Bow shape in rhino

[Andy]

How do people model the bow cone in Rhino? I noticed Doug Frolich has a piccie in the gallery of a bow with bowsprit. The bit I am interested in is the cap over the bow (bow cone?).

Andy

[jehardiman]

There are several ways in Rhino to model something like that. I personally would determine how I was going to build the real item, then model it that way. This prevents problems at a later date when trying to get all the tooling/plating/shell to play together and makes it easier to get the individual pieces out for fabrication. IMHO you model for production, not for design.

[dougfrolich]

Even a simple sailboat hull is too complex a shape the try and model it in a single surface. You would not try to model the transom as part of the hull side right? Dont try to model the bow stem as part of the hull side either. The sides of the hull do not meet each other above the knuckle, From that Point a cone can be shaped tangent to the hull sides up to the sheer.
In Rhino, working in the plan view, you create a a radius tangent to the Port and Starboard Sheer. And then do the same at each Waterline down to the point the two sides of the hull shell meet, Then use the loft command to make the surface, that should work I think---I actually develop hull surfaces in Maxsurf, then import them into Rhino

[SailDesign]

Originally Posted by dougfrolich

Even a simple sailboat hull is too complex a shape the try and model it in a single surface.

I beg to differ, doug - at least if you ignore the transom - and here is a single surface hull to prove it

Steve "waaaayyyyy too much time on his hands some days" Baker

[dougfrolich]

o.k., o.k., I should have sail too complex for ME to.... Nice model Steve. But how did you do it?? and how to you pull usefull information from it for construction drawings?

[SailDesign]

Doug,
Firstly, thanks for the compliments - always gratefully received.
Secondly, that's a secret - although it ain't hard. so here you go...
1. Make a hull shape, including the bow rounding (2nd point on the row must be at the same "Y" value as the centreline one). Add rows near sheer. Pull top row to centreline, and adjust to give required camber. Play with for a while to achieve what you want for a half-model, and make sure that ALL centreline points really ARE on centreline.
Now the cheating part...... In Rhino, mirror the surface to make afull model, and then..
wait for it...
>
>
>
>
>
>
Use the Merge Surface command to make then two halves into one surface. Ignore the naked edge on the bow cos it doesn't matter.

[dougfrolich]

Ahhhhhh-Haaaaaaa---Thanks for the Secrets

[SailDesign]

Doug,
I have to admit your "build it like you'd build the real thing has me baffled. Folks used to say "desing a glass boat just the same as a wooden one and it will be perfect" until they realised that the medium was able to be used in so many other ways.
Similarly, computers give you the option to play with shapes that are impossible to draw any other way (OK, not impossible, but VERY painful to draw, let alone envisage). We had a adical change in procedure at the yard recently when someone wanted (gasp!) a sheer radius that was too big to cut with a router after the deck was glued on. We now have a system that works beautifully for this, and is in many ways easier even for the smaller radii. Don't be afraid to draw the shape you want, and figure out how to build it afterwards - it is more fun than crossword puzzles any day.
Steve

[Tim B]

There is a very simple answer....

Direct manipulation of the surface control points.

What do you mean you can't get the shape you want?

Tim B.

[SailDesign]

And now I have woken up and re-read this thread, I see that I have maligned Doug. It was jehardiman, not Doug, who said "draw it like you would build it."
Sorry, Doug...

[dougfrolich]

That's o.k.

[jehardiman]

Steve, I was wondering about that too...anyway.

What I mean "draw it like you build it" is based upon getting the development correct.

Lets say I carve the hull out of a solid wood block...I could then use a roundover bit and get that deck edge. In drawing I could put in my arc perpendicular to the deck edge and then sweep it to get this development.

Lets say I build it out of plate. I then take piece of pipe, split it, and use that to form the radius. This time the radius is not perpendicular to the deck edge, but co-centric with a line offset from the deck edgeand hull side. I develop that line then extrude the pipe along that line the trim it to the deck/hull. Or now the bow radius is a conicaly rolled plate with a J type joint to the already installed deck radius.

Lets say I make it out of composite... Where is the radius?...in the deck plug?...in the hull mold,plug or split?... or a hand layup over a core after the inner skins are joined?

Each case is different and will actually have a different developed shape even though the base radius is the same. Computers will allow you to design a lot of things that are VERY expensive to make when a little forethought would have made it a snap. I have found computer design without thought to fabrication to be very common plebe Nav Arch mistake. Remember that an engineer and designer are only as good as the mechanics who build it so don't go making it any harder for them than you have too.

(edit:spelling)

[SailDesign]

jehardiman,
Look at many of the Open60 boats out there, and some no longer around, and you will note they have a varying radius on the sheer. There are reasons to want to do this, apart from aesthetics, but no round-over bit or pipe in the world is going to achieve that for you - it must be built properly.
Yes, computer design without thought of construction is a pain, but a good yard can and will built what the client and the designer want. The radius can be in the deck edge (look at the new Spirit of Canada website) or on the hull, or built later and applied with the hull/deck taping. Or the hull could be built in two halves port and staboard, with the roll integral, then joined on centreline. Your choice.
If in steel, then obviously this can only be achieved by a yard that has the skills and capability to do compound rolling. But it is not impossible or impractical.
I have often found that boats designed purely to be built easily are lacking in any aesthetic styling. Nothing wrong with utilitarianism, but not on my yacht designs, thanks.
Steve

[marshmat]

Back to the cap over the bow....
What I sometimes do for these is to DupEdge the top edge of the hull surface, then Trim and Join the duplicated edge so that you have a single curve on the gunwale where the cap is to go. You can then draw the cap profile as a curve; snap one end to the end of your duplicated edge and the other in the same section plane on the centreline. RailRevolve then produces the cap as a surface....

[Hans Friedel]

If you machine the plugg in a CNC-machine you dont have to make any 2D drawings

This kayak has a track modeled in Rhino for a alu keel.



http://www.boatdesign.net/gallery/sh...00/ppuser/1809



Hans