DIY pontoon, 30ft - epoxy and styrofoam...?

Discussion in 'Boat Design' started by bib_ak, Dec 25, 2014.

  1. bib_ak
    Joined: Dec 2014
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    bib_ak Junior Member

    Hello everyone!

    I am playing around with some ideas/dreams of building a low budget houseboat. And really, my experiences with boat design/constructions are fairly limited... But I know how to do woodwork, being a carpenter for 10 years.

    What I am hoping for in this thread, are some tips on the lower parts of the boat - meaning the pontoons to be precise :)

    Alright, some info on my ideas for a build:

    Size: 30ft. long, 8ft. wide. Why so slim? I need to be able to transport it on the road (trailer). To make it more stable sideways, I intend to have some deck and a pontoon extra on each side, which can be (relatively) easily de/mounted. Here are some really unfinished Sketchup's:
    [​IMG]
    [​IMG]
    [​IMG]

    So, the decisions about materials for pontoons... Plywood and epoxy would be easiest, since I'm not afraid of woodwork. But pricier than other alternatives. Stainless or aluminum? Way to expensive, since I'm no good with welding (used water heaters etc.). Empty barrels of some kind of plastic material? Hm... maybe, but should be foamed for safety, and from what I've read, it's not easy/cheap to foam without proper measuring tools.

    What about using a simple design - styrofoam plates (or similar), glued together and shaped as pontoons. Then use a layer of epoxy to seal it, and use fiberglass and polyester resin to make it waterproof. I'm thinking 3 layers of fiberglass. But will it be solid enough? I will be using the boat on salt water, but very protected by lots of islands, so the waves are mostly small, and there are lots of places to find protected from bad weather.

    Any ideas are very welcome, even if it's for warning me to stay away from the sea forever :)
     
  2. bib_ak
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    bib_ak Junior Member

    Don't know why I didn't find this thread earlier, but it answers my idea of using foam core and polyester quite well.... http://www.boatdesign.net/forums/boat-design/design-crazy-51624.html

    So, probably plywood after all then... But I don't like the idea of the boat going down if hitting a rock... Maybe build several isolated chambers would help some. No used pontoon boats in Norway I'm afraid.

    Or are there other cheap ways to build a pontoon?
     
  3. TANSL
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    TANSL Senior Member

    Very nice pictures.
    In relation to the material I can not advise you. As a floating object, I think it may have serious problems with the trim. Not to mention the possibility that with very small waves whole house is flooded. It should make a study of buoyancy and stability.
     
  4. bib_ak
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    bib_ak Junior Member

    Yes, the drawings is not very accurate concerning buoyancy (it will be calculated well), and there *will* be more distance above sea level :) I'm thinking approximately 3ft. or so. The cabin will be really simple, and some water on the "kitchen floor" is acceptable on the way home, if the wind suddenly takes up. But I should design a "wave breaker" in front as well, in case of sudden waves from a larger boat when anchored.

    Stability is more of a concern - yes... The side pontoons should (in my simple mind) be more or less unused when lying still and well balanced, and mainly prevent a fall over from waves or lots of people on the same side. But this would cause the boat to be less stable, right? Should all 4 pontoons be equally loaded?
     
  5. rwatson
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    rwatson Senior Member

    With the boxy topsides on thin hulls, you may also need to consider the engineering, as well as stability. A big wave broadside on with the narrow beam depth in the side decks could be a problem.

    For the easiest engineering, and the least problematic building, I dont know why you don't just do a full flat bottom hull shape (with a few chines for increased efficiency ) and be done with it.

    Those small, streamlined 'pods' seem to be an unnecessary complexity for little performance gain. The big killer in moving boats is wind in the superstructure, and you show NASA style hulls, and a Boxlike superstructure. Wind affect is a huge part of the design problem.

    Also, the idea of a houseboat is maximum capacity with minimum expense, and moving all your weight up on tiny pods defeats the purpose as well as complicating the engineering and building.
     
  6. PAR
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    PAR Yacht Designer/Builder

    To further RWatson's comments, a full hull, permits the accommodations to be lower, which helps (greatly) in stability concerns on structures like this. As drawn, several folks running to a rail, to see a naked girl retrieving her overboard shorts, could cause a capsize. This happens more frequently then most realize, with these types of boats (houseboats, pontoon boats, shanty thingies, etc.).

    With a flat bottom hull, maybe a jon boat style or pram for deck volume, you'll have a more stable platform and the equipment (tanks, generator, fish wells, storage lockers, etc.) can be placed low, where their weight is of benefit to the stability curve. The other benefit of these hull forms is the immersed volume, which will support more than pontoons and if shaped well, will also be more efficient underway. Cylindrical pontoons are about the worst shapes to employ.

    The first thing you should do is a preliminary weight study, given the general accommodations workup you've started. Figure out what it'll take to build the house, with all the stuff you plan to have in it (including max crew and stores). With this, you'll know approximately what you need to hold up, so you can size the immersed volume in your hull(s). Naturally a worst case situation should be envisioned, with an appropriate safety margin worked in as well.
     
  7. TANSL
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    TANSL Senior Member

    As has been previously mentioned the most comfortable would be one hull, or more, parallelepiped with some corrections for better water flow. However, if you insist, for whatever reason, to put NASA style rockets hulls, you should note that it will take to perform highly accurate calculations of ship loading conditions and circumstances of wind and waves it can support. Must perform a structural study on binding of hulls to deck, ... anyway, complications, which can be resolved, but does not make it easier, nor cheaper, the construction.
     
