, SIP, etc.
     
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  3. Eelco
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    Eelco Junior Member

    I came up with another potential solution to keeping my softwood dry: polycarbonate honeycomb sheets. This solution would be targeted more at detection and repair of leaks, rather than absolute prevention. The idea is to glue these corrugated PC sheets on the exterior of the wood, with the internal channels channeling down, into the bottom of the v-hull. Standard glass/kevlar could go on top.

    Any water that would come through the hull, would be guaranteed to go down first, before reaching the wood. So you have a single point you can check for failure; if there is no water at the bottom of your keel, you know there isnt any water in your wood. If there is a little water in your keel due to a minor crack in the outer hull, you can pump it out for the time being, become aware of the situation, and get it patched.

    This type of PC sheet will be quite springy and intrinsically though and as such provides a tremendous impact buffer in itself. Damaging it such that water will go through rather than channel down, is quite hard to imagine, especially with some kevlar on top. Might still happen if your hull gets thrown on a rock by a 10ft wave, but in such situations ill settle for preventing loss of life rather than loss of property.

    Also, its cheap and easily repairable. If a panel gets crushed you can just cut out a section of the outer hull, pull out the loosely bonded PC sheets, put new ones in, and so on. Nothing anyone who knows how to do repairs on composite boats and who has two hands and a functional brain could not figure out.
     
  4. bajansailor
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    bajansailor Marine Surveyor

    Eelco, you do appear to be fixated / obsessed with building your hull from CLT.
    As Rumars says, there is no real need to re-invent the wheel. If CLT was a good material for building hulls with, I am sure that others would have done it and reported on it by now.
    Most folk on here are dropping gentle hints to you that they do not think very much of your plan to use CLT.
    And these folk are experienced boat builders / naval architects.

    Please do at least consider building your boat from a more traditional material like steel - or even ferrocement. LOTS of barges have been successfully built and operated using these materials. You might be pleasantly surprised by what you find out when you do some (more) research. There is a LOT of info out there - ask Google.
     
  5. Eelco
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    Eelco Junior Member

    Yeah, it would be a chined design. Im thinking a shallow v, v-roof, and a slight widening at the middle, for an overall octagonal section, to break up the boxiness somewhat.

    Im thinking if the panels where they meet at the chines are put together with splines / finger joints, and have them slathered heavily in polyurethane adhesive on their entire contact surface, on a 30cm wall, this octagonal box by itself should suffice. Ofc it will have one interior floor and some interior walls as well; but I dont even know that theyd be strictly necessary for stiffness or strength. In any case, I am confident those details can be worked out.

    Building from steel directly would be a lot more expensive than gluing on plates. Building from plates requires a lot of skill and time put into shaping, welding and painting. Glueing on easily handlable flat and relatively thin plates is something I could do myself if I had to.

    Fiber over the wood defeating the purpose of the CLT; I dont think thats quite true. Having the CLT put together in a few days saves a lot of time and skilled labor in the boat yard to put the overall shape together. After that slathering on some rolls of glass is rather easy; a rather different affair than 'proper' composite-curved, load-bearing composite construction. I definitely wouldnt trust myself with a DIY job on the latter, but might on the former.
     
  6. Eelco
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    Eelco Junior Member

    I suppose I chose a good thread title to explore the topic then.

    You could have said the same thing about houses just 10 years ago. Its a rather new material. Or its not so much the material itself; but rather the degree of automation the process comes with that opens op novel possibilities that might previously not have been economical.

    Both their gentle hints and reasoned arguments are appreciated.

    As mentioned before, I have been professionally involved in the design of ocean going structures, both steel and ferrocement. No doubt there are more experienced people out there than me, but I think I have a pretty decent idea of what options are out there.
     
  7. Squidly-Diddly
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    Squidly-Diddly Senior Member

    How about not long range towable, but "get it up a launch ramp and into the parking lot (on one of the uncrowded off days) and a few blocks to a storage yard (at 4am when roads are empty and even cops will give you a pass). I feel that being able to do so will become the diff between needing to abandon the project at some point VS "keeping the dream alive".
     
