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Yacht Hull Types

For many clients purchasing a yacht today, there are many things to consider and the most important is which hull design best suits them. There are 3 types of hull designs to consider in the recreational yachting world. They are:

Planing

A planing hull runs the majority of the time on top of the water, achieving high speeds, getting from point A to point B very quickly. Planing hulls typically are the least efficient and have the least comfortable ride. Rather than going "through the water" they go across the top of the water and are subject to the state of the surface of the water at any given time. Planing hulls are not recommended when purchasing a cruising yacht.

Semi-Displacement

The Semi-displacement hull design is the best of both worlds. While typically most semi-displacement vessels do not cross oceans, many are capable, like an Outer Reef Yacht, and have the range and capability to do so.

A semi-displacement vessel can take advantage of increased power and can achieve greater speeds when needed. Granted, applying additional horsepower consumes more fuel, but typically most semi-displacement vessels only take advantage of this available speed when trying to outrun a storm front or trying to make a dangerous inlet in daylight hours, etc. Most of the time, semi-displacement vessels operate in displacement mode and are very fuel efficient.

Due to the lesser draft as compared to full displacement vessels, semi-displacement vessels have less "wetted surface", requiring less horsepower to propel the hull through the water. A semi-displacement hull can achieve about 35% more speed with the same engine load requirement as compared to a full displacement hull form, or conversely at the same speed use significantly less fuel and energy. Using a 55'- 65' hull as a comparison, the full displacement hull approaching hull speed will use about 95%-100% of engine load. The semi-displacement hull approaching 10 knots (hull speed for the full displacement hull example) will only use about 15% of engine load and consume about 400% less fuel!

The hard chine hull of a semi-displacement vessel is inherently more stable than a rounded bottom full displacement hull. For most vessels the majority of their time is spent either in an anchorage or at a dock. Semi-displacements vessels are far more comfortable at anchor than any rounded bottom design.

Full Displacement

Full displacement vessels are very mission specific. Full displacement vessels typically have deep drafts and rounded hull forms. These design characteristics are best suited for long offshore passages and very low speeds. Being that full displacement hulls can never plane, they are restricted to "hull speed" which means that regardless of how much horsepower is applied to the drive train, the boat can never go above the designed hull speed of that particular vessel.

Typically on a displacement vessel in the 55'-65' range, maximum hull speed is approximately 10 knots. To cruise efficiently, with a vessel of this LOA, speeds of 7-8 knots is usual. To go any faster than this cruising speed, you will be nearing hull speed and the horsepower and engine load requirement will rise dramatically, burning copious amounts of fuel.

The rounded hull form of a full displacement vessel is not as comfortable at anchor as compared to a planning or semi-displacement hull form. Some full displacement hull form vessels with have "flopper stoppers" (pole like outriggers) deployed in an anchorage to help, but not completely prevent the typical rolling of this type of hull.

Obviously the deep draft of the full displacement hull form is not conducive to coastal cruising, especially on the Eastern Seaboard and the Bahamas. Some of the best cruising grounds in the world lie in waters 7' and less. The full displacement vessel is restricted from some of these best cruising grounds.

Conclusion

When purchasing a yacht, choose a yacht for how you are going to cruise the majority of the time. Do not purchase a yacht for something that you may do once in the lifetime of the ownership of that yacht. Many people fall into the trap of dreaming of how they may cruise as compared to how they will likely cruise and most times end up making the wrong decision on the purchase of a yacht. Many Outer Reef Yachts owners don't want restrictions as to where they would like to cruise, and therefore, have chosen an Outer Reef due to the cruising freedom she affords.