design formulas

Discussion in 'Boat Design' started by pazimmer, Jan 6, 2012.

  1. pazimmer
    Joined: Dec 2008
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    pazimmer New Member

    what formulas can I use while designing to calculate specifications?
     
  2. kdhorton
    Joined: Jun 2010
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    kdhorton HM Small Boat Designer

    What formulas can you use to pass a calc and physics exam?

    There are any number of formulas used for naval architecture and marine engineering. They all require a lot of input information which is noticeably void in your post... along with anything else that might help narrow the answer down.
     
  3. pazimmer
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    pazimmer New Member

    Looking to design a 24 ft offshore carolina style center console. what info would you need? im an amateur.
     
  4. kdhorton
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    kdhorton HM Small Boat Designer

    I don't need any of it, really. For starters in the sketchup fun stage there's the freeboard calcs- at ~24' you're looking at ~2.5' of freeboard at the bow, depending on the actual LWL.

    You need to buy a book on design- John Teale's is a good primer, Larsson's "Principals of Yacht Design" may not be exactly what you need but will contain the calcs you'll need to learn.

    Then there's the 800 page Naval Architecture books used for 4 year degrees in the subject...
     
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  5. tom28571
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    tom28571 Senior Member

    There is a strong temptation to run anyone who comes in with a question like that off with a large stick. It is clear that you either are pulling our collective leg or are extremely unschooled in design of just about anything.

    To be more serious, assuming you are serious, you need to start with reading a primer on what a boat is or is not like Dave Gerr's "Nature of Boats". After that you may be ready for the Ted Brewer book on boat design, containing a fairly concise description of many basic design formulas and the Teal book already suggested or Skene's "Elements of Yacht Design". To get closer to a high speed offshore boat like you want, there is "Naval Architecture of Planing Hulls" by Lindsay Lord, "High Speed Small Craft" by Peter DuCane, "Designing Power and Sail" by Arthur Edmonds, "Problems in Small Boat Design" from The Society of Small Craft Designers, and for the more advanced "Principles of Yacht Design" by Larsson and Eliasson and "Hydrodynamics of High Speed Marine Vehicles" by Faltensen which is really getting serious. Then there is Gerr's "Elements of Boat Strength" and his "Propeller Handbook" that are of great practical use.

    If just a having the formulas at hand were enough to design a good boat, maybe there would not be so many really bad ones out there. Those here who can design a good boat have spent years attaining the knowledge and experience to do so. That is why your question may bring out sharp answers. The process of attaining knowledge is just as much enjoyment as building or using a boat. If that does not sound like fun, then the best course may be to obtain a good set of plans from someone who has put in the large amount of effort to learn. There are some good proven plans for that kind of boat available from good designers.

    No shame in that and wisdom should often dictate that route.
     
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  6. gonzo
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    gonzo Senior Member

    Actually the specification are usually what you want off the boat. Then you do calculations to be able to build it to the specifications. On the other hand, I worked with several of the old boatbuilders in North Carolina, and they just build them. At most they would make a rough sketch on a scrap of plywood. I am referring to Omie and Tony Tillet, Sonny Briggs, Buddy Cannady and others like them.
     
  7. tom28571
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    tom28571 Senior Member

    So right Gonzo, but you forgot to mention that there were a couple generations of boatbuilders in their blood. One thing you would never catch one of the Outer Banks boatbuilders doing is to venture way out in a boat they had no prior experience with. They do make incremental changes but nothing that would qualify as a design from scratch of a different kind of boat. Unfortunately the boatyards on Harker's Island are warping into condos like the rest of the East Coast.
     
  8. pazimmer
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    pazimmer New Member

    I ask the question because I have no experience with the technical aspect. I have read portions of Dave Gerr's : Elements of Boat Design and I just dont understand some of it due to lack of exposure to the lingo. I want to design something that eventually will be built. I dont want to make a boat that is proportional in every aspect. So if I wanted to build 24-26 foot center console with a carolina flair, what would be reasonable beam to accommodate the length? reasonable draft? etc. How would I figure horsepower ratings and what not?
     
  9. philSweet
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    philSweet Senior Member

    Do you mean Elements of Boat Strength? That is a pretty good place to start in terms of learning that it is a system and each part has a proper size in relation to its neighbors and to the boat's performance envelope. Keep grinding through the entire sample build. Plenty here who can help you with specific questions regarding that book.
     
  10. pazimmer
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    pazimmer New Member

    27'6" center console. how far should my stations be set apart? im starting the design as a jig just like it would be in construction
     
  11. ancient kayaker
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    ancient kayaker aka Terry Haines

    The Boat Forum Wiki has several articles: http://www.boatdesign.net/wiki/Special:Allpages

    There's an article on design ratios here
    http://www.boatdesign.net/wiki/Design_Ratios

    Normally you would start with a Statement Of Requirements, but since you already have a specific type and size of boat in mind, I suggest you study several good design examples and try to understand the reasons behind their design. Don't forget the location where they were intended to be used, local weather and traffic patterns, materials etc.

    During that process you will find that you to translate boat terminology; here are a couple of links that should help
    http://www.worldwideflood.com/ark/terms/ship_terms.htm
    http://en.wikipedia.org/wiki/Glossary_of_nautical_terms#T

    Now for the usual caveat: if you just want to build a boat, get yourself an established design - you can almost always find what you want either free or for sale on the web, or in boating magazines. trying to save money on the design is like using cheap gas in a Lamborghini. If on the other hand you wish to master design and prefer not to venture down the academic or apprenticeship paths, then I usually recommend starting with the smallest boat that will fit your needs, to minimize the risk.
     

  12. gonzo
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    gonzo Senior Member

    Station spacing is irrelevant at this stage. You need to study dynamics and other aspects of boat design before it is important at all. Caroline flair are difficult to design and make them to look good. There are a few tricks to make it work. For example, the sheer should be straight on the profile view. Also, the "S" should taper into the sheer turndown where it fades into the tumblehome.
     
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