Versatility in modifying hull shapes.
The secret of the Mac is that moving a pointer around on the screen by means of a mouse erforms virtually all commands that control the computer. All operations are highly visual and are in as simple a form as possible. This system is used in MacSurf in many, sometimes amusing, ways. Modifying hullshape is very simple. The shape of the hull is controlled by a network of points that hold the surface in position, rather like the weights on a drafting spline. When working on the profile, for instance, in order to change the shape of the hull, the pointer is merely positioned on the appropriate control point, and the point is pulled into a new position. In about 3 seconds (depending on the precision of the drawing) the complete hull is redrawn in 3 dimensions. And it is perfectly fair. If you then choose, in about another 30 seconds, all the hydrostatic information on this new hull can be displayed on the screen. When you consider that this same operation could take 2 or 3 days by hand, it is easy to see that in the time it previously took to draw and analyse one hull, you could do the same to approximately 100 hulls. (Given the fact that you will need time to think about each permutation.) But, this is still only fast calculating - the program goes much further than just saving time.
On screen dimensioning
On screen dimensioning means that the coordinates of the pointer, which is controlled by the mouse, are displayed on the screen at all times. This means that measurements can be taken directly off the drawing on the screen at any scale.
3D Animation and Perspective
A very useful feature for viewing new or unusual shapes is the perspective view. The on-screen picture can be rotated through any angle and can also be animated so that the hull can be rotated rather like a movie film. This gives a designer and his client a much better opportunity to visualize the shape of the boat than is possible with a conventional 2D drawing.
The zoom feature allows one to inspect any partof the hull at any scale to slightly larger than life size; this takes a little getting used to because when you zoom in on one part, you cannot see the whole of the hull. At first I was not confident that the changes made while zoomed would produce a fair shape on the rest of the hull, however, there are several simple rules to follow in the way that the control points are positioned in relation to each other, that always will produce a fair shape. Once these are known, working between a zoomed image and the larger view is very simple indeed.
Bulkheads and Section drawings
Macsurf gives the option of placing up to 20 stations anywhere along the hull, at any one time on the screen. This means that once the hull is designed, all the bulkheads and sections can be plotted at any scale, up to full size. This greatly speeds up the design process since there is no need for the time consuming process of taking sections and bulkheads from the lines plan and they can be plotted perfectly at the press of a button. One of several automatic features that can be selected is to space the sections evenly along the waterline.
It is now possible to obtain computer drawn full-size frame drawings for the hull, directiy from MacSurf. This saves time for the builder, not only because he does not have to perform the laborious process of lofting the hull from the table of offsets, but also when the mold is built, using perfectly fair frames it greatly reduces the building time and, of course, a better hull will result. To give an example of how this can pay off in practice - recently 4 men built the complete fully-planked (double diagonal) hull mould for a 50 ft hull of my design, in two and a half weeks from receipt of the full-size drawings. Normally they would probably only have finished the lofting in the same time.
MacSurf takes a large number of measurements directly from the hull currently on the screen and allows the user to set up all the relevant hydrostatic equations in a spreadsheet. This calculations page can be called up and recalculated at any time. A recalculation approximately 30 seconds to 1 minute on average. Therefore it is very fast and easy to develop new shapes and analyse them instantly. Once a hull has been finalised, further in depth analysis can be carried out by moving the waterline to any position, or by changing the fore-and-aft trim, or angle of heel, to any angle and recalculating the hydrostatics. The information from these incremental changes can be immediately fed into a graph-generating program such as Cricket Graph to produce a model of dynamic change of any hydrostatic variable. Alternatively, the hull and deck form can be loaded into MacHydro (an as- sociated program by Graphic Magic) and the hull can be floated free to trim at a series of heel angles, or displacements. And, again, graphs of all variables can be obtained directly within MacHydro. The resulting set of images can be animated (like a movie film) so that the hull can be viewed rolling and trimming exactly as it would in reality. This facility opens up a completely new field of research and development for the average yacht designer which was previously virtually impossible to carry out, due to the enormous amount of time it would take to generate even one set of accurate data points with a change in trim, heel or waterline. Loading existing hull shapes into MacSurf is greatly simplified by the facility to set markers on the screen. This means that a profile (for instance) can be defined, and then the curve is fitted to the markers. Depending on the complexity of the hull shape, it can take between 3 and 8 hours to input an existing hull. Once in MacSurf however, all the data analysis is available. It is also extremely easy to modify the shape, and to scale a to any size. This means, for instance, that I can now offer customised lines plans for each boat to account for moving engine position, or even changing from a two-engine installation in a cat to having a single outboard.