Maxsurf - seeking advice on modelling approach

[ldigas]

Greetings everyone,

I'm new to this forums, so please pardon me if I seem a little too straight forward. However, this is something that has been troubling me for some weeks now, and as time is passing by, I'm not making any progress, so am asking for your aid, if you have a little spare time. It would aid me greatly if you could advice me on a few fundamental things.

I have been assigned on modelling a hull, which will be undergoing a rather large reconstruction. It will be lengthened at the stern, and due to rather "inconvenient lines" it is relatively important that the old hull be modelled as accurately (as possible) so that we can work on the new hull at ease (since the "new part" of the hull has to "fit in" neatly to the old one).

Anyways, the hull in question is a kragen design, (I've attached the buttock and lines plan), and I have at my disposal the measured values at different stations which we measured in the yard.

I have at my disposal Delftship (if someone here is also a regular at their forums, they will recognize a similar post there made a few weeks ago) and Maxsurf, albeit a rather old version (13 - it has been some time since our software base has seen updates; mentioning it because it seems the new versions have seen some significant improvements). I've tried modelling it in Delftship, and upon having no luck there (stilll rather confused about their approach on modelling in general - it seems to differ from a lot of other CAD packages - I have not been able to understand their "way of thinking") I'm now trying Maxsurf.

The hull consists of a round hull, with V-sections as you're approaching the bow, the keel starting at the baseline and going towards the bow sections tangentially, and the skeg between the keel and the bow.

I don't have the centerline of the hull, only the line (3d) where the skeg "enters" the hull. That is the outermost line on the buttocks plan in the image.

Now, what I'm having a problem most is how to start modelling in maxsurf something like this. My naive approach of just entering the section data (hull+skeg) and trying to create a TriMesh surface unfortunatelly failed.
I've read the manual, but am still confused upon a lot of things.
a) how to model the skeg individually if possible (skeg doesn't start nor end on any section, but in between)
b) how to get a good bow
c) how to get a good transom

The hull at the centerline has a keel of 10 mm width (so the waterlines don't actually end at the CL but at 10mm width). With that keel I'm having the most problems.

Please, if you have some ideas for a beginner in this area, as I said, I would appreciate them greatly.

Luka

[micspoko]

if you want to do it properly you must have a transverse cross section and start on them

[ldigas]

@micspoko, thanks for answering.

I do indeed have sections as well, although they were not on the attached image. I have the form very well defined on paper.

My question was (now that I read it myself, I see it was rather confusingly put) however, what is a good separation of surfaces for such a motor yacht, to begin modelling with.

[micspoko]

start modelling hull as entire surface. The best software for do this is freeship or delftship.

At the beginning you have to correct the images before adding to the program - horizontal lines should be really the horizontal

I'm doing it this way:
- I create a surface with 4 points - 2 points on the first and last frame - a one point in the CL and the second for example on main deck
- and adding more points modelling this frames
- then added the points on midship frame - and modeling this frame
- and so each of the frames

When you have a hull with hard chines the lines must be a knuckle line - in delftship is edge-crease

[ldigas]

micspoko, thanks for your help on this. I followed your approach and modelled a hull with satisfactory accuracy. Some fairing still needs to be done, but that isn't worrying me now.

I wanted to ask you for advice on another matter though - what do you think would be best, from your experience?

I have a hull/skeg interception line which I need to "hit". Would it be better to model the hull to the interception line down below, and from there model another surface (the skeg)? Or should I model the hull "closed", and then model the skeg as a new surface and then trim then, and get the interception line that way?

I prefer the first way, but don't know whether I will have leaking points problems afterwards when I use it for hydrostatics/stability analysis?

[micspoko]

a hard question but i think is the best to do a hull closed
are the skeg have an effects on hydrostatic and stability

[formsys]

Some videos from our Maxsurf webinar on fitting existing designs can be found at
http://www.formsys.com.au/maxsurf/webinars/webinar-1
I think this will help you out

[ldigas]

Originally Posted by micspoko

a hard question but i think is the best to do a hull closed
are the skeg have an effects on hydrostatic and stability

Yes, the skeg presents a significant part in regards to displacement, therefore it affects both hydrostatics and stability.

[ldigas]

Originally Posted by formsys

Some videos from our Maxsurf webinar on fitting existing designs can be found at
http://www.formsys.com.au/maxsurf/webinars/webinar-1
I think this will help you out

Indeed. I watched those before, and was very pleased with them. They show concepts of modelling in a very clear and understandable way. Praise to the technical team for making them available.

Unfortunatelly, while they offer great help in general, it didn't help me with in particular case.