Need Advice with Houseboat Construction

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

  1. bajansailor
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    bajansailor Marine Surveyor

    If you wanted the barge to be capable of getting underway to a different location, perhaps with an outboard motor (or 2), then a catamaran hull would make sense - it would not need to be anything fancy, just two rectangular hulls with raked stems and sterns would work fine.
    If the underside of the bridge deck is just immersed in the load condition (and just above the water when light), then you will have better stability as a result of the bridgedeck immersion, and less resistance when travelling in the light condition.

    But this is just going to be a sedentary house boat, so a simple rectangular hull, again with raked ends rather than vertical, will be fine for what you want.
    I am thinking that the main driver here is the desired amount of accommodation - what is the absolute minimum area that you can fit everything into?
    There are some very ingenious 'tiny houses' now that make very good use of the space available.
    On your budget, you want the deck area to be as small as possible - in view of this, do you really need to have a walk way all around the boat?
    If you omitted the side decks, and just have patios / open decks (call them what you like) fore and aft, then you can make the house a bit wider, and for the same floor surface area reduce the house length - and hence reduce the barge length, which will save on material costs significantly.

    You should not have an issue with buoyancy with a simple rectangular hull form - but you still want to design your house, and do a detailed weights estimate for it, including all the tanks and outfit items, to see what the total weight will be.
    Then you do an initial weight estimate for all the plywood and framing that will go into the smallest (re length and breadth) hull that will support the floor area required. A spreadsheet is good for this.
    Add the hull weight and the house weight together.
    You know the length and breadth of your barge, so you can calculate approximately how deep it will sink in the water with this total weight.
    Once you know the loaded draft, then you can decide how much freeboard you need.
    The ideal amount would probably be slightly more than the height of the dock to which it is moored?
    If it is a floating dock, then you will always be at the same height approximately (depending on the amount of consumables you have on board), so access will be easy.
    If a fixed dock, then you might have some effect from the tide - do you have much tidal range on the Med coast in Morocco?
     
  2. SNGPSo
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    SNGPSo Junior Member

    Oh, that makes sense! The fact that I can have better stability with the underside of the bridge deck immersed with enough live load. Even if I have very limited shipbuilding knowledge (heck, I google most of the terms you guys throw at me just to know which component you are talking about LOL), I try to imagine miniature models of said ships with said components and how they would react when placed in a bucket of water. Ok, so I should remember to design an underside that barely kisses the surface of the water when enough weight is added.

    Yes, I made the end of the 2 pontoon hulls raked instinctively because I thought it would help when the houseboat is being towed.

    Regarding the plan size; everything is studied down to the last centimetre. The walkway is very important to me because it extends/opens up the interior space both physically and psychologically; it feels much more liberating when you know that you can 'take a walk outside' even in a tiny houseboat. Besides, that balcony space is not wasted because when you slide the doors of the living room or bedroom, the interior space incorporates that extra space and you suddenly feel like you are in a bigger room with a balcony straight to the ocean. See, my baby is pretty special you know!

    Yes, the weight calculations will take time, unfortunately. I will do a diagram of 3D components with all the calculations next to each of them and share it here with you guys.

    That marina area you saw in the map is hermetic from the ocean. The water is still pretty much all the time, I think. That means there is no tidal range, correct?
     
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  3. TANSL
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    TANSL Senior Member

    You start with something simple. Assume the weight of the entire boat is 10,000 kg. As the platform area is 7.7 m2, assuming you use a single pontoon of this surface, it would submerge 130 mm in the water. Is this what suits you?
    A catamaran has much more initial transverse stability than a pontoon. Keep this in mind, if it's convenient for you.
     
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  4. fallguy
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    fallguy Senior Member

    Another reason for raking the ends is this become reserve buoyancy. The more passengers partying on the boat, the more the ends will sink..
     
  5. bajansailor
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    bajansailor Marine Surveyor

    Just a thought re your overall dimensions of 14 m. x 5.5 m.
    I think that most marina berths in Europe come in different standard sizes, and that 12 metres maximum length is one of these sizes - you might well find that you have to pay a lot more for a berth re how the boat is 14 metres long.
    I am thinking that as the boat will live in a marina berth, you want to design it to fit that berth size to the max, to make the most of it.

    And re how the beam is 5.5 m / 18' - where are you planning on building this boat?
    If you have to transport it by road to the marina you will probably need all sorts of special permits and a police escort, if it is indeed allowable.
     
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  6. SNGPSo
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    SNGPSo Junior Member

    If she submerges by just 130mm with the 2 pontoon hulls, then that would be pretty good TANSL. I was thinking she would need to submerge some 30-40cm given our parameters. But 130mm is great! Yes, the main reason why I switched the barge to a catamaran is for that transverse stability, and there's less material so it's a win-win.

