preliminary structure weight calc

Discussion in 'Boatbuilding' started by Armada01, Jul 11, 2016.

  1. Armada01
    Joined: Jan 2010
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    Armada01 Junior Member

    Hey there,

    I have designed a 19m.aluminium trawler (i'm not a naval architect, just designed the concept in Rhino) and approached a yard to build it.

    They need the know the aluminium weight (among other things) in order to make a dependable quotation. I do have the exterior shape of the yacht. Is there a way to apply some factors to the overall surface area of this shape in order to get an approximate weight including hull frames/stringers/longitudinals?

    Once I have a quote, I want to look for clients / investors, so I don't want to invest too much time and money in designing a full-fledged structure right now. That will happen once funding comes in...

    Anyone can advise please? Tx!
     
  2. daiquiri
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    daiquiri Engineering and Design

    Hi Armada,
    I am afraid you will have to design that boat properly, including all structural details, equipment and outfittings, in order to get the correct cost estimate and before you can approach potential investors. They would hardly give you any money anyways, without a very sound business plan backed by hard numbers.

    It may also save you some very bad surprises in the latter stages of the project - like discovering that the engine or some other fundamental equipment cannot be placed where it was intended, because structural framing has eaten up too much internal volume where you needed it. That would immediately translate into another couple of turns of the design spiral (starting from the boat's GA), re-calculation of the cost estimate (which will grow, it always does) and a delay of the entire time schedule of the build.
    Should this thing happen, you will be the scapegoat. Unless investors are your family, I can assure you that their lawyers cannot wait to eat you alive. That's how they make their living, and you would then see what a well-detailed and thorough job looks like...

    So, my advice is - do the design to the maximum possible level of details now, when you are still working at your comfortable pace and not under pressure. If you don't do it now, it will turn into a frentic race against time later on.

    Cheers
     
  3. PAR
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    PAR Yacht Designer/Builder

    You can take a guess, but without an accurate weight study of the structure, equipment and typical ancillaries for a 62' vessel, etc., well a guess it shall be. It's a bit like asking a home builder to provide a quote, with only a picture of the house you want, isn't it?
     
  4. Armada01
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    Armada01 Junior Member

    That's what I was afraid of. The typical catch 21 of the business start-up :)
     
  5. Armada01
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    Armada01 Junior Member

    Anyone got a (rough) idea what it would cost to get the structure developed to a level that a yard could quote based on casco weight (for a 61ft. aluminium yacht)? I also need to define the engine type for the quote, so some work to be done on that too...
     
  6. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Armada01, if you "have designed a 19m aluminium trawler" is supposed you already know the weight of each element of the boat. Otherwise, how could you verify that the boat floats and sails as you need ?. If you have designed it you already know how the structure and therefore the weight of aluminum.
    So I do not quite understand your problem but, in any case, with your design, is the shipyard builder who should be responsible for estimating a weight to make its budget. If not, you can be sure that at some point they will brandish that the data given by you led them to errors in their budget.
    If I can help, do not hesitate to contact me.
     
  7. Armada01
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    Armada01 Junior Member

    "Designed" in this case means that I have the shape above waterline and the interior accomodations (preliminary of course till I know what the effect will be of structure on the interior - some changes will happen for sure, concurrent engineering) and some exterior moving parts such as hatches, placement of cleats, anchor pocket. All designed in the sense that they are given a place and space on the 3D model.

    This is a first "draft" version which, for now, proves that I have the required space to berth x guests, a galley to cook for x guests, bathrooms for x guests, space for a tender of x m. etc etc. ... which shows that the yacht is sizewise suitable for chartering. It doesn't prove yet if the yacht will float, has stability, and can be built for a certain price.

    I'm sure the design can be designed in terms of structure and naval architectural parameters (I'm not reinventing the wheel). For me right now, the big question is whether it can be built for a certain cost, in order to meet the charter prices I'd like to offer and remain competitive in the market.

    Hence my request for a quote from a yard. Once I have the quote, my business plan is finalized and I can look for investors.

    I've put a lot of time into the research and development of the business plan as well as the many redesigns of the vessel, so I'm not looking to fork out another 25K to develop a full structural design. As mentioned above, this would take out much of the risk down the line for sure, but in terms of getting a business up and running in the bootstrapping phase it's about getting your funding together without running yourself into to much debt (ie. the "lean" start-up)

    That's why I was hoping there might be some rules of thumb to be applied to the yacht's surface area to make a not fully accurate but good enough approximation of the weight of the casco. Without anything like this existing, I guess it might be better to look for a yard who can give me a quote based on just a GA and a specification.

