CLT houseboat

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

  1. Eelco
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    Eelco Junior Member

    I have been thinking about a concept for a houseboat, and id interested in gathering some general feedback; am I reinventing the wheel here, or suggesting something completely stupid?

    My goal is to develop a comfortable house boat (more house than boat), but with sufficient boating qualities to be towable basically anywhere; at least in rivers and coastal waters. It does not need to be light or fast, but id like it to be pretty indestructable. The idea here isnt to take regular and pleasant cruises, but to have the ability to take your house with you and survive the trip, should the need arise.

    I think CLT (cross-laminated-timber) construction might be very well suited for this, since it is a quite economical type of process; currently gaining a lot of ground in the housing construction industry, but easily adaptable to boats, I think.

    The basic specs of what I am thinking about is roughly a 20x5x5m barge. Two floors, pretty square, some 200m2 usable surface, but with a polygonal bow-stern so you can tow it at a few knots without completely breaking the bank. The actual design might be somewhat less boxy for aesthetics, but these values should give an idea of the overall size.

    Using about 30cm thick CLT walls, thatd be roughly 150m3 of wood. The cost of CLT as installed (panels cnc-cut to shape and installed) is often cited at around 500e/m3. Thats 75k; well within my budget, not a bad price for a hull that size, and very much overbuilt I think. The CLT panels can be made as single panels over its full 20m span. I dont think thats going to give a creak regardless of sea state, and you get a really nice R-value out of it as well.

    Obviously softwood CLT panels shouldnt be thrown in the water like that. The simplest solution to that would be to wrap the whole thing in some layers of glass. Not for strength (a little glass wont make a difference compared to the mass timber), but to keep water out and provide some impact resistance. That impact resistance is what I struggle with the most. If it does puncture, water will start soaking in, and may never get out again for all intents and purposes. If you hit underwater rock or steel while moving, that glass probably wont do much.

    To make this boat really idiot proof, I was thinking of wrapping it in knitted (loose weave, non-taut) kevlar, and laminate that with a flexible urethane. That should be an almost impossible to puncture membrane; you might crush some wood fibers underneath with a big impact, but you will pretty much need anti-tank weapons to poke a hole in that. Seems like this should also be doable in terms of material cost, but its rather 'bespoke' solution and I probably wont find anyone with experience executing such a project, and while this is an experimental project, I am trying to keep it within the real of 'things that might actually happen'.

    Another alternative that comes to mind is to do a simple glassing, but additionally attach duplex-steel bumpers with m3-5200 in the places most likely to take a big hit; maybe plate the whole underside in say 2mm of duplex steel. Should be easy, no welding or further finishing required, and with corrosion rate measured in micrometers per year, maintenance free for the next few hundred years. And it should only add maybe 5k in the cost of steel to cover all wet surfaces in 2mm.

    But maybe simpler and more proven solutions exist? What would be the best method of making a boat that already has a sufficient macroscopic strength, but is otherwise soft and water-sensitive, like such a CLT boat, puncture-proof? I know simple glassing is considered sufficient for the typical plywood boat; and this essentially but a beefed up version of that. But I am talking about a project here that is probably going to be a good few 100k in total, and id like it to last my lifetime, and then still have a resale value.

    I am guessing the total displacement would come in around 100t (about 75t for 150m3 of softwood alone), so itd have about a 1m draft. Again, not a speedboat. But the cool thing about this type of construction, is that if somebody does take a torpedo to it, and manages to puncture the hull, you will still have your top floor sitting above the water, since the average density of this boat as a whole will be pretty close to the density of softwood itself, and worst case itd sink 'halfway'.
     
  2. bajansailor
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    bajansailor Marine Surveyor

    Welcome to the Forum Eelco.
    I do think that you are rather trying to re-invent the wheel here.
    I must admit that I had to ask Google about cross laminated timber -
    Cross-Laminated Timber (CLT) - APA – The Engineered Wood Association https://www.apawood.org/cross-laminated-timber
    It sounds expensive, especially in comparison to more traditional construction (eg plywood overlaminated with epoxy and glass). Although if you have a very thick timber skin on the hull, then you should need less framing / stiffening on the inside.

    Rather than getting worried about somebody firing a torpedo at your hull, it might be better to simply design the structure such that you have a two compartment standard of sub-division (this is usually the standard employed for passenger vessels).
    This means that you fit enough watertight bulkheads in the hull such that any two compartments in the hull can be flooded, and the barge will still remain afloat.
    In theory. However if you have a two story superstructure on a barge that is 'only' 5 metres wide the damaged stability could be 'interesting'.

