Australian Recreational Craft Scantling Standard?

Discussion in 'Boat Design' started by CADProjects, Oct 7, 2017.

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    AMM-120.jpg

    The trend seems to be to build stronger, here's an alloy 20 footer that weighs 1120 kg bare, with 5mm plate bottom, 4mm sides. Every bit as heavy, or heavier, than glass.
     
  2. CADProjects
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    CADProjects Marine Design Services

    wall thickness is only part of the equation as you know. what about stiffening relative to the panel sizes & their respective pressure requirements.
    my observations suggest the panel sizes and / or stiffening be they ring frames or longitudinal stringers dont meet the ISO requirements on most production Aluminium vessels operating here in Australia.
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    You might price yourself out of the market, if adhering to codes that aren't mandatory, its a competitive game with not much margin to play with.
     
  4. TANSL
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    TANSL Senior Member

    I have the impression that complying, for example, ISO standards will not get you out of the market by increasing their prices and instead are a guarantee that the boat has been designed with a minimum quality.
    But the discussion has a very clear answer, do a test, calculate the scantlings of your boat in accordance with ISO 12215 and check if the boat is heavier or not than what you are building now. In a couple of hours you can have the study done and I am convinced that for one reason or another you will place scantlings bigger than those that ISO demands as minimum.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    There is a lot of rough water over here, TANSL, and if the build quality isn't up to it, then it will become known pretty quickly, bad news travels fast. Most people building boats for any length of time, have a feel for what is required in terms of structural strength, and stick to it, or go out of business quickly.
     
  6. TANSL
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    TANSL Senior Member

    I agree with you but note that I have talked about the quality of the design. The quality of construction is a different thing. Therefore, the better each of the parties, the better the final result. I have always thought (no one feels offended) that the better the design, the more margin there will be for errors in construction.
     
  7. DCockey
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    DCockey Senior Member

    There are no legal standards about scantlings of recreational boats in the US. It sounds like Australia is the same.

    Have you seen evidence of structural failure due to the sixe of the ring frames or longitudinal stringers on those boats?

    Perhaps the thicker plate is for dent resistance to localized impacts and loads.
     
  8. Ike
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    Ike Senior Member

    When you stat talking about scantling standards for recreational boats you are opening a real big can of worms. As was said, in the USA there are no scantling regulations for recreational boats. That does not mean there are no standards. This question has been around for years. When I first got into the regulation side of boat manufacturing in th mid 70's, there was a lot of talk about scantlings. It would flare up, die down and then come back. Most everyone in the industry agreed, they didn't want them, We in the Coast Guard looked at it and decided that we could not justify a regulation. The law requires "minimum' standards for safety. Each regulation has to be based on a demonstrated need. We simply could not put together enough data to demonstrate a need. Plus that the standards would be incredibly complex because of all the different types of boats on the market. In just the monohull inboard and outboard markets you would need separate scantling standards for aluminum, fiberglass and wood. Or you could require a builder to do a FEA or a structural anaylsis. But, that would have a huge impact on small boat builders. Large volume builders could spread the cost over many boats but the custom builder, or small regional boat builder would have to pass the cost onto the buyer. The cost may make them non-competitive. In the USA where you have over 4000 boat builders making everything from kayaks to superyachts such a rule would be incredibly complex and unworkable. Some class associations have their own scantling rules. But those tend to apply to a small class of boats. A broad brush rule would notwork.

    Most builders overbuild their boats based on experience and what they have seen happen with boats they built in the past. The really good designers and builders have an engineer or NA do a structural analysis (FEA). Over my time, since then, I have seen a few failures, one which nearly cost a company their reputation for quality boats, but none that resulted in fatalities.
     
  9. DCockey
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    DCockey Senior Member

    Any idea of what proportions of those failures are due to manufacturing defects or other factors than insufficient scantlings?
     
  10. Ike
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    Ike Senior Member

    I couldn't begin to give a percentage, but it would be small. The problem is that there are different definitions of a defect. in the US the law only recognizes a defect that creates a substantial risk of injury or death and occurs suddenly and without warning. So generally speaking if you have a defect in a boat that develops gradually, it is not going to fall under the law. They are other means of dealing with these through voluntary arbitration or, law suits. But, what an owner may consider a defect might not rise to that level.

    There have been a few notable exceptions. The one I mentioned above was a popular offshore fishing boat that the manufacturer had extended by adding several feet onto the stern, without doing an adequate structural analysis. It was an outboard powered boat. Big 200 hp outboards that were suddenly several feet farther aft. Anyway the boats started cracking and coming apart. Fortunately it was very obvious and the owners simply stopped using them. But the manufacturer knew about the problem and did nothing. We had to force them to do a recall and replace the boats. So this was not a suddenly and without warning situation, but it was very likely to cause serious injury or death if not corrected.

    Probably the most famous was actually in the 70's when a popular brand of cruisers, that was built of plywood, started delaminating when the boat was on a plane, suddenly and without warning. It was a bad batch of plywood. But the problem was so bad that it ruined the companies reputation, and even after they switched to FRP, they went out of business. Actually even today you can pick up one of their fiberglass models for a song, far less than what it would seem to be worth.

    There have been other more minor (that is less catastrophic) failures, but not very many.
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    There are probably several reasons for the shift to heavier gauge plate, and generally more heavily built alloy boats, certainly lighter plate can dish with hard use, even with closely spaced frames and stringers, but I think there is also an impulse to compete directly with glass, for ride quality, and with more deadrise you have to have an increase in weight, though in my opinion the limitations of shaping alloy keeps them inferior to the best glass hulls, ride-wise.
     
  12. CADProjects
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    CADProjects Marine Design Services

    What do you guys think about double sided continuous welding of the shell plates..... In the commercial vessels I design it is mandatory of course but I note in the recreational vessels it rarely makes an appearance. Plenty of those recreational guys give their vessels a far harder time than the salty old sea dogs in the commercial sector yet the single sided welding seams to stand up to the abuse. The Double sided welding requirement in commercial vessels adds significant cost to a vessel and often limits the hull geometry as you need to ensure all spaces are accessible and large enough to get in to weld. Time to rethink the mandatory double sided welding requirement for commercial vessels......?
     
  13. TANSL
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    TANSL Senior Member

    You must ensure that the welding of two adjacent platess is complete and uniform throughout its thickness. This is true for commercial boats and pleasure boats. If you are able to get that welding only from one side, no one will force you to anything else.
     
  14. CADProjects
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    CADProjects Marine Design Services

    ISO 12215 and Lloyds SSC suggests otherwise. Double sided continuous fillet welds to all shell plating mandatory.
     

  15. TANSL
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    TANSL Senior Member

    At this moment I do not have at hand the regulations that you mention but, probably, they are an incorrect interpretation of them. My experience is that welding on one side (there are several procedures) is fully accepted by all Classification Societies. As for ISO 12215, can you tell me which paragraph is required? We could analyze the interpretation of that paragraph together.
     
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