Fair hullshape?

[Red at Night]

After producing the desired hullshape and hydrostatics that I'm chasing (in Maxsurf) how best do I check her for 'fairness' please? By applying the 'smooth controls' option my hullshape becomes a little distorted in key areas.
Thanks and happy days on the bay, RedAtNight.

[ErikG]

there is a command where you can look at the fairness of your lines along waterlines buttocks etc. also in the rendering window you can use the various methods of displaying the rendering to help.


If you use "stiffer battens" (can't remember what it's called at the moment). your shapes will get smoother but a bit more restricted in shape. But you wll see the resrictions in shape that the stiffer battens make and can adjust accordingly. Otherwise you'll just have to work harder at finding the optimum relationship between you points and the net.

There's no such thing as a free lunch.

[Mikey]

Erik, I think you mean transverse and longitudinal stiffness.

It is a good idea to have them set at 4 or higher, any lower than that and it is rather difficult to get a fair surface. You set stiffness in Window => surfaces => Long. stiff and Trans stiff.

Do you use the porcupines? They are critical when you fair.
Create diagonals, buttocks and water lines in Data => Grid Spacing, then display the ones you want to see in Display => Contours, just click on one line that you want to check fairness of and goto Display => Curvature => Show Curvature (there is a button too but its too difficult to try to explain how it looks, click around and you will find it, same with sections, waterlines and buttocks - but none for diagonals which is what I use them most - sod's law...).

Don't use too many rows and columns, you are just making things difficult for yourself if you do, same apply for diagonals, buttocks etc. If you if you have stiffness at 4 or higher, you won't need them very tightly spaced.

Have a good look at your net in the perspective window, it should be fairly regular (smooth lines of controls), if it is not, then it's difficult to fair and you make life difficult for yourself.

Use Display => render => Hidden Surface Elimination and Long, trans, and convexity and also tick Show Surface Contours (diagonals, buttocks and waterlines show also when you render) and have brightness level between 2 and 4 (lower brightness level the stiffer you have long and trans stiffness), not too much light or you will burn out the colour differences.

Good Luck
Mikey

[Mikey]

Forgot, always set Surfaces => Precision to highest. Computers are pretty fast now a days...

Porcupine 'size' can be set in View => Preferences => Curvature Porcupine size. Remember that there is no mathematical definition of fairness so don't blow them up too much, 100 is good to start at, and you can increase a bit when you do the last 'fine fairing'.

Good Luck Again...
Mikey

[Red at Night]

Thanks Mikey and ErikG. Thats top info and a good place to start. Both my trans. and long. stiffness are greater than 4, so I'll proceed with your fine suggestions. She's not a complicated shape but I'd prefer to use the full capacity and power of modern computing before the task of building and arduous corrections at that stage.
Cheers, Red At Night.

[Mikey]

One more hint, you can select and move a whole column or several columns longitudinally or vertically.

This is very useful if you want to make bigger overall hull shape changes like move LCB aft or increase / decrease Cp. You should only do this once your hull already is decently faired!

Sample
Say that you decide that your hull is a bit too fat aft, you can slim it down by adjusting all the control points but that takes time, you can also select a couple of the aft columns and move them all forward a bit. If your hull was well faired aft, then it will be pretty well faired also after, just minor adjustments to make. Manual Parametric Transformation

Remember that it is important to keep a fairly regular net, don't start with this too early, have a fairly well faired hull first.

Mikey

[Mikey]

Another hint

Compress
Sample: if you are in plan or profile view and compress, then the boat gets 4 times 'fatter' (longitudinal stays the same but transverse and vertical increase with a factor of 4). Good for longitudinal fairing since any unfairness is easier to see, it gets 'blown up'.

It is difficult to see the real shape of the boat (since it is distorted) so it is not for overall fairing, mainly for fine tuning. Go in, go out, don't stay in there for too long. Very good for fine tuning of long slender hulls.

Mikey

[Mikey]

Why not, one more...

View => Preferences => Contour Tolerance, default value is 0.2 mm, reducing this value makes the lines that the porcupines are built up of come closer, it sometimes make it easier to see the exact shape of the porcupine. Affects performance.

Mikey

[Danielsan]

Same question but not for maxsurf, how could one check hull fairness in Solidworks?

any idea, or could I use exported iges file in another program?

greetz,