Archive for February, 2012

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.