  8. Eelco
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    Eelco Junior Member

    That depends a lot on your goals and circumstances I suppose. Being able to go to any part of the planet if so desired is part of the dream for me. If moving house-sized objects around the planet is your goal, water has a much better track record than land, os it makes sense to optimise for that.
     
  9. Rumars
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    Rumars Senior Member

    You need to do a cost analysis of different materials to get a definitive answer. Main points:
    Steel needs paint, anything with epoxy on it (wood/fiberglass/kevlar) needs paint, Al and cement do not (better said it's optional). There is not much price difference between the paint systems for the different materials, same topcoat, different primers. Painting work is the same since it is related to surface area.
    Steel and Al need welding, cement needs plastering, wood needs glueing and waterproofing. So you compare welding costs (welder salary + welding machine rent + consumables) to plastering costs (manpower plus pump rent) to glueing and laminating (manpower, epoxy, fibeglass, kevlar felt).
    Steel, Al, and wood all need lifting equipment to position in place (CLT is actually the heaviest of the three). All three also need cutting, CNC costs will be similar. Cement does not need either of them but needs work for frame assembly.
    Last big cost are the structural materials themselfs. Steel plate, Al plate, CLT, cement and reinforcement (steel, fberglass, basalt or carbon).
    A monolithic glass boat is a little bit different but "moldless" construction is not a problem, the costs are some wood frames (CNC cut if you wish), fiberglass and resin and manpower, then sandpaper and paint.

    75k€ is more then enough to get you a hull in any of those materials. How much you can save by doing it yourself depends on what you can do and how many friends you have willing to help. Steel is not more difficult then CLT, you take the cut plates and position them in place by tack welding with a 100€ stick welder. If the plates are all beveled and positioned the actual welding by a pro is not expensive.

    CLT is made of crap wood (spruce/pine/fir). If water gets into it you have two problems, rot and delamination by differential expansion. If the panels are not absolutely void free you can also get rot by condensation in the voids. In order to waterproof them you will need heavy fiberglass in standard epoxy or a sufficient coating of really flexible epoxy (only valid for the inside). The kevlar felt for abrasion protection eats epoxy like crazy. I would say the costs for epoxy, fberglass and kevlar will be greater then the price of CLT.
    I would only consider CLT if I could get it made out of a rot resistant species (black locust, oak, tropical species) and glued with phenol-resorcinol (brown glueline).
    Glueing steel panels is difficult, the glue must be able to take all the forces in sheer, imagine the most likely scenario, you rub on a steel boat or concrete pier, the plate must stay in place. I susspect you will have to mechanicly fasten the plates to the wood (epoxy plugs around the fasteners) or use some really expensive glue.

    You asked about bombproof material, I would investigate textile reinforced concrete. Here the armature is composite (fiberglass, basalt, carbon) and can not rust. The concrete can be formulated to a specific gravity under 1 if you like, but it's easy enough to add enough XPS foam flotation to insure positive flotation. Abrasion resistance can be solved with kevlar felt in epoxy or a polyureea coating (expensive).

    The only material that will have value by itself after a while is Al. Otherwise the value comes from the systems and maintenance, hull material is irrelevant (market preferences aside).
     
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  10. sharpii2
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    sharpii2 Senior Member

    This is one of those ideas which look so good on paper, but are probably bad from the very start. The fact that you are aware that wood can never get wet, tells me that you probably already know this is not a great idea.

    If the wood gets wet, it will likely swell. And when it does, it will put tremendous stress on the glue joints, as the planks run cross wise. This is true with plywood too, but the layers are much thinner per given glue joint.

    Really wet wood does not rot. It's damp wood that does. Hence the term "dry rot".

    If the panels can stand getting saturate with water without the glue joints failing, then you're probably better off not sheathing them at all. Or if you do, have the sheathing mechanically fastened to the wood after the wood has been painted.
     
  11. Eelco
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    Eelco Junior Member

    The idea is to get the hard stuff done professionally; but more DIY repairability of the parts that might need it, is something I would appreciate. In that sense, a fiber exterior appeals to me over welded steel. Note that I am not looking for the cheapest possible option per se, and I know 75k buys a fair amount of steel. I am just figure out if CLT is viable at all. Hoisting together CLT panels is an established competitive industry so im confident that can be worked out; I wont be DIYing that part for sure.

