Need Advice with Houseboat Construction

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

  1. TANSL
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    TANSL Senior Member

    Among the many calculations that must be made, among those corresponding to stability, with and without damage, there are some that seek to ensure that the deck never goes under water, not even when the boat is heeling. In addition, there are specific regulations that require that, with the boat balanced and stable, the freeboard has a minimum value. All of that means setting up an extra buoyancy, or an added buoyancy, whatever you want to call it. I call it giving the boat a minimum freeboard or compartmentalizing the hull so that the margin line can never be submerged, even when one or more compartments have been flooded. No designer, least of all in a houseboat, should ignore these calculations.
    I think these discussions, which are of course friendly, can help the OP to know or remember what to keep in mind. If, for whatever reason, he could not calculate them, surely there are people here who can give him a hand.
     
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  2. SNGPSo
    Joined: Feb 2021
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    SNGPSo Junior Member

    Hello everyone.

    I should thank everyone for giving me a lot of guidance thus far. I would like to put my latest results here so I burden them less, and share them with anyone who might need help with something similar in the future.

    So the pandemic is making gathering the necessary papers really difficult thus far for me, but in the meantime, I thought about changing the pontoon materials to something cheaper.So I decided to use High-Density Poly Ethylene (HDPE).

    Here is a schedule of my materials:
    (Autodesk Revit is giving me headaches getting me material densities in kg/m3, so I am using the native lb/ft3.)
    upload_2021-4-24_16-45-12.png

    33416.66 lbs = 15157.5 kg
    Assuming the live load with loud partying, and full freshwater, greywater, and blackwater tanks on the houseboat total up to 16000 kg, and that 10000 kg needs 10 m3 of displaced water, we would need 16m3 of displaced water for a 16000 kg houseboat.

    The 2 pontoons are cylindrical and 1m in diameter (including the thickness), and 14 m long. The area of the 2 circles is 1.5708m2, and the volume of the 2 pontoons is 22m3. Are the 2 pontoon volumes (22m3) also the same as the water displacement? The calculation is received prior is for a rectangular pontoon shape, so I am a bit lost now tbh.

    I looked around and found this: http://u-fabboats.com/brochure/weightcap.pdf
    It says that for two 39'' (1m) diameter pontoons, which are 45' (13.7m) in length, that the weight supported would be around 10432kg when the pontoons are 50% immersed.

    I did overestimate the densities of some materials, but I still need to use even bigger pontoons, I think.

    What do you guys think?

    Edit: The 2 pontoons will be filled with foam though... I think that should have an effect on the displaced water.
     

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    Last edited: Apr 25, 2021
  3. bajansailor
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    bajansailor Marine Surveyor

    Re your two pontoons, each 14 m long and 1 m in diameter - yes, the total volume contained by them is approx 22 cubic metres, giving a total displacement if both were completely immersed in fresh water of 22 tonnes.

    Note however that with pontoons you should not go beyond half immersion - hence the maximum safe displacement for these pontoons would be only 11 tonnes, and your weight estimate gives a displacement of approx 15 tonnes.
    I see that you have also shown a smaller pontoon on the centreline on your midship section drawing to give you some extra buoyancy - you would want to have the diameter of this pontoon sufficient so that at full displacement, the draft is less than 0.5 m (assuming that the main pontoons are 1 m in diameter).

    The only effect that the foam is going to have is that it will increase the overall displacement of the vessel, causing it to sink a bit deeper in the water.
    It does not give you any more reserve buoyancy - rather, you will have less, as your draft will be deeper.
    The only advantage of filling the pontoons with foam is if the pontoon(s) get punctured - but as you are just mooring the houseboat in a marina, the odds of this happening must be almost non existent.

    Early on, on the first page of this thread, I thought you had decided to go with rectangular midship sections for the hulls, rather than circular - or even just have a simple rectangular barge?
    These would be much more forgiving (especially so the rectangular barge) if you later find that your displacement works out to be a lot more than initially estimated. And this can happen very easily - it is very easy to add weight to a boat, and more difficult to take it off afterwards.
     
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  4. SNGPSo
    Joined: Feb 2021
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    SNGPSo Junior Member

    Then getting the displacement is just a matter of calculating the basic volume of whatever shape your pontoon is... Normally I am super OCD with numbers but this is easy. So if I replace the 1m HDPE pipes with 1.2m ones, I should get a safe 50% displacement of 15.82 tonnes, which is right around where I should be.

    The cylinder in the middle is actually a compartment for freshwater, greywater, and blackwater. So if I'm correct, it's actually a weight liability rather than a buoyancy element.

    I think I still would like to use the foam just to be on the safer side. Knowing that any impact or piercing damage to the pontoons won't affect the flotation of the house just puts my mind at ease.

    I decided to ultimately use the HDPE pontoons after seeing the gentleman use them in that video due to ease of assembly, and also because it will be much cheaper in the end.

    EDIT: I think I am making a mistake in the HDPE pontoon weight calculation... Anyone knows the weight of the corrugated pipes if they were 1m in diameter and 14m long? I scavanged around in Google and I -think- the 2 pontoons would be a little over 500 kgs.
     
    Last edited: Apr 25, 2021
  5. nick branson
    Joined: Apr 2021
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    Location: uk

    nick branson New Member

    Hello, not directly on your houseboat thread but I noticed your build is taking place in Morocco. Ive been trying over many hours trying to find contact details for wooden boat builders in Morocco with no luck. Would you have any suggestions of who to get incontact with?
     
