New Capabilities for Fast Craft Analysis with HydroComp NavCad 2012

DURHAM, NC, December 02, 2012 (Press-News.org) New capabilities for fast craft analysis with HydroComp NavCad 2012

New features for the industry-standard resistance and propulsion software
HydroComp NavCad is a software tool for the prediction and analysis of vessel speed and power performance. It also provides for the selection of suitable propulsion system components - engines, gears and propellers.

An extensive development effort has been undertaken to enhance fast craft performance analysis in NavCad 2012. This includes new definitions for planing hull geometry, as well as improvements to the prediction techniques and critical components of performance.

Planing hull geometry
Definition of planing hull geometry principally focuses on the bottom shell "planing surface". One of the challenges in reasonably defining planing hull geometry is that the important data changes with speed and loading. Therefore, we have to rely on meaningful static data that can then be manipulated as the "dynamic" requirements change.
NavCad 2012 now determines appropriate characteristics of the shape as the planing surface changes with speed and trim. Since the shape may vary in beam and deadrise, more than just a simple prismatic wedge geometry is needed. Results of an internal study pointed us to a new description of the planing bottom surface for NavCad 2012 using two longitudinal data sets (e.g., at the transom and near LCG) to determine the proper "significant" or "effective" values for chine geometry and deadrise. (See graphic.) This new method also quantifies the shape for a proper hull warp correction to bare-hull drag.

Trim angles
Most planing hull prediction methods use the hull's baseline as the zero-angle position when determining trim. To account for variations in deadrise (warp), vertical chine position, and keel line "rocker", NavCad 2012 uses a "virtual baseline" determined from chine height and deadrise as the zero-angle basis for the prediction of trim. It then correctly calculates and presents trim as the angle against the initial static waterline.

Propulsor lift correction
HydroComp has developed an estimate for the effect of propulsor lift on equilibrium planing drag for three different propulsor types - conventional propellers, surface-piercing (SP) propellers, and waterjets - as well as for a horizontal tow (to mimic a typical towing test). Propulsor lift force has traditionally been omitted in the equilibrium analysis of planing, since there had been no prediction methods readily available prior to this feature for NavCad 2012. This new prediction method was developed employing various empirical test data and analyses that compared propulsor vertical lift to its effective thrust.

Flaps, trim tabs, and interceptors
Flaps (also known as trim tabs), wedges, and interceptors are devices used to reduce drag by altering the running trim of vessels, and to change pressure distributions at the stern. The full hydrodynamics of these devices are complex, but NavCad 2012 provides for the application of these devices for planing hull analysis (including proper orientation of force vectors).
The principal prediction method for flaps (and wedges) is based on model tests of rectangular flaps with (span-chord) aspect ratios from 1.25 to 5.0 and deflection angles nominally less than 5 degrees. HydroComp conducted a re-analysis of the original data to develop an improved prediction method using an aspect ratio correction for the lift coefficient and the longitudinal center of effort of lift. (See graphic.) The new correction greatly improves the precision of the prediction of flap lift (and also drag) and center of effort, and extends its applicability to a broader range of flap and tab shapes.

New to NavCad 2012 is the ability to model the effect of interceptors - flat plates attached to the transom of a hull that extend into the flow stream. Like flaps, the performance benefits of interceptors are mostly across the pre-planing "hump speed" where both drag and trim can be reduced. However, there is a significant drag penalty at post-hump speeds. The implementation used for NavCad 2012 is based on the drag of an extended plate with a correction for aspect ratio. Validation of the new interceptor method has been very good.

Contra-rotating propellers
Many contemporary fast craft are outfitted with contra-rotating propellers (CRP), and NavCad 2012 includes new functions to model performance of CRP systems. Analysis of a CRP in NavCad 2012 is with a performance model using only the definition of the forward propeller in the set.

HydroComp evaluated a number of published studies that made direct comparison between conventional and CRP propellers. From this evaluation, a number of corrections were developed and are applied without user interaction when a CRP propeller type is selected. The CRP model includes appropriate changes to system KT and KQ to account for effects of changes to blade loading, induced velocity, wake field, rotational losses, and hull efficiency. The intent of the new CRP method is to reasonably model the overall performance of a CRP propulsor set for an application.

Summary
NavCad 2012 represents the effort of nearly three years of work by HydroComp's development team. This new version is built upon a baseline architecture that will allow for modular development of new features for the coming years. These significant core improvements for designers and builders of fast craft are the first of many modular innovations from HydroComp's team of engineers planned for the NavCad platform.

User list tops 500
HydroComp is pleased to welcome its 500th user of NavCad. Currently at work in more than 50 countries, notable recent purchasers of NavCad include DINAIN (Spain), Orion Naval Engineering (France), Vectorworks Marine (USA), SAFE Boats (USA), Metalmec (Mexico), JB SeaForm (Sweden), COPPETEC (Brasil), Petter Hakanson Marine (Sweden), Farrell and Norton (USA), Concept Naval Degagnnes (Canada), REINTJES (Germany), and KND Naval Design (South Africa).

About HydroComp
Celebrating its 28th year of operation in 2012, HydroComp provides software and services for the performance analysis and design of marine vehicles to industry, research, academic, and government clients. The company is proud to have served over 700 customers from more than 60 countries.

Forecasting Hydrodynamic Performance from Design to Manufacture since 1984.

Download at: http://www.hydrocompinc.com/company/news.htm

For more information, please contact: Jill Aaron, Managing Director
HydroComp, Inc.
13 Jenkins Ct, Suite 200
Durham, NH 03824 USA
Tel (603)868-3344
Fax (603)868-3366
ja@hydrocompinc.com
http://www.hydrocompinc.com
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