From Army idea, 4 mt. Diamond monocoque with Sika adhesived 0.7 mm stainless steel

Discussion in 'Boat Design' started by mustafaumu sarac, Oct 15, 2021.

  1. fallguy
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    fallguy Senior Member

    Let's not beat up Umut too much.

    My first boat was a 16' Gil Gilpatrick Laker and I still own it today, 21 years after launch.

    A proa can get him to Greece safely if he is careful and the cost is not horrible.
     
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  2. clmanges
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    clmanges Senior Member

    It should be more the opposite, at least at the most basic level. Remember the square-cube law. When you make a bigger boat, what you're buying is more displacement, which is volume, but what you're paying for is more surface area.
     
  3. fallguy
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    fallguy Senior Member

    Well, what happens is systems become far more complex.

    You won't be using air conditioning on a skiff, nor heat, nor cooking, nor a shower or head; you won't need to worry about railing heights, the anchor won't be so damned heavy it requires a windlass. And this is why a sailing proa is so perfect for Umut. He doesn't even need to moor it, or even a trailer if he can cartop.
     
  4. clmanges
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    clmanges Senior Member

    Which is why I specified "most basic level".
    Hard to beat for ease of build, too; basically a two-plank hull with enough framing to hold its shape, and the deck does some of that for you. Might also be the best choice for tooling around the Med in terms of seaworthiness.

    Umut seems to like the exotic, though, the more the better.
     
  5. cracked_ribs
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    cracked_ribs Senior Member

    Should be? In a way, absolutely...but never has been that I have seen. Every build I have been involved with, exceptions only being strip built art canoes or really nicely set up ocean kayaks, has scaled in price very similarly. My belief is that the inherent structural rigidity of small objects allows for less complex designs. The bigger and heavier it gets, the more complicated it becomes and the greater distances spanned so the thicker the cores and more layers of glass or thickness of bulkheads and inches of welding and so on and so on and so on.

    It's like the classic "I want to go 10mph faster" problem. The boat is designed to do 30 knots on 150hp, but you want to do 40...there's a 200hp on the same block that should get you there. You reinforce your boat it to withstand bottom loading...but now it's heavier, so 200hp isn't enough, you need 250. But that's straining your transom, so you reinforce that, and now you take at a nice new 250. Oh, next size block? Now I'm heavier again, dammit...okay, what's the total weight? Okay 250 should work...jeez it sits low. Maybe a couple of floatation boxes on the transom. How much could they weigh? Wait do I need a 300 now? Will that push it to 45? Do I need to reinforce the bottom again?

    It just spirals as you move away from spartan extremes. The contrast between that reality and the intuitive reponse about surface area and volume (which I also have, I get exactly where you're coming from) is precisely why I find the concept interesting. More volume requires less surface area in a given shape....but the internal structure to maintain rigidity and the basic requirements of a functional boat get exponentially more expensive, so the cost scales (in my experience at least) inversely to the surface area-volume equation.
     
  6. clmanges
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    clmanges Senior Member

    That's not a spiral people should let themselves get caught in except on paper. Makes a good argument for just selling the slower boat and putting the proceeds toward one that was designed from scratch to do the speed you want--plus a little more if you can afford it, though, as you've pointed out, that seems to jump by large increments.
     
  7. cracked_ribs
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    cracked_ribs Senior Member

    Obviously - it is just there to illustrate why costs scale as an exponential of displacement even though the surface area gets relatively smaller.
     
  8. comfisherman
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    comfisherman Senior Member

    Would like to reference the op, and a trend that comes up fairly consistently in this space. This is the desire to use non typical materials for certain applications.

    Stainless 22 gauge for a small punt is not a good idea for several reasons. If it's non marine in salt water it will be highly susceptible to electrolysis. I've seen guys use 304 instead of 316 over the years and be shocked at just how fast it can dissappear in salt water, the wormholes go quick.

    Second, it's going to need some internal structure, shape or corugation in order to be rigid enough. All things an appropriate alloy aluminum or cored glass would be better at for an equivalent density.

    Cost of a suitable marine stainless compared to any other material will be rather high. For a material that's heavier for a givin rigidity it makes little to no sense.


    I'm reminded of a friend wanting an oil cooler made of titanium. He wanted the best, that would last forever. Sent him a link to a silicon brone one, he wanted ti..... so I found a guy who could weld to and got a bid. It was just shy of 10x the cost. He was 58 and had no kids. I politely pointed out that if the silicone bronze one lasted its lifetime it would outlive him by 15 to 20 years and the ti by 40 years. How nice a cooler did he want to leave after he was dead.

    The inconvenient reality of boat planning is looking at all aspects.
     
  9. fallguy
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    fallguy Senior Member

    I have a few 304 parts in my build. Might be replacing them somewhere down line.
     
  10. Rumars
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    Rumars Senior Member

    It's not like one has to reinvent the wheel, just listen to what we say, and watch youtube.
    Here is an example, it's self explaining:

     
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  11. gonzo
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    gonzo Senior Member

    There is no inherent structural rigidity on small objects. "Rigidity" is a function of the material properties and the design. In fact, if you were to build a small boat at scaled down scantlings from large ships, the plating would be too thin to weld with most available methods.
     
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  12. cracked_ribs
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    cracked_ribs Senior Member

    I occasionally forget about the absolute literalism of some corners of the internet but it rarely forgets to remind me after the fact.
     
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  13. fallguy
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    fallguy Senior Member

    Well, the statement you made was rather silly to be fair. Someone might translate that into my boat is small, so I can use 1/4" ply on my transom.
     
  14. cracked_ribs
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    cracked_ribs Senior Member

    The problem with being overly literal about this stuff instead of attempting to grasp the actual meaning is that every statement becomes silly unless filled with clauses to explain the specific circumstances in which it applies.

    For example, the nature of your objection is obvious and the fact that I own a boat and could list countless other examples that have 1/4 inch ply transoms - tons of small sailboats - doesn't prevent me from understanding that you meant "powerboats with transom-hung engines."

    But I have to grasp the meaning without requiring you to be that specific and saying "your objection is rather silly, lots of boats have 1/4" ply transoms."
     
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  15. Ike
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    Ike Senior Member

    Don't ever discount the Army's nautical abilities. The Army has over 500 ships, mostly transports but they also have cargo, oilers, tugs etc. The Army Corps of engineers has a fleet of 2300 small craft, consisting of all kinds of barges, tugs, dredges, work boats, crew boats, rhibs, regular inflatables, and so on. during WWII they actually had a larger "Navy" than the US Navy. They make the Coast Guard fleet look small and the Coast Guard is thought to be the seventh largest Navy in the world. I have known quite a few people who list their army career as a Captain of a boat, tug, ship, etc.
     
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