Author Topic: shape3D guru (help please!)  (Read 3946 times)

burchas

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Re: shape3D guru (help please!)
« Reply #30 on: August 21, 2020, 04:45:52 AM »
Perhaps there is another effect I'm not thinking of?

Have you considered water wrapping? It seems to me that when it applies there are a whole new set of forces to take into account. At least that's the sense I got trying different boards.
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PonoBill

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Re: shape3D guru (help please!)
« Reply #31 on: August 21, 2020, 07:23:39 AM »
Well, first make the overall width the same.

The calculated righting moment probably only looks at buoyancy location which is the source of static stability. The shape of the rail (or any other element) also has a dynamic effect on stability from its resistance to flow in the lateral direction from tipping, which I doubt is included in the embedded calculation. Curved edges reduce the flow resistance like a less effective version of rounded bottoms--allowing fewer direction changes and therefore having less inertia to overcome in the water flowing across the shape during tipping. You can have a very wide cylinder sunk to its midpoint offering lots of stability from buoyancy which actually has almost no dynamic stability and rotates easily in the water. Add flat surfaces at the waterline with even just a tiny bit of buoyancy to keep them at the water's surface without materially changing the righting moment and the shape becomes far more dynamically stable.

When I try to understand something like this it helps to consider the extreme cases that have some common elements with the change I'm considering.
« Last Edit: August 21, 2020, 07:33:53 AM by PonoBill »
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

burchas

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Re: shape3D guru (help please!)
« Reply #32 on: August 21, 2020, 07:43:57 AM »
Well, first make the overall width the same.

The calculated righting moment probably only looks at buoyancy location which is the source of static stability. The shape of the rail (or any other element) also has a dynamic effect on stability from its resistance to flow in the lateral direction from tipping, which I doubt is included in the embedded calculation. Curved edges reduce the flow resistance like a less effective version of rounded bottoms--allowing fewer direction changes and therefore having less inertia to overcome in the water flowing across the shape during tipping. You can have a very wide cylinder sunk to its midpoint offering lots of stability from buoyancy which actually has almost no dynamic stability and rotates easily in the water. Add flat surfaces at the waterline with even just a tiny bit of buoyancy to keep them at the water's surface without materially changing the righting moment and the shape becomes far more dynamically stable.

When I try to understand something like this it helps to consider the extreme cases that have some common elements with the change I'm considering.

OK Great! Can you  now put it simply in one sentence? Geek speak is a known cause for brain pain ;)
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PonoBill

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Re: shape3D guru (help please!)
« Reply #33 on: August 21, 2020, 07:49:53 AM »
Nail a 2X4 to a log and it's harder to roll it.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

liv2surf

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Re: shape3D guru (help please!)
« Reply #34 on: August 21, 2020, 08:38:13 AM »
Nail a 2X4 to a log and it's harder to roll it.

And of course, this is how an outrigger on a canoe works too I suppose.
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9'6" CRUZ Surf foil SUP (152L)
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liv2surf

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Re: shape3D guru (help please!)
« Reply #35 on: August 21, 2020, 08:52:44 AM »
Thanks for all your help Burchas - working from your file got me close enough to where we can do just a bit of hand-work after the CNC cut.     Here's my shaping notes after CNC cut

You're welcome. Just few minutes of tweaking your file. Looking over your shaping notes, it's not hard to get there with shape3D just by adding 1 curve (between rail to apex), 1 slice  for the  rail transition in the front and two 3d layers for tail and nose. The rest is just tweaking controls to generate nice transitions. Probably an overkill with the cuts i've seen from most machines though my board required almost no touching out of the CNC.

As for the handle, having only one on the bottom did the trick for me as DW pointed out.

