There is no such thing as a perfect boat. There is only a boat that is the best possible compromise between your budget, plans and preferences. When buying a yacht, there are several things you should bare in mind, such as sailing ground or sailing seasons when you will be using your boat. Another thing you should bare in mind are your physical abilities – how fit and strong you are to jump around, climb the ladder, transport fuel or water by jerry jugs and other physical activities are important factors when choosing a yacht. New models are designed to make all the things that need to be done aboard easier and simpler.

Still, these are all your personal preferences and individual thoughts. When buying a boat, you should take a reasonable and analytical perspective of things.

Even with all the available date, people still choose a specific boat, based on economic and aesthetics.

When it comes to sailing yachts, there are some formulas that can help us get clear perspective of the boat, and keep the expectations realistic.

These formulas give valuable clues to the relative motion and performance of different sailboats. This way you can, with mathematical precision, calculate certain important variables, and get the idea of what the sailboat is truly like. Interesting thing is that the most important factor in most calculations is not length, but displacement.

- The
**length-to-beam**ratio (LOA divided by maximum beam) indicates interior storage space and nominal stability. An L/B value of 2.8 to 3.2. is common for smaller vessels and normally increases to between 3.6 and 4.0 for those in excess of 40 feet. A ratio higher than these numbers may mean an excessively narrow boat, while a lower ratio may prove to be too beamy to sail well. - The speed-length ratio is used for traditional speed estimates of displacement hulls. It is a constant multiplied by the square root of the waterline length (LWL). The constant most normally used is 1.34; thus a cruiser with an LWL of 36 feet would have a theoretical hull speed of 8.04 knots (square root of 36 = 6, times 1.34 = 8.04). Modern cruisers may exceed an S/L ratio of 1.4 on a beam reach, but on a long-term offshore cruise, the constant is probably closer to a value of 1.0. It is helpful to remember that the power needed to exceed hull speed is enormous relative to that used to drive the boat at or below hull speed.
**Displacement-to-length**is a non-dimensional ratio that allows comparison of displacement boats having different LWLs. The displacement is stated in long tons of 2,240 pounds per ton, and this is divided by 0.01 LWL cubed. Values of 280 to 320 are typical for cruisers. Boats with lower D/L ratio accelerate faster, even to the point of planing, but they may have an unacceptable motion in a seaway and have reduced carrying capacity.- The
**sail area-to-displacement ratio**(SA/Disp 2/3) is perhaps the most important, but also the hardest to derive without a scientific calculator. The boat’s sail area in square feet at 100 percent of the foretriangle is divided by the displacement stated in cubic feet of seawater (displacement in pounds divided by 64) to the 2/3 power, that is, first squared, then taken to the cube root. The SA/Disp 2/3 can be considered like the horsepower per pound of a motorboat. Higher ratios indicate better potential performance, but also increasing the need to reef as winds build. Most single hull cruisers have a ratio of between 14 and 18.