    That's great because I imagine lots of people will be partying, fallguy! Hahaha

    Thanks for the comprehensive advice bajansailor! You are bringing thing that I honestly did not think about. I checked the berths in Saidia and they accept up to 40m, which sounds like a lot to me. I should check the berth sizes again just to make sure. The boat is to be built in a warehouse right next to marina, and the construction guys are also located in Saidia.

    Thanks for all the input, guys! Hopefully, when construction begins, I will start putting progress images in here.
     
  7. TANSL
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    TANSL Senior Member

    Sorry but 130 mm depth is with one pontoon 14x5.5 m (77 m2). Just do the calculation. 10000 kg need 10 m3 of displaced water to compensate this weight. So : 10 m3/77 m2 = 0.1298 m depth
     
  8. fallguy
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    fallguy Senior Member

    What part of the ocean is not affected by tides?

    something seems amiss with that concept
     
  9. fallguy
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    fallguy Senior Member

    Instead of referring to one pontoon; don't you mean a single barge hull? That is, a single barge 14x5.5 with a load of 10,000kg sinks 130mm, or about 5"?

    We had just succeeded in convincing him pontoons may sink too far and now we are referring to the barge as a pontoon.

    Or am I confused?
     
  10. fallguy
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    fallguy Senior Member

    If you use two rectangular hulls one meter wide each, they have area of 14x1 times two or 28.

    10m3/28m2 is 357mm deep or roughly 14" (sorry, but I need inches for sanity)

    Of course, this is all against the same assumption, but one quickly realizes the difference.
     
  11. SNGPSo
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    SNGPSo Junior Member

    I thought any part of the ocean the is sealed off by rocks is not affected by rocks, but I guess that's a stupid thing to say hahaha. Sorry for my very limited knowledge about the topic.

    Saying one pontoon confused me for a while as well, but I quickly realized what TANSL meant. I ran another calculation for 2 rectangular hulls, one meter wide each, and I got exactly the same number as you, fallguy. Two 14'' pontoons are perfect for me, especially with the free additional transverse stability we gain.

    After checking with the wood construction guy, I am adding some wooden framing members for walls/ceiling. I will run a weight estimate once I have all the structural framing is in place.
     
  12. TANSL
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    TANSL Senior Member

    I am sorry that my poor form of expression misleads you. But I must say that I have not seen anywhere that a floating object that supports a load is called barge but that if there are two supporting the same load they are called pontoons. But, of course, English is not my strong suit.
    As naval architecture is more familiar to me, regardless of its English terminology, I would advise @SNGPSo to seek help from a technician (not amateurs) in naval architecture. I think that a technician who starts making houseboats should be able to detect what the problem is, regardless of the words I use
     
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  13. fallguy
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    fallguy Senior Member

    I said a one meter wide square box sinks 14"; not that a 14" pontoon is adequate. Pontoons sinking 14" is all assumptions based on 10,000kg and no change in the ends of the pontoons for reserve or motion.

    I second tansl here and think it best you get na involved. It may be required for the insurance anyhow.
     
  14. bajansailor
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    bajansailor Marine Surveyor

    Just a rather left field suggestion - re your side decks, you could consider having them cantilevered from the main hull, rather than part of it.
    This would save a bit on the materials required to construct the hull.
    And the stability (re the reduced beam of the hull) should be ok (but you should assess it properly first) if you just have a very simple barge shaped hull form, similarly the amount of buoyancy available, especially if you do not intend to add accommodation on the top deck as well.
    You could even have the side decks capable of being hinged and folded up (rather like the various folding catamaran and trimaran designs that are available) if there is a beam restriction anywhere - but it sounds like this will not be an issue.
     

  15. SNGPSo
    Joined: Feb 2021
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    SNGPSo Junior Member

    Alright, I will try to get professional help once I am back in Morocco, as I am in Spain right now.

    I do want the top deck to be accessible, bajansailor. That's very important to me. The plan has changed considerably since last time. I changed things around in order to make more easily built.

    My weight study shows that the whole thing will weigh 10100kgs, excluding the live loads and weight of tanks. I picked an approximate weight of 12000kgs after those weights are added, which will need 12m3 of displaced water. The new pontoons are 13,395m and 1.05m each. They have an accumulated area of 28,1295m2. 12/28,1295=0.4266m. I think a freeboard length of 1-0.4266m=0,5734m is good for me.

    Here are the new drawings so far. Note that the pontoons use marine plywood that is in 2,44m increments. I did this in order to be able to use the plywood's size with minimal manual measuring/cutting. Please check it out and let me know what you think guys.

    Edit: Please note that the schedule displays the weights in pounds.
     

    Attached Files:

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