Alright, where do I start looking for a design?

Discussion in 'Boat Design' started by parkland, Nov 4, 2012.

  1. parkland
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    parkland Senior Member

    I think, I might have found a design, and hull design I want, and think I have everything to a "feasible" level.

    The next step, is to find a real hull design so I don't have to guess what the right design and material might be.

    The included pictures are of a houseboat, which is the closest hull design I can find to what I want. Looks like a single chine design, with the sides being perfectly straight.

    Of course, as seen in MY design, I want to separate the bow and stern, on hinges, so they fold over the decks for transport.
    I don't think this will be hard. The front should be a piece of cake; the stern will need a couple special parts.
    Basically, I plan on using a star style coupler, so when lowering the stern in the water with a winch, someone would have to "wiggle" the propeller untill the coupler lines up.
    The shaft inside the folding stern would house the thrust bearings, along with packing. Packing would also be needed for the engine compartment.
    Steering could be hydraulic, so I don't see any problems with this design.

    On the trailer, it could be 36 ft long, and in the water, would be 48 ft long.
    10 ft wide permits are 30$, 12 ft wide are 70$.
    Depending on the design, will determine how big of a boat this could be, before exceeding weight limits.

    So, my question is; where could I find a design for an aluminum boat roughly this size, in the style of that houseboat hull?
    Something simple, utilising commonly available extrusions.
    I don't want to buy a CNC machine to make 1 boat. haha.
    I also don't want to waste too much weight on a stupid design, as that will reduce the size of the boat.
     

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  2. gonzo
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    gonzo Senior Member

    Couplers on boats are aligned to 0.005" that it five thousandths of an inch. That is a hard thing to do with a hinged system. Any folding boat is much heavier than a standard design. Also, the sections are going to be a handful to handle. How do you plan on lifting them to re-assemble the hull without a crane? 48 feet is within the legal length limit anyway, so what is the reason for the added complication?
     
  3. parkland
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    parkland Senior Member

    I bought a set of spider couplers for another project, they are not aligned that tight. There is a rubber seperator that goes between, it would be held in place by grease I suppose, till the section is fastened. They are available in lots of shaft sizes.


    41 ft I was told is the limit, although you can get permits. Shorter = less trailer= less weight. Although you raise a point, having them fold will add weight. I like the design though, it actually solves a few issues. One being the propeller hitting the road driving over uneven surfaces.
    The other nice thing, is that the bow section could be taken off and fixed it it happens to take a beating.
    The weight added would be the 2 bulkheads, and hinges, and extra material along the area where they are connected.

    But that also serves as a safety measure, should you flood the front or rear; it's not connected to the main body.

    I imagine the folding bow and stern could be lowered with a winch cable in some way. I don't have every detail worked out, but I don't see anything that would present a major problem.
    Those sections aren't giant, and out of aluminum wouldn't weigh all that much.
    I think you'd have to put them down before going in the water though; or you'd never push them down to fasten them in position lol.
    I don't see why adding seperations and hinges into a design would compromise the design; there is extra support from the "bulkheads", so as long as the hinges are beefy, I see no problem.


    So anyone know where to find a single chine 48' aluminum hull design with 12' beam?

    ( With the straight sides, like in the above houseboat pic?)
     
  4. Edwardn
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    Edwardn Junior Member

    Seems complicated to gain 12 feet of deck space, plus you loose 24 feet of deck space for any permanent fixture when you fold it all up, so why not build the hull 12 feet shorter and have 2 light weight folding or slide out decks, one on each end ?

    my 2 cents

    EDD
     
  5. SamSam
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    SamSam Senior Member

  6. parkland
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    parkland Senior Member

    I don't mind doing that haha :p

    Is there a general rule of thumb, for converting steel to aluminum?

    FOR EG, say I find a steel boat, and the hull is 1/4", and there is 4"x1/4" plate welded in as ribbing, every 16",what aluminum would I use?

    Would the same dimensions and design be close, or should I go thicker plate, closer ribs, etc?
     
  7. Eric Sponberg
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    Eric Sponberg Senior Member

    Parkland: Technically, such a conversion should be overseen by someone who is capable of the necessary engineering to do the conversion properly. All boats support loads--loads from the water, and loads from the people and things on board. And boat structures are sized to support those loads. If you found a steel design that was suitable but wanted to convert it to aluminum, you will find that you will just about double all the thicknesses, keeping the frame spacing the same. You'll also see that the hull weight will be about 70% of the weight of steel structure, so the boat is going to float higher out of the water, all other things being equal. That may have some implications on other matters, like speed and power, propeller submergence, and the like. The heaviest part of the hull is the plating, typically making up about 2/3rds of the structural weight. To reduce thickness and weight significantly (and therefore cost) you have to add more frames and possibly stringers. That takes some engineering and design to do it properly. Those are some of the considerations at hand.

