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EN342 Hydrostatics & Stability

Hints for HULLSPEEDA Parametric-Based Resistance Curve

From the File menu select Open DesignSelect Surfaces to Measure

Select all surfaces (make sure all surface have a check mark in front). OK

From the Data menu, check to see that:Units: Check they are Decimal Feet, Long Tons, Knots, Pounds Force, Horsepower. OKFrame of Reference: Verify correct DWL draft, FP, and AP, Zero Point.OK

From the Display menu, select ContoursCheck Sections, Datum Waterline, Edges, and Bonded Edges. OKView the hull and sections in the Perspective window (not rendered).

The sections are the data which are used to take the hull measurements which are then used in theparametric equations, so it is essential that these have been correctly formed.The sections shown are the immersed sections. By default, these sections are white. So if you wantto change background color to white, make sure you also change the color of the immersed sectionsto a darker color.

View the Data windowAny of these values can be changed by typing in new values.Under most circumstances the data will be correct. But, it is often necessary to change Chine type HardChine or Round Bilge. For the sample workboat, we have a Hard Chine, so you may need to change this.

From the Analysis menu select MethodsThese are the available methods (parametric regressions) for estimating a resistance curve. They all havespecific limitations and ranges of applicability.For the sample workboat, select: Savitsky Pre-planing, Savitsky Planing, and Compton. OK

From the Analysis menu, select SpeedsFor the sample workboat, enter a range of speeds from 2 to your maximum speed in knots. OK

View the Graph windowSelect Resistance vs. Speed from the pull-down menu.Note the ranges of applicability for each of the methods (they are only plotted in those speed ranges).Select Power vs. Speed from the pull-down menu.

View the Results windowThis provides the data in tabular format. This table may be copied and pasted into Excel.Hint: When copying data from the Data or Results tables, hold down the Shift key to also copy the columnheadings.

Notes about Hullspeed parametric analsyses:

Hullspeed has a number of regression methods which are suitable for different vessel types and sizes. Keepin mind that these are purely empirical methods with one exception, an analytic method based on the slenderbody theory. The accuracy can at best be described as fair. Types include displacement ships, semi-planinghulls, planning hulls, and sailing yachts. See the Hullspeed manual for the full details and explanation of thedifferent methods and their application. The commonly used methods in our classes include:

- Compton: Useful for typical coastal patrol, training, or recreational power boats type hull

forms with transom sterns, operating in both the displacement and semi-planing regimes.

- Savitsky pre-planing: Useful for typical planing hulls, operating in the pre-planing regime.

- Savitsky planing: Useful for typical planing hulls, operating in the planing regime.

- Delft: sailing yachts

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There are also upper and lower limits for the parameters used in the various regression methods. For someof the methods there are upper and lower speed or Froude Number limits, outside of which the equations arenot valid. Hullspeed will check that the entered data is within the valid ranges for the selected methods. Inthe Data window, if the values are okay they will be displayed in black; if they are too low they will bedisplayed in red with the word (low); and if they are too high they will be displayed in orange with the word(high). Note: in some cases, the limiting values for the method may be derived from two or more input data,normally resulting in one parameter being too high and the other too low. For example, if for a specifiedmethod, Transom area/ Max Sectional area was a critical parameter then Transom area would be highlightedhigh and Max Sectional area would be highlighted low if the ratio was too high, and vice versa if the ratio wastoo small. To have confidence in the results you should ensure that all the values are within the acceptableranges.