Houseboat floats

Discussion in 'Boat Design' started by wirescale, Oct 30, 2022.

  1. wirescale
    Joined: Oct 2022
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    wirescale Junior Member

    Hi

    I am planning to build a houseboat 8.5’ x 24’ max weight 5000 pounds.

    I am looking for the best/safest cost effective floats and I have come up with 2 options

    1. A set of 2 aluminium 24" diameter pontoons
    2. A set of 2 wooden/fiberglass cat hulls 2’ x 4’

    which one of these would you recommend? How do we calculate the floatation? Do I need more than 2 pontoons/hulls to support the 5000 pounds and/or larger/higher pontoons/hulls?

    i have seen pontoons using HDPE r320 culverts. Would that be a safe alternative for the houseboats floats?
     
  2. Andrew Kirk
    Joined: Jul 2021
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    Andrew Kirk Pedal boater.

    You need to work out how much flotation you'll get from your options. 2 floats of 24" diameter and 24' length would be half submerged by only 4,700 lbs of weight. You also need to be able to move around a house boat without it being unstable so you'd need, I believe, more than the 4 such floats which would fit under your boat.
     
  3. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Welcome to the Forum wirescale.

    May I add a third option please?
    This would be to look up the many plans available online for building houseboats, and find one that comes closest to your requirements.

    Especially as you say :
    For a rectangular shaped hull, that has dimensions L x B x D, if you want it to float at half the depth of the hull, then the floatation required is L x B x 0.5D.
    This will give you a volume in cubic feet or cubic metres.
    If you are using imperial, 1 cubic foot has approx 62 lbs of floatation, and in metric, one cubic metre has 1,000 kg of floatation.

    Here are some links for plans to start you off with.

    Shop - Plans and Kits - Houseboats - Glen-L Marine https://www.glen-l.com/Houseboats/departments/7/

    Clark Craft - Boat Plans, Boat Supplies & Marine Epoxy https://www.clarkcraft.com/cgi-local/shop_responsive.pl?type=item&categ=010&item=933342054&cart_id=847386fa0f6aac971bba3ec132cd76a1

    Here is one example of Sam Devlin's houseboat plans - there are some others as well.
    Lingcod 27 | Devlin Designing Boat Builders https://devlinboat.com/lingcod-27/

    And a motley assortment on Duckworks -
    Plans & Kits - Plans by type - Powerboats - Houseboats/Livaboards - Duckworks Boat Builders Supply https://duckworks.com/houseboats-livaboards/
     
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  4. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    It seems that the OP has come to the conclusion that he is offered 2 options. Why not comment on them before offering him another option among all those that, I am sure, he already knows?
    Another question : Why should the draft at full load match the radius of the cylindrical floats? Thanks in advance for the clarification.
     
  5. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    I guess this is directed at me.
    How are you so sure that Wire knows about the other options available?
    I listed some links for plans, just in case he is not aware of them. I thought that they might be useful reference.

    Re commenting on options 1 and 2 - Andrew has offered opinion above.
    If Wire uses 24" diameter pontoons that are 24' long, then for a displacement of 5,000 lbs the pontoons will be immersed more than halfway - and this is not very safe really.
    Ideally the draft on circular pontoons really should not be more than 40% of the depth.

    If Wire uses 2' wide pontoons that are of rectangular cross section, then he will get a lot more buoyancy / floatation - assuming that the cross section is uniform along the length, then he would have approx 5,950 lbs of floatation at a draft of 1'.
    Whereas the circular pontoons only have approx 4,675 lbs at a draft of 1'.

    I suggested Option 3 simply because Wire does not appear to know much about boat design (re his question about calculating floatation), and buying a set of plans is by far the safest / easiest / most economical / least stressful option for him in the long run.
     
    Last edited: Oct 30, 2022
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  6. wirescale
    Joined: Oct 2022
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    wirescale Junior Member

    Thank you everyone. You are right I am really novice but my plan is to build the houseboat with simplicity in mind, not over complicated and I want to keep it as such, still it has to be safe. I did more research as I am completely new as I said to this and still have more to learn. I find this formula to calculate the max weight:
    Floats volume (cubic feet) X 60lbs

    That’s the max load which means the density is neutral. Beyond that number, the boat will sink. If I want the floats to be 50% out of the water and increase the positive buoyancy I will have to lower the load by half or add more hulls. Does it make sense?

    I still need to understand how to distribute the weight on the platform, how to counter balance the engine load and a couple of other things.

    We are 2/3 weeks away from the first snowflakes here at the north of the border and I will try to do some experiment outside with a miniature replica of the houseboat in the pool so I can better understand how I should distribute the load, find out the right hulls dimensions and form etc.
    I will try to share my findings. Based on that I will eventually start building the hulls in the garage if not using HDPE drums or aluminum floats, and wait for next spring to build the platform and continue with the house build.

    I have found this brilliant idea to build a floating dock, would that be a good/safe alternative for the houseboat platform if I want to use the houseboat for cruising?
     
  7. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    @wirescale your reply above further reinforces my opinion that your best bet is to buy a set of plans for a houseboat design that you like, and go from there.

    Please do have a look through the various links I have posted above - there must be something in those links that appeals to you?
    There is no shame in buying plans - and by doing so you will invariably save yourself a lot of money, time, heartaches, stress and grief.