  8. bib_ak
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    bib_ak Junior Member

    Thank you for your feedback! Much appreciated :)

    Alright, what about this: I make the main/middle part of the boat a flat bottom hull - a bit like this, made of plywood and epoxy (or polyester resin?):
    [​IMG]

    But I need the "addon's" on the sides making the boat practical to use - these should have pontoons, generally designed with a buoyancy of holding only the weight of people (let's say 10 adults, 800kg + the weight of the structure of the "addon's". Would the shape of these pontoons matter in this case? I mean, if they are round or flat bottomed?

    Keep in mind: I do not plan on living in this boat - it's purely for pleasure and summer holiday. The boat will only be in the water for 2 month's a year. Primary use: bathing, making simple meals, reading a book, having a few beers and sleeping. Very basic interior.
     
  9. PAR
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    PAR Yacht Designer/Builder

    I don't think you really have sufficient enough of a grasp on the realities of something like this (no offense intended).

    For example a 30' x 8' barge like hull with modest rocker (assuming about a 27' (8.8 m) LWL, will displace in the 3 ton range, with just 6" (152 mm) of immersion, not counting your two 3/4's of a ton pontoons attached to the sides. Are you capable of designing a structure, to resist the loads that the water and wind might impose, let alone the equipment and crew?
     
  10. rwatson
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    rwatson Senior Member

    If you want to have side decks, which would be a plus on a narrow boat, you could have hinged platforms on each side, with 'drawbridge' style cables or chain supports.

    If you kept the side decks open, like a lattice or patio deck, that would allow the odd larger wave or wind to have minimal effect. You still have stability issue to think about, given the high superstructure.

    It wouldnt be very expensive to have a qualified person calculate the amount of ballast required to avoid a capsize from 4 or so people and their kayaks on one side.

    From similarly configured hulls, you could even do it with water ballast, of which a fair amount could be fresh water, a desirable asset on a houseboat.
     
  11. bib_ak
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    bib_ak Junior Member

    I am absolutely aware of the fact that I'm a carpenter, not a boat builder, and are humble enough to agree - I'm far from an expert, and unsure if I'm up for the job to make this right. I have been reading quite a few threads in here before I registered, and knew I would be discouraged to continue on my ideas - and that's fair. But that doesn't mean I'm giving up :)

    So, back to the drawing table. I need the superstructure to be lower, to reduce wind impacts. Using a hull design for the middle part would make it possible to reduce it with 3' or so. The fence on top deck is not supposed to be a wooden one, just something to held a pair of ropes, so no wind impacts above the roof/top deck.

    I'm surprised the side deck's are making more bad than good to the design, I was certain this would make it much harder to capsize, and make it more stable in general...
     
  12. TANSL
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    TANSL Senior Member

    I'd like to encourage you to continue with your idea but probably need some improvements. I think everyone here want to advise you not to let drop the idea, but for you consider some of the problems that may occur.
    What you have to do is to write down everything you want your boat to be able to do, all the services you expect to receive the boat, and an expert can then define how they should be hulls so that the boat support the work to be perform.
    Therefore, do not be discouraged, work together with a technician. You do your part and let the technician get the boat afloat correctly.
    Good luck.
     
  13. rwatson
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    rwatson Senior Member

    You are not wrong, just not calculated.

    If you make the side decks, say 150mm thick, they will provide bouyancy, true.

    BUT

    Will they stay intact when submerged , either from the pressure of the listing main hull, or a large wave trying to lift the side deck against the weight of the main hull ?

    If you have a list on the main hull, will the beams or whatever is supporting the side decks be strong enough to not snap ? This is double important considering they have to be removable.

    This is what Tansl and others are saying - get it checked by a professional to ensure safe and satisfactory performance.

    Re windage - a lot of benefit can be gained by slightly sloping the sides, and also by putting a radius on the edges. ( vertical and horizontal )

    This may also make a side benefit of reducing that annoying wind whistle you get on windy nights.
     
  14. gdavis
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    gdavis Junior Member

    hello bib-ak,you can buy Styrofoam billets that are used for docks and floats. Just cut a 45% angle on the ends and call it good. I've seen these things 25,30 yrs old with no fiberglass on them, you can't use fiberglass resin because it melts the styro, big mess. Epoxy, yes.How often are you taking this puppy down the road? You could build it wider and get a wide load permit or build it kinda modular and put it together on the shore. Maybe? Check out Ron Hubbards book "Shantyboat",a perfect simple design that was taken down the Ohio and the mighty Miss. rivers. This design is more than proven! As a carpenter you could easily build this, its a little barge hull with angled ends with a simple cabin on top. The bottom of the hull is basically the floor so the weight is kept low. You should really try to keep this whole project as simple as possible. I see so many projects get way too complicated, this isn't a spaceship and you don't need rocket science to build it. The more complicated it is the more costly it becomes and the longer it will take to finish! Google shanty boat and look at the designs that are simple and practical then take it from there. Again Hubbards shanty boat is proven enough to just go ahead and build one. Also, Wooden boat mag did an article a while ago on a riverboat, sternwheeler museum and in that article was a picture of a rivermans shantyboat, another really nice design that would be easy to build, no need for rounded anything. And again maybe put it together at the waters edge. So good luck to ya, living on the water is a beautiful thing. I've been doing it for 17yrs now....peace........g
     

  15. gdavis
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    gdavis Junior Member

    me again, that's Harlan Hubbard not Ron.....later
     
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