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= Total System Performance =

Developing a specification for building a boat involves many complex trade-offs. By focusing on key differentiating factors (what makes your boat better than the next one) and their impact on total system performance (TSP), you can build a better boat that others will admire. 

TSP is the concept that every decision in designing a boat is examined for its impact on all systems. To a degree designers and marine architects always do this; they will have brought years of experience to the task. But, especially in the yacht market, decisions can be influenced by marketing factors. When you purchase a production boat, the designer and boat yard have considered many options and trade-offs to achieve a specific price point for a specific demographic. 

In developing your own specification the main areas of interplay are propulsion, electrical, heating and air conditioning, water and plumbing. The TSP analysis is iterative, with consideration given to safety, performance and traditional value.

== Voltage Example ==

To illustrate TSP, consider that it is a given that navigation lights will operate on direct current (DC), not alternating current (AC). This has been sufficiently understood for so long that there is nothing to discuss here in DC vs. AC. It’s a “no brainer”. The standard practice is an industry best practice.

But should the DC be 12 or 24 or even 150 Volts (V)? This is an interesting question for a smaller boat, with numerous pros and cons from a TSP perspective. Choosing between the common 12 or 24 V impacts many systems (e.g., motors, lights, toilets, furnace, navigation instruments, engine controls, stereo, etc.) and its infrastructure (e.g., wiring size, length of wiring runs, batteries, chargers, inverters). The DC voltage is an example of a key differentiating factor. It is what makes your boat significantly different from the next one, because your functional and performance needs are different.

Deciding the best choice of voltage requires an analysis of impact on the boat's total system, not just one part of it. The analysis must also consider the availability and cost of equipment in one voltage vs. the other. (For example, there is a much wider range of equipment available in 12 V and almost none for 150 V.)

Common yacht lengths of 38-75 ft (12-23 m) are well within the capability of a 12-VDC system; although at the upper end 24 VDC might be a better choice. Say your estimate of water consumption requires a certain size of watermaker that is only available in 24 VDC. Now you have a requirement that affects batteries, wirings, chargers, inverters, lights and consumer items like televisions and stereo equipment. Fortunately DC-DC converters are cheap. But also consider the impact on plumbing: Did you know the performance of reverse-osmosis water makers deteriorates the colder the water?

== Propeller Example ==

Here’s another example: The traditional boat you’re looking at probably has a single screw and a three-bladed propeller. Yet research shows twin screws give superior thrust efficiency and we know they cancel stern walking. Theory says that fewer blades on a propeller increase efficiency; although we know just one will shake, rattle ‘n roll. Yet many modern propellers have four or five blades. What does this mean?

A single blade might be more efficient theoretically but it is obviously unbalanced and so has serious practical side effects: The vibration will shake the boat to pieces. Then, practical experience has shown that four blades are best with a large single screw; three blades with smaller double screws.

== Get Me Home Example ==

If you don’t feel safe with a single engine and want an emergency get-me-home wing engine, with a tiny emergency propeller, think again. Should you instead go for twin engines and screws, even though the fuel efficiency will be less?

If redundancy is important the real choice boils down to a single engine with a four-bladed propeller or twin engines and twin screws with three-bladed propellers,. There is no point in having a wimpy get-me-home auxiliary engine and propeller that are not likely to do the job in heavy weather, no matter how good it makes you feel.

Other combinations are possible, such as two engines and one screw mated with an expensive mechanical combining transmission; or one engine and two screws with a hydraulic or electric drive. From the perspective of a single-point of failure neither of these is attractive.  However, there might well be other good reasons for such a choice.

== Conclusion ==

These are the kinds of things you must think through as you develop a specification to meet your unique operational and psychological needs. When you develop your own specification for a bespoke boat, you have to resolve many of these issues yourself. But, like building a custom home, in the end you will have a unique and better product suited to your needs. The design considerations are complex. It is not easy to work through the trade-offs and understand the impact on performance and safety. In many areas you will need guidance from experts.