Hullform's Drag and Power Capacities

Hullform includes six drag and power parameterisations, including two forms of the well-known Standfast series (by Gerritsma and others), two small-ship schemes (Holtrop and Oortmerrsen) and the two Savitsky planing-drag schemes.

Using Hullform, you can complete a preliminary review of the likely performance of your design. The program's drag calculation schemes cover the full range of likely monohull types, and you can even compare estimates graphically to see by how much they differ.

For each drag scheme, you can display a detailed review of the calculated drag and power, for any speed. You can also plot any estimate as a function of speed, on-screen or to a printer, plotter or file. The program allows up to 6 drag curves per plot.

The sample plot shown here illustrates an important principle - no two schemes ever agree perfectly. This is where the professional naval architect has to earn his/her commission!

You can also evaluate drag implications in more detail. Below is an analysis based on the Holtrp and Mennen scheme, for a 310 ton trawler at 12 knots. (You can see that the measurement units are feet and tons. The analysis functions equally for all measurement systems)

For speed                                       20.267 ft/s
Waterline length (LWL)                         115.676 ft
Wetted surface                                3100.705 sq ft
Skin friction coefficient (I.T.T.C)          2.263e-03 
Prismatic coefficient (CP)                       0.586 
Form factor                                      0.265 
Centre of buoyancy (LCB)                        -2.477 %
Half-entrance angle                             18.273 deg
Beam                                            29.066 ft
Draught                                          7.604 ft
Reynolds number (Rn)                         1.829e+08 
Froude number (Fn)                               0.333 
Thrust deduction factor (t)                      0.272 
Wake fraction (WT)                               0.174 
Open water prop eff.(eta 0) @  97 rpm,Ja  3.0    0.297 
Hull efficiency (eta H)                          0.881 
Relative rotative efficiency (eta R)             1.000 
Drag force: friction                             1.288 
          + form drag                            0.341 
          + wave drag                            1.342  = 2.971 ton
Effective power needed is                      245.241 HP
Thus total power needed is                     937.380 HP