Freeship Layer intersections
I’m using Freeship to design a 30’ proa, and I have the hulls pretty much done I think…
Now I’m trying to add a leepod, and I’m doing that by adding a cylinder, modifying it (squashing it), and then i presumed i could intersect the layers and snip the top of the hull off to leave the correct panel shape when I develop the panels, but I can’t get this to work…
In general I find Freeship to be be unintuitive!
any thoughts on this much appreciated.
Here’s an image to illustrate better what I mean.
As you can see the hull topsides bisect the pod.
What I want to do is to remove the section of the hull that extends into the pod space…
Hello Cuica, welcome!
The solution I have been using (which is NOT always working accurately) is as follow.
On your toolbar above the active window, click on the first active icon on the right of the layer section pulldown menu (see your screen capture above). It looks like 2 intersecting plane of purple color.
A pop up window shows up and asks you to select 2 layers: the first one is the one on which you want to insert points (and create new faces); the second one is from which layer intersection you want those points to be created from.
Once you have done that, it creates on the first layer new “faces”.
You can now select the faces you want to remove and delete them.
“Et voilà!”
WARNING: it works better when both layers have a similar grid of faces. If one layer has 5 longitudinal “sections” and the other one has 3 and they don’t match, it is going to look ugly or weird.
WARNING 2: depending on the cases, it can create some creases and change to a hard chine or a “hard point” an item which was not such a hard chine/point before, and therefore modify the shape of the surface.
WARNING 3: if you want to do hydrostatics (righting moment) analysis afterwards; this new edge will be considered an opening and will not allow you to see the performance of the leepod as a capsize preventer to a full knock down. Once the edge of the leeside of the hull is fully immerse, Freeship will no longer compute.
I found a way around that, but it is more complicated, let me know if you are interested.
WARNING 4: this is a disclaimer more than a warning, I am self-taught on freeship, and after many hours of trial and error, and some forum surfing, and manual reading (not very helpful…), this is the best solution I could come up with. I am not claiming that there is no more elegant way to do this.
Cheers,
Laurent
PS: is this enough warnings, or what?!!!
Hi Laurent,
Many thanks for your reply…
I’ve been doing what you suggest but it doesn’t give a good result at all, sadly.
I think if the hull had a smaller ‘mesh’ it would work better, but I don’t know how to change this.
If you can describe the ‘other’ method I would appreciate it!
You can add more sections using the button to the left of that, “insert multiple points”, then enter transverse plane and how far back you want them.
Fantastic! That works much better…
Adding the extra stations means I’ll need to do a bit more work on the lines, but it closes up the net spacings and makes the layer intersections much more accurate.
Many thanks.
Two other suggestions:
1. A bit crazy, you could model the hull “sideways”. (Try rotating your current model about the longitudinal axis). Then you could make the leepod as a “transom”, and extrude it.
2. You can import VRML models. Perhaps you can model in another program and export as vrml, if you need to do hydrodynamics?
I’ve never tried these two things by the way.
I’ve tried modelling hulls sideways, to make an asymmetric hull, but I find it very confusing!!!
In theory it should work of course…
Also, what other programs do people use? Free ones if possible!
I’ve used Art of Illusion in the past. http://www.artofillusion.org/index
Good balance of features and ease of use. I’ve also played around a bit with FreeCAD lately which is a solid modeller like Solidworks.
Hi cuica,
I use DelftShip which is similar to FreeShip and free of charge too. I made the design of the P12 with. The best way to build up a proper model ist to design the parts of the boat as individual parts in FreeShip/DelftShip and the import and arrange them into a final layout.
Cheers
Othmar
Hello Othmar,
Thank you for your message.
The P12 is an interesting design. Were you able to make calculations about the effectiveness of the lee pod in preventing capsize, and if so, how?
Hello cuica,
to include the efficiency of the leepod in case of heeling is only one part of calculation of rigthing moments.
