Boat Builder Central - Builder Forums

A Customer wrote: Greetings,

I was wondering is there any way to scale a CS23 down to a 19' or a 21' ?

Thanks in advance for your time!

Shouldn't be terribly difficult. I would say keep it within 10%.
Please read the following article for all scaling-related questions:
http://bateau2.com/howto/scaling.php

10% would take it down to 20.7'

Scaling her down to 21' would work well. There is enough safety margin in the sole height to guarantee proper cockpit drainage when scaled down to about 21'.
For a small fee, I would provide scaled stations and panels dimensions.

Would scaling a CS23 in the height dimension only work? Say 70-80% of full sized to produce a "carolina bay" style boat? (See Tidewater Carolina Bay 2300)

Marshall Moser wrote: ↑Thu Apr 08, 2021 4:44 pm Would scaling a CS23 in the height dimension only work? Say 70-80% of full sized to produce a "carolina bay" style boat? (See Tidewater Carolina Bay 2300)

Your talking of reducing side panels. You can certainly do that by simply marking the frames and side panels down by the amount you want to reduce them by. Just remember by reducing the height the boat is less safe as it has less freeboard. If you don't want a true Carolina Fisherman it makes sense. Get the plans and I would leave at least 21-23" at the mid-deck from the deck to the side deck for safety. Sounds like a good idea to me.

The problem with scaling the CS 23 down and reducing the sheer line height to make an offshore boat into a bay boat is that you still have the offshore boat bottom with 17 degrees of dead rise at the transom and more draft than you might want or need.

The FS19 already has a bay boat vibe to it. It might be possible that you could add some Carolina flare and tumble home to it by modifying the transom, mid and bow frames. Adding slits to the side panels to accommodate the tumblehome and flare would be required too,

The FS19 that I built is in my opinion a fine looking boat, and based on the number of people that stop my brother every time he uses it to ask about the boat confirms my opinion.

Because of the lack of an interior liner the FS19 has as much interior room as my fishing buddy’s 22 Bay boat, is lighter, more fuel efficient and achieves the same speeds with a lot less HP.

Lots of good designs for bay boats to choose from here.

I love the lines and look of Carolina style boats myself, but your intended use and the design requirements to meet those needs should take priority over the lines of the boat.

Of course there are many versions of production built boats that have been adapted to include Carolina flare styling applied to everything from flats skiffs, bay boats, center console and express offshore boats. A used version of one of these will be your quickest, easiest and probably cheapest route to achieving what you want.

I however would love to see someone adapt one of the BBC designs to achieve a Carolina style bay boat and do not want to dissuade you from your boat building project.

If you don’t do it, perhaps I will.

Browndog, if I did scale the CS23, I’d scale it completely in the vertical orientation and lower the 15° deadrise. I own the FS19 plans as well. I like the FS19 program, but I think it would be easier to scale the CS23 down than to try to modify the FS19 to have flare and tumblehome. I’d probably take some of the tumblehome out if I did it though. Also, I’d want to respect the scantlings of the CS23. My only concern is how the scaling would affect the projection of the panels and how to calculate that.

The problem with scaling the CS 23 down and reducing the sheer line height to make an offshore boat into a bay boat is that you still have the offshore boat bottom with 17 degrees of dead rise at the transom and more draft than you might want or need.

I don't know what you guys are looking for in an 'off shore' boat versus a 'bay boat', but for what its worth I don't think a 15, 16, 17 or 18 degree dead rise at the transom makes much difference. For a off-shore boat I would be looking for at least 21 degrees of dead rise.

My boat has 18 degrees of dead rise at the transom. Its spends 90% of its time in rivers and estuaries and only about 10% of its time in what might be called 'off shore', where its certainly nice to have a bit more dead rise. I was told it would 'rock and roll' at rest because of the 18 degree dead rise - it doesn't. Its just as stable as my almost flat bottomed 14' 'tinnie' - probably because its (1) wide, (2) has some reverse chine and (3) all of the fuel is in tanks set centre-line under the soul - resulting in a low C of G.

If you look through some of my fishing videos you will probably see my son and a mate walking around on the gunwales - the boat barely moves.

Hulls with dead rise need more water? True! How shallow do you need to go? I regularly run in about 3 feet of water at 28 kts! At idle I can do about 18" - maybe a bit less.

28 kts in a 22' boat in 3' of water takes a bit of getting used to - but we do. Having a hydraulic jack plate helps - particularly for getting on the plane in shallow water.

If the CS23 design appealed to me for what I wanted to do, I would have no hesitation in scaling it down by 10% to need my needs.

If you go ahead with scaling down, get te Metric plans and a metric ruler, they have them at Lowes, they will be combined womith a US scale. It makes it much easier to scale down as all the numbers are whole and not in 1/2" etc. Makes it much easier to scale down.

Tom

Some of us would say that metric is just easier full stop.

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

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

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.

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.

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.

cracked_ribs wrote: ↑Mon Apr 12, 2021 1:33 am Anyway pretty easy to do, just a bit of extra work.

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.

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.

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.

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!

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.

The slits would also be my area of concern, I can't think how I would do those. I'm sure there's a way but I am also a hack and not a pro, so I couldn't tell you how.

Comparing the panels to the printed plans is a good idea for sure.

The slits will be shown on the plans and will run from Frame C to just short of the bow. They are needed for the inward curve of the Carolina shape. Tied to the frames.

Tom

We were referring to a new / modified design. Not per plans.