Autodesk Fusion surface lofting a boat hull logic

[Marquinius]

OK, so I got around how to ensure rails and profiles are connected by using the intersect thingy. And I can position canvasses.

But what is the best approach to create a hull? Loft from waterline to waterline, so top down, and use the profile lines (the ribs) as rails? Or loft front to back and use the horizontals as rails? I think the latter doesn’t work, but I’m curious how others solve their lofts.

Feel free to elaborate or digress.

 

[Kevin the Lubber]

I make no claims to being great at this, but when I made my little ships boats last year, I found it best to use the station profiles (what you're calling front to back), as these are all on flat planes. I was rightly advised to use the least number of stations possible and found 8 or 9 was ample. The trick is to keep tweaking the bezier curves until you get smooth curves both horizontally and vertically. The greater the number of stations, the harder this is to achieve. Note that you need the same number of rail points on each station profile and the rails have to join (connect to) every profile. I distributed the rail points more or less evenly along the profile and tweaked later as part of the fairing process. Something I realised, which I suppose is a little obvious, is that no-one, not even you, is going to go along the hull with a set of profile gauges, checking for accuracy. Close enough will be good enough.

F360 can be a swine for lofting, so I only lofted a half hull, to reduce the computational load, then mirrored this when done.

 

[Marquinius]

It is rather like Fusion doesn't like ships and boats. And you're right: less is better. In the meantime I have create a few test hulls, trying station profiles, and found this indeed the best method.

 

[Kevin the Lubber]

One thing F360 definitely dislikes is having to compute lots of mathematically complex sketches. Station profiles, being all bezier curves etc, are nothing if not mathematically complex. I'm told Rhino is miles better but for me, the timeline in F360 is too valuable to give up.

 

[Roger Pellett]

I’m not a CAD user, but offer this as it may be helpful. Before CAD, long sweeping curves; waterlines, diagonals, and some buttocks were drawn using a bent wooden batten called a spline held down with a series of lead weights called ducks. Mathematically, bending of a beam, or in this case a spline is described by a cubic function. In other words, deflection is proportional to length cubed. I don’t know what a Bézier curve is or what mathematical function governs it but some CAD programs have a “Spline” command that might work better.

Roger,

 

[Peter Voogt]

Hi Marco.
In this thread on the Dutch forum, Jan (JaFa) is constructing the hull and whole model in Fushion. Perhaps he can give you some advice and Tips&Trics:

Tug 22 (Port of Antwerp)

Even een werkje tussendoor... Omdat verandering van spijs doet eten, zo men zegt. Maak ik even een rompje van de 22, waarom nu terwijl de Wrestler...

www.modelbouwforum.nl

From post #18 his print-screens.
On page 2 a video of his hull.

And here also:

PoA T51 & T52 Reversed Stern Drive (RSD) Damen 2513 ADS Tug

Tijd om een nieuw bouwverslag te starten, deze bouw zal veel verschillen van mijn andere builds, bij mijn tijdelijk gepauzeerde bouw van de T22 had ik...

www.modelbouwforum.nl

In post #7 he shows how he starts with the length contour and the bulkheads.

I used Fushion for drawing the outlines of the frames for my Balder. But that was a big struggle before I was there. With a simpel outside loft to check the flow.
Regards, Peter

 

[Kevin the Lubber]

Splines and beziers are kind of the same thing, for dunces like me anyway, just different ways of realising the same end product. In F360, bezier-type curves are called 'fit point splines', where the bend points are on the line itself, with handlebars to control the shape of that section of curve. Splines (B-splines, NURBS curves, CV-splines and probably several other terms that mean nothing to me ) are called 'control point splines', where the bend points are off the curve, creating a cage-like structure for controlling the curve shape.

There are probably good reasons to use one over the other in lots of circumstances. Hull lofting is one of them, so this is a timely point for technicalities. As I mentioned earlier, the rails and profiles must be connected for successful lofting in F360, which means fit point splines/beziers are the better tool because the points are on the lines themselves. Therefore, you just have to 'constrain' the respective points together and they definitely connect. With control point splines you can be chasing your tail to get them to connect in the right spot. (In passing, control splines seem to fair much more easily than fit points, so it's a shame they aren't so good for lofting). That, at least, has been my experience, but I'll be very happy indeed if someone can share a better method in F360.

 

[Roger Pellett]

In manual lines drawing you plot points, either from a table of offsets or measured from a drawing. The spline is then bent and weighted to pass through the points. If there are points laying off the curve, the spline must be adjusted to achieve a Best Fit. The rigidly of the spline prevents correction of only one point so several must be moved. Whatever command most closely matches this manual drawing technique will produce the best results.

Years ago, I did use CAD to draw a set of lines. I used Geneic CAD, sadly dropped by AutoDesk. This was a great program for drawing lines as it did not “correct” for points off the curve. The user moved points using his judgement until all points fit a fair curve.

Roger

 

[Kevin the Lubber]

By the way, surface lofting in f360 can both solve problems and create them. I use it as a tool of last resort, as I often find the extra work to thicken a surface adds new opportunities for the software to choke. For me, it’s easier to loft two solids, one of which is used to cut the other to a thickness.