Let's get creative! Cat in less than 200h.

[Luovahulluus]

My classes in experimental designing have just begun. We are supposed to do something with a light weight structure. We are encouraged to experiment with unusual materials. We have 96 hours of these classes and after that we have another 80h of other classes in which we can continue the experimental project, if it's a big one. And this will be. I also have a chance to use the workshops at school a few hours here and there, so I'll have about 200h of time to build this thing. My plan is to make a catamaran (or a model of one, if I can't make the whole thing).

The spesifications for the cat (in order of importance):
Very quick to build
Cheap (I'm a student and broke)
Crew of one.
Carrying capacity about 200kg
Lenght 4m (the maximum lenght I can store and move around)
I'd like it to be fast, but with all the limitations, it's not a priority.

Hull is the biggest problem at the moment. It doesn't have to be hydrodynamically optimal. I will not laminate the hulls. It's too expensive, too slow process and not at all experimental. Now I have three ideas on how to make the hulls and I would very much like some comments on these:

1. Aluminium v-hull. Two 4 meters long aluminium plates, weld both of the short edges and one long edge, formed to a v-shape in the middle. This will not be that cheap and the wet surface is very big. Will also need some structure inside to keep it in shape. The structure is very likely difficult (=slow) to make.

2. Get/make a metal cylinder and form it into a hull by flattening the front end vertically to make it pierce through waves and cut the bottom open from the rear and make it overlap a little to make it smaller. This is visualized in the attached pictures.

3. Make a mesh out of metal and cover it with pvc. I have access to pvc cloth that has been used as an advertising on a wall or by the roads. I have doubts about the durability of the mesh if it's light enough.

http://lh6.ggpht.com/_htVh7sYTwi0/SQzgzrOXpBI/AAAAAAAAAI8/gmpDULbUSes/cat%20front.jpg
http://lh5.ggpht.com/_htVh7sYTwi0/SQzg1tb6VdI/AAAAAAAAAJE/KBrenz5spS8/cat.jpg
http://lh5.ggpht.com/_htVh7sYTwi0/SQzg2Z4TuVI/AAAAAAAAAJM/LOqG-nnfEiA/Cat%20front%20right.jpg
http://lh3.ggpht.com/_htVh7sYTwi0/SQzg3Wm5-zI/AAAAAAAAAJU/PxR8UV14psE/Cat%20top.jpg
In case you don't see the pictures, you can find them in here: http://picasaweb.google.fi/Luovahulluus/Catamaran#

[Chris Ostlind]

Two hulls from aluminum plate are OK for you but a glass laminate structure is too expensive?

The absolute cheapest form would be to buy, or beg, some very large, (about 12-14" in daimeter) plastic drain pipes from a home supply store, heat the end that will be the bow and squeeze it so that it forms a vertical seam. Glue the seam with the appropriate solvent based adhesive and clamp it tight. Use sheet metal screws to fasten a rudder mechanism and use wooden beams to tie the two hulls together and make your mast. Use that cheapo PVC cloth you have found for the trampoline and maybe even the sail.

Get it on the water and go sailing.

You did say that the hull forms do not have to be Hydrostatically correct, right?

Chris

[rasorinc]

bundle cheap stryene pipe 1200 lb. crush tested-- say 4" and put 5 together each side. They use this pipe for rigid septic line pipe. don't buy the pipe with weep holes. they have end caps for it.

[Fanie]

bundle cheap stryene pipe 1200 lb. crush tested-- say 4" and put 5 together each side. They use this pipe for rigid septic line pipe. don't buy the pipe with weep holes. they have end caps for it.

:D I was going to suggest almost the same thing !

[rasorinc]

Further thought. create a bow out of anything and glue it on. bundle the pipes in 2 layers of 2 with the fifth on the bottom. this will give you a V shape. wrap it with cheap tape maybe 2 layers then coat it all with epoxy. Lash bamboo to them for the cross hull tie pieces. total cost $100.00 us get 2" bamboo poles use hemp twine or fishing line 100 lb. when I was a kid we made neat boats out if anything to use in the creek. I was in those before I knew how to swim and was saved by a adult one day. Thank God......

[Fanie]

Plywood is also cheap, simple basic sticth and glue can also do it.

In about 20 or so posts we'll be getting close to the proper way of doing it, I can see we're heading there :D

four poles and some rope or wire may not cost anything.

[rasorinc]

Fanie, we wired together old rusty corrigated tin and used a tar emulsion to waterproof the ends to make very tippi boats. I'm lucky to be alive. my idea for a cheap cat will work--boy it would be fun to take out in the bay - won't sink. can use lashed bamboo for a mast. Should we go together and get a patent on the idea? Stan

[Chris Ostlind]

...boy it would be fun to take out in the bay - won't sink...

If you find it cool to move around at less than 1 knot. ;-) No sail and drifting with the current would be more effective.

[Luovahulluus]

Great ideas!

How about laminating corrugated cardboard? My brother works at a shipyard making these huge passenger ships. I might get some epoxy-paint from him for a good price. Maybe that could be used in the laminating process. I'm not sure if this is any cheaper than the usual glass fiber lamination, but there is a lot of cardboard in the recycling bins around the city. I could make thicker walls in in fewer layers than with glassfiber. Thicker walls increase stiffness even if it's mostly made out of air. The outermost layer must be something harder, if the epoxy isn't good enough.

There could be some problems with cardboard and water...

What do you think? Any feedback/ideas are welcome here.

