Small quay punt lines.

A hollow garboard effectively decreases windward performance, by subtracting lateral area, just when you need it most. You do need a reasonably fair body at the root of an appendage, but not the excesses typically seen in a built down, hollow garboard style of hull form. The full keel hull type requires the same hydrodynamic approach as a fin keeler, for efficiency. The last generation of CCA's proved this handily, as the floors became flatter, the fair body given a tighter radius and appendages separated and more defined. They crushed the previous generations of CCA's so badly, the whole class was distorted enough to bring on the first generation of IOR's.

 

In my opinion, I feel that Freeship also tends pinch the bow sections of it's own accord. Especially in the area where the centerline sections transition from longintudinal control elements to vertical control elements. Nurbs love rectangular control grids and inevitable excursions from four sided networks spoils this uniformness. I usually end up adding additional vertical control elements (tighter station grids if you will) in the bow sections to help draw out the "pinchiness". In essence, regaining control of the hull form from Freeship.

 

PAR, Thank for the input. The fullness of the bilge also adds to displacement, and buoyancy where it must be overcome by ballast, and an increase in sail area. I'll post the lines so far. I think they are pretty close to where I want be, but with the bilge radius as is it is eating up lateral area.

 

LP, Yes that is one of the problems i an having with freeships. I will try what you suggest.
Maybe just hit the increase control points button.

 

Frank,

You can select a series of control edges sequentially and then select the add control point button. Then, if the edges were indeed selected sequentially, the split face (green slash button) will highlight and when selected will create a new control edge connecting all of the new control points.

 

LP, thanks, good to know what that button is for.

F

 

Here is an example of what I am talking about. Both images have the same number of control points. The second has the additional control edges inserted to bisect some of the forward face sections. If you do this and you are using these edges to create fairing curves, it really screws with the fairing function. When I use these curves, I fair the hull first, then insert the diagonal control edges to fill out the forward waterlines.



Edit: This is a multi-chined hull so the waterlines have vertexes at each chine edge. The effect round hull will be the same though.

 

mesh for developable plates in freeship

LP, you have the right idea, but there is a systematic way to do this. You need to read Rabl's paper on how to draft developable plates on paper.

In Freeship, you want to get your edges that cross between chines to lie naturally along the zero curvature axis of the plate. To do this, you reproduce Rabl's method step for step in the program.

try the following on a new model-
set stations to 6, waterlines to 3

1. Select the point on the keel-line near the cutwater and shift it to 11,-15,-5 and deselect.

2. Cntr-select each remaining keel-line point and select the one you just moved last.

3. The point box shows the coord of the last point. Position the cusor in the x coord and enter. Tab and enter. Tab and enter. All the points are now at 11,-15,-5. Deselect all.

4 Crease the chine. The entire surface is now developable, and the edges all run in the desired direction. Just split these edges with a plane or however you want to trim the plate back to the center-line leaving the edge vectors unchanged. You now have a surface with a workable mesh for developable surfaces.

5. You don't actually have to move all the points on the keel to the same location. You can move two adjacent points to 11,-15,-5. Then when you want to handle the adjacent piece, the next keel-line point can move to any location on the edge vector formed previously. Usually, though, you don't end up far away from the previous focus point.

The result is you have lost some design freedom in terms of what the center-line looks like in profile. Assuming you want to hit specific displacement distributions and stability or other beam requirements, the profile shape is what it is. You have to redo the chine and start again if you don't like it.

 

Phil,

I'm going to have to digest what you have just said. It sounds like you have a system wired for developable hulls. I like having tools like these to help with hull design problems.

I wasn't actually trying to show the OP how to do a developable hull. Freeship really likes to pinch the pointy ends of boats. I was showing him how I fill out those pinched areas. Adding the control edges the way I did pulls the nurbs surface out from the original plane. Joining the opposite control points will pull the surface farther inboard and pinch those sections even more.

 

While you can aline the control points to approximate those used to produce a conical development , Freeships will do that for you, and it can be checked by using the development function. I am still not sure how you are locating the apex for the lines in developing the conical section.

 

LP, I just added a new set of control points, and it smoothed out. I see in your example that you are confining the control point to the stations. I think of the the control point as if they were at the end of a pencil perpendicular to the surface. If you think of a sphere, it should be easy to see how it should work.

 

Phil,

I've read some of Rabl's literature on conic development. I've never taken the time to try it in Freeship. Thanks for the leg up. I tried your system this morning and then mulled it over all day. Rather than take hull layers and pull them out to an extended conic, I think I'll mess with a conic layer for each strake or panel and then match panel control points to the conic layer. I'll be curious to see how much work is involved in a multi-chined hull. I never tried conics in Freeship before and have relied heavily on TLAR, Freeship developability checks and finally on edge errors on the flat plates feature in Freeship.


Frank,

As far as I know, Freeship does not develop conics. I would be happy for someone to prove me wrong. It does some checking that might get you close. You might be able to use the cylinder feature to do it in some manner, but that sounds cumbersome. The control edges on station lines is just something I do. I think that it makes for neater work and if I see a problem at a particular station, I can go right to those control points to work a solution. Sometimes, in the bow sections, I will cant the control edge to be more radial(?) to the hull. This helps to keep the control edge spacing a little more uniform and the fairing tools like consistent edge spacing.

 

Phil,

I've been creating a alternate surfaces to define my conic shape. I pick the defining chine edge and place control points for my conic definition surface at each control point on the chine. I then run control edges to a singular point that will be the apex of the conic. This let's me play with the shape of the conic by moving a single point. I set the incremental step between .25 and 1.0 feet and simple cursor the single point an opportune location. The hull surface is then manipulated to be co-planer with the defining conic. I will either match section lines on the two surfaces or, in places, I'll manipulate the control point in one window while watching the 3D window in fill mode and watch for the hatch interference pattern. For multi-conics, I'll break up the singular point into as many points as necessary to match the number of conic sections in the panel. Each singularity needs to be co-linear with it's adjacent control edge as you stated in your first post. Thanks for the inspiration to mess around with development tool.

 

LP , been trying something similar, but I moved model off the center to allow me to move the generator freely

 

You can have control points with negative values. Maybe I'm missing your meaning.