    Eric Sponberg in the USA has designed some houseboats - here is a link to his thoughts on the subject.
    https://www.ericwsponberg.com/boat-designs/houseboats/
     
  3. Eelco
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    Eelco Junior Member

    Thanks for the feedback!

    CLT is basically just heavy-duty plywood. The cost per m3 is actually substantially lower than plywood though; plywood, especially marine grade, is many times $500/m3. Plywood is usually not applied in thicknesses of 30cm though, of course. So overall, you probably spend more money on wood. But for that money, you get a heavily overbuilt structure, excellent isolation, and complete CAD design freedom afforded by the highly automated process of CLT construction. That 500/m3 includes cnc machining of openings and joints, and glueing the whole thing together. If I can get all that for 75k, that sounds like an option I am definitely willing to consider. Not looking to build the cheapest possible drafty plywood boat here. Ideally id be able to tow this thing across the open ocean, should that strike my fancy. Ive designed ocean going hulls for a living, and I wouldnt trust a 20m plywood box with that. But using this approach, I do believe it can be done with generous safety margins.

    I am not really worried about torpedos; but still its nice to realize that even they could at best half-sink this boat, even without any bulkheads (dont think true bulkheads are really feasible in a houseboat; take a lot of hardware and machinery to have something that works).

    My main concern is maintenance intervals. I want to minimize dependence on dry-docks, and if some idiot bumps his boat into mine, I dont want to have to be paranoid and get my 100t house out of the water to check if my glass cracked and my hull is soaking up water. Unlike a regular hull, I will not be able to check for water inside and patch it up for proper fixing later. Water seeping into the wooden structure would be a rather insidious problem I think. It wouldnt cause any sudden sinking, but once wet the softwood is basically scrap. It would take years to dry fully again, and would probably rot long before then.

    This strikes me as the main drawback of this CLT concept, and I am trying to see if I can come up with a sound solution to that. So im not expecting any torpedoes; but what I am hoping for is a construction that will be able to absolutely shrug off any everyday wear and tear. It sounds a bit 'out there', but other than that I have not really been able to come up with a reason why the glued on duplex steel plating would be impractical.
     
  4. fallguy
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    fallguy Senior Member

    It sounds to me like you need a lesson in hydrostatics. Just my gutcheck wonders are about stability and immersion for the vessel. Until you can talk about the hydrostatics, yours is as much conjecture as mine.

    The glued on steel plating, for example, might be too heavy.

    One of the reasons houseboat hulls are often steel is exactly the ability to be beat up a bit then welded back up on haulout. How you gonna weld it without a fire? Gonna cut out the steel damage and reglue steel patches? Sounds like a bit of trouble to me. What if you hit the beach a bit hard? Thinner plate sounds less than ideal.

    kind regards, but practicality was found long ago on houseboat hulls; I see little reason for reinvention
     
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  5. Eelco
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    Eelco Junior Member

    I am confident that can be worked out.

    For 2mm, it would come out to about 4 tons or so, or 4% of the vessel. Since its the highest density material used, and sitting mostly on the bottom, it will be great for stability; and together with fuel/water/batteries/ballast tanks on the bottom, I think in fact self-righting from full capsize would be attainable.

    No, the steel wont be welded. Just glued on in scales. If the steel takes significant damage, then obviously there will be drydock work that needs to be done. But with 2mm on the flat sections, and perhaps a lot more on the forward moving bow sections; all backed by at least 30cm of solid wood, the idea is that even with rather heavy abuse, the steel will at most scratch and dent a little. Even if it were to shatter in a million pieces and fall off, there wont be an immediate problem, as long as the resin underneat doesnt crack and the wood stays dry; its purpose is really only as abrasion/impact protection. In case some steel does need to be replaced, I imagine putting it on in sections of a managable size in the first place, well under a meter square. Hit them with a torch until you get it hot enough to destroy the urethane adhesive underneat (will give out long before the wood), and pry it off? If they are in such bad shape they need replacing they are probably at least already partially peeled off anyway. Not sure what the best solutions are here, but this does not strike me as a showstopper. That said, id definitely rather avoid such oddball solutions as much as possible, and work with technology people have experience with across the world, if I can.

    Perhaps just regular epoxy-kevlar would simply suffice, which is a rather well established solution. It would for most intents and purposes suffice I think, but hitting an underwater concrete block head on... i am not so sure. The kevlar wouldnt completely fall apart, so thats good enough for a typical hull. But itd still crack, and that is what I am absolutely trying to avoid. That said hitting a thick layer of kevlar hard enough to crack it isnt an event that is going to go by unnoticed, and the softwood will only slowly absorb water, so it should give you enough of time to get it docked and repaired? Perhaps all that is true but I am not entirely confident about it, id have to think about the details a bit more.