Shape 3Dx has many different versions with different suites of features (different versions can be activated for a month, a year or even permanently). burchas, what version of Shape3Dx did you use. Seems that it must have been the Design Pro version to allow putting on the 3D Layers. 
6'6" CRUZ 'CIM' Wing Foil SUP (130L)
9'6" CRUZ Surf foil SUP (152L)
Cabrinha Crosswing X2 4m, 5m, 6m
Axis 1020; Axis 1150, standard fuse, 500 stab
65cm (and 90 cm) Project Cedrus carbon mast
Chinook Thrust 92 Paddle -- fixed 78" length
Me: 190 lbs, 64 yo Half Moon Bay, CA

tarquin

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Re: shape3D guru (help please!)
« Reply #36 on: August 21, 2020, 09:41:35 AM »
I find it interesting rail shape would make a difference on stability on such a short board when you have a mast and foil under it that should give you plenty of stability.
 I would think you want a rail shape that releases as easily as possible. Square not rounded. If you have a round rail with water wrapping around it wont want to release as easily as a square rail ??

PonoBill

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Re: shape3D guru (help please!)
« Reply #37 on: August 21, 2020, 10:21:31 AM »
Nail a 2X4 to a log and it's harder to roll it.

And of course, this is how an outrigger on a canoe works too I suppose.

Actually an outrigger canoe is stable mostly because of the buoyancy of the ama located on a long moment arm. the dynamic stability of the hull is not enhanced much as anyone who has hulied can attest.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

jondrums

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Re: shape3D guru (help please!)
« Reply #38 on: August 21, 2020, 10:24:09 AM »
Awesome, I'm glad you guys are as interested in this as I am!

Well, first make the overall width the same.

ok, I'll try that.   I'll make the deck a little lower so the overall board is the same volume.  I think it is important to change one variable at a time.  In the last study I changed the rail profile and width to keep volume constant.  Next one I'll keep width the same and change rail profile and deck to keep volume the same.  I'm pretty sure I know what's going to happen from a pure righting moment perspective (very little change). Let's see.

The calculated righting moment probably only looks at buoyancy location which is the source of static stability. The shape of the rail (or any other element) also has a dynamic effect on stability from its resistance to flow in the lateral direction from tipping, which I doubt is included in the embedded calculation.

correct, I did not include anything to capture dynamic flow of water.  The dynamic effect on stability would act as damping (righting moment is like a spring).  This could well be the main thing people are noticing - but let's remember we have a huge foil underwater with a big moment arm acting as a pure damper.  Hard to believe the rails are contributing much damping beyond that - but maybe so!

You can have a very wide cylinder sunk to its midpoint offering lots of stability from buoyancy which actually has almost no dynamic stability and rotates easily in the water. Add flat surfaces at the waterline with even just a tiny bit of buoyancy to keep them at the water's surface without materially changing the righting moment and the shape becomes far more dynamically stable.

That's because a cylinder has zero righting moment and zero roll damping, so anything you do will infinitely improve both the righting moment and the roll damping.  Don't think this is a relevant analogy.


jondrums

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Re: shape3D guru (help please!)
« Reply #39 on: August 21, 2020, 10:28:32 AM »
back on topic of shape3D

Nice. Nah, don't hand shape it. Move the current 'post CNC features' into the Shape3Dx file (so you can duplicate it, build on that shape later and share it).

yes, I would much prefer this.  Burchas and I are both using the pro version, with the import option to get the STL ghost file into the program.

That said, shape3D cannot replicate the tail feature I want as far as I can tell.  It is fundamentally designed to create lofted surfaces based on orthogonal cross-sections (slices and rocker profiles).  I might spend a few more hours fiddling with it, I am not an expert yet.  But the tail feature I want is modelled accurately by using slices that are not orthogonal, the slices wrap around the tail at an angle.  More complex CAD programs can compute that surface, but Shape3D cannot.  Anything I do in Shape3D will be an approximation of that surface and will not be true and fair without post-work.

PonoBill

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Re: shape3D guru (help please!)
« Reply #40 on: August 21, 2020, 11:02:09 AM »
That's because a cylinder has zero righting moment and zero roll damping, so anything you do will infinitely improve both the righting moment and the roll damping.  Don't think this is a relevant analogy.