  6. SNGPSo
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    SNGPSo Junior Member

    Hey Nick, does your boat motor along or is it stationary? Getting the necessary papers to be able to build a boat is incredibely tough here. I think I mentioned that before. Many builder I contacted refused working with me fearing that the boat might be used for illegal activity, especially considering that Europe is just a few kms away.

    I am still waiting for approval. I will let you know how that goes.
     
  7. nick branson
    Joined: Apr 2021
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    nick branson New Member

    Thanks for getting back! I'm after a wooden shell, without engine etc for shipment back to the UK. If the builder wanted reassurance I would be happy for them to include the cost of shipping out of Morocco! Sorry to hear about the paperwork, that must be frustrating for you. Maybe using spudlegs that support the houseboat from the seabed may reassure office staff?
     
  8. SNGPSo
    Joined: Feb 2021
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    SNGPSo Junior Member

    Hello everyone!

    I am slowly progressing. I have the wooden mold for the pontoons ready, and have decided to use Isophthalic Polyester Resin for the pontoons.

    Wood mold measurements:
    upload_2021-6-30_20-43-24.png

    ---

    Please take a look at this:
    upload_2021-6-30_20-55-22.png
    The idea is to have wood reinforcement (Orange+Red) inside the polyester resin in order to provide the pontoons with stiffness. The green lines show areas where the pontoons are subdivided inside with fibreglass composite against plywood walls. The blue lines are the floor joists of the houseboat nailed to the Orange+Red reinforcement.

    ---

    Wood mold:
    upload_2021-6-30_20-39-16.png
    Here is a picture of the construction progress of the wooden mold. It's ready for laying in the first fiberglass composite, which will itself be used as a mold for the final polyester cast.

    Since this is done on a tight budget, the little dents are 5 cm tracks for seat belts to wrap around the pontoon to attach to the floor joists and provide extra hold.

    For the fiberglass composites, I got 450 CSM and 800 Roving fiberglass. I intend to use the Roving sandwiched with 2 layers of CSM. I also got black gelcoat for UV and moisture resistance.

    Any feedback is welcome!
     

    Attached Files:

  9. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Thanks for this update - however I am a bit confused (this is easily done with me, don't worry).

    Re your wooden mould, are you going to use this as a plug to make a fibreglass mould, from which you will then make two hulls?
    Or will you use the wooden mould as a male mould, and take two fibreglass hulls off it?
    Either way, be aware that you need to have the top of the mould wider than the bottom, otherwise you will not be able to release the fibreglass component from it.

    I am a bit dubious about how you are going to lash the pontoons to the cross beams with these 'seat belts' - can you describe this in more detail please?
     
  10. TANSL
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    TANSL Senior Member

    @SNGPSo , as the title of the thread you started, "Need advice with house boat construction," says, listen to yourself and seek professional help. It will be cheaper and safer than everything that you have invested, going around on the subject, without being sure of hitting the correct design or the correct construction method.
    A nice render does not guarantee anything. Make a good SOR yourself (that's the only thing that only you can do) and consult a professional.
     
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  11. SNGPSo
    Joined: Feb 2021
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    SNGPSo Junior Member

    I have been looking for professional help for some time now, and still am, but without success thus far yet. I could not find any local professionals who have previously designed houseboats, but only boats.

    Yes, bajansailor, I am using the wooden object as a plug to make a fibreglass mould, from which I will then make two hulls.

    The belts are to wrap around the floor joists in this way:
    upload_2021-7-1_10-57-23.png
     
  12. TANSL
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    TANSL Senior Member

    Very bad solution. Quickly erase it from your design and keep looking for help, but first, write a realistic SOR yourself and decide on the material to use in the hulls. With that, I am sure, you will give the impression of knowing what you want and it will be easier for you to find help. Allow a professional to give the appropriate constructive solutions to what you want to build.
     
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  13. SNGPSo
    Joined: Feb 2021
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    SNGPSo Junior Member

    I appreciate your honesty. For the material of the hulls, I am using isophthalic polyester resin and have already ordered a container.

    For the fiberglass composites, I got 450 CSM and 800 Roving fiberglass. I intend to use the Roving sandwiched with 2 layers of CSM. I also got black gelcoat for UV and moisture resistance.
     
  14. TANSL
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    TANSL Senior Member

    The most resistant materials should be placed as far as possible from the neutral axis of the laminate, which is where the highest values of tension / compression occur. In other words, the layer arrangement that you have envisaged does not seem to be the most suitable, although it could happen (some number would have to be done) that was sufficient.
    Although the technicians in your country have not made any house boats, a qualified technician should have no problem designing this type of floating element.
     

  15. bajansailor
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    bajansailor Marine Surveyor

    Please do not do it this way! I can see endless problems with those strap lashings getting worn / chafed, and it is not an efficient way of transferring loads.
    It would be much better if your transverse beams were attached to frame upstands securely glassed into the hulls.
    If you anticipate the need to dis-assemble the vessel at some stage in the future then they could be through bolted; if no need for future di-assembly they could be laminated together.
    And if you are planning on including these 5 cm tracks in your mould, and laminating fibreglass into them, they will probably make it even more difficult to release the moulding from the mould afterwards.
     
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