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Bulbous Bow Benefits

With the development of the 62, P.A.E. began extensive tank testing of new models in order to verify hydrodynamic characteristics of hulls, with emphasis placed on resistance and “seakeeping” qualities. Most Nordhavn displacement hull forms are tested with both conventional as well as bulbous bows. Bulbous bows have been used for years on most tankers, freighters and large fishing vessels because the bulb reduces hydrodynamic drag at the speeds ships travel resulting in a considerable fuel savings over the lifetime of the vessel.

P.A.E.’s interest in the bulbous bow was originally focused on reducing resistance, improving efficiency and thereby increasing range. By affecting the bow wave, tank testing has shown that a bulbous bow reduces resistance in the range of 3 to 15 percent depending on the model and speed. This reduction in wave making resistance allows less horsepower to be used for a given speed, thereby increasing range and reducing engine rpm with a corresponding decrease in engine noise. While the primary intention of bulbous bows was to increase efficiency, it was noted that that they also contributed to decreases in pitch motion on some models. Pitch amplitude on the Nordhavn 62 was reduced by 20% and pitch acceleration was reduced by l8%, contributing to the “seakindliness” of the boat in most sea conditions.

At present the bulbous bow is offered as an option on all the larger Nordhavns, starting with the N76 (and it is standard on the new N120, where tank testing points to a wave reduction of at least 10%). Specific cruising habits and locations might influence a buyer’s decision to include a bulbous bow, and most of the larger boats do end up leaving the factory with a bulb attached. In fact, every N86 to date has been built with a bow bulb.

On the smaller yachts it was found that the bulb can cause what some might consider to be an unwelcome amount of noisy pounding or slapping while going to weather in rougher seas. In order to make the ride as quiet as possible, bow bulbs are not fitted on the smaller Nordhavns. Even though a bow bulb would certainly bring an improvement to the lifetime fuel economy of the N55, N47 and other smaller boats, it was decided that the benefits were not worth building a boat that some might find noisier than they’d like.

 

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