OK, just think about a round bottom surfski. Same principle.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

burchas

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Re: shape3D guru (help please!)
« Reply #41 on: August 21, 2020, 11:56:40 AM »
That said, shape3D cannot replicate the tail feature I want as far as I can tell.

I believe there is a way to get really close to the effect you're after (maybe enough to forgo post work). You'll have to model the tail lines in the same shape you model the rail lines.
Then you'll have to create another curve between the rail line and the apex. This curve will allow you to control the transition from the rail to the tail when you edit it in both dimensions.

Finally, you add a 3d layer to cut the tail to fit the outline you originally created and you can also add the bevel at the top of the tail like in your original model.

for that you'll have to add few more inches to the shape length in order to leave enough meat to work with at the tail.

What I did was butchering all the intricate touches of your original shape just to demonstrate the structure simplicity in 10 minutes. You can dig a lot deeper.
« Last Edit: August 21, 2020, 12:06:35 PM by burchas »
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TallDude

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Re: shape3D guru (help please!)
« Reply #42 on: August 21, 2020, 12:05:58 PM »
back on topic of shape3D

Nice. Nah, don't hand shape it. Move the current 'post CNC features' into the Shape3Dx file (so you can duplicate it, build on that shape later and share it).


More complex CAD programs can compute that surface, but Shape3D cannot.  Anything I do in Shape3D will be an approximation of that surface and will not be true and fair without post-work.
I've done some pretty detailed work in Shape3D free version that are much easier with the pro tools, but can be done if you know how to work the program. I draw in 2D and 3D CAD for a living. Solidworks, AutoCAD, Revit, etc. Shape3D is an old version of AutoCAD at it's core. It doesn't work in solids, just surfaces. The surfaces are a mesh that you push and pull. The amount of points you can edit are really limitless except for a few. Doing a fish requires a tool. The length of the board is fixed at the center line of the stringer. It defaults to a mirror so everything you do to one side of the stringer is mirrored on the other. Asymmetrical boards must require a pro tool. I drew a chair in Shape3D one time.
 
The thing is, why not just do a little hand detailing? It's quick and easy. Dicking with the program to get perfection is a waste of time unless you are doing production runs.
I was at my friends glassing shop last year, and the foil board they had just got from the CNC shop had a squared block tail. They owner wanted a wedge from tail to plate. They both looked at me and asked If I could do it. I marked it with a pencil and hand shaped the tail in about 5 minutes. Done. Off to glassing. 
It's not overhead to me!
8'8" L-41 ST and a whole pile of boards I rarely use.

burchas

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Re: shape3D guru (help please!)
« Reply #43 on: August 21, 2020, 12:15:28 PM »
The thing is, why not just do a little hand detailing? It's quick and easy. Dicking with the program to get perfection is a waste of time unless you are doing production runs.
I was at my friends glassing shop last year, and the foil board they had just got from the CNC shop had a squared block tail. They owner wanted a wedge from tail to plate. They both looked at me and asked If I could do it. I marked it with a pencil and hand shaped the tail in about 5 minutes. Done. Off to glassing.

It can work as described or end up a disaster. I designed a board for a friend and he wanted a complex nose shape beyond Shape3D capabilities. I told him no problem, I'll finish in Rhino so you
can have the exact model to work with the shaper. He said "Nah, I know what I want, I'll be able to work it". It ended up like a Frnakenose.

F*ck around on the computer and you can always "undo". F*ck around on foam and you're f*cked ;D
« Last Edit: August 21, 2020, 12:21:58 PM by burchas »
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jondrums

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Re: shape3D guru (help please!)
« Reply #44 on: August 23, 2020, 04:12:43 PM »
creating this tail in Shape3D is a disaster.  I ended up making a while bunch of slices to replicate the ghost board.  Its a bit ugly on screen, but will be really easy to fair out with a sanding board - no creative shaping necessary, just cleaning it up.

I also redesigned with sharp transition on the bottom edge of the rails but nice big round-over on the top.  I'm not going to ignore everyone's advise about stability, and I think that sharp corners increasing roll-damping makes total sense.  But I don't think the round-over on the topside is going to matter much.


 


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