The March 2012 issue of Westlawn Institute's free journal The Masthead is posted
The March 2012 issue of Westlawn Institute's free online journal, The Masthead, is now posted.
Highlights in this edition:
Understanding Engine Power Curves
By Dave Gerr
Deep in the bilge of the boat you're designing, building, surveying or repairing is her beating heart-her engine. The recipient of endless tuning, cleaning, and fuss, it's the boat's engine that drives her from anchorage to anchorage. Engines, however, come in a wide array of sizes, shapes, and flavors. Whether you're repowering, determining which propulsion-package option to install in a new boat, trying to optimize performance on an existing boat, or to understand why an engine isn't achieving full rated RPM, good information on engine behavior can seem hard to come by. The key to deciphering engine performance is the performance curves that are included with the engine manufacturer's literature. We'll examine these curves here.
Westlawn Alumnus Will Allison of Imaginocean Yacht Design
On The Drawing Board
C.Way Pty Ltd has tapped Tasmania-based designer Will Allison and his design firm, Imaginocean Yacht Design, to design both a 47 meter motor yacht and its 8 meter tender. The decision to custom build a tender was born out of the need for an attractive, functional day boat that offers protection from the weather, whilst still permitting the enjoyment of water sports. Will Allison says, "There's any number of limousine-style tenders out there: but they are a single use vessel. The objective here was to create a practical boat that would serve as a comfortable tender, but also be suitable for a range of other activities." The result is an edgy-looking 8 meter boat with seating for up to eight guests and crew. IYD employed a combination of aluminum for the hull and structure, with composites for much of the interior, to produce a durable vessel that is also light enough to be lifted onto the aft deck of the mother ship. Hull number one is currently under construction in Hobart and is due to be launched by the middle of 2012.
Surface Normals and Hydrostatic Calculations
By Larry Leibman, Principal Naval Architect, DRS Defense Solutions,*LLC
In order to compute the hydrostatics properties of your hull model, Orca3D performs a numerical integration on the surfaces that you select for the hydrostatics analysis. This numerical integration is affected by the orientation of the surface, where in this context “orientation” refers to the direction that the surface normals are pointing. By convention, Orca3D assumes the surface normals point into the water (i.e. the normals are on the wet side of the surface). One might be tempted to say that this is the equivalent of assuming the normals point “outward” from the hull surfaces; however, this is not always true. Consider the case of a bow thruster opening in the hull. Here, pointing into the water will have the normals pointing inward. Surfaces whose normals are outward create positive displacement; when surface normals are inward, the displacement of that surface is negative. For the bow thruster example, it’s correct for the buoyant volume of the surface to be negative.
Read the complete articles and more in this issue.
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Director, Westlawn Institute
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