making a scale cardboard model

Simple boats are simple to design. Normally if they look right as a half model, they are right. If the original poster needs a powerful north atlantic fishing boat with a fish hold then he would be foolish to self design. Get a Pro, the chance of error is just to great. If its a simple inshore skiff with an outboard and a fuel tank in the bow...go for it. No need for CFD simulation on a Cray XE6 supercomputer

 

We're still talking about a plywood boat, right? No matter how simple the boat looks if it's planked it may not be buildable in ply.

Having got that out of the way, once you have accurate photos that can be transferred to a suitable planning medium like FreeShip or pencil and paper, you're now as close as you're going to get to a set of plans based on a boat that you know works. The model seems superfluous apart from bragging rights at the pub.

The big problem with such photos is distortion from parallax, unless you can take the pics from a fair distance with a telephoto lens. One way around this is to take some pics in fairly poor light from dead ahead and astern, with a vertical lazer line shining on the boat from square off the beam. Do that a few times with the laser line at known places along the length of the boat and you have some useful and accurate stations. Include something of known length in each picture of course, and you need both sides of the boat visible in each pic to determine the centerline as the laser will outline only one side. The profile picture will help to align the stations. Hard part is determining the waterline.

You can do the same thing with a few rolls of tape but better ask permission first . . .

Most software is a pain with this approach so just do a drawing.

 

This summer I snapped a whole series of shots of Messolongi boats. These are ancient, elegant plank on frame boats. To discover how I must change the shape for ply construction Ill have to build a half model .

Im just not smart enough to use a computer.

 

Rwatson
Let's clarify the thing: models are not the lone way to go. And also computers are not the lone way to go. There is no lone way to go.

So I'm going to put simply the facts;
PREMISES
- Models, computers, lasers, spreadsheets, pencils, rulers etc are just TOOLS, with their limitations.
- Without theoretical and empiric knowledge these tools are useless.
- Computers, by their capacity of calculation, are good for complex and repetitive tasks, like calculations of centers, surfaces, volumes etc.
- Like any tool, CAD softwares need a curve learning more or less step and long which is an "investment" in time. This investment is valuable only if you have a use that "repays" this investment, or you are wasting time.
- Delft Ship and Free Ship are complex softs with long times of learning, made primary for complex tasks like ship design, and for exploring multiples choices in the design spiral. It's the 120 tons bender...

So the question is; is it valuable to spend X amount of time for learning the use of a complex and powerful soft for designing just ONE LOBSTER BOAT 20 FEET LONG MADE IN HARD CHINE PLYWOOD?

For me the answer is NO. Because:

* A 20 foot Lobster is very simple boat, with a very limited choice of working shapes when built in hard chine plywood. So you won't have to tickle between a large array of choices. You are going to take the solutions known since ages as good. That's the main reason.

* Buying plans is the more economical and more sure solution when your goal is just to build a small boat and go fishing and not to learn design. It's also a good base when you want to tweak the details without modifying deeply the general layout. The most common mistake I see in this forum is to believe that buying plans is a waste of money; it's all the contrary, when you buy plans you don't buy only sheets of paper or mylar. You buy also the experience of the designer...plus bonuses as list of materials. Plans for a small boat are from free to 200 USD, most at the 100 bucks. For example the plans for a 20 feet Panga I've found in a 5 mn reaserch http://www.bateau.com/studyplans/PG20_study.htm?prod=PG20 are 80 bucks...These are clever for the use of the plywood. Pangas are proven good boats, very close in appearance with lobster skiffs. Compare 80 bucks with hours and hours of design, errors and pain for maybe a dog boat...

* Another more subtle reason. These softs use NURBS. For the problems and limitations of the NURBS, make a search. I won't detail here, it's out of subject. In short terms NURBS are not the universal solution for CAD design of boats.

Hard chine plywood is peculiar; the material is not ductile but is also able to take compound shapes within a limited range.
NO FREE SOFT will tell you if the obtained shapes are "buildable" without pain. Nor it has the ability to predict the amount of compound you can introduce in the panels to get a nicer shape. These softs are limited to tidy mathematical solutions that limits the possibilities of design.

A 1/12 model made in aviation plywood can give serious clues, and show you what works and most important what do not work. It's very formative to learn visually and instinctively the facts of developable, regulated, compounded surfaces and the junction of plans in the space.

Also good thing for a beginner; he will have to reproduce grossly the steps of the building. Good lessons without wasting expensive materials on the 1/1 boat.

I do agree with michael pierzga, eye and hand can learn to you a lot. It's part of the acquisition of knowledge. Boat building needs a mix of intellectual and manual skills. Models are a help in that task.

 

Good thread, wise words, fine wine

 

Very good cover of the subject, Voyager.

I recognize the great value of software programs for many projects. Some would be extremely difficult to duplicate without such programs. I am not a computer person but have sat alongside a designer who is well versed in that field and have witnessed the hours of work and often the frustration in completing some tasks. Some of these tasks became complicated because of the software, often because the inputs were not specifically developed for such design programs.

I marvel at what can be easily accomplished with software but, for the small and relatively simple boats that most of us work with, I can get along just fine without dedicating the time and effort to become competent in computer design. I like to see the design on paper that has been drawn with pencils and simple tools and I like to see the physical model too.