Important is to consider the change of pivot during the heeling process (http://proafile.com/multihull-boats/discussion-forum/viewthread/390/). This is IMO the main factor of the effect of the leepod. With the distances between pivots and the centers of gravity of main parts of the boat you can calculate/estimate the righting moments for all heeling angels. Put the results into a spreadsheet analysis in relationship to the decrease of projected sail area during heeling process (heeling moment) gives you an overview of balance (http://proafile.com/forums/viewreply/3179/).
Cheers
Othmar
Hello Othmar,
Thank you for the links, and for the suggestion to import a part.
I saved the ama as a part, and imported, and then moved it on the transverse axis, but I get the problem that can be seen in the image - the ‘beam’ of the ama is now some four metres, and my proa now looks more like a trimaran! Is there a way I can save all of the ama as a part, both port and starboard sides, so that it all moves in the same direction?
Many Thanks!
I saved the ama as a part, and imported, and then moved it on the transverse axis, but I get the problem that can be seen in the image - the ‘beam’ of the ama is now some four metres, and my proa now looks more like a trimaran! Is there a way I can save all of the ama as a part, both port and starboard sides, so that it all moves in the same direction?
First, because this SW is made for symmetrical boats you cannot use the function “Show both sides”.
If you design an asymmetrical vaka you have to export both sides of vaka as parts. Then import and mount it in a new file together. If you have finshed the eg. symmetrical ama - show both sides of it, mark all points, and then export the whole ama as part. Afterwards you can import it to the vaka, and position it. It’s tricky, but it will work.
The main problem with this SW is, after you have made a nice sktech of the whole boat, the hydrostatics will not more work properly. So you have to get the data of vaka and ama from separate saved files.
It’s a lot of try and error with this SW, and the manual is not very helpful, especially if you design a proa 😉
The way I deal with this is for each layer, I go to the Layer Dialog window (pulldown menu “Layer” and then “Dialog”... or the equivalent icon on the icons bar) and I UN-check the symtric option on the right.
YES, when you do that, that means that you will have to model BOTH sides of each hull. But then you can see the boat as a whole and have non-symetrical hulls if you want to.
To do the righting moment curves, here is how I proceed:
- I estimated the location of the CG (how far to windward and how high from the origin point)
- I select the WHOLE model (pulldown menu “Selection” and then “Select all”; be careful, ALL layers must be visible)
- I rotate the whole model by x degrees longitudinally (pulldown menu “Transform” and then “Rotate…” and then X degrees on the pop up window in the “Longitudinal Axis” field)
- I have made the hydraostatic calculations visible by pushing the icon looking like a small calculator. This way, I see the center of buoyancy
- the whole boat has rotated around an axis defined by y=0 and z=0, so the rotation has changed how much is immersed in the water; you will notice it because the buoyancy center location will show a different displacement than what you want
- I go in the “Project” pulldown menu and then “Project Settings” and click on “main dimensions” tab. I adjust the “draft” field, until the displacement shown on the bodyplan view is back to what it is supposed to be. You have to do it by trial and error.
- Then still in body plan view, I put my mouse cursor exactly on top of the center of buoyancy and note the y coordinate value (it is shown on the title bar of the window).
- Since you knew the position of the CG at the start (y and z value) and the rotation of the whole boat is done on the origin longitudinal axis, you can calculate the new coordinates of the CG, especially its y axis value. With both y xis values (CG and C of Buoyancy), you can calculate the righting arm. Multiply that by displacement, and you get the righting moment.
You repeat every 5 degrees and you can generate a nice righting moment curve.
(I would recommend to do it every degrees for the first 5 degrees, or until the ama is completely out of the water, for better accuracy)
Easy….
HAHAHAHA
Freeship has a function under “Calculations” pull down menu to do all of this.
On my version, this function is VERY buggy. For all those calculations to work, you need to ensure that there is no “leaky point in your model” and you have to make sure that ALL surfaces normal vectors are pointing OUTWARD on all faces of the wetted areas.
The “calculation” menu had the tendency to FLIP some of those normal vectors orientations; so when you do the next heeling angle and click on this function in “calculation” menu, all results are messed up because the software does not see all the surfaces providing a barrier to the water and therefore contributing to buoyancy!
All messed up.
The procedure above is the only way I found to get around this.
Good luck…