Finite element analysis

I'm clinging on to the top of Cangarda's main engine with one hand (the crocheted glove is a style thing) while leaning back to take this picture. The point of this exercise was to get a better 'grip' on the geometry of the cylinder head for a finite element analysis of the pressure forces. Our first cut at determining the stresses in the head was to assume it was a flat plate. A simplification that was ...simple, but clearly incorrect. The stress result was ~9600 psi for the test pressure, which for an old casting of unknown quality, could be too high...it could fail.

So, we made a 3D, virtual solid model of the head (omitting the stud on the top, which is probably not important).And, after applying simplified boundary conditions, subjected it to the virtual test pressure force.

This is a plot of the Von Mises "stress" for the test pressure. The result is that the predicted stress is actually ~3700 psi...a stress which is much less likely to result in failure.

I put "stress" in quotes since it really isn't a stress. It's a numerical way Von Mises, whoever he was, developed to combine the three principal stresses into single number, which he then compared to the yield stress of the material.

Cangarda Overtime

"Hola, amigos. How's it going with you? I know it's been a long time since I rapped at ya. I been trying get through a jungle of bullshit, but it grows back as fast as I can cut it down.."*

As all the homies know, Cangarda (and Jeff Rutherford) moved out in January. The marina is reverting to the swamp and fenland from whence it came. We have a semi-resident female sea lion now, which is in a way preferrable to yachts, boatbuilding and commerce. Our landlord (of whom I must speak in the gentlest terms, lest we be kicked out as well) evidently prefers it this way as only our office and a houseboat remain.

Cangarda's new berth is on a westerly facing end tie in the Richmond Marina (Marina Bay). It's a little exposed to the West, but they have some strong fenders out and it looks in pretty good shape.


It's in a picturesque spot (across the Marina from the old Ford assembly plant), and the docks and bathrooms are way better than at 320 West Cutting, but the boat is a full seven minutes walk from the gate, making it a time/management nightmare. Still, it's a veritable hive of activity there with the owner, captain, Jeff, Steve, electricians and assorted helpers on board, as well as three super experienced steam engineers laboring away, trying to make the thing run. Here's Chief Jordan and Gary upside down in the bilge...Pull up your pants fahcrissake!
Getting it to run is still problematical, but perhaps a bigger hurdle is getting the permission to run it at all. Steam boats have been pretty strictly regulated in the US since 1871 with the formation of the Steam Boat Inspection Service (merged into the Coast Guard in 1942). The law, still very much in force, regulates all vessels, even yachts, greater than forty feet in length with a steam pressure greater than 50 psi, i.e., Cangarda. In general, yachts are only subject to very weak oversight by the Coast Guard. As an example, a lunatic could quite well have the idea to build a fifty foot sailing catamaran, out of disposable plastic bottles, attempt to sail to Hawaii, and the Coast Guard would do nothing to stop him. But steamboats, even privately owned pleasure yachts, are subject to all federal regulations. Period. That's why I stopped by Cangarda on Friday.

The new boiler is hotter and more energetic than the original Almy, and is currently set to run at a high pressure. Although the boiler has been tested to the higher pressure, and the piping is rated at much higher pressure, the Coast Guard has no assurance that engine itself can withstand the higher pressure.

Here are the decorative covers to the cylinder head covers. Each cylinder, and the adjacent steam receiver, has a seperate, bolted head.


This is the head of the high pressure cylinder.
The complex shape of the head makes any simple analysis of the pressure forces a little dubious. Tomorrow I will put up some images of a finite element analysis of the pressure forces on the head.

*Jim Anchower, The Onion