    Can I fully trust the quote? Probably not. Could it jeopardize the project later on? Maybe. But without the quote no investment, and without investment no project in the first place...

    I wish I had the funds to do everything by the book, but unfortunately -like most startups I have to be "creative" to get from point A to B without the funds to do so.

    Once this project gets traction, funds will come in and I'll have the funds to do things as they should, but at that time I won't need it anymore... hence the catch 21...
     
  8. TANSL
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    TANSL Senior Member

    OK, I will not comment on your last post but will try to answer your main question.
    In my opinion, for these boats, there is no formula to subtract the weight of the structure. I do not know it.
    What you could do is define a midship section, with plates and all the reinforcements. Calculating scantlings of these elements (this is pretty fast) and thus, the weight of the main section. Multiply that by the ship's length and weight by a factor 0.8 for example (I just made it up and has no scientific basis) to thereby obtain a hull weight. If you want more accuracy, calculates three main sections, aft, center and bow.
    To this figure you add 15% for welding and apply the margin of error that you want, and you have the total weight of the hull.
    If someone with that fact, gives you a budget, I advise you do not trust him.
     
  9. daiquiri
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    daiquiri Engineering and Design

    That was a piece of dry humour at its best. :D

    And it is also a great advice.
    Our firm works with many reputable and trusted metalworking companies, and not one of them would venture into giving numbers for the construction of an artifact before seing the technical drawings. A few times we needed to get a ballpark cost estimate during the preliminary design stage, we have been turned back until sufficiently detailed drawings with BOM (Bill Of Materials) were available for them to examine and estimate types and amount of materials, tooling, eventual rental equipment and man-hours required. Only then the cost was quantified.

    Armada, if you don't have technical qualifications for performing the scantling of that boat, and you don't want to or can't spend the money on a service from a professional NA, then IMO you should team up with another person who has the required technical competence and who will share your vision about the goals of this project. Together you can work this out in your free time, slowly but at least with no other additional costs.

    Cheers
     
  10. rwatson
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    rwatson Senior Member

    "I wish I had the funds to do everything by the book, but unfortunately -like most startups I have to be "creative" to get from point A to B without the funds to do so."

    This is the epitaph of most "startups"

    The big missing question is "Why my design is so much more superior to other similar designs", and the next question for you after that is "Why and Who will find my design so valuable that they will pay me for my ideas".


    Until you can answer these questions, you are just "playing with CAD"
     
  11. pdwiley
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    pdwiley Senior Member

    I can answer that one - nobody. Nor would any investor sink money into it.

    Perhaps this is another boat design best pursued by the origami method....

    PDW
     
  12. Petros
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    Petros Senior Member

    you can surmise a real rough estimate by comparing similar sized boats, similarly equipped. The finished costs would likely be within the same range. Consider that the profit is so small, you can take the dealer price as pretty close to the production and transportation cost. Many times the dealer cost is actually below the production costs, which is why so many start ups do not last longer than the first few deliveries.

    There are not very many production boats companies, particularly making pleasure boats of that size, that last more than a few years. The exceptions are rare.

    You will likely be tempted to make cost adjustments for the differences that make your concept unique. This might be okay if it can be rationally justified, but do not be too optimistic, particularly with a new design. There are always details that have to be worked out, no matter how good the plans, that never seem to come together quite as planned. You may break even by your ninth or tenth delivery, if you last that long.

    Sorry to sound so negative, but the realities of building boats, particularly pleasure boats, is that it is a very tough business with very few that are successful. How large is the market for your concept? Realistically how many customers are there willing to fork over the money for you boat? I would research THAT question before I spent any more time and money on developing the design further. If there is no market for that size and cost of boat, than there is no point in going any further with it.

    If there was a commercial use for such a boat, and you can deliver it for a price that the customer can actually make a profit with it, than you actually have a fighting chance. Particularly if the features that make your design unique makes their boat business more profitable, so much the better.

    good luck.
     
  13. Armada01
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    Armada01 Junior Member

     
  14. Armada01
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    Armada01 Junior Member

    I guess that's the ideal way to go, find a co-founder / naval architect.

    But that can take a long time also to congeal, so I'm not putting all my eggs in that basket either and working on plan B too, where I have to creatively see my way through the hurdles on my own and keep the ball rolling forward. But thanks for the advise!
     

  15. TANSL
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    TANSL Senior Member

    I do not want you to feel annoyed by my brusque way of saying things, but apparently, you know what it is to design a boat pretty well, you know the charter market very well and, this is most important, you have one product much better than the competitors well differentiated (there is nothing similar in the market) . With all this in your baggage, you should not ask for advice on this forum, but give it.
    Cheers
     
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