    Looking at bulk materials on aliexpress, putting on some simple layers of non-load-bearing fiber seems really cheap compared to the rest. But given that id rather have a professional do it than DIY it, having figures for actual costs per m2 including labor would obviously be strongly preferred. Note that if I would go ahead with such a project id try to get it done in czechia or estonia or the like. The cost difference in interior finishing alone would be at least 100k.

    Its possible and has been done; but I cant find any prices for it, and I imagine it wont be pretty to venture off from the defacto standard, cost wise. If I could get a good deal on oak though, make the walls a little thinner, and keep the interior all unfinished oak... yeah id pay a little extra for that. But what I know from wood prices I am guessing 5x the price of pine, not accounting for the extra costs of this niche order... hey who knows the earliest id start this project would be two years from now; still have time to win the lottery...

    Not sure I agree. Matching the tensile strength of steel with glue is difficult (or rather impossible) but thats not what im after. If the steel bends and comes loose during a terrible impact thats alright; it has done its job. I dont imagine youd shear off a full m2 of urethane adhesive with the first piece of rock you grind against though but I might be wrong about that; hard to intuit or simulate the forces involved of a piece of steel being stuck between concrete and 100t of moving mass. Obviously its a rather untested concept so thats never a plus.

    Yeah, Ive considered fiber cement. But building in fiber cement such that it may take the tensile forces associated with worst case scenarios out in the open ocean, isnt that easy. Making the most of it requires pretensioning; and all this has been done before with good success offshore. But its too much to DIY properly, and I dont think I can find any crew with experience doing this on a houseboat-scale. There is an active concrete houseboat building industry in the netherlands actually, but they specialize in the thin wall zero freeboard pontoon style houses with suicide-tier seaworthiness.

    Yeah; not entirely sure what to think of Al; never designed anything with it. Its no silver bullet in sea water; but I dont expect to be there often. Not sure what to expect of Al in fresh water actually. I think it also depends? What about brackish water (quite prevalent here), or acidic boggy water? Common wisdom on Al boats seems to include paint and regular maintenance thereof I think? Other than being a little less paranoid about your paint being scratched, my mental model is that its pretty similar to steel, for my intents and purposes. Except with more thermal bridging, and being even more impossible to insulate to modern standards...
     
  12. Eelco
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    Eelco Junior Member

    If you have a hole in your hull, you have a problem; thats not really unique to CLT. CLT can actually handle about 10% in variation in water content by mass; so a tiny crack in your hull that slowly seeps in water but wicks away and spreads faster than it comes in, or dropping your glass of water for that matter, isnt going to ruin it. There are several tons of water you could soak up across the whole of a 75t hull without getting it wet enough for rot, relative to its moisture level as delivered, assuming that water is spread evenly.

    That suggests another strategy for avoiding trouble; if the wicking and evening out of moisture could be encouraged (rather than providing hard barriers in glue joints etc), small water ingressions would be more easily tolerated. If such leaks are small enough and spread fast enough that they cannot manage to exceed critical levels locally, the AC could simply carry away many liters of water a day from your inside walls in the long term, and itd be fine. Even if you AC was broken, and again if it spreads well enough, you could still leak 10L a day for a whole year, and youd still only have used up half of your dryness safety margin. If the moisture spreads evenly, that will also make monitoring a lot easier.

    That suggests another simple but perhaps effective solution. Just glue a thick layer of OSB (maybe there is an even better material; but I think it will do) on the exterior of the CLT, without edge-bonding those panels, so moisture can spread around and will not readily concentrate in one location. Then just glass/kevlar as usual. Should the composite skin develop small cracks due to impacts, it should not cause either immediate or even long term problems to the load-bearing CLT. If you hit something hard enough to really tear out a piece of kevlar; well that wont really happen with everyday wear and tear, and if it does, its an event that is not going to pass by unnoticed, and you can treat it with standard composite emergency repair methods.

    With apologies to the skeptics; but that sounds like a pretty down to earth, feasible, and idiot proof approach to me... but by all means shoot some holes in it!
     
