Need Advice with Houseboat Construction

Discussion in 'Boat Design' started by SNGPSo, Feb 4, 2021.

  1. Rumars
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    Rumars Senior Member

    I'll try to explain the houseboat in land architecture terms, so it's challenges are better understood by the OP.
    You are building a house on a bridge, in a high seismic activity area (daily earthquakes). The bridge ends are mounted on steel balls, and the balls sit on very soft rubber dampeners. The house has no direct connection to the ground, all of its weight is borne by the bridge deck. This deck has to be stiff enough to not deflect under load, even if one corner support collapses. If it's not stiff enough the house will either also flex, or be ripped apart. The loads position on deck must be calculated so that the rubber elements all bear the same static weight, otherwise the bridge deck is at an permanent angle. In addition to the static weight you have movable weight (people) to account for, the worst case scenario beeing that all movable weight is concentrated at one corner and jumps up and down (dance party). Under this load condition the deck must remain stiff and heel only a predetermined amount, or the whole bridge falls over.

    There are several ways to solve this problem. One is to build the deck as a single box girder that is of sufficient volume to float the whole weight, this is then known as a monohull, or barge. Another is the multihull solution, where there are at least two box girders acting as longitudinal stringers and of sufficient volume to float the weight, connected by several crossbeams and/or plate. Both of this solutions incorporate the flotation into the structure. If this is not desired, for example because one wants to use separate, non load bearing, flotation elements like barrels, or plywood boxes, or a big slab of foam, the stuctural deck does not need encolsed volume, and can be buildt as a grid deck or cellular deck. Another elegant way is to incorporate the house itself into the deck structure (instead of it beeing a separate item on top of it), using the walls and roof as parts of a box girder (creating what is known in the bridge world as a through-truss bridge).

    As for construction materials, everything has been used, from all concrete to wood. Drywall panels (cardboard gypsum board) as interior walls are no problem as long as the underlying structure is stiff enough, and you use an appropriate grade (type H, for humid environment, aka greenboard). The alternative is to use (fibre)cement boards, and altough heavier they have better structural properties and you could use a reduced thickness.
    I advise doing a weight and cost study per square meter of installed wall, then balance the initial costs vs. maintainance cost over the life expectancy of the materials.
     
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  2. SNGPSo
    Joined: Feb 2021
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    SNGPSo Junior Member

    Thank guys for all the input, especially Rumars, your analogies helped explain many of the structural doubts I had.

    The single box girder is an appealing solution to the torsion (?) problems. However, my aim is to find a solution that uses less material while also achieving appropriate structural integrity. After a bit of pondering, I made some more adjustments to the overall structure; the incorporation of the house itself into the pontoon structure is a very appealing option to me. I did that in my first iteration but ended up bringing the 2 pontoons closer together in order to shorten the joist spans (the ones going between the 2 plywood pontoons), which caused the wall framing of the house to be separate members from the pontoon framings.

    What do you think about this solution? The horizontal/vertical blue elements are all homogeneous to help resist torsions. I am also thinking about adding the green members to help the joists carry the load, and blocking for support on the longitudinal direction. The red 'A' area is meant to stay open to the sea waters.
    Alternative Structure.png

    I would like to iterate on the structure until it is presentable enough so that when I do seek professional help, the process would take less time and dolla' bills. Thanks again for all the help, guys. You are all invited to a house party on this bad baby once it's ready! Hahaha
     
  3. fallguy
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    fallguy Senior Member

    I would think you'd need some deck clearances to water.

    It isn't so much for slamming and such, but sloshing at rest could be annoying and towing would be difficult without.
     
  4. Rumars
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    Rumars Senior Member

    It's possible to do it like in your latest drawing, but it does not make sense. If you are using the house roof as one plate of the box girder you need the equivalent strength on the bottom. It's much simpler to close of the bottom and make it a monohull, then cantilever the sidedecks from the house floor. One word about the sidedecks, while the all around terrace you drew is nice, it's only usefull if the house is moored in the middle of a lake. In a marina it's useless, all you will see from it is your neighbors hull, and nobody sane goes swimming in a marina. People will all sit on the roof, wich gives a nice elevated view. You only need one sidedeck, on one of the short sides, where the entrance is, and maybe a stair to the roof.
    Another point you need to keep in mind is soundproofing, nobody likes to be wakened at 4 in the morning when the fishing fleet goes out, or kept awake by the neighbors loud athletic activity.

    Back to the structure, there is no need to align the house framing with the pontoon framing, they are not strip foundations. The whole thing behaves like a raft foundation, it does not matter where the framing lands. You should decide if the pontoons are structural or not, so you know where to place the primary longitudinal load bearing members (inside the pontoons, or outside).

    May I ask why you decided for a wooden construction with gluelams?
     
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  5. SNGPSo
    Joined: Feb 2021
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    SNGPSo Junior Member

    Alright, I will revert the last changes and connect the 2 pontoons to make the monohull. Anything with better resistance is good in my book.

    The all-around terrace is still useful to me. The emotional agency of an all-around balcony is important to me, even if it may not be used to sit/relax in. Also, I was thinking about using a ladder, but I might substitute that with wooden stairs I think. Also, I decided on wooden construction with gluelams because the cost for materials and labor is more affordable where I currently am. I am thinking about using epoxy and fiberglass to make the barge waterproof and long-lasting.

    Thank for bringing up soundproofing. Yes, I am thinking about using Mass Loaded Vinyl with putty and sealants where necessary. Since floor-to-ceiling glass elements are important to me, I am thinking about simply using sound-absorbing curtains to help with soundproofing in those areas.

