Question: How long does it take to design something? What steps do you have to take in order to produce it?

Alexander Zacheshigriva answered on 21 Mar 2012:

Excellent question. One could write books about this, so what ever answers we give they will not cover the topic completely but I will try to give a few examples.

Any engineering design will have the following stages:
1. Realization of need (someone has to decide that they need something)
2. Requirements definition (all the people that will use the product need to agree what does it have to do and make sure that they don’t constrain the design options by being too specific)
3. Preliminary designs (different ideas of how to meet the requirements)
4. Rough estimate and trade-off analysis. (Next we need to choose the optimal arrangement. We need to have a rough estimate of costs, time and risks involved in each option. We also may have to trade off some things to get others, eg: if you reduce the size of a fuel tank, you car will be lighter and faster but will have to stop more often for fuel, you trade off range for speed and efficiency)
5. Concept design. A rough design is worked up.
6. Detailed design. Once we know roughly what all the items are and what shape they have, we need to work out all the details: fixings, manufacturing process.
7. The design gets build, tested, commissioned and evaluated.

The process that I drew up looks sequential (one step after the other) but in real life it is a mess of loops, you often have to come back from one point to the other and so on, new problems arise as you get on with the design and you have to go back to the drawing board.

Lets say to design a ship can take between six months to years (many years). Navy ships tend to take longer to design. Main reason is that they have to be very novel with new technology, ideas and requirements. To work all of this out takes a while. On the other hand a tug may be designed quite quickly, because you can use a design for another tug and just modify it to suit.

When designing a ship we start by working out what the capacity has to be (people, tonnes, cubic meters, etc) this gives us general dimensions, then the hull form, then we work out the power requirements and rough size of main systems (fuel, water, oil, air), once we got to that point we review the general dimensions to check that they fit well. After that we start drawing the “general arrangement” which is like a plan view of the ship for each deck, where you assign areas to each compartment. It can be quite fun and frustrating at the same time trying to fit all bits of the puzzle into the space that you have. Then the structure (big beams and frames that hold the ship together) are designed. By that point we have a good idea of where the weight will be so we can work out the trim and stability calculations and decide where the ballast has to go. Next we need to select suppliers and do the costings. This is the concept design. If all that is done and accepted we can do the detailed design: routing pipes, cables, design the minor structure (smaller beams and bulkheads (that’s walls)).

Sorry I had to cram the whole thing in to reasonably short message. But hope it helps understand how ships are designed. Feel free to ask further explanation of any of the stages.