[Fanie]

Ah, we're gaining :D The man wants to spend some bucks now. This changes the picture again ;)

Luovahulluus, there are some things you have to consider. If you are going to use this thing once or twice in some fun event then use the pipes and condutes or cardboard boxes by all means.

If you however are looking at something slightly better and more durable, then consider buying a 2nd hand boat for less, or even one to restore, which by itself is a lot of work if that is what you're really after :D or if you are a masochist, then you have to do some planning on paper or computer.

If you do go for the something slightly better and more durable, do make it worth your while to do, else it's just money throwed away. Don't use the student excuse to do it poorly.

[keith66]

Many years ago some friends & i built a dreadful 26 ft outrigger canoe. She was a rough framework wharram style and was covered in Terram geotextile membrane, this is woven polypropylene cloth used in road construction, we just found a road being built and "borrowed" some! Waterproofed with black tar varnish it worked. The ama was made from a piece of 6" plastic gas main pipe (also "borrowed") with wooden plugs driven in the ends. We spent no money whatsoever building her apart from beer. She was dreadfully unstable but thats another story!

[eponodyne]

Seaplane floats are very light for their capacity and are designed to withstand very high loads. Contact these guys (http://www.ultralightfloats.com) for more info.

[sandy daugherty]

Scoop out a half hull for a double-ender in a sandbox with a little clay mixed in. Drape the depression with terrain cloth and roll on a thin slurry of epoxy and chopped fibers. Fill with two-part self-expanding foam. Level with a hot wire.* Repeat. Glue two halves together to make one hull with a piece of dimensional lumber between for rigidity and to attach cross bars. Leave slot for dagger boards. Wrap seam with 4" glass tape and epoxy. Repeat. Make a two-piece wing mast the same way. Steer with skulling oar, Pose for pictures!

* At this point you could finish one half-hull as a plug for the remaining sand molds for more refined product. If available, pull a slight suction on the first sand mold while heating a stiff sheet of ABS to conform to the depression while retaining a fine finish. This will require a different technique to join the two halves.

[Petros]

The metal will also be costly as well as the fiberglass laminate.

The least expensive way to go is make skin-on-frame (like a Greenland sea kayak) hulls. Espcially if you have PVC fabric available, it should be plenty durable for a cat that small.

The least expensive way to do this is use five full length stringers with thin plywood bulkheads about every 45 cm. Lash the stringers to the bulkhead (drill small holes in the bulkheads at the stringer location) with heavy polyester string (not nylon!) or fine stainless tie wire. Cover the hulls with the PVC fabric and hand stitch it closed, pulling it tight as you go. YOu can also use stainless staples to close the fabric over one of the stringers, but it is difficult to get tight. Use bungies to hold the beams to the hulls.

This type of construction is fast and light, and uses very little materials. I built a 4.26 meter sloop with all salvaged wood and materials for only $35 US using this construction method. I want to build a catamaran the same way next.

[Luovahulluus]

Ah, we're gaining :D The man wants to spend some bucks now. This changes the picture again ;)

If you do go for the something slightly better and more durable, do make it worth your while to do, else it's just money throwed away. Don't use the student excuse to do it poorly.
You are absolutely right. This is too big project to properly build AND design in these 200h I have. I have decided to make a model 1:4 or 1:5 now, and maybe I will do the full size version as my degree work next year. I might be able to spend a little more bucks then, and I'll have more time to build it. The emphasis will still be in easy-to-build low-cost light construction.

If you however are looking at something slightly better and more durable, then consider buying a 2nd hand boat for less, or even one to restore, which by itself is a lot of work if that is what you're really after :D or if you are a masochist, then you have to do some planning on paper or computer.
This is a design school, and I actually love to design stuff, so I'm not buying a boat. I guess that makes me a masochist then...

There are still two options:
1. Make the hull out of plywood. The current plywood hull shape is attached.
2. Sea cayak method: http://www.feathercraft.com/technology/construction.php

The more I think about it, and knowing myself, the cat should be able to take pretty high winds. Can I make the fabric-covered version rigid enough?

What kind of stucture I need to have inside the plywood hull?
Are the 8 bulkheads 50cm apart enough, or do I need more? In other directions?
Is 4mm plywood strong enough if I cover the hull with a layer of glass?

[Petros]

1. Make the hull out of plywood. The current plywood hull shape is attached.
2. Sea cayak method: http://www.feathercraft.com/technology/construction.php

The more I think about it, and knowing myself, the cat should be able to take pretty high winds. Can I make the fabric-covered version rigid enough?


The skin-on-frame method can be made as strong and rigid as you want, especially if it will not be a folding version like the feathercraft. You choose the stiffness and strength you want by building the frame to your requirements. I have found this method is far less prone to damage from ruff handling or poor seamanship.

it also can be made from all non-toxic and inexpensive or even recycled materials. No costly, smelly, nasty epoxy and fiberglass.

You can design a very durable wood and plywood truss structure and cover it with heavy fabric for less time, money and weight than any other method. Your plywood hull design can be adapted for the skin-on-frame construction by using either built-up bulkhead or simple plywood ones, with stringers and cross bracing. It will look like a truss before it is covered, very stiff. It will be the lightest, strongest structure you can build for the money. It builds fast, it is low cost, and easy to build or repair with available materials. The only disadvantage is you can not have hollows in the hull shape and the frame limits inteiror hull space (not as much of an issue with a catamaran hull).