Request your input on my design

I have been doing this with just some algebraic relations and a pocket calculator for many years. If you want, I can send or post a short paper I wrote on the subject "low tech developable design".

developable-surface-boat-designs.blogspot.com

 

I'm interested in seeing your short paper. Does you method have any limitations on the types of developable surface?

 

Richard- I have skimmed over your thread- pls forgive me if I come across as a bit uninformed about your thread. but seems to me from what I can glean from my limited time allowance, to read your thread that you:
1. want your own design?
2. want to cruise?
3. want a spacious boat? or at least enough to enjoy your cruising
4. not going to be in heavy weather(?)
5. the other stuff haven't mentioned.
hope its ok to add my 2 cents?:

If I wasn't so goddess damned obsessed(and extremely stubborn on the issue) with having my own personal tugboat(and accommodations barge)...I would hands down buy a set of either Pars floom plans or his egress.

I very very seriously considered it for my own boat. but the tugboat won out due to my love (and hate) affair with them.

you would be well advised to build something or something like it.

Im currently studying Naval architecture, and I can be the first to say it has taken me ten years to understand a good tugboat design. and I specialize in them. I get that yours is a pretty basic shape from your first post. it will probably be fine but...

although -I always argue its easy to make a boat that floats and most boxes will do, if you want it to be a good vessel- the Egress is a great design. or something similar-

save yourself the astonishing amount of work and education and get yourself a set of stock plans. You simply absolutely cannot go wrong(unless you -like me- have an obsession with a certain type of boat)...

yes-you will need to look the plans over many times to fully understand what the blueprints are trying to say-( if you are not versed in reading BP's)but in the end- you'll thank yourself a hundred times over...
you cannot go wrong for the couple hundred bucks they cost...

 

Check out Samuel L. Rabl, he wrote a paper in 1958 for the SSCD 'Planimeter'

 

love Rabl...my fav boat of his is the Kittiwake...

 

I'm sure the question of developability puzzles a lot of people. The simplest definition I know of is that to be developable, at every point on the surface there must be at least one straight line able to be drawn through that point that touches the surface everywhere along the line, and secondly that the "normals" or perpendiculars to the surface at every point along that line lie in the same plane. Then of course there is the matter of the minimum radius the material will consent to be bent without breaking, which applies particularly to plywood.

 

Yes, Wayne, please post your paper.
Thanks,
Richard

 

I wonder how designers like Glen L Witt were able to develop so many "developable" plywood designs before having the use of a computer (or even hand calculator when he started). I guess all on a drafting board and a slide rule. Must have been a lot of genius there.

 

The one thing that is nice thing about drawing on paper -at least for me - is the process is a lot more intuitive- but of course that means a lot more re-working the drawings- and rhino- for guys like me is a godsend. It allows us less talented guys (me) to design a decent boat.
I think those guys had the genius already. But I sadly wonder too- if when cad came out it ended an era of some of the greatest designers ever. I can personally tell you- I have tried to emulate some of Hankinson's lines on rhino and I cant come close...
guys like Rabl, Hankinson Witt, Atkin, Alden, and some of the great names in design will be hard to top using rhino..i have a soft spot for the "old school" designs.

 

It also allows undecent guys (not you) to design things that look like boats, but they are not. May those who are addressed go down with their creations.
RIP: Ripped Into Peaces.

Drawing-Magic: I knew a master builder once, who would pass my drawing with only a short glance on it, and then pointing out errors. Over time one develops an 'eye' for such things.

 

It was likely an art learnt by eye and experience. It can't be too difficult, because I can do it ! You really need to first fully define one line, most likely the chine, by drawing it in plan and side elevation, and partially define another, i.e, in one dimension only, the keel or sheer, and have the intersections of the straight lines drawn from vertices meeting the stations where the chine intersects them define the missing dimension. Obviously in the case of the keel, it is defined as a straight line in plan view, but not defined as yet in side view. Or at least that is how I have done it ! If you don't like what you get, you can redraw your chine, move the vertices, or both.

 

For me Rhino makes it easy to calculate things like the displ. and area etc.
But it really takes a good eye to fair out and proportion a good hand drawn vessel. that is an art and made Naval Architecture a true art. now its more like a science than an art....which makes what guys like Alden and Witt could do - all the more incredible in MHO.
it still floors me to see a lines plan from the 40's and how incredibly technical the hull was/is. it's truly mindboggling. I wouldn't even begin to know how they developed half models into such works of art...

 

I read comments on how difficult it is to determine if a surface is developable. Instead of looking at the rules governing such surfaces as constraints, look at them as guide posts. Follow the rules, and the surface will always be developable. For visualization, just pick up a sheet of paper and see how you can manipulate it without causing folds and creases. There are really only three types of developable projections- the cone, the cylinder, and the plane (neither the cone or cylinder need to be round, but a plane is always flat). All ruling lines in a cone emanate from a common apex. All ruling lines in a cylinder are parallel. Simple planes are rarely used. It gets interesting when you link together a series of projections through use of common ruling lines to create more complex surfaces.

In a cone the ruling lines link a curve with an apex of common origin. In a cylinder, all the ruling lines are parallel and pass through a curve. In a plane, the ruling lines can go in any direction as long as they stay within the plane. But you can't just say that a curve goes from here to there or draw a picture of it, you have to describe it mathematically. That is the critical step. What is the simplest boat-like curve you can think of? How about a trajectory curve (a form of parabolic curve)? A projectile is fired skyward at some angle and then is pulled back to earth by ever-present gravity. Sort of like the water that is pushed aside by an advancing hull form and then is brought back to place by gravity. And this can be described by an equation. Y=b(1-X squared/L squared) where b is the total offset and L is the total length. The slope at any point is 2Y/X. The equation can also be integrated to find curve length.

I find that the most critical curve in a design is the chine. It links the hull bottom with the topsides. So I start by defining a curve (or several curves end-to-end) to create the chine shape I want. Of course it may end up being an iterative process as things progress. Once that is done, the anterior keel is next to be shaped. You have three choices: Place a cone apex on the same side amidships and project forward through all those many points you have defined along the chine to find their intersection with the midline; or place a cone apex ahead of the bow on the opposite side and find the intersection of those many points on the chine when they are projected toward the apex; or use a parallel projection with a selected x:y:z slope from the many defined points on the chine anteriorly toward the bow midline. I have at times used each of these choices but most commonly use parallel ruling lines with a defined x:y:z slope. You could also link two different projections together through a common ruling line. That was done for my last build with a parallel projection projecting forward linked to a conic projection extending aft.

Hey, you are probably all asleep by now, so let me stop here. This is all very easy for me because I have been doing it for so long. In 2008 I posted a paper at my website with a diagram of a sample hull; it may help.
http://developable-surface-boat-designs.blogspot.com

 

No need for a calculator or slide rule. All that's needed are splines and ducks, a couple of triangles (or a T-square and a triangle) and a pair of dividers. Mr Efficiency concisely described a method above to design a conical surface, which is developable.

Some software, such as Rhino, has the capability to easily and rapidly create accurate developable surfaces, both conical and non-conical.

 

Drawing by hand is a bit of an art form, that requires a good bit of experience. Anyone can be taught to draft up something, but making legible plans, ones that a builder can read, without confusion or guess work, not making them over crowded with information, knowing what to include or more importantly what not to include on a particular drawing, requires a lot of experience. This assumes you already know how to design a structure, capable of the loads it will be imposed to and a set of shapes that do what the SOR dictates it must. And yes a slide rule was all we had back in the day, but this was enough to get men on the moon, so a lowly 'ol boat could be too hard, right . . .