    Can you give me examples of a houseboat hull that would survive the open ocean, is literally unsinkable since lower density than water, provides 200m2 of practical living space, is virtually maintenance free, very well insulated, and can be designed to spec (unfurnished) for around 100k? If so, I am genuinely interested. That said reinventing the wheel is also part of the fun for me, and i realise that is not everybodys hobby; thats ok too.
     
  6. fallguy
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    fallguy Senior Member

    The reasons houseboats are not on the ocean is windage.
     
  7. Eelco
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    Eelco Junior Member

    Thats the problem of the tug you hook it up to being up to the task. I am not planning on keeping this vessel longer on the ocean than is necessary to move it from A to B. Crazier things have been towed than vessels with 20x4m sticking out of the water.
     
  8. bajansailor
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    bajansailor Marine Surveyor

    If I was going to build myself a houseboat, I would be looking at a very simple catamaran hull form with two rectangular box shaped hulls that have some rocker fore and aft (more rocker forward, so that the bluff bow is above the waves when towing).
    Ideally I would build it in aluminium, with watertight bulkheads in the hulls.
    And large tank capacity near amidships for fresh water and black water.
    With a nice 'house' design on top.
    If aluminium is too expensive a material for building the hulls and deck, then I would go for steel.
     
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  9. Eelco
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    Eelco Junior Member

    Cats are pretty cool; but both width and depth have their limits if you want to make the most of internal waterways, and packing all flotation and useful space together in a simple displacement hull is the most space-efficient, given these constraints, I think.
     
  10. kapnD
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    kapnD Senior Member

    The softwood below the waterline is a very poor idea, no matter what you put over it for protection, it WILL get wet and soon rot.
    If the hulls structure is dependent on the strength of the wood, that will be greatly diminished when wet too, as well as becoming massively heavier, then impossible to even haul out for repairs.
    Glued on steel plating would only stay glued until the rust prevailed, which it will without frequent hauling for maintenance.
    The towing vessel would necessarily be large, deep draft, and would surely hit any snags before the tow.
    Wheels are very difficult to re-invent!
     
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  11. Eelco
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    Eelco Junior Member

    Well a 30cm thick panel of solid wood taking up water, even if only halfway decently protected, wont happen overnight, but if through small leaks will take months or years. If it does get properly wet I do think its scrap; but with 75t of wood capable of taking on another 75t of water at full saturation, you are going to get a nice progress bar in terms of how wet it is, in terms of how deep your boat sits in the water; so youll have plenty of time to haul it to the scrapyard without loss of life.

    Note that I am planning on completely glassing this thing from all sides as if it were a giant surfboard. It doesnt have prop shafts or other forms of bilge-water-nonsense. Just a single door on the second floor capable of withstanding big waves crashing into it, should the need arise. Internal humidity will be tightly controlled by the internal air conditioning. 'If' the outer hull remains in one piece, the wood should remain dry. My only concern is just how optimistic that 'if' is, exactly.

    Duplex steel corrodes a few micrometer per year; in seawater. In freshwater, where it will be sitting probably always, its practically inert.
     
  12. kapnD
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    kapnD Senior Member

    It would be a good idea to check with your insurance company!
    Some won’t insure a home built boat, unless the construction is inspected (and approved) at certain points of the build.
    Have you looked at concrete epoxy materials?
     
  13. Squidly-Diddly
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    Squidly-Diddly Senior Member

    "If I was going to build myself a houseboat, I would be looking at a very simple catamaran hull form"

    "Can you give me examples of a houseboat hull that would survive the open ocean,"

    "My goal is to develop a comfortable house boat (more house than boat), but with sufficient boating qualities to be towable basically anywhere; at least in rivers and coastal waters."

    Oh, I thought you meant "towable" on roads. 38' trailerable,containerable,modular Work/Play cat | Boat Design Net https://www.boatdesign.net/gallery/38-trailerable-containerable-modular-work-play-cat.17326/ This could both carry and be towed by a heavy duty truck based RV.
     
  14. Eelco
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    Eelco Junior Member

    Nah. I pretty much accept my ideas are too crazy to bother convincing those suits. Mortgages are overrated anyway.

    For flooring, yes. Also, ive considered doing the external cladding in fiber-concrete tiles, polymer impregnated (so frost insensitive). What are you thinking of?
     

  15. Eelco
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    Eelco Junior Member

    Nah, id prefer to keep my 100t in the water if I can. With 5m beam getting anywhere by public roads will be a challenge as well, to say the least. Its a factor two oversize for normal transport by road in terms of both weight and dimensions. Its an interesting question though; whats the biggest house that will fit onto a truck. 2.5 meter beam is quite restrictive though. Still more than British narrowboats and people live on those... but thats not quite the lifestyle I had in mind.
     
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