Hullspeed FAQ list

• What restriction does the Hullspeed Demo version have?
• Why Hullspeed?
• Does Hullspeed predict the running trim angle of my design when it is planing?
• What level of certainty?
• Does Hullspeed calculate propeller efficiency?
• How does the efficiency of my propulsion arrangement influence Hullspeed results?
• The Solve Resistance Analysis menu command is greyed out

The demonstration version of Hullspeed only allows to calculate the resistance of vessels that are within +/- 10% of the Hullspeed Sample model. This sample model can be found in the C:\Program Files\Maxsurf\Sample Designs directory on your computer after installing the demo.

The demonstration version also has the analytical slender body method disabled.

[top]

As well as the regression method for resistance prediction, Hullspeed also has a theoretical based, slender-body method. This can be applied to multihulls and other vessels that fall outside the parameter range of the regression methods (provided that the individual hulls are symmetrical and reasonably slender).

Using the slender-body method, Hullspeed is also able to predict the far-field wave pattern which can be useful for assessing the wake generated by the vessel.

Version 12 of Hydromax is compatible with visual basic for applications (VBA) -- this means that you can use a VBA macro in Microsoft Excel (or similar) to modify a model in Maxsurf, then test the vessel in Hullspeed automatically and very quickly compare the resistance curves of a parametric series of hullforms.

[top]

The methods that Hullspeed uses to calculate planing resistance don't predict the trim angle of the design.

This does not mean that the resistance prediction is not correct. The regression tables where the resistance coefficients were extracted from are based on the upright hull parameters.

[top]

Hullspeed is a resistance prediction program which principally uses a number of standard regression methods to estimate the resistance of the vessel. In addition, Hullspeed is able to use a slender-body theoretical method to estimate wave-resistance.

It is not possible to give a percentage uncertainty for Hullspeed because the accuracy depends on the vessel type and the regression method(s) used. If your vessel is very similar to the parent hullform of the regression method, then you will get results that are within the uncertainty margins of the regression. If however, you have a hullform that is further from the parent, the uncertainty in the accuracy of the results is increased.

Having said that, it can be expected that regression methods will correctly classify design alternatives – i.e. vessel A will have a lower resistance than vessel B. So although there may be 10-15% uncertainty in the absolute value, you can generally correctly rank the design alternatives.

[top]

No, Hullspeed does not calculate propeller efficiency. We recommend using NAVCAD for this purpose. The propeller efficiency can be fed back into Hullspeed for powering predictions.

[top]

Hullspeed simply calculates the resistance of the hull. In case you wish to determine how much power in [kW] is needed to overcome that resistance the following formula applies:

Power [kW] = Resistance [kN] * speed [m/s] * overall efficiency [% / 100]

By selecting [Data | Efficiency ] you can specify the overall efficiency of your propulsion arrangement. By default Hullspeed uses a 100% efficiency. By selecting [Data | Graph type ] you can select which unit you want Hullspeed to show in the graph versus speed.

[top]

The Solve Resistance Analysis menu command is only enabled when you have selected an analytical resistance analysis method like the Slender Body method. To solve an analytical resistance prediction method:

Step 1:  Select the method in the Analysis | Methods dialog

Step 2:  Select Solve Resistance Analysis from the Analysis menu.

[top]