What is the difference between a full displacement and semi-displacement hull design? Essentially, the full displacement hull remains completely in the water at all speeds. It virtually "pushes" the water away from its bow. The water then travels down the length of the entire hull, finally leaving a wake behind the stern. This "bow wave" creates a resistance to the hull, from which it can never escape. The length of the wave is dictated by the length of the hull, and there is a clear relationship to the theoretical hull speed and the boat's waterline length. A simple rule is that a boat can travel at a speed of about 1.34 times the square root of its waterline length. A 36-foot boat, at waterline, would theoretically have a hull speed of 6 X 1.34 or a little over 8 knots. Regardless of how much power was applied, the boat would be limited to about that speed.
On the other hand, a semi-displacement hull does not live by these rules. In effect, its shape allows the hull to partially escape the confines of the bow wave and to "get out of its own way." By flattening the stern sections and by limiting the deep entry forward, a semi-displacement hull will provide a certain amount of lift, similar to a planing hull.
Within limits, adding more power will increase speed. Throughout the past few years, much has been made of the ability of older semi-displacement designs to go faster and faster simply by adding more power. The problem with these "fast trawlers" is that the hulls were never designed to go that fast in the first place. The results are not always favorable, as evidenced by their very wet ride and uncomfortable running angles. Massive trim tabs and ugly splash rails have been added to try to compensate for what is essentially a design limitation. While various marketing goals may have been met by adding more and more horsepower to these dated designs, unsuspecting owners have been disappointed with the performance of these fuel-thirsty, noisy boats. Ironically, most owners find themselves throttling back to the speeds the boats were designed to run in the first place.
Nordhavn's 35 Coastal Pilot was designed from the beginning to run efficiently at speeds in the low teens and with extraordinary economy at lower speeds of 7 to 10 knots. Her moderately-deep forefoot eliminates pounding, and her flat aft sections provide a natural lift as higher horsepower is delivered to the prop. Because a single engine is used, the full-length keel protects the running gear and provides the support for a fully attached rudder. This keel delivers superior directional stability, particularly noticeable in sloppy, following seas. It should also be noted that the chines, or areas where the bottom of the hull meets the sides, benefit from slightly curved transitions. This shape provides a more natural, gentle motion in a beam sea. Outdated, but heavily marketed designs have sharp-edged chines, which create a snapping, uncomfortable resistance to roll. Sea trials of the first 35 Coastal Pilot have confirmed what PAE's extensive tank testing has predicted: She is seakindly, dry, stable, very efficient and runs full speed at only a 3-degree angle.
The construction of the hull, deck and superstructure is all Nordhavn. The hull is hand- laminated featuring solid fiberglass with vinylesther resin below the waterline to prevent blisters. The hull is available in a Gray or Buff gelcoat. A ½" end-grain balsa core is used above the waterline for stiffness and weight reduction. Heavy-duty, longitudinal fiberglass stringers over polyurethane foam are bonded to the hull for added strength and stiffness. As in all Nordhavns, the tooling is highly polished and precisely finished, resulting in a flawless yacht appearance. An integral swim platform with molded-in diamond pattern non-skid is protected with a 1 ½" solid stainless steel guard. A beautifully styled stainless steel breast plate protects the bow from errant anchors and represents a typical Nordhavn touch.
The decks feature an attractive, practical molded-in diamond pattern non-skid in two-tone colors. To assure a lifetime of trouble-free service, the deck is bonded to the hull with 3M 5200 and mechanically fastened every 6 inches with stainless steel thru-bolts. The inside of this joint is then bonded with two layers of mat and roving to further strengthen and protect the hull-to-deck area. Heavy-duty, molded-in rub rails at the sheer and quarter sections are protected with solid 1 ½" stainless steel striker rails. This is a boat that can be laid up against a commercial wharf or docked without extreme timidity. Both Klegecell and end-grain balsa materials are used throughout the pilothouse, cabin sides and deck to provide extra stiffness while controlling weight above the waterline. Inspired by commercial fishing vessels, the pilothouse face has reverse slope windows that quickly shed water and spray. Built to handle rough conditions, the windows are constructed of highly-regarded Diamond Sea-Glazed painted aluminum frames with 3/8" tempered glass. Like all Nordhavn's the 35 is built to go to sea.