howdy, folks! I’ve been modeling a sailYacht since last week. I need professional assistance for hull fairing…

The surface of the hull is a Brep multiPatch. Each surface patch was originally built in third order, mathematically smoothest degree possible… but later on, it was increased to fourth order improve the tangency between srf patches for better looking zebras. the control net was doubled for better control over convex areas of the hull. partially below the waterline. is there anything i can do to fair these patches… some people suggest having the hull built in a single surface, but thats not recommended because in that process a lot of information and mathematical properties are lost… check out my hull please…

the curvature porcupine or curvature comb are said to be the best tool for surface fairing… i really dont trust crv porcupines because if you study the way they work, they only display good results for ‘‘arched’’ curves or quadratic curves since the radius remains constant. so, with that criteria we could state that the ‘‘perfect hull’’ should have spheric shape… what???

cad softwares rebuild nurbs curves into ‘infinitely’’ small segmented arcs (depending on crvs complexity), tangent to each other, to display an approximate ‘’’‘curvature analysis’’’’ which is * lit. how radius ® of arc varies as a function of crv length*, During this segmentation, the original nurbs curve losses significant mathematical properties… therefore we may state that curvature analysis does nott display very accurate results as we might think.

also, lets suppose you sketch a complex curve (**DEG 5**) and try to match it to a **cubic** crv. (we assume the following:

- number of control points to be appropiate for accurate curve matching.
- the weight associated to be rational (1),
- almost ‘’’‘0 deviation’’’’’ from original cubic crv.

if you toggle on the crv porcupine, the results are going to be significantly different in each curve. thus, the shape may be almost identical (or have negligible deviation) but nonetheless the crv analysis is, and shall be always significantly different because the mathematical representation is different…

but then, you sketch another crv (almost identical curve) made up of **segmentated arches**… that quadratic curve (DEG 2 for circles, arches & ellipses) is going to be the smoothest possible representation of both DEG 5 & 3 nurbs crvs?

Rebuilding a deg 5 crv with a quadratic is not that easy, instead its easier to approximate the original DEG 5 crv using a cubic if increasing control point net… that should give the smaller dev among other choices mentioned above. since the order or degree is strongly associated with the distance between the Control point and the actual trace or path of the curve. (among others such as the weight input)

question… what curve is the smoothest?

Quadratic shows

- areas on the curve where curvature remains constant or linear (porportional)
- radiuses of arcs never coincide (discontinuities between curvature circle.)

Cubic shows

- special distribution of curvature
- continuity…

is there any tool out there for better representation of my surfaces? also, some say that increasing the order or degree of surfaces gives better looking crv comb… but in reality you are making your model’s mathematical representation stiffer and ‘’’‘squarer’’’’ i guess you could say…

What tools are commonly used by nav architects to generate accurate production lines???

Thanks again!

- Oliver