  13. Rumars
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    Rumars Senior Member

    Normal CLT is simply not suitable because your requirements do not match the way it is made. Softwood planking, particularly pine and douglas fir, has been used as planking without any epoxy, only paint and screws and has lasted well. But it is a maintenance intensive material that needs regular inspection and paint. Once you use epoxy on wood it must be completley sealed and this sealing must be maintained. Once breached water can only get in and not out, rot starts or the wood swells and delaminates. This happens even with thin veneered plywood, thick boards like in CLT will have much bigger movements. If you look at CLT certifications you will see it is only approved for protected areas. House walls, even exterior ones are considered protected, since they are under a roof. Immersion or permanently wet rooms are forbidden. The glue that is normally used is also not immersion rated. To use it in it's normal form you need a very heavy layer of fiberglass for puncture protection and to resist movement (felted kevlar is only good for abrasion). Once you go down this route you can just put the money for the fiberglass, epoxy and wood, into fiberglass and polyester and forget the wood and it's problems. Or buy metal, wich is less expensive overall for commercial production in the required boat sizes. Remember, at 30cm thick CLT weighs 150kg/sqm. This is equivalent by weight to 19mm steel or 50mm Al. Both would conform to your definition of bulletproof and low maintenance. Yes, Al has some unique corrosion situations that must be observed but those are adressed at construction and then it is regular annode changing and some common sense. Painting Al is a choice not a necessity, the french made plenty of unpainted Al yachts. A boatyard in Poland can cut, weld, paint and insulate steel for a price that will astonish you. There are even cheaper yards in the EU but transport from the Romania or Bulgaria is likley to cover the price difference. Al is more demanding in welding and I would do it in the Netherlands, Belgium, France or Germany, there are competitive yards with good expertise in all of this countries.
    Fiberglass construction is easy, plenty of boatyards are geared for it and can do one off moldless construction.

    A custom run of CLT with resorcinol glue and a rot resistant species is certainly doable, but I doubt economical. The best european species to use is not oak but black locust (robinia). Robinia is harder, more rot resistant and significantly cheaper than oak. It also glues better. A custom run should have thinner and more layers, 20mm maximum. With this wood you can put only a thin layer of kevlar in epoxy on top for abrasion and worm protection. For tropical wood, bilinga is likley the cheapest.
    I do have to say that if you really want laminated wood going the custom CLT route does not make much sense. If not homebuildt you need a wood boatbuilder to do it and at the prices they charge plus the custom panels price, they can also cold mold in place. Structurally a 20m, 100t hull would require around 60mm of hardwood planking (80mm in softwood) on laminated frames. That is usually done with a layer of strip planking and several cold molded over it all glued with epoxy and plastic nails.

    Textile concrete is not fibercement. Fibercement is mixing small chopped fibers in the cement mixture, textile concrete is using a conventional armature made out of composites. The rebar (wich looks like normal rebar) and mesh (wich can look like standard square welded mesh or can have the strands woven to specific load patterns) are made out of fiberglass, basalt or carbon set in epoxy or vinylester and silane treated to promote adhesion to the concrete. The big advantage is that there is no minimum concrete thickness for corrosion protection and the weight. But at present there are still few specialists knowing how to deal with the material structurally and boats have only been made by universities (and I am not talking about the canoes). Lamiantion is by hand or sprayed, over or in a mold. You basicly need a crew of plasterers to do it. If you like I can link a construction video for a small speedboat made this way.
     
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  14. clmanges
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    clmanges Senior Member

    How does one weave basalt? Same as weaving granite? You must be thinking of something else ...
     

  15. Rumars
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    Rumars Senior Member

    Same as glass, slag, etc. You melt the rock and spin thin filaments out of it. Then you can do whatever is possible to do with filaments, for example yarns wich get woven into fabrics or pile it up for fireproof insulation.
    Basalt fiber - Wikipedia https://en.m.wikipedia.org/wiki/Basalt_fiber

    The still-promised potential of basalt fiber composites https://www.compositesworld.com/blog/post/the-still-promised-potential-of-basalt-fiber-composites
     
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