THE DESIGN PROCESS
THE BASICS, PART 1
 By Russ Lenarz

In the past two YD 101 articles, we have taken a look at two different types of design rules, the IACC Rule and the ORMA 60 Rule. We have looked at the evolution of both of these rules and where they might be headed in the future. It could be said that these two rules are in many ways at opposite ends of the design spectrum, with one being a pure open development class and the other a formula based rule where there exists certain limitations. But interestingly, the process of designing boats for both of these rules is very much the same. In this installment of YD 101 I will begin a series that will cover some of common principals of yacht design. These principals make up the foundations which are the basis of all yacht designs

A yacht designer must not only be a technically minded person, but also an artist. The technical side of the mind must be able to understand and work out the various formula and calculations that cover everything from balancing centers of buoyancy, gravity, moments of inertia and resistance calculations, as well as the complex task of engineering a boats structure. The artistic side must be able to produce complex curves and lines that are not only efficient through the water, but are pleasing to they eye. Even a barge can float, although they may not be the best looking boat on the water. (And even that depends on who is doing the looking I suppose.)

Most people have seen lines plans and associated other drawings of in various sailing magazines. Additionally, designers are now often using computer generated color renderings to showcase their ideas. An often asked question is, just how did a designer come up with that particular design? In the field of racing yacht design most designs either are created to fit within a specific design rule, such as the Transpac 52 Box Rule, IMS, or an Open Development Rule, or the design might be a One-Design concept. Now and then a new design is developed with a specific purpose in mind such as breaking a transatlantic record or an outright speed sailing record. No matter what the boats purpose is, the initial process of the design itself follows the same method. The design process, and within the process a design spiral is applied to each step. There are several variations of design spiral, but the end result is the same. We will look at the design process and how a design spiral is applied to the individual steps of that process. This approach is the foundation from which the majority of the boats we sail and see are developed.

The design process itself can be broken down in to 4 steps. The are as follows:

  • The Design Statement
  • The Conceptual Design Phase
  • The Preliminary Design Phase
  • The Detailed Design Phase.

With the exception of the design statement a design spiral can be applied to each phase. A design spiral is a series of related analysis which when applied to each of the remaining steps of the design process results in the best fit to the design statement. The same, or similar spiral will be applied to each of the remaining three phases. A typical design spiral for these three phases of the design process might include the following steps.

  • Hull Definition
  • Hydrostatics
  • Weights
  • Powering
  • Stability
  • Structures
  • Arrangements

Another variation of a design spiral could have the following steps.

  • Hull and Deck Design
  • Keel and Rudder Design
  • Sail and Rig Design
  • General Arrangements
  • Propeller and Engine
  • Hull and Deck Scantlings
  • Rig Dimensions
  • Weight Calculations
  • Hydrostatics and Stability
  • Evaluation

A designer will often modify the spiral to suit their own needs or as it applies to a specific design. It is important to point out that a designer does not always follow every step and the exact order of the design spiral in each phase of the design process. For example in the early stages of development, it may be necessary to go from hull and deck design to general arrangements before developing the keel and rudder design. No matter how a designer approaches a particular design, the design spiral will always play an important role in the design process.

Yacht Design is an iterative process that, depending on the type of design being developed may require several runs or iterations through the design spiral in any or every step of the design process in order to achieve the optimum goal. We will see later in this article, and in following articles just how important it is to work out as many possibilities in the early stages of the design process, before the detailed design phase. The reason being, the further into the design process, the more difficult it is to fix problems. If a design reaches the detailed design phase and a number of factors are still unresolved then it is absolutely necessary to go back to the preliminary design phase and work out these details. There is nothing worse than going through the design process and discovering that you new ULDB racer does not float on its waterline. Not to mention you will more than likely have a pretty short career as a designer.

So, lets take a closer look at the design process and how the design spiral is applied to each phase in the develop a new design. The first step in the design process is to develop a design statement, sometimes called a design brief. The design spiral is generally not applied at this phase. The design statement can be just a few sentences or a couple of paragraphs that give an outline as to the purpose of the design. This is often developed by the client and designer together. The design statement serves as the foundation for the new design. Throughout the design process, it is imperative to refer to the design statement from time to time.