    If you want to build a floating platform, this will work - but if you want to use your houseboat for cruising, then please do not build hulls like this.
    Again, please see the links I gave you above, where you either have a barge shaped hull with a rake on the front (no worries then about loading it past the halfway mark on the tubes) or you have 'proper' boat shaped hulls in a catamaran configuration.
     
  8. clmanges
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    clmanges Senior Member

  9. wirescale
    Joined: Oct 2022
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    wirescale Junior Member

    Thanks for the links. I am looking for a design like these sitting on a floating deck, a tiny cubic house, more than a classic boat actually

    EDAEB5BF-BF33-4919-A025-AE49309DE3C8.jpeg 8F239F36-423D-405B-BBF9-A147536A5659.jpeg
     

    Attached Files:

  10. TANSL
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    TANSL Senior Member

    In the photo on the right it is clearly seen that the freeboard does not have to be linked to the draft of the floats. That is, whatever the floats submerge, the "safety" of the boat may be sufficient. On the other hand, the difference between the light weight and the fully loaded weight will not be very large, so a prop can be provided to ensure that the pontoons have enough buoyancy reserve to always have adequate freeboard.
     
  11. fallguy
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    fallguy Senior Member

    Typically pontoons are not sufficient for houseboats. The weight of the pontoons and the engines and fuel and water, sole, roof, walls, deck and gear will rapidly exceed 2.5 tons.

    Most amateurs build heavy.

    Most small houseboats are built on a barge hull. A 20 gallon water supply and small 15 gallon b/w tank alone is 200 pounds.

    A tiny house with a kitchen and galley and fridge quickly add.

    Structure to support an 8' wide roof, not light.

    Most 25' houseboats need barge hulls or something with excess displacement.

    I have a powercat that is 34' oal and about 16.5' wide. If I made it all house; the hulls would be too small.
     
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  12. wirescale
    Joined: Oct 2022
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    wirescale Junior Member

    I have decided to go with fiberglass for the hulls 2x2x24’. There will be 3 hulls total. It will be designed so that I can easily add/remove/replace a hull when required.

    Phase 1:
    - hulls and platform build this winter
    - floating/load testing next spring

    starting this weekend…
     
  13. bajansailor
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    bajansailor Marine Surveyor

    Building three hulls will be a lot more effort, and cost a lot more, than building two.
    And a trimaran will most probably have more resistance (requiring more power from the engine) than a catamaran.
    Not to mention extra antifouling paint to buy and apply!

    If you have a good design to start with, why would you want to easily add / remove hulls?
    Do a very careful calculation of the buoyancy that you will have at different drafts with different sized hulls (eg 2' x 2', 2'6" x 2'6" etc) and then compare these figures with the detailed weight estimates listing the weight (estimated or calculated) of every part of the hull and all the outfit items - and if you are doing it in a spreadsheet, mention the centre of gravity of each item as a lever distance from the transom, so that you can take moments about the transom to find out where you calculated centre of gravity of the boat will be.
    If you do not do this, you might well find that she is trimming down by the bow or by the stern when you launch her.
    Please don't start building until you have become proficient at calculating the weights! You might find that you will need to alter the design. This is called the design spiral, and if it works out 'perfectly' on your first loop around the spiral, you have done very well. Most people have to go around the loop many times, changing things slightly as they go.

    Please do also consider buying a set of plans online for a boat that comes close to what you are thinking of, even if you only use them for general reference to help you design your own boat.
    The cost of buying a set of plans will be a very tiny percentage of the cost of building the boat.
     
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  14. wirescale
    Joined: Oct 2022
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    wirescale Junior Member

    Totally agree. The problem is that I can’t find a plan/design that I like. The one that I will probably buy is this one ECO 62 Houseboat Plans https://duckworks.com/eco-62-houseboat-plans/ but only to help building the hulls and the frame. I don’t really like the houseboat design in that plan because I already have another houseboat design in my mind, something more luxurious and futuristic like this one

    E93C2616-B558-48D2-A4E5-1D8ECE6B5AEF.jpeg

    When we talk about center of gravity and buoyancy, is it for the hulls and the platform or for the whole houseboat structure including the hulls? In other terms, if I build the platform and the hulls based on the plan above and the calculations provided, would it be safe enough to continue building my own designed houseboat with substantially the same size and weight but again a different design inside and out?
     

  15. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    That Eco 62 design by Bernd Kohler is a very nice design - a lot of thought and experience has gone into it. Please bear this in mind.
    I think that the Eco 62 looks more futuristic (and certainly a lot more practical and sensible) than the boat shown in your photo above.
    Be aware also that the Eco 62 will be a LOT more 'seaworthy' than the boat in your photo - and if you want to go 'cruising', even on relatively sheltered waters, your hull(s) still need to be able to cope with some choppy water perhaps induced by wind and / or tide.

    No.
    How do you know that your houseboat design will be substantially the same size and weight as Bernd's, especially as the design will be (very) different?
    You will have to be VERY zealous re your weight calculations and estimates re your centres of gravity for all these weights, simply because you are deviating significantly from a known design, with known weights.
    Be aware that the Eco 62 has relatively slender hulls, and will not take kindly to being 'overloaded'.
    Re your photo above, I am guessing that it just has a very simple barge hull form underneath that house - do you have a link for it?
     
    Last edited: Nov 3, 2022
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