Metal Round Bottom Sail Boat

Wynand - Mike Jones,

Not nice to call people "Clowns". Try to refrain your anger over someone pointing out the limitations or radius chine. We are all in this together.
I really expect an apology from you- Wynand.

Wynand, you quoted a line from my web site. It is so simple, I can not understand why you can not see the simplicity of it all. Use the right toolbar - The prototype boat is being built right before your eyes. I do not get where on Earth you and Mike Jones are coming from.

Anyway, it is Thanksgiving here in the USA. I am going to put this aside for the holidays.


Happy Holidays
Dennis Schaffer

 

Sorry, no apology - your claims were so downright funny I thought you are in the entertainment arena. No insult meant or intended.
I had been called worse names like that on this very forum and usually it makes me look at myself why someone would do that and try to take it as constructive criticism, sometimes changing my ways for the better of others...

Secondly Dennis, it is just not so simple for an amateur...

May you have a wonderful Thanksgiving in your country and a blessed coming festive season with family and friends.

 

Wynand,

Accepted!

Let us agree that we can disagree?

 

The point was that there was a lot of talking up the difficulty of metalworking wrt using rollers to shape metal. But my point was that you can show someone how to use a roller or a press brake on a Youtube video or even reading a guide for an hour. After that you know how to use the equipment. But how long does it take to learn to weld alloy proficiently? and there is a huge amount of welding in this method. So if you go to welding school for a course then what's the big deal learning to use the rest of the equipment if you really want to build a wooden or fiberglass or ferro cement style round bilge hull out of metal.

How is forming a conic section on a press brake new?

Also the so called "Bezier" method is neither a bezier method nor new. For example the so called Bezier chine example is just a variable radius chine of constant arc.

I think you already bought it by the sound of it
But the website contains lots of marketing hype which is probably not so obvious to the non professionals. There are other major blunders in the site too but to do with hydrodynamics.

I think Wynand posted the Dudly Dix examples to illustrate how silly the remarks were about radius chine by the poster mr Bezier aka 'thesecondwind' .

Weld shrinkage can add up when you have so many sections ! There's as many Butts as a small ship and you'd always consider the shrinkage. But I wanted to see what the designer pushing this method had to say.

 

So that I may form a picture in my head at what your doing would some one please post what thickness of steel and what size are the sheets that is being used here.

 

Frosty
If you read the site referred to you'll see some plans being sold for small classic day sailors which would have quite thin and easily rolled plate. Hard to weld though !

But he offers to convert others chined designs to what he calls the bezier method which is just a marketing catchword for rounding the chine.

 

Interesting thread. The metalwork issues are outside my expertise but the “bezier method” is just 3D geometry, “constant chine radius” is a design limitation intended to simplify construction, and the radius chine method is just a way to create a surface bent in 2 directions using sheet material that doesn't want to do that, at the same time reducing waste.

From what little I have read on metal hull construction a decent radius chine hull can be achieved by welding sheet metal sides and bottom to longitudinal pipes for the chines. Of course that way you really just get a soft chine hull. For a true rounded hull I suspect Mike Johns is correct, if your working with metal take advantage of its ductile nature and roll it to minimize seams; I wish plywood would do that.

I have been working out an adaptation of the radius chine method for smaller plywood boats. I had in mind a 12+ footer but the concept can be stretched to 20+. Caveat: development is incomplete, but FWIIW here is a capsule description of what I have been calling the vertical chine method. BTW there is no particular reason for making the chine radius small or constant.

A typical radius chine hull is built with longitudinal planking for the sides and bottom, which are connected with planking applied circumferentially around the bilge in relatively narrow strips. For small boats I believe this can be achieved within the width of a single sheet.

In my proposed method parallel slits are cut partway across the sheet width to form the teeth of a sort of giant comb. The uncut long edge of the material is attached to the inwale, and the "teeth" are bent into shape over the building mold. One edge of each tooth is trimmed to fit the edge of the previous tooth. The “back” of the comb forms the sheer and the teeth form the bilge. The teeth may meet the teeth of the far side along the centerline, or for larger hulls they may be joined by a bottom plank, or - for a vee-bottom hull - by garboards and keelson. For plywood construction I plan to employ stringers to aid stiffening and fairness.

Note that, in the plan view, the teeth are radial, or rather normal to the sheerline. Material waste is minimized, especially if the sheet is trimmed to the required shape before cutting the slits, as the large offcut may well fit elsewhere on the hull.

For an adequately fair hull the number of vertical planks or teeth is large, typically around 40, whereas for a typical rounded hull with longitudinal planks perhaps 11 would be used. However, length being much greater than hull circumference, it works out that the width of the planks is similar. Since the area is the same, it is obvious that the total length of seams to be joined is similar.

 

Mike Johns,
I am giving up on you. Besides the weld shrink issue you know nothing about sheetmetal layout or metalwork in general. You will not take your blinders off or willing to learn anything new.
Dennis Schaffer

 

I was hoping for some discussion from you.

I’d like to give an example and I hope you don't mind me showing the image here.


http://www.metalsailboats.com/CONVERTING-HARD-CHINES-TO-BEZIER-CURVE-SURFACE.html

Here it shows the lines of a multichine hullform converted to the so called Bezier method.
I quickly applied a constant radius to this example (I just took your radius from from station 9 ) and the resulting lines are shown on the left below. On the right are your so called Bezier curves and their derivation ( simple circles).