We dinosaurs who follow this path are probably being gradually phased out and that does not bother me as long as I am allowed to work the way I like.

 

Thats the sticking point that I want to refute. Sure, if you want to learn everything about say Delftship, you could take years and you could go mad. I also say again, models hardly tell you anything useful.

If you want to create a manual sketch, take some basic measurements off it, and see a 3 D shape, rotate it, show it around the pub - it takes minutes !!! The skill to do it will take 2 hours to teach yourself. (For those interested, read the help topic Import Chines )

The other point I will risk overstressing, is that the info you get from the few hours required, will tell you more about the basic facts of the hull performance than any model ever could.



I notice you haven't tried to explain how you could possibly produce an accurate displacement for waterline table from a scale model that you said was one of the purposes of building a model. I attach a sample hydrostatic report that I challenge you to produce with any scale model at all, in less than 1:3 !!


I also attach the 12 lines of hull dimensions of the simple 16 ft kayak that I created from basic dimensions from a hand sketch, that the hydrostatics report is based on. I now know that my 130 kilos will require a .11 metre draft. The whole exercise took 20 minutes.



Finally, for anyone who would like a leg up to the skill, I attach an illustration of the relationship between the simple text file, and the 3d result that may help you visualize the concept. Don't let people scare you away from the easy methods.

.

 

It's amzing how much passion can be generated over which tool to use for boat design - it's a sign of the enthusaism we share for our chosen craft. Spreadsheet, sketch, boat design software, carved half-model, card model, all-out detailed scale model - each has value for the job in hand if used appropriately. It’s like my gardening tools; the lawnmower is more complicated than a spade but I need them all.



Thanks RW for the kayak chine file, it is a good example of how simple an import file can be and still work. I hadn’t realized FreeShip would work with so little data as I usually get import files from Carene which creates much larger ones. It’s an excellent example how simple working with DelftShip or FreeShip can become, and still deliver the tools that such programs provide.



For those interested in learning to use FreeShip, there's a tutorial here http://www.hapby.v-nam.net/FREEship/FREEship-Tutorial1.html that is far more useful than the manual for a beginning user, and Googling "tutorial freeship" will turn up others I am sure.

 

Absolutely AK. I knew I ran the risk of 'overdoing' the presentation - its hard to judge how each person will understand points made, but there are a lot of out of date preconceptions around.

Bear in mind, the technique I find most useful, ( and have mentioned ad nauseum ) is to do the hull profile and plan drawing manually ( using personal style and preferences) , before putting the numbers into DS or FS to do the 3d model, and Hydrostatics, and not doing the entire 'creation' on the computer.

I. Voyager made the very valid points that messing around with 'Nurbs' and 'Control Nets' is a real brain shredder - and I agree, totally.

Its just that a lot of people still think that models are actually useful for performance and displacement info - and it just isn't that valuable. Even just for 'presentation', 3d images are a lot easier to build and more accurate than a scale model, and you don't get left with 'dozens of them under the bed'. And when you want to make changes on the advice of others, its a matter of minutes to create an improved model.

I hope a lot more people can take advantage of the less arduous ways of envisaging, creating and and accurately assessing a hull

 

I think that with training it is less arduous to picture the boat in your head. I can visualize the whole thing including the building process. I think that designers nowadays depend too much on a computer doing the thinking for them. However, I may be a tad old school.

 

I've come to some rather specific views on how I want to use conics to develop my surfaces, then unwrap them to panels so they can be assembled stitch & glue without elaborate aligning of a bunch of temporary station molds on a strongback. The problem with any piece of software is that you have to get into the head of the programmer a bit, and the programmer's approach may not be consistent with what you believe to be the best or most intuitive approach. I'm basically with Mr. Watson, and what he has said has me interested in checking out DelftShip, but the ability to accurately develop a shape conically without a lot of fuss, then unwrap that shape to an accurate flat shape, nest shapes for cutting on a sheet of material, and export the file types needed for CAM & any other required collaboration - these are all factors in selecting what software to invest time & money in. And whatever direction one goes and sequence one uses, building a model at some point before going full size, at least as a check, is not a waste of time.

 

- with some of my designs I tend to start with the plank development I want - such as all straight lines - and see what kind of hull I can get out of that. I've had some nice little boats starting like that, not the way to go for a big cruiser though. I recently got my own copy of "Instant Boats" with several Bolger pywood boats and he obviously had the same thought when he was designing them.

 

I think the brain will never be superseded as the ultimate tool also. there are guys in India and Arabia that only need some markings on some ancient bits of timber to start measuring up, and laying the boat out.

Its when inexperienced or innovative designers need rapid prototyping that the computer can 'prove' the basic points, where software is the biggest help.

 

While many Bolger designs have real merit, he did not push conic development into shapes with as much visual complexity as is possible. Here are some examples of what can be done:
http://www.mothboat.com/Building/howidoit.html

 

I don't want to limit myself to what a programmer decided a boat should be. Battens (thin sticks) do whatever I want them to do. Also, there is too much emphasis on the conical development of plywood. It will take all kinds of other shapes too.