Maxsurf - modelling a skeg which goes tangentially into the hull

[ldigas]

I have a round hull and a skeg/keel. The keel enters the hull in the bow area tangentially.

(I've attached a picture to better illustrate the problem).

I've modelled the hull as a separate surface, and the keel as a separate surface which penetrates the hull in the desired area, but does that very "shallow" (tangentially).

If I don't trim that surface, but just leave it like that ("inside the hull") could I expect problems with Hydromax later (or should I say, could the fella using Hydromax expect problems from my model), or does Hydromax only concerns itself with the "outer surface shape". For example, if he creates a tank where the keel is "inside the hull" will that cause problems?

Is there a better way to model this apart from the trimming approach? Everyone says "use bonding edges" but I don't see how they could be applied here.

[formsys]

That kind of keel hull intersect is a bit unusual, can you show us the full body plan? You may want to continue the hull surface down around the transition to the keel. Send the design to FormSys support for more assistance.

[ldigas]

Hello formsys, thanks for answering,

I've attached the interesting part of the bodyplan in which the skeg is shown. The upper part I've trimmed away, since it was too large for attaching.

Due to the time factor, I did this - this time - the "rough way", but I would appreciate your comment as to what would be the proper way of modelling a skeg like this.

Kind regards

[ldigas]

Originally Posted by ldigas

Hello formsys, thanks for answering,

I've attached the interesting part of the bodyplan in which the skeg is shown. The upper part I've trimmed away, since it was too large for attaching.

Due to the time factor, I did this - this time - the "rough way", but I would appreciate your comment as to what would be the proper way of modelling a skeg like this.

Kind regards

To further illustrate, while searching the internet, I found a hull which from what I can see, is rather similar to my problem (except this one has a conic bow). I cannot see the distribution of the width of the skeg, but the stern part is almost the same as mine. Also the way it goes from the skeg to the bow transition part.

It is a product of kastenyachtdesign; from their gallery. I've attached the image below.


Could you perhaps (or anyone) comment as to the surface planning, when modelling a hull like the given in the image?

(all copyrights go to its respectable authors - the image used is just for illustrative purposes of the discussion)

[bhnautika]

Idigas I wouldn’t discount the “bond edges’ in maxsurf as a way of achieving what you want .I did a quick model to show the result.

[ldigas]

Originally Posted by bhnautika

Idigas I wouldn’t discount the “bond edges’ in maxsurf as a way of achieving what you want .I did a quick model to show the result.

Hi bhnautika, thanks for answering,

looking at the attached picture, indeed, that seems to be the way to go. I'm still however unexperienced at this so pardon, if the next few questions seem too simple.

a) the only way I know of that could produce such geometry would be to use compacted points in maxsurf (i.e. 2 points at the same position; 2 at CL, 2 at lower knuckle, 2 at the knuckle where the keel "hits" the hull" and then from there normally going up towards the deck). Am I somewhere close?

b) I've read a little about bonded edges in the manual and ... some internal in-house script we have, but I wasn't quite able to see how they would help. From the different colors it seems you used 2 surfaces, and then bonded their edges together. Was it that you modelled the skeg and the hull separately? How did you accomplish in that case, such a smooth transition in the bow area?

With the above in mind, I was wondering, would it be too much to trouble you for a little detailed explanation of how you came to the resulting geometry?

[bhnautika]

Idigas here is the maxsurf file so you can pick it a part and experiment. In this case I created three surfaces starting with a surface of two rows and six columns and a longitudinal stiffness of four, then just duplicating the other two, as the “bond edges” requires all the surfaces to have the same number of points and stiffness. As the hull to keel joint was going to be a corner I use the “no tangency”. Now that I have three surfaces bonded together I start to edit the surfaces to get the shapes I want. You are correct in thinking that the front of the keel has compacted points, the front corner points of what will be the keel side and bottom are compacted onto the lower front bottom point of the top surface which will become the hull these were then grouped so as they can be edited as one. I added two more rows of points to the hull surface and changed the stiffness to four from the original straight line two. As a personal preference I also changed the hull surface from B spline to nurbs so as to be able to change curvature at points with “weighting” rather than adding more points. Once you have the profile shape of the bow close to what you want then select the centre line of the keel and bow, turn on the show curvature and start nudging the points around to get a smooth transition of the bow curvature to the keel. You can add more columns and row to a surface at any time if you need to also in contours turn on bonded edges.
Hope this helps or you have any further questions.

[formsys]

Nice example. Also, sometimes you want to have a discontinuity in the aft part of the hull/skeg join and then have it fair into a smooth transition in the forward part. In that case, just use the Align To Vector command for the forward columns of control points. Select the point below the join, the one on the join and then align the one above to the vector formed by the lower two. The attached image shows this for the forward column.