Paper and pencil

Oh, about this:

Basically, you're wrong. You can get by with a lot less than a professional designer would have used in the good old days, but even with making some of the stuff yourself you will still end up spending some money. Off the top of my head, to get a good but basic kit together you will probably spend enough to buy the current pro version of Delftship (sans plug-ins).

 

I do not understand why you say that. Many years ago the shipyards walked off the job to 1/1 scale and performed all his work to 1/10 scale. The accuracy achieved was more than enough. Advances in computers made these techniques were abandoned.

 

Have you seen this?

https://www.youtube.com/watch?v=WHpiAKMe3MA

a winters project?

If you are building a sheet ply boat you will only really need a straight edge and splines, no need for curves. It is really hard to draw fair lines without using splines, French curves are never the right shape. I have never owned a T square

I never found Dixon Kemp curves (which are egg shaped) much use, but then I don't draw typical displacement monohulls (nor do you)

I sold my unused for years planimeter, curves and weights for GBP150, the buyer knew he had a bargain, my planimeter alone cost me more than that 40 years ago. I would check with your local schools universities, architects to see what they have available secondhand

You can draw by hand to 0.5mm, most sheet plywood boatbuilders work to 3mm accuracy, so a 1:10 drawing is usually accurate without lofting

You can "cheat" the lines plan by drawing the widths to a different scale to the length. (say 5:1 widths and 10:1 length)

Richard Woods

 

What's up with these ducks anyway? From what I gathered, they serve a very simple purpose. And you said people use random stuff instead of them. They are basically just weights with a sharp tip. So why they are expensive?

And where do the heck would I get a planimeter? I only found some antique shops in my country that still sell them (at exaggerated price)

Forgive my ignorance, but with my profession being far from drafting, I never understood what these curves are used for, and why these specific shapes. I saw them sold in office supply shops, sometimes separately, sometimes in sets. I understand that you place them on your sheet, and trace around with pencil. That much is clear. But why do you need them in the first place? What does each shape stand for, and when is it used?

Yeah, I don't expect that to be easy. But people have done that for centuries, so there must be a way. Any of the books people suggested here that address these two problems?

I just can't wrap my head around this, why would it cost so much. A drawing board costs a lot, sure. But wouldn't large table suffice? A couple of rulers, edges, splines, pencils. Maybe it's these ducks and curves that add the cost up.
Or maybe I just know too little of this to even guess.

Now that's a beautiful instrument. Doesn't look too complex to make. It just puzzles me why there are none for sale nowadays (at least where I live), and why they are so expensive (from what you say).

Anyway, these are very good tips, thank you.

 

Now that's cool. Pity he doesn't provide any details on how to build it.

Nothing is ever the right shape. French curves can be useful, IMO.

The problem is that the sort of person who works to 3mm when building is not likely to get everything correct to 0.5 mm or less when drafting. I'm sure we've all heard stories about tables of offsets that needed quite a lot of correction when lofted at full scale.

 

Because nobody wants them. They are a specialty item. This means they cost a lot for what they are.

You need them to get curves that are too sharp for splines. It stands for a curve. You use it when it fits what you want to do at the time.

Skene's covers it, IIRC.

 

Yeah, but how do you know which one to use in any given situation? These are beautiful shapes, but I red that they are governed by specific formulas. Do you just look and say "oh this curve would look nice if I used it for transom gusset", or do you chose because of mathematical reasons? An why do these curves cost so much - are their shape accuracy so important, if so, why?

Sorry if my questions are silly. I'm trying to google as much as I can before I ask.

 

You pick whichever curve gives you a shape that looks right. That's how traditional boat drafting works (although obviously you have to check the figures to see if displacement, etc are where you want them).

And yes, accuracy is important, because if they aren't accurate your lines will have lumps in them. This means your boat will have lumps in it.

 

Lumps sound horrible. All right, I'll now dig into these books and try to find answers there before I ask anything else.

Thank very much If anyone has anything else to add, please do!

 

For the same reason you cannot buy a new slide rule these days...

Slight aside, years ago I designed a boat for the guy who made most of the worlds slide rules. He got out of that business and made credit cards instead, same sort of plastic apparently.

