Paper and pencil

Fudgy. Thanks, these numbers will come in handy. Anyway, in small boats such accuracy probably hardly matters.

 

Yup. The errors you are likely to get in the calculations will be on the same order as the errors from varying porridge consumption by the crew before sailing.

 

Off topic really. Here is a photo of Greyhound that I took a couple of weeks ago. The spars are bigger than telegraph poles. The lower horizontal one is the bowsprit, pulled back on board for berthing. Greyhound is in keeping with the old mill house behind! What you don't see are all the carbon fibre multihulls surrounding the luggers (there were three of them on this quay)

Lots of reasons for big scantlings on traditional boats:

everything bolted/trunnelled together - no glue, no accurate saws, no good paint, small crew and no engine so damage likely when berthing, "because that's how we always do it"

Richard Woods

 

Sometimes you have to use too many sections so that the calculation is correct.
If you do not want to use any software you could use a planimeter. You can also draw the curve of areas (or perimeters) on cardboard, cut it and weigh it. This is a very old method and, I suppose, with low exatitud, but always within 4% or 5%

 

Pencil and Paper

Well, lets separate the Young from US SENIORS. I use grid pads all the time and have one in front of me constantly. I draw on these a lot every day with pencil. Houses, boats, interiors, and structural drawings of all types. It is relaxing to me and has been for decades.

BUT, when I want reproducible drawings I go with LeRoy on Onion.............
No mistakes allowed. Stan Rasor

 

Discussions of various quadrature (numerical integration) formulas used for hydrostatic calculations can be fascinating (to me at least), but going beyond the basics of probably accuracy and applicability to boat shapes has little relevance to improving design skills.

Designing and creating good drawings are two different skill sets. I've worked with folks who have one skill set and not the other. Some folks can design, as in innovate and synthesize. Some can create good drawings starting with a design. And some can do both.

 

The interesting thing to find out from younger designers is - are they taught any traditional techniques at college, or only CAD?

Richard Woods

 

Interesting point Richard. I recently went back to my old Polytechnic now of course a University and they only used CAD. However I was pleased to see that they did teach drafting properly rather than just using the 3D model as the fount of all information. Personally I was a bit underwhelmed with the actual quality of the detail component drawings I saw. Maybe this is just the way the CAD package does things, but I don't think so. My old paper and film drawings were definitely better presented and easier to read. My first ex college drafting job was drawing a new compression moulded rocker cover(s) for a marine diesel engine where the pistons were 12" diameter (only a small one... Those were on mylar film and had to be pretty good because the PhD engineers at the client company were very critical about drawing quality. As it happens everything went OK, with one change from an M52 ultra fine thread I had specced in metric to a 2" BSP thread instead!. All done on an A0 with parallel motion. The sliding arm and rotating head type are definitely quicker to use if the OP is interested.

Later when using 2D software, I went to reasonable lengths to customise it to create clear easy to read drawings. Fortunately the package we were using allowed a lot of this type of thing. I doubt todays students want to burrow into custom scripts, create custom menus etc and especially burrowing into the depths of DOS.....

As far as I can work out, production drawings should convey the maximum information with the mimimum number of lines and be clear and easy to read. I find it helps to be pretty logical about dimensioning and notation so contractors and sub contractors fully understand the drawing. TBH the worst disaster I've ever had was some components were made in Korea - the problem was partly the toolmakers could not read all the notes on the drawings. They also got some fundamental dimensions wrong too, but the drawings were correct!.

 

That explains a lot. I actually wondered what people used for glue and waterproofing agent back in days when epoxy and other synthetic glues weren't available. Burnt tree resin was used to paint hulls below waterline, but apart from that, I have no idea.

By the way, these spars look cracked. Why wasn't the timber properly dried before using for these spars?

 

Solid spars will always get checking, no matter how well you dry them. It's just down to the basic properties of timber. Tangential shrinkage on the outside is more than at the core (where it is effectively zero) so this creates stress across the grain, leading to checking.

 

Checking of solid spars is a bit more complicated. It's due to the circumferential shrinkage rate being greater than the radial shrinkage rate. If those two shrinkage rates were the same then the change in circumference resulting in the change in radius due to radial shrinkage would match the change in circumference due to circumferential shrinkage.

 

It's another reason why older boats were overbuilt relative to today

Grayhound has done a few tropical miles as well, which never helps

RW

 

I learned with paper and pencil. (mid 70s)

Now I avoid it where I can.

 

Yes. This is how I do it. I'm not a professional designer, just a student at YDS. Prior to the course I went out and bought all the stuff for manual drafting. Lots of it from e-bay as it was a PITA to find new ducks and planimeters at reasonable prices. It was also difficult to find the Copenhagen Ship Curves, even at well sorted dealers. They also came from e-bay eventually. Drawing film was bought locally at quite a high price. Drawing board and battens were home made. I spent several $100 on all of this because I didn't want to spend 10 times that on the YDS CAD course. After trying to draw manually and realizing how much time it took (I have a full time job and a family as well and usually study between 10 pm and 1-2 am before going to work at around 7.30) I figured that buying a Rhino student license and learning how to use the software myself would save me a lot of time done the line.

It took some time before I got the hang of it and I still struggle on some things, especially when building surfaces from my lines, but boy am i glad I did it. My ducks and my very old but very beautiful planimeter will (hopefully) some day make good decorations in my design office

The designs in the pictures were done "exactly" as you would on paper, working back and forth between stations and diagonals for fairing. Only difference is that the process is much faster using the tools of Rhino. Especially when I have to go back and change something, which I do a lot.

I did the motor boat part as an assignment for the YDS carriculum and part for a design competition in a magazine, it didn't win Everything was don "manually" with lines, working back and forth between different lines and views just as you would on paper.

The sailboat is an ongoing project for the lesson I'm working on now. Same here. All the lines done one by one. The surfaces you can see are all built from the lines.

I'm not trying to sway you one way or the other. Just trying to show that even with CAD software there are different approaches. I have tried designing from surfaces and even from solids. I've tried numerous CAD softwares including Maxsurf and Freeship/Delftship. The method I'm using now is the one that most resembles drawing on paper and it's the only one I've really felt comfortable with.

Edit: During the design process I do the calcualtions "manually" (measuring areas under the stations using Rhino and feeding the numbers into a spreadsheet) to make sure that the displacement and prismatic coefficient and whatever else is the way I want them. Same with resistance calculations. Once the surfaces are created and fiddled with to make a watertight model Rhino will give me more accurate numbers on wetted surface and displacement. This far my manual calculations and Rhino's calculations have been quite close to eachother.

 

The models you show us are really good. Think about the work you should do if the hulls were not so rounded, if they had several knuckles.