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Loft Problem


Jonathan A

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I am working on a catamaran boat hull using lofts for a college drafting project, this is a part of the hull bottom. The loft is not the way I want it. In the first picture I have close to what I want the loft to look like. I want the loft to complete the middle section with the triangular shape down to the single point. In pictures 2 and 3 this is what the loft is doing, and that is not what I want.

 

Thanks

Catamaran Boat hull loft1.jpg

Catamaran Boat hull loft2.jpg

Catamaran Boat hull loft3.jpg

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You have a different amount of section points between your two sections, so you have to tell the loft feature where you want the shared point to be. Edit the loft feature, select the "Transition" tab and redefine the vectors between the section set points. Pick the points that are locating in the middle of the section line and drag them to the vertice that will be the point of your triangle.

 

As an aside, I spent a number of years as designer at a sport boat company. Our modeling technique was to model one side of a hull or deck, then mirror it. Also trianglular (3 sided surfaces) always gave us fits, with tangencies and surface curvature not blending the way we wanted with the adjacent surfaces. A four sided surface is much easier to work with. I can remember the days when three sided surfaces were not possible to model. There were techniques we used to model a surface with three sides, by splitting it into three 4-sided surfaces. (this was before nurbs? I'm getting old!). I still find modeling programs are still lacking in handling a three sided surface. Unfortunatly boat designs have lots of triangular shapes, especially around the keel/stem and chines.

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You have a different amount of section points between your two sections, so you have to tell the loft feature where you want the shared point to be. Edit the loft feature, select the "Transition" tab and redefine the vectors between the section set points. Pick the points that are locating in the middle of the section line and drag them to the vertice that will be the point of your triangle.

 

As an aside, I spent a number of years as designer at a sport boat company. Our modeling technique was to model one side of a hull or deck, then mirror it. Also trianglular (3 sided surfaces) always gave us fits, with tangencies and surface curvature not blending the way we wanted with the adjacent surfaces. A four sided surface is much easier to work with. I can remember the days when three sided surfaces were not possible to model. There were techniques we used to model a surface with three sides, by splitting it into three 4-sided surfaces. (this was before nurbs? I'm getting old!). I still find modeling programs are still lacking in handling a three sided surface. Unfortunatly boat designs have lots of triangular shapes, especially around the keel/stem and chines.

 

Ok, thanks i will try what you said. I am modeling one side of a catamaran, it is going to be 12' wide, I am modeling the right (starboard) 6', then mirror that.

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As an aside, I spent a number of years as designer at a sport boat company.

 

Snice, you worked as a boat designer, when i am done with my model, can you look at it and see if you think it work in real life. I may want to build it one day for my self.

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I am yachty too, 30 years + of toying with them,. design and construction + cruise. I'm actually preparing mi life raft right now and after I'm off to the pacific islands.

 

 

To my experience, the best shape for the section of the hull is the parabola. You can get that curve by simply hang a chain and divide it in the most convenient points for the seeming of the chines. A 3 points spline in inventor unfortunately dose not produce a true parabola. (earlier realise.)

The hull the way is designed now, at my opinion, has a too flat bottom and will suffer severe stress.

Also, why do you want that step at the keel?

One thing inventor is good for it gives you the flat pattern, how ever as far as I know, the chines are to be lofted one by one, correct me if I'm wrong please.

Ceers.

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I am yachty too, 30 years + of toying with them,. design and construction + cruise. I'm actually preparing mi life raft right now and after I'm off to the pacific islands.

 

 

To my experience, the best shape for the section of the hull is the parabola. You can get that curve by simply hang a chain and divide it in the most convenient points for the seeming of the chines. A 3 points spline in inventor unfortunately dose not produce a true parabola. (earlier realise.)

The hull the way is designed now, at my opinion, has a too flat bottom and will suffer severe stress.

Also, why do you want that step at the keel?

One thing inventor is good for it gives you the flat pattern, how ever as far as I know, the chines are to be lofted one by one, correct me if I'm wrong please.

Ceers.

 

This is my first boat that I am doing, I saw a picture of a cat that had the step in it. I don't know how far forward it goes i am just guessing by what i can see in the picture. I am gussing that it will give it a lower draft. Once I get the boat done for my drafting project, I can adjust things in the design of it for me in the future. I may have time to adjust it for the project, but may not. I would really like to do it in a boat design program that will do water trail test on it, but I don't have one of those programs.

 

Thanks

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Once I get the boat done for my drafting project...

 

I noticed that you are using unconstrained 3D sketches for what are really 2D sketches. You should do the tutorials in my signature. I see no evidence of classroom instruction on how to use Inventor in your file.

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I noticed that you are using unconstrained 3D sketches for what are really 2D sketches. You should do the tutorials in my signature. I see no evidence of classroom instruction on how to use Inventor in your file.

 

yes, i choose to use a 3d sketch my hull. In my inventor class all we used was 2d sketches, for parts and things. I am basicly doing my sketching in classic autocad and than doing my modeling in inventor, than use inventor to get my final section drawings and such. I am going to use 2d sketches to make my cabin, pilothouse, deck, etc.

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I noticed that you are using unconstrained 3D sketches for what are really 2D sketches. You should do the tutorials in my signature. I see no evidence of classroom instruction on how to use Inventor in your file.

 

yes, i choose to use a 3d sketch my hull. In my inventor class all we used was 2d sketches, for parts and things. I am basically doing my sketching in classic autocad to get my measurements and than doing my modeling in inventor, than use inventor to get my final section drawings and such. I am going to use 2d sketches to make my cabin, pilothouse, deck, etc.

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I am basically doing my sketching in classic autocad to get my measurements ....

 

I would not use AutoCAD as my sketcher.

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  • 1 month later...

I was able to finish it enough to turn in with the time i had i could not focus on details and modeling it correctly. I am going to redo the whole thing better. i did ended up changing to 2D for the everthing. i will try to get some kind of file on here of it, but i cant get the file size small enough.

 

Thanks

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