I assume laukejas only wants to design sheet ply dinghies, so I am suggesting the minimum he needs to do that. Curves were/are expensive to make because they can have no "lumps", as noeyedeer says

Lead is also expensive, even if you make your own weights, as I showed earlier. Maybe use old fishing weights? or car tyre balancing weights?

RW

 

Fortunately I have a copy of a manual of Drafting standards to the now replaced BS308 (replaced by current BS8888) which is still largely good enough to give very good guidance on engineering drafting. If you are lucky enough to find a second hand copy of this book it will show much about drafting but not a lot about boats. However the basic skills or representation transfer across many disciplines. The book I have is an old one published in the UK by Hutchinson circa 1984 but very, very good. I actually don't know why a newer version has not been published with the necessary updates including CAD standards etc.

For boat design, and assuming small craft it is worth looking at any books with lots of lines plans. Preferably with as many types of craft as possible. There is a vast ammount of information in those drawings IF you read them properly. Often you will find diagonals, curve of areas, maybe C/B and CLR and sail distribution CE. The books with photos only are sort of OK but the drawings show the designers thinking, and how structural problems are adressed too. Remember there are many years worth of experience in a lot of the drawings so you can save a lot of heartache by fully understanding them. Why reinvent the wheel?

A drafting board with parallel or better a sliding arm and rotating head should be available for very little money. They almost throw them away in the UK.

When I was at school I started Tech drawing (O level) and they stopped it after two terms probably thinking it was not academic enough. After that I sort of taught myself a fair bit of drawing including several boat projects, which remained on paper. Some years later I did and have done a lot of real production drafting of lots of different things for many industries which also encompass marine products and boats. I tend to look at technical drawings as partly artistic too, a good drawing is a rather beautiful object. The old part watercolour semi rendered visual schemes, part shaded, some perspective or isometric projections from the C19th and early C20th are very pretty to my eyes. Even a dimensioned production drawing should be well executed so part of the modern art is to make the software do what you want it to do. It is the tool for your thought.

 

I make my own ducks. The price of scrap lead is about $0.65 and it takes 3-8lb of lead each. The hooks are a piece of coathanger epoxied in a hole I drill after they are cast. To keep them form staining the paper a glued piece of felt helps.

 

How expensive is expensive? At Abebooks.com The Nature Of Boats is US$ 5.53. Shipping to Lithuania is US$ 6.75 for 1-3 week delivery, and US$ 10.25 for 1-2 week delivery.

http://www.abebooks.com/servlet/BookDetailsPL?bi=14253656110&searchurl=tn=The Nature Of Boats&sts=t

http://www.abebooks.com/servlet/FrameBase?content=/servlet/ShipRates?vid=52829084

 

I'm assuming he'll want to play with curves sooner or later, probably sooner, even if it's just things like adding a slight curve to a stem for aesthetics or whatever. A basic set of decent French curves should be adequate for what he'll want, and he'll be able to find them and afford them. I find them quite handy sometimes. But sure, he doesn't actually need them to start with.

Laukejas: if you do get some French curves, make sure to get ones with square edges. Some have one side recessed relative to the other, which is a PITA when you want to use them that side down and don't want your pencil wobbling. Linex make some decent ones.

 

Well, that started a bunch of posts.

The reason you need accurate curves is because in "on paper" design you take your offsets from the drawings. If the curves are not accurate when you measure the offsets they, as someone said, come out lumpy.

How you use those curves is you keep trying different ones until you get one that smoothly goes through maybe three points, then find one that goes through a couple of those points and the next one, and keep doing that until you have a nice smooth even curve for the length of the drawing. Then do it again for each of the curves on the drawings. Whooo!

One of the reasons I suggested freehand sketches to help you visualize what you are wanting to do, and then just use that to guide your CAD drawings.

As one of the guys said, if you are only interested in building sheet plywood boats under maybe 12 feet length then you could probably get along with just a spline. A spline is just a thin wood piece like maybe a 1/8 inch x 1/8 inch strip maybe a foot long that you lay along your curve, hold down with some heavy weights, and run your pencil along to draw a smooth curve. Simple but limited.

I was not suggesting you look for those American books over there, but books published over there on yacht and small boat design. Surely, with all the boats in Europe there are experts writing about that who live there?