Fab your own rowboat from cheap pvc tubing, tent fabric and underlayment ($70!)

This instructable is about building a 12 foot rowboat from very cheap materials: 20 pvc electrical conduit tubes (5/8"), 2 sheets of 9mm underlayment (3/8") and polyester tent fabric for the skin. The only hard part is you need access to a large cnc router. Perhaps you can use one at a fablab nearby?

Step 1: Design

There are a few free ship modeling tools out there(like hulls and carene), but most of them only work on windows and are not open source. Freeship is open source, but is only compiled and released for windows. It runs fine however with wine, so on either Linux or windows you can use this nice tool for designing hulls and ships etc. Do not make the mistake to take the newer release of delftship however: the file format is not backwards compatible, delftship has fewer features and is not open source anymore (great shame really).

By far the easiest way to get started with freeship, is to create a new generic model, and adapt that to a linesplan you have found on the internet. Even with this tool designing a nice looking boat takes a lot of effort, copying the effort of others will make your learning curve less steep. Freeship works with nurbs-surfaces, which means in practice you can not alter your model with an exact amount. You can however import a lot of file types to carry on with a previous design mad in another progam.

When you are done with your design, make sure all your surfaces that you want to make in plywood, should be put in their own layer that is marked as developable. That way, you can export them from the "tools->develop plates" menu item. in here you can mark which surfaces you want to export. It might be best to export each surface in its own dxf file. Not every program can understand this dialect of dxf (it uses a vertex to describe the surfaces), but you can open it in most 'real' cad programs or in Rhino. The stations (the cross-sections at the hull can be exported when you choose file>export>2D polylines.
With these, I went to inkscape (not a real CAD program yes, but it was good enough for my purposes). I drew some help-lines on the bottom layer, to help determine where the notches for the conduit tubes should go. I know now that it would have been easier to define as many hard edges on the design as you want stringers, and then use the resulting ridge as a guide for the tube locations.
A trick in inkscape is to determine the shape of your notch, duplicate it, select your station and then subtract the first from the last (Ctrl -).
Of course, if you don't want to spend much time on design, you can just take mine and perhaps adapt it to your materials circumstances.

Comments

[Scruffy Marc]

There is no way to be nice about a boat that is distorting before leaving the dock.

Lets have a little reality and quality in this site.

The truth often hurts, so ban me if being nice is the only criteria on this site.

This boat is a danger to those who might make it. When someone drowns will it help if everyone is nice?

[namora]

With scantlings this light distortion is to be expected and no one in their right mind would use this craft but on a calm pond that they could swim across,. US marine safety laws require a PFD anytime a person is on the water in an open boat. I was impressed that the distortion did not cause a leak. By the by I tried to house a foundry in a similar construction with much more unplesant results.

[skaar]

oh yeah, i saw the ripple, and thought you should use a stronger floor, it was just the misplaced rib... though, it couldn't have taken all that much effort to move it to the right place.

[hohum]

very nice, a great piece of work, great instructional, you should feel very proud of your accomplishment

your boat looks good in the water, I'd bet the boat just glides along while rowing

[rickharris]

Looks good. Similar approach to http://gaboats.com/boats/

Although I guess quite a bit heavier. their boats weigh in at around 40 pounds.

Dacron which gaboats use is not the same as polyester. Dacron is a Terylene fabric. This shrinks quite a lot compared to polyester.

If you want to try a harder wearing covering try to find some ballistic nylon. This is what soft luggage is made from and much more wear resistant although rubbing strips would still be sensible.
If your prepared to suffer the holes and high wear for cheaper cost a standard poly tarp or even Tyvek house wrap will do the job. If you use Tyvek rub it between your hands to soften it to get a better match to the curves of the hull.

I agree a strong back is the best way to go in building this type of boat. In my efforts to build a ga type boat I didn't want to go to the cost of Kevlar cord to strengthen the hull so I used a polyester strapping band such as you see wrapped round pallets and large objects.

This is much cheaper and seems to work just as well. Fastening was done with stainless steel staples and a staple gun. this speeded up the covering enormously.  Finished weight was just over 50 pounds for a 14 foot open canoe as the ballistic nylon was somewhat heavier than dacron.

[jelleAtProtospace]

Indeed, Plat Montfort's designs were a great inspiration while designing this boat. I really don't care if Dacron is polyester or not; it is heat-shrinkable which is what I needed. Ballistic nylon is an option too, but I wonder how well it heat-shrinks. The heavier weight might be a problem though, the idea of skin on frame is to be very light. For a larger boat that is heavy to man-handle anyway, it would be suitable, although a glassfibre + kevlar skinning might work then too.

[snotty]

Wow, nice work! A few questions: Is the CNC router essential? Could I just use a jigsaw instead? How much does the finished boat weigh? Again, nice work.

[jelleAtProtospace]

It is essential if you want to build it in one week's time. :) You can of course do it the manual way if you want. In that case, you should be able to generate an offset table from freeship that will tell you where to drill a hole for the tubes in the station-to-be. Then you saw out the station shape while leaving about 3/4 of the hole intact. The wood needs to recede a bit between the tubes, so that the skin only touches the pvc tubes. With a belt sander you can correct later on. If you go the manual route, you would do good to experiment a bit if you can do with less stations. I think you can bend pvc pipes to function as ribs too, so that you need less stations. Bending the pvc can be done by filling it with sand and heating it with a hot air gun.