Author Archive

Oslo and model progress

Saturday, April 21st, 2012

During a recent business trip to Norway I was able to take a look at the real thing in the Vikingskiphuset in Oslo. Beautiful spring day, very few people, I only had a few hours to run through a whole set of museums (also the Fram museum, that could take a full day, what an undertaking!), taking pictures like a Japanese tourist and looking at them later. Anyways, I got a thick book in the museum store as well- everything you always wanted to know about vikings etc.

This is the Oseberg ship, looks a bit flimsy (more a show boat than a real war and trade vessel). But it had plenty of associated artifacts buried with it.



I took this photo in the back of the room, now I would like to know what it really was. Not the Oseberg but pretty close sizewise what I want to end up with.



And here is the real thing:  the Gokstad ship, about 100 years younger than the Oseberg – simply beautiful. Not even Apple could have made it better.


Now back to home to the trusty garage.

I had been playing with a model idea for quite some time and finally got to set it up. Even after reading all these books that I started collecting, there are quite a few puzzles hidden. Trying them in model scale first is always worth it. In particular the tapering of the planks is quite mysterious. As shown here from the real thing in Oslo, the planks are not straight at all at the ship’s ends (this is the Oseberg stern plus rudder, below is the Gokstad bow).






















One early thought going round in my head was about handling of the hull. The shell is made in clinker / lapstrake fashion. Epoxy will be used sooner or later in the process and epoxy works great if being applied in the right orientation like ‘lying down’. So instead of setting up the keel on palls and ending up with a lot of over-head work, I plan on constructing this gigantic tube that allows arbitrary rotation of the hull. In model scale this is quite simple: Four rings with spacers in-between support the keel. The rings sit on rollers and the whole package rotates quite easily.


Full scale is going to be another issue – the spacer tubes are probably 6″ sewage pipes etc. etc. On the other hand, the tube will be easy to cover with a tarp and provide sun / rain protection. I had had fun with the Miniflower in that aspect.

Here is the main section (frame 5) set up between keel and strong back. The dashed line on the upper side of the keel represents the rabbet, i.e. the first plank will rest in a notch that must be chiseled into the keel.


The keel shown here is cut from a single sheet of plywood, scale 1:10. For the real size I think about using 2″ x 6″ or 2″ x 8″ stock, epoxied together and cut to shape. Timbers sawn to the chamfer at the side of the keel will be epoxied on as well. An application of the ‘ship saw’ (almost like my experience with San Salvador’s futtocks).

For my model, I glued small plywood blocks with cutouts for the moulds and planed / sanded them down to the right angles.


The hull will be made from 1/2″ plywood – this comes in sheets 4′ x 8′. I bought some aircraft model plywood that has about the right thickness (1.5 mm). To stay within scale, I cut model panels of 122 x 244 mm as a starting material – very convenient with a sharp knife. Most planks will have a maximum width of 120 mm so shown here are a few of these plank starters as well. The planks will be scarfed with a 4 :1 ratio to handle the overlaps.


And finally, all moulds are set up in the turning cradle, two temporary battens mounted to keep the moulds properly spaced.  Show here is the first garboard strake – starboard side. Glued with Elmer’s glue and kept in place with most of my clamps.

The rabbet was cut with a Dremel and a sharp knife – this is where I do not yet claim true mastery of craftsmanship. But if I get the hang of it through building the model, the full size ship will be even nicer.


To be continued.

The link to the past – Ducktape Engineering DTE

Wednesday, February 29th, 2012

click here to get to the old content in a new window:

There should be a way to make this appear in the left sidebar under Links. Not so intuitive…

DelftShip – first impressions

Tuesday, February 28th, 2012

So I got this iMac with the dual core capability plus the virtual machine environment to run both OS X and Windows on the same machine. It runs really well! The next step was to get the free version of DelftShip, a nav arch software that can do a lot of things. Not everything but quite a few tricks. Of course it took a while – as one of their forums says in the footer: ‘if something does not work well on the first try, have a beer’.

So here is a body plan from my paper version:


And a lines plan. Not clear yet what the two bodies mean


Finally a curvature plot that indicates a vew weak spots (the blueish areas inside red – this means no compound curvature but more like a saddle configuration.


But what I really wanted are hydrostatics etc. The model predicts a displacement of 1.5 tons. I had done two planimeter exercises (sectional areas plus Simpson’s rule) before with results between 1.3 and 2.1 tons. Something is still a bit off. Metacentric height is 1.8m above base. Total hull area is about 26 m^2. If I use 1/2″ plywood, the hull will come to about 300 kg plus say another 150 kg for keel, frames and rigging (hollow spars). So I will need about 1 ton in water ballast, close to the floor. This will put the CG to about .4 m above base, leaving a nice 1.3 m or so of MG for a stiff flyer.

 And Delftship gives me a resistance curve as well:


Not quite clear what that will mean. At 5 knots the Froude number is already at .34 or so which means that we either plane or won’t get far beyond that speed. We’ll find out, I guesss.

That’s it for another late night.

After the project is before the project

Tuesday, February 28th, 2012



dear followers of Ducktape Engineering, I hate to admit it: I just managed to stupidly loose the old look of the Miniflower and kayak projects by going ‘blog’. The data are still somewhere in cyberspace – I hope I can reconstruct an access to them. Until then, stay tuned. This is the beginning of a new project. Tada.

So we bought a new iMac as the old warhorse eMac reached its capacity limits. All pictures are transferred (>4000) and now I have to rearrange the albums to get some structure back in. Obviously, I did not get it.

It’s been a quiet couple of weeks in Tierrasanta. The Miniflower project has reached maturity – all that remains is the article for Wooden Boat. But that is not really fun.

Fun is to get started on a new project. And somebody said writing a blog with Worldpress is a piece of cake. Well, so far I wonder.

Here is a book that I managed to get from Germany after doing some basic internet research. The backdrop is good old lines drafting, ducks and splines on our grand piano that has been turned into a drafting table. How is this for the complainers about photo sizes? The pictures are clickable in case they are larger than the display window.


Anyways, since mid November I had started taking some notes and built a scrapbook of thoughts. Again, this phase is probably the most fun. Energy flows well up to midnight.

So here are some objectives:

  1. The vessel shall be trailerable on US roads (8′ max width) by my trusted old F150.
  2. Easy to set up the rig and strike down.
  3. Have a cabin at least for 2 people. With a stove and other basic.
  4. Have a tent for many friends
  5. Minimum deadweight but must sail well. So probably a water ballast scheme.
  6. No metal or minimal usage
  7. Must be seaworthy (coastal and light offshore navigation, like the Channel Islands and possibly Guadaloupe Island, off Baja, just at the upper edge of the blog theme cover)
  8. Beautiful. Did I mention beautiful? Yes, clear wood, white/red sail.
  9. Be a challenge as to building technology.

So If I do the math right, a scale factor of 47% will create the 8′ width about right, length over all is 36′, 3′ height at midships (the stems more than twice that). A formidable size for our backyard. An amphibious assault vessel of yore, built with epoxy and a few other tricks.

Anyways, enough damage done for a day. Stay curious my friends.