Don't you think the constant radius is a very sensible option, would not look any noticeably different. And is often available from a designer anyway.

Again the question is why would you form numerous parts to a slightly different radius when you get a better result overall with less welding and a smoother surface from a constant radius?

Look at Wynand’s results . And he certainly has a right to reply strongly to negative comments about the constant radius method to sell this supposed superior Bezier innovation.

The industry tends toward sensible design and good practice and it produces good results. A lot of existing practice is actually a very hard act to follow. And are you interested in the hydrodynamics assumptions you have made that are wrong ? Do you even care that you could be misleading people with your assumptions?

 

Exactly why constant radius chine is the preferred "round" bottom steel build method for the last 25 years and more.
There is an old saying that goes something like this; "any fool can be complicated, but it takes genius to be simple..."

I took liberty of using the same picture of the "bezier" method and added some on it.

First and foremost, with the "bezier" method the sides and bottom plates are flat with hard joints at the bilge to keel. This is exactly like the constant radius method.

Secondly, with proper round bilge method these panels would have curvature with soft turn at the bilge to keel joint.

Finally, the bow area with the "bezier looks very awkward and with the constant radius the upper tangent of the radius get sharper (blue line in sketch) (and getting it right is the trick that set some designers apart from others) until it meets the lower tangent at the bow - station 0. This gives a very smooth and balanced transition from sharp bow to round.

In a nutshell, the "bezier" method is a constant radius chine made complicated and less aesthetically for the sake of inventing a supposedly new method to build a round bilge boat faster and better from radius chines. These claims made by the author is not very honest and smell like snake oil to me.
There is a reason why this old method is not used commonly by the steel boat building industry and the opening quote from MikeJohns sums it up nicely.

 

You are a very brave man. Mike is a qualified structural engineer with many years of practical experience to boot. What do you bring to the table to back up your claim:?:
Mike can do a stress analysis of every joint or plate in your design if asked upon and can you?

Be very careful with assumptions and remarks that may come back to haunt you....

 

From what I have read, it would fall on deaf ears. Seems like another B.Swain type mentality....it would be about 30mins of Mike's life he wouldn't get back doing this analysis..sadly!

 

Well I wanted to hear from the big boys. Watch what you wish for it may come true. Thanks for the beating. I will rethink the conversion thing. Maybe I got a little over zealous. Thanks for the lesson.
Dennis Schaffer

 

All the talk of steel when I already stated early on I was to go with aluminum due to size of the boat and the weight to strength ratio.
I recommend anyone that is local to New England, take the time to drive up to Mass, and meet with Denis.
He was nice enough to take the time out of his holiday weekend to show me one of his current builds, using his method, this hull is fuc?ing gorgeous, and very similar to what I was looking for.
As for all the sales hype, and clown comments. My impression of the man says you couldn’t be any further from the truth.
I was very impressed with his previous builds, and that one of steel boats built many years ago has only gone up in value with each sale, as it has changed hands. After making multiple trips across the Atlantic this 34 foot boat of his stood the test of time.
I don’t want to put too much of Mr. Shafer out there that he does not want to divulge himself, but I will say this, the man is of means that clearly display he is not interested in the sales or profit; rather he wants to provide a method of construction that would allow the average skill set individual an optimal build.
The weld shrinkage comments are for ****, and if you spent five minutes on the phone with him, which I am certain he is willing to do, you will most assuredly feel like an ***.
By the way, no one here has asked what I do for a living now and how I got here. I don’t appreciate the non professional comment or at all questioning my experience.
And for the test weld comment, great NDT is a short course, and if you want Mr. Schaffer or myself to school you it won’t be a problem. I started this tread asking for input not a bunch of my dick is bigger than yours and the most modest man on all theses posts, is the one that has the most under his belt, and can back it up.
Highly recommend talking to him over the phone or in person, I don’t know why he even waists his time with you “professionals”
I should have never asked.
BTW nice use of smily faces. you fools!

 

Bézier curves are merely adaptable shapes as you all know, which can be expressed in relatively simple equations to be solved and drawn by computers. They have no esthetic significance whatsoever.

When converting a hard chine hull shape to a rounded form, a 2D bézier curve can be created for each station that will pass through the existing chines. It should also pass through the waterline too to preserve some of the hydrostatic characteristics of the original. A curve forced to fit so many constraints can be downright ugly.

A radius can be made to touch the sheer strake and garboard. It too should pass through the waterline; the solution is a simple geometric exercise. It is unlikely that a single chine radius can be found that will satisfy all of these contraints at all stations so a constant radius adaptation of an existing hard chine design is going to change something, apart from taking some notchiness out of the cross-curves. Same thing applies to beziers of course.

There's not a great deal of difference between ply, steel and ally as far as the math of the shape is concerned. With metal you can use smaller radii. There is the option to create shapes that bend in 2 axes, but the skill levels required to get predictable results are high. Something similar can be created in plywood - tortured ply method - which is repeatable but the first item is rather unpredictable.

With a relatively thick material such as plywood which exhibits high stiffness when the sheet thickness is sufficient to provide adequate strength, controlling the bend to get an exact circular arc is not as easy as it sounds. A curve such as a hyperbola is actually easier to create - provided the total bend angle is not too great.