Hi, first post, wanna build a monstrosity....

Discussion in 'Boat Design' started by parkland, Jul 15, 2012.

  1. parkland
    Joined: Jul 2012
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    parkland Senior Member

    I've landed up on this site several times now looking for information, so I thought I might as well sign up.
    I have had little quick boats before, row boats, now I want to build one from scratch to exactly what I want.
    Basically, I WANT a giant boat, but have decided to build something as big as possible that can tow behind a 1-ton truck.

    Weight limit would have to be under 20,000 lbs including trailer.
    Width limited to 8' 6"
    Length, around 40'

    I am not after a sailboat or water ski machine, just a cruiser.
    Picture maybe a 40 ft boat, with the middle 20 ft being about the same dimensions as a 20' camper.

    I'm thinking of making the hull 4' tall, 8' 6" wide, and square, except for the front and back which would get rounded into something more aerodynamic. Then the cabin would extend about another 4' or so above that.
    power wise, I was thinking so far of using a cummins 3.3l 4 cyl diesel. Or something similar. 60-100 HP. Hoping for 10-15 knots out of it.
    Basically a powered barge, 8' 6" x 40', with a touch of elegance put to the bow and stern, (more than a 1 angle taper, lol).

    I am pretty good at building things, but I've never welded aluminum before...
    I am thinking of using 1/4" thick aluminum plate fur the hull. And 3" x 1/4" aluminum bar for framing inside the hull.


    I would just use steel, but I don't want the extra work cleaning rust.

    So far the only downsides to aluminum seem to be that it might take a while to get the welds right, but from what I've been told, 1/4" aluminum should be pretty easy to weld.

    Also, 6051 aluminum?? I see alot of boats are build with 5000 series aluminum, my metal guy only has 6051 aluminum, but says many boats have been built from 6051.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    20,000 lbs towed behind a one-tonner must be illegal and dangerous. To design and build such a "monstrosity" ( not to mention house it) is expensive, time consuming, and has a lot of potential for disappointment. There would probably be better outlets for your creative urges.
     
  3. gonzo
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    gonzo Senior Member

    Aluminum is not that easy to weld. Whatever you've been told, take a course and see if you get the hang of it. 20,000 lbs behind a 1ton truck is neither legal nor safe.
     
  4. parkland
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    parkland Senior Member

    My truck is rated to tow over 16,000 lbs stock, and I'm looking at getting some spring and suspension upgrades.

    I know people that have towed 20,000 lbs without upgrades.

    From what I understand, 20,000 is high, but even around 16,000 should be reasonable. I think it can be done.... think...
     
  5. gonzo
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    gonzo Senior Member

    Check the road regulations. You may be stopped and taken off the road at the first scales you cross.
     
  6. parkland
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    parkland Senior Member


    I also have a guy to help with the welding, who has experience.

    Are you saying that aluminum is just to much work for a "one off" boat?
     
  7. parkland
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    parkland Senior Member


    I asked ford, they said 16,000 lbs is legal for a trailer.

    From what I understand though, the cops don't care unless you're truck and trailer is over 26,001 lbs.

    Don't worry about that though, I also might buy an older 5 ton in the near future.
    Is aluminum really that terrible?
    I'm just petrified of building it from steel and having rust issues on a yearly cylce instead of enjoying the boat.
     
  8. Edwardn
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    Edwardn Junior Member

  9. parkland
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    parkland Senior Member



    Haha

    I found that ad several days ago. I wanted to look around to see if I could buy a used one and refinish rather than build from scratch.

    It seems like most boats are built to either be tiny, or massive.

    Not many big ones that are still small enough to haul down the highway without special permits.
     
  10. Stumble
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    Stumble Senior Member

    The highest capacity truck I know of is the Ford F450 rated at 24,000lbs. But why in gods name would you want to tow this around? The cost to move it will be nuts in fuel alone. And going to this size of a boat that is restricted to 8'6" will result in a really strange hull design.

    Finally there is no reason for a boat this size to be this heavy. My Beneteau 381 weighs in at 14,000lbs. I can't imagine this would almost doubt the weight in a boat 2/3 the width, no keel, and 2' longer.
     
    Last edited: Jul 16, 2012
  11. philSweet
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    philSweet Senior Member

  12. parkland
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    parkland Senior Member


    Well I'm not that great at figuring things out, but I roughly calculated that the aluminum hull would weigh 4000 lbs when done, then the engine, cab, contents, fuel etc...

    I could see it easily getting to 15,000 lbs
     
  13. PAR
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    PAR Yacht Designer/Builder

    A 4.7 beam/length ratio provides the opportunity to have a pretty economical cruiser. It will be tight on elbow room, but you'll spread out the accommodation across considerable length. With the exception of a few box boats, finding a design for something like this will be difficult, without a custom or semi custom being drawn up.

    As to weights and towing requirements, all of these things would be addressed in your established SOR, which is derived through conversations with your designer. The best recommendation you could get, isn't about towing or weights, but a frank discussion with a designer or NA. You'll quickly learn what is and isn't possible, within your budget, which is usually the limiting factor. Contact a designer and see where you stand in the real world of materials, building skills, building times and budgets. Just to bring you down to earth, try pricing out some marine diesels, say 60 HP, for a narrow 40' displacement cruiser, add a transmission, shaft, steering and tankage and see if the numbers are tolerable. Once over the first $20k in engine, fuel tanks, steering, controls, keel cooler and transmission, the rest isn't so painful.
     
  14. gonzo
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    gonzo Senior Member


  15. Deering
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    Deering Senior Member

    What do you intend to use this boat for? Where will you operate it? And how far do you anticipate towing it?
     
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