Scaling Question

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TomW1
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Re: Scaling Question

Post by TomW1 »

I think we are a little confused here. Correct me if I am wrong. First is the builder that sent his note into Jeff wanting to reduce the CS23 to 21' That has been answered by many that yes it can be done, including by Jacques.

Second Marshall Moser asked if "Would scaling a CS23 in the height dimension only work? Say 70-80% of full sized to produce a "Carolina bay" style boat?" I answered that, since he is not scaling the boat, he only need to cut down the sides and frames the amount he desires. So Marshall are you scaling your boat or just reducing the sheer.

Regards all, Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

Marshall Moser
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Re: Scaling Question

Post by Marshall Moser »

I’d be completely scaling in the vertical axis rather than cutting the sheer down. This would be to maintain the flare.

OneWayTraffic
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Re: Scaling Question

Post by OneWayTraffic »

Marshall Moser wrote: Sun Apr 11, 2021 9:32 pm I’d be completely scaling in the vertical axis rather than cutting the sheer down. This would be to maintain the flare.
That would mess with the 2D unwrapped panels. I was thinking about stretching my C17 longitudinally and the same problem occurred. In my view the easiest solution is to find a plan that works as is. JMN has designed a lot of good boats in the 18-21' size; one should fit the need.

Matt Gent
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Re: Scaling Question

Post by Matt Gent »

Can't just cut the shear lower on a boat with tumblehome and flare. Well you could but it would be ugly and lose a lot of the functionality & style.

Scaling in one dimension only isn't scaling in the sense of how it is normally used here...that will change all the bend radii and the total panel development. Same goes for trying to change the deadrise. It essentially makes a related but new design.

I think the request is for something like a Bayshore or Tidewater bay boat, and I think that is really a new design effort in this case. Or you could get the CS23 plans, adjust all the stations to what you want, and make new devleoped panel shapes from that. But you need Rhino or similar to make it happen.

cracked_ribs
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Re: Scaling Question

Post by cracked_ribs »

If I really wanted to scale the vertical on a design like the CS23, I'd buy the plans, input all the dimensions into Delftship, and loft out the panels straight from my laptop. That's basically what I did with my own design, you can see it in my build thread if you're interested.

I'd probably cut an inch or so large all the way around just to make sure there wasn't some weird artifact with DS that distorted a panel too much. But as soon as you started hanging the panels it would be pretty obvious.

It's a bit of extra work but not too bad. Use the scantlings as designed, don't change too much and you're pretty set to go. I wouldn't bother changing the deadrise from 17 to 15 - at that point you're changing actual stuff that interacts with the water, and in exchange you're not getting much of anything, maybe an inch less draft? But personally I doubt whether doing so would cause you any serious problems. A couple of degrees of deadrise isn't a huge change.

Anyway pretty easy to do, just a bit of extra work.
I designed my own boat. This is the build thread:

viewtopic.php?f=12&t=65349

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Re: Scaling Question

Post by jacquesmm »

cracked_ribs wrote: Mon Apr 12, 2021 1:33 am Anyway pretty easy to do, just a bit of extra work.
:D :D :D
A little bit of extra work: learn new software, enter the lines from another design, scale, trim, develop panels.
If you like it, do it. it can be enjoyable.
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cracked_ribs
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Re: Scaling Question

Post by cracked_ribs »

I guess that's the thing...I like this kind of stuff so to me it would be pretty fun and I wouldn't hesitate to do it.

But then, I know a guy who's running a 50k next week and he would probably describe it the same way. For him, that's just a fun day. For most people that would be a day of misery they would never forget.

So in my opinion this is nothing too difficult, but I am a hobbyist of this kind of thing and I do it because I like it. But it might not be fun for most people.
I designed my own boat. This is the build thread:

viewtopic.php?f=12&t=65349

Marshall Moser
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Re: Scaling Question

Post by Marshall Moser »

jacquesmm wrote: Mon Apr 12, 2021 9:20 am A little bit of extra work: learn new software, enter the lines from another design, scale, trim, develop panels.
If you like it, do it. it can be enjoyable.

My concern is that I would mess up and the panels wouldn't be developable and I'd end up having to do something like cold-molding, which I'm trying to avoid.

cracked_ribs
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Re: Scaling Question

Post by cracked_ribs »

Certainly possible...you can usually get a sense of that within the software but then, that requires sufficient familiarity with the software to judge whether the surface deformation exceeds a workable maximum.

Taking a proven design that is developable, like one of Jacques, and making minor scaling changes...if you make no mistakes on the sofware end, it'd be easy to make developable panels from that. But how do you know whether you made a mistake, unless you spend the next year getting super good with the program and making models and learning what the translation from digital to real looks like and where the problem areas tend to be?

I guess you could buy the plans, input the numbers into software of your choice, make the changes you want, develop the panels, and build 1/5 scale models from the panels, and if you cut it all very precisely it'll tell you if you have it right. The model build would be the only way I can think of to confirm scaling success before you commit to a full build.

But if it's not the type of stuff you do for fun already, well, there's a reason it's a lot more popular to buy a set of plans than create your own!
I designed my own boat. This is the build thread:

viewtopic.php?f=12&t=65349

Matt Gent
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Re: Scaling Question

Post by Matt Gent »

In order to check your process you could build the boat per the drawings in the CAD program of your choice, unroll the panels to flat, and compare them to the drawings. I've done this a couple times and its pretty helpful. Plus you can back out the hydrostatics from boats that work well and figure out what you want to do with your own design.

Its a lot harder if the plans don't include stations, but I would think the CS does for all the bulkheads.

There are tricks to how it is done...like where in the panel thickness you are taking your developed sheet from. And I'm sure many others, which separate the actual designers from the hack hobbyists like me. I wouldn't know how to handle the slit panels to get pseudo-compound shapes from flat panels.

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