    In my houseboat designs to date, my client has relied on plywood and fiberglass with vinylester resin. We have also considered a fiberglass molded hull. But aluminum has a lot going for it, in my opinion, because it would be pretty easy to shape and build, pretty quick to weld up, and be quite robust when handling on and off a trailer or up against docks. I am not so sure about the wisdom of the hinged bow and stern sections, as pointed out by others above, but that's your call if that's what you really want. In my searches around the internet and discussions with other houseboat builders, I am not really impressed with the level of design and construction in their hulls, so I would not be surprised if you have a bit of searching yet to do in order to come up with something. I am not aware of any steel designs of the size you are contemplating. Anyway, I hope the above helps, and good luck on your search.

    Eric
     
  8. Red Dwarf
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    Red Dwarf Senior Member

  9. parkland
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    parkland Senior Member

    An observation so far has been that the steel on boats I checked out is the same thickness on the bottom, as the sides of the hull.

    I was thinking 1/4" aluminum for the hull bottom, 1/8" for the hull sides, and 1/16" for the cabin walls, 1/8" checker plate for decking.
     
  10. Eric Sponberg
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    Eric Sponberg Senior Member

    For a boat this size, actually, with appropriate framing, 1/4" thick aluminum is not unusual. However, going down to 1/8" thickness becomes really hard to weld--thin plating distorts, warps, and walks all over the place when you weld it because of the heat of the weld. So for welded construction, 3/16" is about as thin as you can go. Thinner than that, and you must resort to riveting, and even then you need appropriately sized frames for internal stiffening. Also, even walking loads can easily distort 1/8" plating unless it is reinforced with lots of closely spaced frames, and again, 3/16 is about the least that will work reasonably well for appropriately sized framing (reasonable size and spacing). It's even better is you back it up with sprayed-on polyurethane insulation foam. So there are a number of practicalities of construction that you have to consider with aluminum.

    Eric
     
  11. parkland
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    parkland Senior Member

    You can really get a headache trying to make a boat fit a certain weight.

    If I'm dead set on a boat this big, and to keep the weight legal, I might have to abandon the hull, and go with pontoons. They are so darn light compared to a hull.

    This hull will likely weigh about 8000 lbs just for the plating, if all 1/4".

    40 ft x 36" pontoons weigh about 2200 lbs.
    Granted, the hull would hold a lot more weight, but I don't need more capacity. Those pontoons can hold 17,000 lbs at half immersed.

    I think the hull would make a nicer boat, but for making a cruising style boat as I want, it just isn't in the cards... unless downsizing is an option..... and it IS, but doesn't make much sense, when the goal is to have the largest cruising boat possible.

    BTW the measurements on the deck and cabin drawings are how many ft of material to make each frame section, roughly every 36".
     

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  12. WestVanHan
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    WestVanHan Not a Senior Member

    I live in BC..and every wide load I've seen on the road has a pilot car or even two...big signs,flashing lights etc. can see them 500 meters away. It's all about not having people flying around corners and piling into you.

    Never seen a wide load with a pickup out front and the hazards blinking.

    Just an FYI you likely need to hire a pilot car company. I imagine they charge a fair amount.
     
  13. parkland
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    parkland Senior Member

    Hey, no worries.

    Remember the POR circle, and how it keep recycling back to square 1?

    I'm back at step zero :eek: ;)

    lol.
     
  14. DavidJ
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    DavidJ Senior Member

    I 100% agree with Edwardn. Consider fold out decks to increase deck space. That is a much much simpler/cheaper option. Also like Gonzo pointed out folding up whole sections of the bow and stern would be very difficult to handle.

    I've worked on some very complicated fold out decks that are operated hydraulically and fit seamlessly into the hull creating a watertight seal. I've also worked on ones that were nothing more than a lightweight folding deck that is raised and lowered with a rope and locked in place with a simple locking mechanism.

    You could have a side deck off a sliding door, perhaps off a cabin like the private decks on cruise ships. Or a aft deck right down at the water as a swim platform or docking platform for toys. Or you could just have fold out fore/aft decks to simply increase deck length.
     

  15. Eric Sponberg
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    Eric Sponberg Senior Member

    Parkland: Heads up on your math. 1/4" Aluminum plate (6061) is 3.52 lbs/sq.ft., and 1/8" plate is 1.76 lbs/sq.ft. I think you transposed two of the digits there. Assuming your areas are correct, this would bring the total plating weight up to 4460.5 for the 1/4", and 2230.3 for the 1/8" = total = 6690.8 lbs. By the guideline of the plate being 2/3rds of the hull weight, then, the total boat weight with framing is 6690.8 x (3/2) = 10,036 lbs.

    In our rectangular barge house designs, we've had all up weight of the 16' x 40' boat at about 30,000 to 32,000 lbs, which are for architectural type houses, not boat type houses. The plywood and fiberglass hull weight is about 14,500 lbs, the house weight is about 7,400 lbs, and all the interior joinery, furnishings, systems and supplies makes up the rest. I dare say boat type houseboats would be lighter simply because they are not as big and can be made with lighter materials than what we were using. Our barge depth, by the way, is 4'.

    Anyway, just thought you might like this info to think on.

    Eric
     
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