    What about this barge design? I definitely want to go with the safest, most structurally sound system, even if that involves some additional materials. I will control water displacement by changing the height of the barge. I just want to nail down the overall system first, before tunning the finer details.

    Barge Design.png
     
  6. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    I think you are making your life too complicated. What need do you have to carry 50 m3 of empty space (I have not done the calculation, I do not know if it is 50 or 32 m3). The ship will make very few movements and, I suppose, towed, so why do you want to make a hydrodynamic hull? But you know better than I what you need.
    The structure you drew days ago (post #38), in which all the elements were connected, seemed very correct. In the latter, each element seems to be independent of the others, the longitudinal bulkheads above the deck do not have their corresponding reinforcements below the deck, there are no b rackets that join horizontal reinforcements with the vertical frames, ... in short, everything seems a bit disjointed .
    I have the feeling that things are getting complicated but not getting better. If my comments are meaningless to you, please forget them, they are only opinions.
     
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  7. SNGPSo
    Joined: Feb 2021
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    SNGPSo Junior Member

    You guys are kind enough to lend help, so please keep in mind that I learn from and appreciate every single comment, from everyone. I just like to work in an iterative process, and I have every previous iteration saved, including the one from post #38.

    I too feel like this last iteration I did might be overengineered. I do my best to research and understand the concepts you guys bring up, and I feel like my executions in the design might not reflect what you guys communicate to me, potentially. If that is the case, I apologize.
     
  8. fallguy
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    fallguy Senior Member

    I think you are to a point where the NA you choose will want to influence the design to their preferences. Rather than beat the horse; find the architect.
     
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  9. SNGPSo
    Joined: Feb 2021
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    SNGPSo Junior Member

    I proceeded to calculate the center of gravity for the whole structure a few days ago. My plan is to get a CoG coordinate for every type of material that has a uniform density, and then figure out a way later on to take the average of those points based on material density. I feel like that is a logical way to get the final CoG for the whole boat.

    The spheres are just to help me display the points better:
    CoG 1.png

    All the results I got so far are right in the middle, which I think is good.
    CoG 2.png
     
  10. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    I just saw this posted on the Wooden Boat Forum group on Facebook, and I thought of your house boat - not that there is any resemblance, far from it - yours is much more stylish - but this one is the essence of simplicity, and obviously works well.
    Here is a link -
    Kent Sampler https://www.facebook.com/groups/45928256385/permalink/10157469028376386

    It looks rather like they started off with a trimaran shape with pontoons, and then added the vertical drums for additional buoyancy between the pontoons.
    Maybe they did a weight estimate calculation halfway through the construction, after the hulls were built - or maybe they launched her, and then realised they needed some extra buoyancy.

    Perhaps what this photo is trying to say is 'keep it simple'.

    Houseboat.jpg
     
  11. TANSL
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    TANSL Senior Member

    What meaning do you give to the term "additional buoyancy"?. Because I can't quite understand it. A floating object must have the necessary buoyancy to correctly withstand the various conditions in which it will find itself throughout its life. In my view, "additional buoyancy" is a misleading term that seems to give the object a higher safety factor, but it is not correct. The designer must provide his design with the necessary buoyancy, correctly distributed, to face all the circumstances foreseen in the SOR, and nothing else. The rest, honestly, I don't know what it means nor do I know, of course, how it is quantified. How much additional buoyancy can we advise the OP to plan for his house boat?.
     
  12. bajansailor
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    bajansailor Marine Surveyor

    Oh Tansl! I think that you are being pedantic now.
    If you launch a vessel, and you find that you did not do your sums correctly, and you find that she is floating with the deck almost awash rather than at her design waterline, what would you do?
    I would try to add some 'additional' buoyancy somewhere.
    We do not need to advise the OP to plan for 'additional' buoyancy for his boat, because he is designing it properly, and doing detailed weight estimates.
    But if for some reason he launches the boat and finds that she is much deeper in the water than expected, then he might have to consider retro-fitting some additional floatation (is this a better term?) to bring her back to her intended waterline.
    A bit like what the folk in the photo above might have done.
     
  13. TANSL
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    TANSL Senior Member

    @bajansailor I do not want to be pedantic but to express a point of view. Anyone can make a mistake in a design but trying to foresee everything predictable and, just in case, add a supplement of whatever it is, I think that is not the way to design a boat. If that's a pedantic idea, well, okay, I'm pedantic. If, as a designer, I feel so insecure about what I do that I force myself to take extra assurances, in addition to what my calculations say and rules aks for, the best I can do is stop designing.
    And please do not be angry with me, I have high esteem for all the comments you make but if I see something that seems unnecessary or superabundant, I say so.
     
  14. bajansailor
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    bajansailor Marine Surveyor

    Dear Tansl, I am not angry with you.
    But I never suggested that our OP should add a 'supplement'.
    Nor that he will need to do so.
    The comment re the 'additional' buoyancy was in regard to the photo that I posted above.
    To me, it looks like they might have added some 'additional' buoyancy (for want of a better term) at some stage, to cope with the (additional?) weight of the vessel.
     

  15. fallguy
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    fallguy Senior Member

    I will take some credit for bringing reserve buoyancy up. The point about it was to not design for zero deck clearance or to design 'too close'. Zero deck clearance would cause splash and slosh in the marina from the smallest wake. It would also prevent raking the hulls to make them easier to tow to design too close. There are many ways it could be done, but deck clearance is part of the design and reserve buoyance is a way to achieve it.

    But we are falling to friendly polemics because there is little else to offer the OP.

    Any NA is going to imprint their own ideas on the design.
     
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