Subject: Re: [baidarka] Offsets question
From: dawgen (dawgen@shaw.ca)
Date: Tue Dec 11 2001 - 01:23:33 EST
Paul Raymond wrote:
>
> Hi Damien,
>
> Are you interpolating points to draw the curves, and if so which
> parameterization are you using?
>
> I've played with the trial version of Rhino in the past to redraw a North
> Alaskan Retrieval kayak, but keep in mind I was trying to figure out the
> program and didn't really know what I was doing. Anyway, I used splines to
> recreate the gunwales, following an article in Sea Kayaker magazine.
Ok, you're going about it the long way....:) Better to at least start with
a table of offsets (if you have one) and create hull profiles at each
station. Then you can use those profiles to loft the hull directly. The
program uses "natural" curves and so far has been incredibly accurate. If
for some reason the curvatures are not to your liking you can either play
around with the lofting parameters or "extract" the lofted curves right off
the hull and tweak them till you're blue. Try this, it should put a smile
on your face....:)
> I
> created the center spreader, and then bowed in the gunwales to the proper
> distance at the ends, and figured out the lengths and positions of the deck
> beams with extreme accuracy.
>
> That is until I got the actual pieces of aluminum and found they wouldn't
> bend according to what the cad program said it would.
In all fairness the CAD program is simply trying to please you. If you say
make a curve this sharp, it will.
> Played with the darn
> parameterization settings and couldn't figure out any combination to get > the
> cad program to follow what the tube or wood would do.
>
> Then I got to thinking that I have to first build the gunwale section and
> then model it. More points. Always needed more points. Well anyway, the > cad
> program didn't last too long. If you are already woking from an > established
> plan then you should be able to do a lot better than I did.
I've found that if you want a "natural" curved object or surface you need to
try and describe the object with the least amount of points possible. Let
the computer do one of the things it does well, natural flowing curves.
Every time you add a point you're taking over for the machine. Let it do
it's job as much as possible and I think you'll have far more success.
> I read somewhere that you have to work with the pieces of wood (or tube)you
> have, not try to force them into something they're not. I imagine that
> someone who is good with cad will do a lot better than I, but I think if > you
> concentrate to hard on using Rhino, you are losing part of the feel that > is
> inherent in kayak building.
Absolutely. The computer is a wonderful tool. It isn't a boat builder. I
have never designed a boat from scratch, only modified existing designs to
meet my needs. This way, you're always starting with something that works
already (hopefully) and only needs to be slightly tweaked to satisfy a new
set of parameters.
> >I on the other hand am working from fresh modern plans.
> Hmmm. Fresh modern plans?
I mean plans that come right from the designer or horses mouth if you like.
Whatever was intended is right there in black and white, no guess work and
estimating.
> Cad has its place in boat design. Rhino has been used for quite a number > of
> designs. Have you seen all the boats on the Rhino site? Wish I could do
> that. If you're up to it, maybe you could put up a tutorial somewhere.
Again I'm not a boat designer, but with a bit of practice you would be
amazed how easy it is to "parrot" a set of plans into something very
useful. Try the method I described above and if you have any questions I
will do my best to answer them. When the 5 meter is done I'll upload a few
rendered images somewhere if there is interest.
Cheers,
Damien
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