Anyone know of plans for a CNC boat kit that is riveted NOT welded together?

Discussion in 'Boat Design' started by wannarivet, Apr 1, 2018.

  1. wannarivet
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    wannarivet New Member

    Good Morning,

    I searched google and this forum but could not find any link to a website where could build my own 27 foot (8.2m) aluminum boat CNC kit that is riveted together. There are lots of plans for a welded aluminum boat but none for a riveted boat.

    Why rivets?

    Well, 1) aircraft are riveted because welding distorts the metal and removes the heat treat, causing fatigue cracking behind the welded area. 2) I can't weld. 3) I want substitute carbon fiber honeycomb for aluminum sheet.

    I know that using carbon fiber will cost 5x as much as aluminum but it is half the weight and 5x stronger. The cost of making a really good mold, laying up the carbon fiber and vacuum bagging it all is just too way high for one boat. A good CNC machine can cut carbon fiber just like aluminum and steel.

    I found some boat plans for a riveted boat on *************** but no way to see what kind of boat. I'm looking to build a trailerable hardtop cruiser and light weight is very important to me.

    I'm guessing that making the keel rib and lots of brackets would be challenging.

    Any tips and links would be greatly appreciated.

    Thanks.


    P.S. I'd love a step hull but that might be out of the question.
     
  2. gonzo
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    gonzo Senior Member

    Carbon is not an overall stronger material. There are different ways of measuring strength. For example, tensile, compressive and shear. Many of the "high strenght" fibers do badly in shear. That is why sheaves for kevlar lines have to be of large diameter. Also, toughness is also a very important characteristics. Aluminum or steel with dent or deform, while carbon will break. The first has a larger margin of safety.
     
  3. Barry
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    Barry Senior Member

     
    Last edited: Apr 3, 2018
  4. gonzo
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    gonzo Senior Member

    I think that riveting is probably harder and requires more skill than welding. A poorly fitted plate can be fixed with a fat bead of weld. With rivets, that would mean discarding one or more plates and redoing them.
     
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  5. valery gaulin
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    valery gaulin Senior Member

  6. Magnus W
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    Magnus W Senior Member

    Riveting is challenging, although I haven't any experience with said tech on boats but I do on aircraft and seaplane floats.

    One thing to consider is that riveting requires tools which may, most likely, be of greater cost than a really good welding equipment. Especially if you're upping the size from what's used on aircraft.

    Also, riveting takes time. And not only for you but for the friend that needs to be on the other side of the hull.

    While a welded construction can be said to be in one piece", a riveted cannot. Airplane floats have sealant between the parts that are riveted together and they still leak (but in all honestly they are quite fragile). It's more common than not to see corrosion between the rivets and the holes, maybe not on a new float but surely on one that's been around for a while. Because the joints move, ever so little, and that will let oxygen in and so it begins.

    All modern floats are FRP and even the aircrafts are moving away from rivets to fiber/matrx, composite, glue, whatever. For a reason I'd suspect.
     
  7. Barry
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    Barry Senior Member

    Magnus, what is the typical thickness on the aluminum sheet on floats? and perhaps airplanes wings
    Valery looks like a nice completed project. I don't think that a .06 inch thickness would not be sufficient for a 27 foot sedan
     
  8. Angélique
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    Angélique aka Angel (only by name)

    There's a nice suggestion on the thread: Kiribati 36 opinions ---> post #2
     
  9. gonzo
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    gonzo Senior Member

    The average hourly pay for a welder is about $25 canadian dollars. If you pay cash, $20 will do it.
     
  10. Magnus W
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    Magnus W Senior Member

    Hmm, I don't know for sure. On floats .06 seems about right for the bottom but I reckon thinner on the sides. Fuselage skin is also less than .06, at least for a non pressurized fuselage. Maybe .06 on the leading edge of a wing but in general thinner.
     
  11. gonzo
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    gonzo Senior Member

    Airplanes don't get pounded by waves, so the skin is much thinner than a boat of the same displacement.
     
  12. valery gaulin
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    valery gaulin Senior Member

    Sorry Gonzo, think about this one more time! Wave at 6 - 10 knot versus birds, ice, snow, etc. at 200-400 km/hour with 120 to 400 passenger. Which one needs to be stronger?
     
  13. gonzo
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    gonzo Senior Member

    The boat hull. The density of water is about 750 times that of air. Birds can cause major damage on an airplane. Also, the leading edge of a wing or fuselage is reinforced and not the gauge you are discussing. I can cut my way into an airplane with my pocket knife.
     
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  14. Angélique
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    Angélique aka Angel (only by name)

    return to sender​
    Aircraft are not designed to fully withstand these kind of impacts like ships and boats deal with their normal impacts, since this would make aircraft far to heavy for any economical operation or to fly at all. So aircraft are designed to have no more than survivable damage in these occasions, which makes repairs or at least inspections after every kind of aircraft impact standard procedure in aviation.

    This in contrast to ships and boats which don't need, nor would this be acceptable, to go to a repair yard after every heavy wave impact, which heavy impacts aircraft don't have to endure due to air having a so much lower density than water.

    Displacement aircraft like balloons and zeppelins are even weaker than planing aircraft, otherwise the displacement type would be to heavy to float in such a light medium with such a low density as air.
     
    Last edited: Apr 3, 2018

  15. wannarivet
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    wannarivet New Member

    Hi, thanks for the many responses to my inquiry.

    I've since given up with my idea to rivet the entire boat, but still believe that boat plans designs for sheet aluminum that can be cut on a CNC machine can be used to cut a composite sheet that will be half the wight and 2x as expensive as alu. The 5x figure comes from having to buy peel ply, resin mat, vacuum bags, hoses, etc. That was just my cost estimate for materials NOT including a mold. A boat mold runs $1,200 a foot and then if you want a mirror finish, add $8,000. Allmandboat has a mold calculator. $125,000. And you need 2. One for the hull and one for the upper deck. All I would want to rivet now would be the keel rib and 2 chines under the waterline to help lateral stability and strengthen the boat's bottom. The transom and other structural cross members could be fastened to the inside of the hull with epoxy and carbon fiber bent like angle iron where as aluminum would be welded. That's how the fiberglass boat builders do it.

    The issue that I'm running into now is that no boat builder wants to sell me enough data to be able to create my own design with the intent to modify it and no one really understands what I'm trying to do.
     
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