making a scale cardboard model

hey all, has anyone built a cardboard model that they were able to scale up into a full size plywood boat? i am thinking of building a small 18 to 20 ft lobster boat but can't find a design I like. If I made a cardboard model could I then scale up the cardboard sections and make templets for the 8x4 plywood sheets. I know there is a lot more information you can get from a model if built correctly, but at this stage I just want to get the shape right!

 

Yes and no. To see if your shape is build able with ply take a chunky block of softwood ,then with a band saw cut your proposed shape and make a half model from the block of wood. Then bend sheet metal or mylar over the half model to simulate the behavior of plywood . Paper is to flexable. use mylar or metal sheet. If all looks good , slice the half model into sections and take off the measurement for full size stations. Set up the stations then measuer and fit your ply panels. Google model making and you will find plenty of clever, experienced small craft builders, doing this.

Just because you prove that the shape is build able doesnt mean it will float.

Good , proven, small craft plans are widely available and are cheap. The price of a sheet of marine plywood.

Why go thru all the hassle and possible mistakes when proper plans are availble. ?

 

Here... free professionally drawn and engineered plywood fishing boat plans

http://www.fao.org/docrep/007/y5649e/y5649e00.htm

 

Yes, it is a common way of developing panels. I have done it several times. The shapes scale up directly.

 

Even better than cardboard is Coroplast.

http://www.amazon.com/s?ie=UTF8&page=1&rh=i%3Aaps%2Ck%3ACoroplast

It is 100% waterproof and easy to form with a razor. Use packing tape to join the panels and you can make a model in an evening and it will float.

 

The larger the model the more accurate the results. 1mm modeling plywood is excellent, behaves just like marine ply, and most model shops carry it.

 

John you can develope a boat in the way that you describe. But as Michael suggests, it is not a reliable way to design a boat. You say that you want it to look a certain way. That is fine but you need to have some technical justification for your choice of appearances (shapes) other than merely what you fancy.

Tell us more about what kind of boat that you want and perhaps you can get more detailed responses.

 

There is very little information you can get from a model, except to show it around to friends. Things like dimensions are much easier to get from inexpensive hull software like Delftship, which also calculate the hydrostatic information. In the process, you get a 3d, rotateable view of the hull.

As previously mentioned, the hull shape has to be able to float level and with sufficient freeboard with all the gear ( engines, people) on board and be stable. You cannot calculate that from a 12" hand made model.

You also cant extrapolate anything much in the way of performance from a model until you get to 1:5 scale, and even then, the performance is not very close to the real thing.

Basically, making a model is a great way of collecting toys, but not very helpful in designing real boats.

 

I disagree. A model lets me check out such things as build method . . . I tend to be unconventional so it helps.

 

Chipboard is my model making material of choice. It's the cardboard found on the back of note pads and is cheap and available from print shops with a bindery department.

Scale models can be handy to sort out building details, but shapes, not so much. Simply put, it'll either be a cylindrical or conical surface, which will permit the material to conform, or it will not. Shape development needs to be carefully "developed" to save a bit of cutting and material waste. In other words, unless you have a good grasp on hydrodynamics, working from a set of plans is the reasonable and logical route.

Some scales just lend themselves to models better, particularly if making scale framing, so consider your scaling factor carefully.

 

I dont think its that helpful for any 'build method' either. Its hard to get small scale materials to scale up to the full size, - maybe on very small craft, but usually not.

Pars suggestion of material is interesting, but you cant expect it or any other small thickness 'stuff' to accurately represent real life hull material.

Even if you did manage to get some relationship of the model material to the real build material, that is not such a huge discovery - that sort of stuff is easily inferred from existing full scale boats.

 

good advice guys, over on my other thread 'building a crab boat', I asked about modifying existing plans to make a more salty looking boat. What do you think about taking say a Tolman 20" skiff and modifying the bow to create less deadrise, and squaring the sides at the stern and transom? that way your not messing with the hull below the water line. Also skiffs seem to take changes in load very well, some people build just the hull, some fit a centre console, cubby cab, or full size cab. Some people stretch the hull while others shorten theirs. So I'm guessing they are very adaptable?

 

DO I get this right --you make a cardboard cut out of the half a boat them measure the bits and increase the size by the scale you are using .

So if you using say 10-1 scale and you measure incorrectly by just 1 mm you mistake will be 10mm on the build. Thats a big hole to bog up.

 

Too true Frosty.

Sailing ships and other boats were never built from the small scale half models they you see in museums etc.

As well as a test of the line drawings done first, it was just a way of getting a 3d view for the owners and builders before the days of computers.

 

And with a 3d printer a (half) model if you like