SuperyachtNews.com – Technology – Bray Yacht Design and Research Releases Hull Efficiency Report
Analysis of a 45m hull, with and without a bulbous bow, demonstrates significant fuel consumption and a reduction in power required…
Maximizing the efficiency of hull design will play an important role in the maritime industry’s aspirations to reduce emissions. Multihulls are gaining popularity in recent concepts and new build projects, both for their optimization of floor space and gross tonnage, as well as for their hydrodynamic characteristics. Another hull variant, more closely associated with larger and commercial vessels, is the bulbous bow. The summary below of the results of a long-term study undertaken by Bray Yacht Design and Research.
Using a basic 45m hull form as a baseline, this analysis compares a bare hull to a bulbous bow, to assess the reduction in strength. This project was carried out using an extensive suite of Computational Computational Fluid Dynamics (CFD), utilizing the expertise of the National Research Council of Canada’s Center for Ocean, Coastal and River Engineering in numerical modeling . The project also received support in the form of advisory services and research and development funding from the NRC Industrial Research Assistance Program (NRC IRAP).
Resistance reduction is achieved by constructive/destructive wave interference. The appendages (bulb) alter the overall wave train through small wave and pressure patterns and it is this interaction that reduces the overall wave train, resulting in a reduction in overall resistance.
Fully hung form at 13.5 knots.
The reduction in resistance, and therefore power required, had a significant training effect. In this example, the version without appendage (bare hull) has 338 tons of displacement compared to 364 of the final version with appendage, an increase of 8% in displacement. At the same time, this heavier and more efficient final version has up to 116% greater range if the same 45 cubic meter fuel tank is retained.
Theoretically, however, the final attached version requires only 42 cubic meters of fuel for similar ranges, a saving of 2450 kg, as shown in the figure below. Additionally, it will require smaller motors and lower SHP (Shaft Horse Power), which will theoretically save an additional 910 kg per motor installed. These savings are significant, and this initial calculation does not take into account any reduction in hull plating.
The non-appendage version is calculated to have 24% to 26% more resistance over the majority of the speed range. This equates to a difference of over 1,100 hp at 20 knots. The added hull, therefore, relates to considerable fuel savings, reduced carbon footprint, flatter wave train and lower underwater noise signature. For electric propulsion, this can also be correlated to smaller electric motors with smaller battery system consumption.
Reducing a ship’s environmental impact isn’t just about the propulsion system, it starts with the power needed to move the hull. Bray Yacht Design and Research sees many ship applications for these appendages in reducing fossil fuel consumption and the impact of ship wakes on shorelines, as well as reducing the amounts of raw materials needed for construction of these more efficient and therefore lighter ships.
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