The next step of the design process, is the conceptual design phase. This is the first phase where the design spiral is applied. The conceptual phase is generally seen as the most creative part of the design process. It is not uncommon for a client as well as a designer to have unrealistic goals for a particular design during this phase. The designer should not limit his ideas too soon and should take as many possibilities into consideration at this time. Once the designer has gathered as many ideas as he or she can for a particular design, then they will begin to determine just what is feasible within the design statement. It is in this phase that principal dimensions, general arrangements, powering options and major weights are all developed. Designers approach this phase in many different ways. Some will take ideas from previous projects or an existing design and mesh them together to come up with a new concept. I personally like to develop a number of rough concept hull shapes on the computer first, and then work out other aspects of the design, such as deck, cabin top and rig profile the old fashioned way using a good old pencil and curves etc, with several overlays on mylar drafting film. This way I can sketch out a number of ideas to scale quickly and flip through them before a series of CAD concept drawings are developed.

As mentioned within the conceptual design phase the first of many design spirals will be created. It may take several iterations in the conceptual phase to come up with a feasible design. A lot depends on the size and complexity of the particular project. Once the goal has been reached in meeting the basic criteria as stated in the design statement, then a series of CAD concept drawings are developed and now in many cases color renderings of the proposed concept. This is then submitted to the client for review. Although many basic particulars of the design have been worked out the idea is still just a concept and a great deal of work is needed to pull the project in to shape.

We then go from the conceptual design to the preliminary design phase. It is within the preliminary phase that the intended design begins to really take shape. The purpose of the preliminary design phase is to create a set of preliminary lines plans, stability calculations, hydrostatics, early performance data, (such as preliminary VPP and comparison to other known designs), specifications as to construction materials and calculations for hull and deck structure. This preliminary data is combined in a bid package and submitted to builders to obtain a rough estimate of the final cost. It should be stressed here that a designer usually will not quote the final price of a boat until a builders bid package has been submitted based on information from the preliminary phase. There are many variables that can determine the price of a boat. Although a designer might have a very rough estimate based from previous projects or existing boats on the market, it is best not to attempt to come up with an accurate price until the builders take a look.

Like the conceptual phase, designers approach the preliminary phase different ways. By this time a number of concept hull profile as well as basic arrangement drawings have been developed, and so the designer will begin the process of the design spiral again to work out more finite details of its shape and address any problems that may occur. There are many designers who can create very good-looking ideas either by manual drawing or with a computer. However it the lines plans, which are developed at this stage of the design process, which really are the true test of the design and the designer. It is the lines plans that will determine the true shape of boat. The important nature of the lines plans is illuststrated when taking a structured course in the field of Naval Architecture. Instructors will go immediately to the set of lines plans to grade the assignment before looking at the other drawings.

There are a couple of ways one can approach the development of a set of preliminary lines plans. With the development of computer software for hull fairing and shaping, the designer can now create a complete hull surface by using a basic set of dimensions. Although this process does save some time and does allow a greater ability to develop a number of concept hull forms in a shorter period of time. The process of fairing and shaping does require a great amount of skill and time for the final product, and so I want to put and end to the myth that the computer makes the job for the designer any easier. We will go much further into detail in the preliminary design phase and how the design spiral applies here in the next Yacht Design 101 article.

The final step of the design process is the detailed design. This is the meat and potatoes of the design. The goal here is to produce the final working drawings, which will be used by the builder. Also it is in the detailed phase that final performance, stability and structural data will be created. In addition lamination schedules, tables of offsets and construction details are detailed. It was not long ago that all of this was done by hand and one has to appreciate the work that went into producing such complex plans. Today the use of CAD / CAM techniques are replacing the older methods, but I must stress that no matter what method is used it takes a fair amount of time and skill to produce the final product. By the time a design reaches the detailed design phase there should be little need to make adjustments in the design of the boat. However, there does exist some latitude for minor corrections. As mentioned before if too many problems are still unresolved then it is absolutely necessary to go back to the preliminary phase and run through the spiral again.

As one can see we have just begun to scratch the surface of the design process. It is a process that requires time and in many cases very tedious work. It will require a number of runs through each design spiral to develop a new design from concept to a set of lines plans. In the next installment of YD 101 (the Basics), we will continue our path through the preliminary phase and the applied design spiral. The fundamentals of hydrostatics, stability and exactly what goes into construction considerations and specifications will be discussed further.

06/03/2003